Paediatric Abdominal Imaging

Gastroschisis

In patients with gastroschisis, there is a small defect or split in the ventral abdominal wall, classically to the right side of a normally positioned umbilicus. Gastroschisis typically occurs in the absence of other anomalies and is thought to be caused by either a localised intrauterine vascular accident or asymmetry in the lateral body wall folds with failure of fusion.

The incidence of gastroschisis has increased worldwide over the past two decades and it has been documented to occur in clusters in some geographic regions. Mothers under the age of 20 years are at greater risk of having a child with the condition.

Antenatal ultrasound shows bowel loops floating freely in the amniotic fluid, with the diagnosis being possible early in the second trimester. There is no covering membrane. ‘Complex gastroschisis’, as determined by the presence of intestinal atresia or stenosis, bowel perforation, volvulus or necrosis is found in 10% to 20% of infants. Exposure to amniotic fluid causes damage to the bowel; postnatally, this can result in a thick, fibrous ‘peel’ coating the loops of bowel. Short bowel syndrome, liver disease secondary to intestinal failure and intestinal dysmotility are serious consequences of gastroschisis. Necrotising enterocolitis (NEC) is reported in up to 20% of patients with gastroschisis.

Upper GI contrast studies in infants with repaired gastroschisis will often demonstrate gastro-oesophageal reflux (GOR), dilatation of small bowel loops and a markedly prolonged transit time. Malrotation is inevitable and in this situation it should be evaluated in context; it does not necessarily require surgical intervention. Careful discussion with a paediatric surgeon is needed.

Repair of the defect may be possible soon after delivery, but often the abdominal cavity is too small. In this scenario, a sterile bag (silo) is sutured to the abdominal wall to prevent fluid loss and, gradually, the volume of the bag is reduced over days or weeks. This gently pushes bowel back into the abdominal cavity, giving time for the abdominal wall to stretch and expand.

Omphalocele

An omphalocele ( syn. exomphalos) is a midline anterior abdominal wall defect through which the solid abdominal viscera and/or bowel may herniate. The extruded abdominal contents are covered in a sac. Larger omphaloceles containing liver tissue are probably caused by complete failure of fusion of the lateral body folds. Omphaloceles containing only bowel are thought to arise owing to persistence of the physiological herniation of gut after the 10th week of fetal development. The umbilical cord inserts at the tip of the defect. A giant omphalocele is said to be present when the liver is contained within the herniated membranes or when the defect measures more than 5 cm in diameter.

Antenatal ultrasound can detect an omphalocele from the second trimester onwards. The prognosis of the infant is dependent upon other associated anomalies. Chromosomal and structural abnormalities are seen in more than 50% of patients. The Beckwith–Wiedemann syndrome has an omphalocele (exomphalos), macroglossia and gigantism as its primary components (the ‘EMG’ syndrome).

The method of surgical closure of the defect is, in part, driven by its size. Immediate closure, staged procedures or delayed repair following epithelialisation are all surgical possibilities. As with gastroschisis, malrotation is inevitable.

Bladder Exstrophy—Epispadias—Cloacal Exstrophy Complex

The terminology of this spectrum of complex disorders is confusing, with many texts using the term OEIS complex (omphalocele, exstrophy, imperforate anus and spinal abnormality) and cloacal exstrophy, interchangeably. In reality, they probably represent different entities of the same disease spectrum. The epispadias–exstrophy spectrum is rare and complex, extending from epispadias, where males have a urethral meatus opening on the dorsum of the penis, and affected females a cleft urethra, to bladder exstrophy, where the bladder is exposed on the lower abdominal wall and drips urine constantly.

At the extreme of the spectrum is cloacal exstrophy, one of the most severe congenital anomalies compatible with life, and which encompasses abnormalities of the genitourinary (GU) and GI tracts, the central nervous and musculoskeletal systems. This condition is thought to arise owing to abnormal development of the cloacal membrane and its premature rupture before the fifth week of gestation. The cloaca opens onto the lower abdominal wall, where it is seen as an open caecum and prolapsing terminal ileum between two hemibladders. There is an omphalocele of varying size and a blind-ending short gut. The external genitalia are ambiguous. Bilateral inguinal herniae are common to both sexes. There is spinal dysraphism and an ‘open book’ pelvis. Associated renal and lower limb anomalies (club foot and reduction defects) are well described.

Antenatally, the ‘elephant's trunk’ sign of the prolapsed terminal ileum is said to be pathognomonic for the condition on ultrasound. Non-visualisation of the bladder in association with an omphalocele and myelomeningocele would also be strong predictors of cloacal exstrophy.

Early postnatal imaging includes the extensive use of ultrasound to evaluate the spine and brain, the GU tract and the hips. Computed tomography (CT) can be used for assessment of the bony pelvis before reconstruction. Upper GI contrast studies document GI tract anatomy. Magnetic resonance imaging (MRI) of both the pelvis—assessing the genital tract and pelvic floor—and the spine are also required.

Surgery in the immediate postnatal period includes diversion of the faecal stream and colostomy formation, bladder closure ± vesicostomy fashioning, omphalocele reduction and repair, and closure of any open neural tube defects. Genital tract surgeries are complex and multistaged. It is normal for these to be postponed until later in childhood.

Oesophageal Atresia and Tracheo-Oesophageal Fistula

OA with or without a fistulous connection to the trachea is one of the more common congenital anomalies of the GI tract. It is caused by failure of the normal separation of the foregut into respiratory (ventral) and GI (dorsal) components early in the first trimester of fetal life. Five different major anomalies result ( Fig. 71.1 ). The atretic segment of the oesophagus tends to be at the junction of its proximal and middle thirds. Occasionally an isolated TOF occurs without OA; this is the H-type fistula, which may present later in childhood with recurrent chest infections.

More than 50% of those children with OA and TOF will have other congenital abnormalities. Most commonly, these abnormalities constitute some part of the VACTERL spectrum ( v ertebral anomalies, a norectal malformation, c ardiovascular malformation, t racheo-o e sophageal fistula with OA, r enal anomalies, and l imb defects). Other GI malformations—notably duodenal atresia (DA), small bowel malrotation and volvulus and a more distal congenital oesophageal stenosis—have been reported.

OA is usually suspected on antenatal ultrasound owing to the presence of polyhydramnios and the absence of a stomach bubble. One should be aware that fluid passing through an associated TOF (when present) between the trachea and the oesophagus can cause a false-negative examination. Identification of a dilated and blind-ending upper oesophageal pouch adds certainty to the diagnosis. Numerous additional features of OA can be seen on fetal MRI, and functional MRI can be used to assess for the presence of a fistula.

Typically, infants will present in the immediate postnatal period. Choking, coughing, cyanosis and drooling exacerbated by feeding are the cardinal features. Patients with an isolated H-type TOF may not be symptomatic at birth and can present later in infancy or even in childhood.

Postnatally, the diagnosis is usually made on a chest radiograph following attempted insertion of an orogastric tube, which shows the tube coiled in the proximal oesophageal pouch. The presence of gas in the abdomen implies a distal fistula. A gasless abdomen implies no distal fistula, as seen with isolated OA, or the extremely rare OA plus proximal fistula. A Replogle tube will often be visible on postnatal radiographs; this is a multiple side-hole catheter that keeps the upper pouch clear of secretions ( Fig. 71.2 ).

In most cases, a primary repair is possible and, whilst urgent, the surgery is not considered an emergency and is usually performed within the first few days of life. If a primary repair is impossible this may be termed ‘long-gap OA’. In such cases, it is necessary to measure the gap between the proximal and distal oesophagus to plan further surgery. The distal oesophagus is accessed from the stomach following creation of a gastrostomy. Under fluoroscopic guidance, a Hegar dilator is inserted though the gastrostomy and passed retrograde into the distal oesophagus. The tip of the Replogle tube is used to demonstrate the distal extent of the upper pouch. As both tubes are radiopaque, the degree of separation between the pouches is easily visualised and measured. The exact definition of a ‘long-gap’ atresia is challenging because there is no consensus. From a practical point of view, if an atresia cannot be closed at primary repair, it is a long-gap atresia.

A tube oesophagogram is the method of choice for assessment of an H-type fistula. There are a number of different techniques described, which vary with institution. The classic technique is to insert a nasogastric tube into the lower oesophagus, then turn the child prone. With the x-ray tube in the lateral position, contrast medium is injected under pressure whilst the tube is slowly withdrawn ( Fig. 71.3 ). There is a high risk of aspiration and associated vasovagal collapse, so appropriate medical support should be available in the room. A negative tube oesophagogram does not exclude an H-type fistula, and in those patients with a high index of suspicion, rigid bronchoscopy combined with oesophagoscopy should be performed.

All children with OA/TOF require assessment of the heart, spine and urinary tract preoperatively to detect other abnormalities of VACTERL.

Obstruction of the Stomach

Congenital gastric obstruction is rare. It is usually caused by a web or diaphragm in the antrum or pylorus. Total gastric atresia is extremely rare, but readily identified with fluoroscopy if necessary. Pyloric atresia is associated with epidermolysis bullosa simplex. The diagnosis may be suspected antenatally, owing to maternal polyhydramnios and a large fetal gastric bubble. Postnatally, non-bilious vomiting and upper abdominal distension are found. Microgastria is a rare congenital abnormality caused by failure of normal foregut embryogenesis. It is rarely an isolated abnormality and is associated with VACTERL. On upper GI, the oesophagus appears hypoperistaltic and patulous. The stomach is small and tubular.

Enteric Duplication Cysts

Enteric duplication cysts are uncommon congenital anomalies of obscure aetiology. They can occur anywhere along the length of the gut but are most frequently found in the ileum. Gastric duplications account for less than 7% of cases, and are usually found on the greater curve. When located in the antropyloric region they may cause gastric outlet obstruction and present in the neonatal period with non-bilious vomiting and a palpable mass. Confirmation of the diagnosis is by ultrasound. The cysts may have a layered wall, with an inner echogenic layer corresponding to the mucosa/submucosa and an outer hypoechoic layer that represents a smooth muscle layer ( Fig. 71.4 ). This appearance is referred to as the ‘gut signature’, and whilst it is frequently associated with duplication cysts, it is not pathognomonic. The contents of the cyst are usually hypoechoic, but debris is seen if there has been haemorrhage or if an infection has developed.

Gastric Perforation

Gastric perforation is uncommon but accounts for a significant proportion of cases of neonatal pneumoperitoneum, and is a life-threatening condition. The underlying cause is unclear and it has been described as a spontaneous event. Risk factors are known to include asphyxia, rate of enteral feed and mechanical ventilation (in particular ‘bagging’ during intubation). Iatrogenic gastric perforation is recognised after insertion of orogastric tubes. A massive pneumoperitoneum is seen on plain radiography of the abdomen.

Small Bowel Malrotation and Volvulus

During weeks 4 to 12 of gestation, a complex process of gut rotation occurs. It is a precise process partly governed by genes expressing molecules that are key in determining left and right asymmetry. Complete rotation consists of a 270-degree anticlockwise rotation that eventually results in the duodenojejunal flexure lying to the left of the spine at the level of the transpyloric plane and the caecum lying in the right iliac fossa. These landmarks demarcate the length of the base of the small bowel mesentery that is anchored to the posterior abdominal wall. More recent work by Metzger et al. and Kluth et al. proposes that the anatomical position of the gut relies critically upon localised growth and lengthening of the duodenal loop, which pushes it beneath the mesenteric root. Malrotation is not, in itself, a pathological entity. It describes some failure of this complex process. The end result is a shortening of the length of the mesenteric base ( Fig. 71.5 ). This creates a fulcrum around which the midgut can twist (volvulus), compromising the arterial inflow and venous drainage of the superior mesenteric vessels, which can lead to ischaemic necrosis of the small bowel. Untreated small bowel volvulus has a high mortality rate.

In most cases, small bowel malrotation is an isolated abnormality but any interruption of the normal embryological development of gut results in some form of malrotation. Therefore, the bowel of children with conditions such as congenital diaphragmatic hernias, gastroschisis and omphalocoele is malrotated by definition; however, it is rare for these children to present with volvulus once the primary abnormality is repaired, possibly owing to the formation of adhesions. The heterotaxy syndromes, Hirschsprung disease and megacystis–microcolon–intestinal hypoperistalsis syndrome are also associated with malrotation and volvulus, as are cloacal exstrophy, prune-belly syndrome and intestinal neuronal dysplasia.

Symptomatic babies with malrotation commonly present within the first few days of life, with bilious vomiting. Older children may present with non-specific symptoms of chronic or intermittent abdominal pain, emesis, diarrhoea or failure to thrive. Volvulus, though less common in the older child, still occurs and one must be alert to the possibility in an older child with a history of recurrent abdominal pain who presents with bilious vomiting. Malrotation and volvulus has even been described in adults.

There are no specific plain radiographic findings in malrotation, even with volvulus. The radiograph may be completely normal if the volvulus is intermittent or if there is incomplete duodenal obstruction caused by a loose twisting of the bowel. If the volvulus is tight, then complete duodenal obstruction results, with gaseous distension of the stomach and proximal duodenum. The classical picture is of a partial duodenal obstruction, with distension of the stomach and proximal duodenum, with some distal gas ( Fig. 71.6 ).

A pattern of distal small bowel obstruction is seen in a closed-loop obstruction and represents a more ominous finding; the small bowel loops may be thick-walled and oedematous, with pneumatosis being evident. These findings represent small bowel necrosis. A gasless abdomen is seen if vomiting has been prolonged, and in both closed loop obstruction with viable small bowel or massive midgut necrosis. In other words, one cannot give a definitive diagnosis using radiographs alone. In the neonate with bilious vomiting and a complete duodenal obstruction or a seriously ill child with obvious signs of peritonism, radiographic examination should cease after the plain radiograph; urgent surgery is indicated. In all other children with bilious vomiting and incomplete bowel obstruction, further investigation—usually in the form of an upper GI contrast study—is required. This examination is optimally performed with barium (single-contrast study), though surgeons may prefer water-soluble contrast if surgery is thought to be likely and imminent.

Determining the position of the duodenojejunal flexure (DJF) is paramount in an upper GI study and meticulous radiological technique is required. It is important not to overfill the stomach with contrast medium because this can obscure the position of the DJF directly or secondarily by duodenal ‘flooding’ following rapid emptying of the stomach. It is important that the first pass of contrast medium through the duodenum is observed because opacifcation of distal loops may confuse anatomy on later passes. Some operators prefer to pass an enteric tube into the first part of the duodenum and perform a duodenogram, therefore preventing obscuration of the DJF by contrast material within the stomach. Care must be taken with this technique not to advance the tube beyond D1 because the tube can distort the duodenal loop and alter the position of the DJF.

On a supine radiograph, the normal DJF lies to the left of the left-sided vertebral pedicles at the height of the duodenal bulb ( Fig. 71.7A ). When malrotation is present, the DJF is usually displaced inferiorly and to the right side. It is important to remember that the DJF can be displaced temporarily, particularly in the neonate, by a distended colon or stomach, an enlarged spleen, an indwelling nasoenteric tube, or manual palpation (see Fig. 71.7B ).

The ‘corkscrew’ pattern of the duodenum and jejunum spiralling around the mesenteric vessels is pathognomonic for midgut volvulus on the upper GI study, the calibre of the bowel decreasing distal to the point of partial obstruction ( Fig. 71.8 ). If there is an abrupt cut-off to the flow of contrast medium in the third part of the duodenum, volvulus cannot be excluded with certainty and these infants, too, must proceed to surgery.

A number of processes occur in malrotated gut in an attempt to fix the bowel to the retroperitoneum. This malfixation usually takes the form of peritoneal bands, often referred to as Ladd's bands. These bands attach the caecum (often high in the right upper quadrant) to the retroperitoneum in the right lower quadrant. Their path usually crosses the duodenum and can cause obstruction. They are divided during a Ladd's procedure to fix malrotation and volvulus.

Ultrasound may be the first investigation in a neonate who is generally unwell. Ultrasound will demonstrate the dilated, fluid-filled stomach and proximal duodenum when obstruction is present. The relationship of the superior mesenteric vein (SMV) to the superior mesenteric artery (SMA) is abnormal in approximately two-thirds of patients with malrotation, when the vein lies ventral or to the left of the artery, a finding that is neither sensitive nor specific for malrotation. Many authors advocate the use of ultrasound to identify the third part of the duodenum between the SMA and the aorta (normal position). Overlying bowel gas in the sick neonate can complicate this but it has been proposed as a screening test. Current evidence indicates that the upper GI contrast study remains the gold standard, with ultrasound serving as a potential useful adjunct. A volvulus may be demonstrated with ultrasound as the ‘whirlpool sign’; colour Doppler studies show the SMV spiralling clockwise around the SMA. This is diagnostic of volvulus in a sick neonate and no further imaging is required before surgery.

Management

The standard operation for small bowel malrotation and volvulus is the Ladd's procedure, whereby the bowel is exposed, untwisted and inspected. Any Ladd's bands are divided, and the base of the mesentery is widened. Finally, the bowel is returned to the abdomen, with the duodenum and jejunum to the right side, and the colon to the left; a prophylactic appendectomy is often also performed.

In those patients with small bowel malrotation diagnosed incidentally on an upper GI contrast study performed for another indication, management is less certain. A surgeon may opt to perform an elective Ladd's procedure; however, a Ladd's procedure does not result in a normal anatomical position of the bowel because the DJF will always be malpositioned in these patients. More importantly, volvulus can recur if the mesentery is not widened sufficiently and thus a previous Ladd's procedure does not exclude volvulus as a cause of abdominal pain.

Duodenal Atresia and Stenosis

The duodenum begins its development in the fourth week of fetal life. As the mucosal lining proliferates, the lumen is temporarily obliterated in the fifth and sixth weeks. There is a gradual process of recanalisation over the subsequent few weeks. Both DA and stenosis result from a failure of this recanalisation. Duodenal obstruction may also be caused by webs or diaphragms. Extrinsic duodenal compression by an annular pancreas or preduodenal portal vein may contribute to the obstruction in some patients. Regardless of the cause, in 80% of cases, the level of the obstruction is just distal to the ampulla of Vater, therefore resulting in bilious vomiting.

Associated anomalies are present in most patients with DA or stenosis. Down syndrome is present in 30% of patients and congenital heart disease in 20%. Malrotation is present in 20% to 30% of patients and can only be diagnosed before surgery if the duodenal obstruction is partial. Components of the VACTERL association may also be present, with OA coexisting in up to 10% of infants.

DA may be diagnosed on prenatal ultrasound as evidenced by a dilated and fluid-filled stomach and duodenal cap. Intrauterine growth retardation and polyhydramnios may also be demonstrated and often result in prematurity. Otherwise, infants present early in the postnatal period with bilious vomiting and upper abdominal distension. Non-bilious vomiting occurs in those infants with a preampullary obstruction.

The classical radiograph is that of the ‘double bubble’, representing a dilated stomach and first part of duodenum ( Fig. 71.9 ). If the obstruction is partial or in the rare cases of a bifid common bile duct straddling the atretic segment, then distal gas will be present. A classic double-bubble appearance without distal gas in a stable child does not require further imaging before surgery.

If a partial obstruction is suspected, an upper GI contrast study is warranted. Duodenal stenosis is demonstrated as a narrowing in the second part of the duodenum. A duodenal web may be seen as a thin, filling defect extending across the duodenal lumen with pre-stenotic dilatation. Duodenal obstruction can be demonstrated on ultrasound, especially if clear fluids are given first to distend the proximal gut.

Small Bowel Atresia and Stenosis

Unlike DA, jejunal and ileal atresia can be considered as a common entity. Jejuno-ileal atresia is thought to result from an intrauterine vascular accident. The vascular insult may be a primary or secondary event (e.g. due to antenatal volvulus or intussusception). Jejuno-ileal atresia has an increased incidence in patients with gastroschisis and meconium ileus.

There is a distinct form of jejuno-ileal atresia known as ‘apple peel’ syndrome, which is thought to follow intrauterine occlusion of the distal SMA. There is a proximal jejunal atresia, with agenesis of the mesentery and absence of the mid-small bowel. The distal ileum spirals around its narrow vascular pedicle, an appearance that gives the syndrome its name. A malrotated microcolon is also usually present. A second, more complex type of syndromic intestinal atresia consists of multiple atresias with intraluminal calcifications.

The majority of infants with a small bowel atresia present with bilious vomiting in the immediate postnatal period. With distal atresia, abdominal distension and failure to pass meconium are commonly recognised clinical features.

On plain radiography, there are dilated loops of small bowel down to the level of the atresia. The level of obstruction can be defined as either high (where only a few loops are dilated) or low (where the majority of bowel loops are dilated). It is not possible to define small or large bowel obstruction on a neonatal x-ray because diameter of distension can be the same and the haustra are poorly developed at this age. The loop of bowel immediately proximal to the atresia may be disproportionately dilated and have a bulbous contour. Meconium peritonitis with calcification of the peritoneum will be present if an intrauterine perforation has occurred. In a low obstruction, a contrast enema may be required to distinguish a low ileal atresia from other causes of neonatal low intestinal obstruction.

Management is surgical, with bowel resection and primary anastomosis if possible. In infants with multiple atresias, the surgeon aims to preserve as much of the bowel length as is feasible.

Necrotising Enterocolitis

The precise aetiology of NEC remains unknown. In the past, the term NEC has been used as an umbrella term for any pre-term infant presenting with abdominal distension and complications including pneumoperitoneum and pneumatosis. It is now accepted that NEC is not a single disease entity but a multifactorial condition associated with a variety of risk factors and outcomes. Animal studies have identified a receptor within the gut mucosa implicated in the pathophysiology of NEC. TLR4 has been shown to increase ischaemia within the gut mucosa in response to pathogenic bacteria. Risk factors for NEC include hypoxia/ischaemia (which is the cause of so-called ‘term-NEC’ in babies with congenital cardiac disease), prematurity, delayed enteric feeding, exposure to abnormal gut pathogens (owing to prolonged antibiotic use), enteric pathogens (implicated in ‘cluster-NEC’ seen during infectious outbreaks on neonatal units), multiple blood transfusions and early cow's milk protein allergies. Many of these risk factors are additive, and some result in more severe forms of disease such as those associated with multiple blood transfusions. There is an inverse relationship between birth weight, gestational age and the development of NEC. As above, those term infants prone to hypoxia and ischaemia are also at risk of NEC.

NEC usually presents in the second week of life, following the commencement of enteral feeds. This is thought to be secondary to relative ischaemia in the postprandial period. Initially superficial, the inflammatory process in NEC can extend to become transmural. Diffuse or discrete involvement of the bowel can occur, with the most commonly affected sites being the terminal ileum and colon. The clinical symptoms and signs are non-specific to begin with and include feeding intolerance, lethargy, hypoglycaemia, temperature instability, bradycardia, oxygen desaturation, increased gastric aspirates and gastric distension. Disease progression leads to vomiting, diarrhoea (often with the passage of blood or mucus in the stool) and, eventually, to shock.

There are four important radiographic features of NEC that are often quoted. One of the earliest features of NEC is a non-specific global dilatation of bowel loops. On serial radiographs, attention should be paid to the presence of persistent dilatation of specific bowel loops, the so-called ‘fixed loop’. Pneumatosis intestinalis or intramural gas can be seen in many conditions ( Table 71.3 ). In the context of NEC, more extensive pneumatosis correlates with increased severity. Portal venous gas is seen as branching linear lucencies over the liver that radiate from the region of the porta hepatis to the periphery of both lobes. It develops in approximately 30% of cases and, when seen, it is poor prognostic indicator ( Fig. 71.10 ). Perhaps the most important feature is free gas.

One-third of children with NEC will perforate, most commonly in the ileocaecal region. The radiologist should be aware of another phenomenon known as neonatal spontaneous intestinal perforation (SIP). This occurs in low birth weight infants without demonstrable cause and is most common in the terminal ileum. It is a different entity to NEC and the prognosis is much better than perforation caused by NEC. In many cases, a single anteroposterior (AP) abdominal radiograph is sufficient to make the diagnosis of perforation. Where clinical suspicion is high and the AP radiograph is inconclusive, a lateral view is obtained. There is no consensus as to the optimal technique. The supine, cross-table lateral view is useful to detect small amounts of free intraperitoneal air, typically as triangles of gas between bowel loops or over the dome of the liver. There is no need to reposition the infant when the image is taken. Alternatively, a lateral decubitus radiograph may be used, which requires the child to be repositioned on their left side for several minutes to allow air to collect over the liver surface on the right side of the abdomen.

Ultrasound has been shown to be highly effective for the assessment of NEC. At present it remains an adjunct to the more widely accepted plain radiograph; however, ultrasound can detect signs of NEC before there are plain radiographic abnormalities. As a dynamic study, one can also evaluate parameters such as peristalsis. Most of the radiographic abnormalities described above can be seen on ultrasound. Free air (usually seen above the liver), absent peristalsis, echogenic ascites and focal fluid collections are amongst the most important prognostic features on ultrasound ( Fig. 71.11 ), and have been shown to predict the need for surgery and adverse outcomes, including death. Bowel wall thickening or thinning (defined by some authors as >2.6 mm or <1 mm, respectively) and bowel wall perfusion (increased or absent) should also be evaluated during the ultrasound examination.

Perforation in infants with NEC is not an absolute indication for surgical intervention. Peritoneal drains may be used as a temporising measure in these critically ill infants, delaying the need for surgery and allowing time for systemic recovery. Surgery will be required in 20% to 40% of infants, whereby necrotic bowel is resected and as much bowel as possible is preserved.

A late complication of NEC is stricture formation, which occurs in up to a third of patients. Contrast studies (with water-soluble contrast media) are indicated to assess the calibre of the gut downstream before reanastomosis of defunctioned bowel. The study is usually performed antegrade via the distal limb of the stoma. Alternatively, or as a complimentary study, an enema can be performed.

The overall mortality rate from NEC is approximately 30%, with this figure being even higher in very low birth weight infants.

Intra-abdominal Lymphatic Malformation

Intra-abdominal lymphatic malformations may be found in the mesentery, omentum or retroperitoneum, which explains the various names that are used to describe them (mesenteric and omental cysts being two of these). The most common location is in the ileal mesentery. These lesions are increasingly being diagnosed by antenatal imaging, meaning asymptomatic infants come for follow-up imaging early in the postnatal period. Symptomatic babies may present with neonatal obstruction. Mesenteric lymphatic malformations can also act as a fulcrum for small bowel volvulus in the absence of intestinal malrotation.

Ultrasound will show a thin-walled, multiloculated cystic lesion that may be adherent to adjacent solid organs and bowel. There is no layering of the cyst wall, which may help to differentiate from an enteric duplication cyst; however, the distinction may be challenging on imaging. If the fluid within the cyst is chylous, infected or haemorrhagic, then it will be echogenic (see the section ‘Mesenteric Cysts’).

Megacystis–Microcolon–Intestinal Hypoperistalsis (Berdon) Syndrome

This syndrome is a rare and severe form of functional intestinal obstruction. The aetiology of the condition remains obscure, but recent research has identified mutations in genes controlling smooth muscle contraction in affected families and animal models. The affected neonates (usually female) present with a flaccid, massively distended abdomen, and delayed passage of meconium. They are often unable to spontaneously void. Antenatal ultrasound shows a massively dilated bladder. Postnatally, an abdominal radiograph will show dilated small bowel with a large soft-tissue mass arising out of the pelvis. The megabladder and the degree of renal upper tract dilatation can be assessed by ultrasound. An upper GI contrast study will confirm malrotation and a short bowel. A contrast enema shows a non-obstructed microcolon. Treatment of this condition is largely unsuccessful—the mortality rate approaches 80%.

Hirschsprung Disease

Hirschsprung disease (HD) is a neurocristopathy that presents as functional low bowel obstruction. It occurs owing to the failure of caudal migration of neuroblasts in the developing bowel between the 5th and 12th weeks of gestation. There is a genetic susceptibility with mutations seen in the RET (REarranged during Transfection) proto-oncogene pathway of affected individuals and their families. Histology reveals an absence of parasympathetic intrinsic ganglion cells in both Auerbach and Meissner plexuses in the bowel wall, which is associated with an increase in the number of acetylcholinesterase-positive nerve fibres in the aganglionic portions of the gut. The distal large bowel from the point of neuronal arrest to the anus is aganglionic. In approximately 75% of cases, the aganglionic segment extends only to the rectosigmoid region (short-segment disease). Long-segment disease involves a portion of the colon proximal to the sigmoid. Variants of Hirschsprung disease include total colonic aganglionosis (TCA), which may also involve the distal ileum, and total intestinal Hirschsprung disease. Ultrashort segment disease is rare and involves only the anus at the level of the internal sphincter. Diagnosis of ultrashort Hirschsprung disease may be delayed because it is often a diagnosis of exclusion. The existence of ‘skip lesions’ in Hirschsprung disease is very rare.

A definitive diagnosis of Hirschsprung disease is made by a suction or full-thickness rectal biopsy. Current treatment involves resection of the aganglionic bowel segment with a ‘pull through’ procedure, and anastomosis of the normally innervated gut close to the anal margin. There are different techniques that are performed according to surgeon preference. The management of total intestinal Hirschsprung disease is notoriously difficult and, at the present time, these patients are supported with parenteral nutrition.

Approximately 10% of children with Hirschsprung disease have Down syndrome. Other associations with Hirschsprung disease include ileal, colonic and anorectal atresias, cleft palate, polydactyly, craniofacial anomalies, cardiac septal defects, multiple endocrine neoplasia types 2A and 2B and other neurocristopathies.

Ninety per cent present in the neonatal period, with delayed passage of meconium, abdominal distension and vomiting. Symptoms may be relieved by a digital rectal examination or the insertion of a rectal thermometer, but will recur without definitive management. Regular enemas are often used to relieve symptoms. Children with longer-segment disease and TCA often present later because their symptoms can paradoxically be milder and their diagnosis missed clinically.

Severe bloody diarrhoea, sepsis and shock are associated with Hirschsprung enterocolitis, which occurs in 18% to 50% of patients in both the pre- and postoperative periods. Enterocolitis is the leading cause of death in Hirschsprung disease and has an increased frequency in long-segment disease and those in whom diagnosis is made after the first week of life.

Other postoperative complications of Hirschsprung disease include anastomotic leaks, fistulae, abscesses and stenoses. Up to 10% of patients will eventually require a permanent colostomy.

The abdominal radiograph will typically show a low bowel obstruction. If the diagnosis is unclear, a contrast enema is recommended, largely to exclude other causes of low obstruction. Some centres may prefer to proceed straight to rectal biopsy to exclude Hirschsprung disease, with an enema serving to assess the length of aganglionic bowel before surgery. Enemas performed to assess low intestinal obstruction of any cause should be performed with the same technique. No pre-procedure bowel preparation is given and, ideally, there should be an interval of at least 48 hours since the last enema or rectal examination. The catheter tip is placed just inside the rectum. It is important that the catheter balloon is not inflated. A catheter balloon can obscure the diagnostic features or, worse, perforate the stiff, aganglionic bowel. The most important image is a lateral (or oblique) view of the rectum during slow filling ( Fig. 71.12 and 71.28 ). In short-segment disease, the rectum will be narrow and there will be a cone-shaped transition zone to the more proximal dilated ganglionated bowel. Irregular contractions may be seen in the denervated rectum. A useful calculation is the rectosigmoid ratio; the rectum should always be the most distensible portion of the bowel and have a diameter greater than that of the sigmoid colon (rectosigmoid ratio >1). In short-segment disease, this ratio is reversed. The radiological features of Hirschsprung disease may be absent in the neonate because it takes time for the ganglionated bowel to dilate.

It is common during the course of an enema to see features of mild enterocolitis such as ulceration, mucosal oedema and spasm (see Fig. 71.12B ), but if a child has clinical features of severe colitis, an enema is contraindicated. Giant stercoral ulcers may also be seen in older children with a delayed presentation. Overall, the contrast enema has a reported sensitivity of 70% and a specificity of 83% for the diagnosis of Hirschsprung disease, and the negative predictive value of a normal contrast enema in patients older than 1 month of age is 98%.

In TCA the contrast enema may be entirely normal. Positive findings include shortening of a normal-calibre colon, with rounding of the contours of the hepatic and splenic flexures.

Functional Immaturity of the Colon and Meconium Plug Syndrome

Immature left colon ( syn. small left colon) and meconium plug syndrome are relatively common causes of neonatal bowel obstruction. There is overlap in both the clinical features and radiology of the two conditions, and the terms are often used interchangeably in the literature. The former refers to a transient functional obstruction of the colon, which occurs as a result of immaturity of the myenteric plexus. It is common in the infants of diabetic mothers and in those whose mothers have a history of substance abuse. Meconium plug syndrome is a temporary colonic obstruction caused by pellets of meconium. It is associated with both cystic fibrosis (CF) and Hirschsprung disease, both of which should be excluded if a diagnosis of meconium plug syndrome is made. Premature infants and infants of mothers who received magnesium sulphate therapy have an increased incidence of meconium plug syndrome, though the latter is disputed in the literature.

In both conditions, the affected infants present with symptoms and signs of bowel obstruction. There is delayed passage of meconium. The plain radiograph shows distension of both small and large bowel loops to the level of the inspissated meconium plugs.

In small left colon syndrome, the contrast enema typically shows a microcolon distal to the splenic flexure, at which point there is an abrupt transition to a mildly dilated proximal colon ( Fig. 71.13 ). The main differential diagnosis is long-segment Hirschsprung disease, and biopsy may be required if symptoms do not improve.

In meconium plug syndrome, the lodged meconium plugs are the cause of the obstruction, but the findings are essentially the same. The plugs lodge in the region of the splenic flexure, proximal to which there is colonic dilatation. Unlike small left colon syndrome, a microcolon is unusual. The (water-soluble) contrast enema is also therapeutic and once the meconium plugs are passed per rectum, the infant mechanical obstruction recovers.

Meconium Ileus

Meconium ileus is a form of distal intestinal obstruction caused by inspissated pellets of meconium in the terminal ileum. Approximately 80% to 90% of infants with meconium ileus have CF, and meconium ileus is the presenting feature of CF in 10% to 20% of affected patients. Children with the ΔF508 mutation have an increased incidence of meconium ileus, and those who are homozygous for this mutation have a higher incidence still.

More than half of the affected infants have uncomplicated (or simple) meconium ileus. In utero, these babies produce meconium that is thick and tenacious, and which fills and distends the small bowel loops. The meconium desiccates in the distal ileum and becomes impacted, causing a high-grade obstruction ( Fig. 71.14 ). Failure of meconium to pass into the colon results in a functional microcolon, whereas more proximally the small bowel loops are dilated and filled with greenish-black meconium of a toothpaste-like consistency.

Meconium ileus is described as complicated when intrauterine volvulus, intestinal atresias, bowel necrosis, perforation or meconium peritonitis supervene. The presenting clinical symptoms and signs of non-complicated meconium ileus are those of a low bowel obstruction. The plain abdominal radiograph will show dilatation of small bowel loops, which are of varying calibre. Often, there is a visible ‘soap bubble’ appearance (classically in the right iliac fossa), which is caused by the admixture of meconium with gas.

The contrast enema in meconium ileus demonstrates a virtually empty microcolon. Where possible, attempts should be made to coerce contrast medium into the terminal ileum. This will demonstrate multiple filling defects consistent with pellets of meconium ( Fig. 71.15 ). More proximal reflux of contrast medium will show the dilated ileal loops. The contrast enema in uncomplicated meconium ileus is intended to be therapeutic as well as diagnostic. The contrast media alters the intraluminal osmotic pressure and increases the fluid content within the terminal ileum and colon, encouraging the passage of the obstructing meconium. Water-soluble contrast medium should be used and the choice of medium is institution specific. Dilute Gastrografin (between 1 : 2 and 1 : 4 Gastrografin:water is the suggested dilution) is commonly used but other iodine-based contrast agents can be used and may be safer in small neonates owing to the large fluid shifts that can result when using Gastrografin. If the infant's clinical condition remains stable, the enema can be repeated, as necessary, until the obstruction is relieved.

If a child with meconium ileus presents with volvulus or perforation, it is known as complicated meconium ileus. This occurs in approximately 50% of patients and can lead to intestinal stenoses, atresias and necrosis. Perforation of bowel in utero leads to chemical (sterile) meconium peritonitis. The extruded bowel contents cause an intense inflammatory reaction, with fibrosis and calcification to follow. A meconium pseudocyst is formed when there is vascular compromise in association with an intrauterine volvulus; the ischaemic bowel loops become adherent and necrotic, and a fibrous wall develops around them. The presence of complicated meconium ileus may be suggested by findings on plain radiographs such as intra-abdominal or scrotal calcifications, bowel wall calcification, prominent air–fluid levels and soft-tissue masses.

The management of meconium peritonitis is surgical.

Colon Atresia

Colon atresia is rare when compared with other intestinal atresias, and colonic stenosis is rarer still. Atresia has long-been thought to be caused by an in utero vascular accident; however, Baglaj and colleagues have suggested compression of the bowel wall against the closing umbilical ring as an underlying cause.

The affected infant presents after several feeds with abdominal distension, failure to pass meconium and vomiting.

The abdominal radiograph will show the features of a low intestinal obstruction, with the loop immediately proximal to the atretic segment being massively dilated. If multiple atresias are present, then the bowel will be distended only to the level of the most proximal atresia. A contrast enema usually demonstrates a distal microcolon, with obstruction to the retrograde flow of contrast at the point of the atresia.

The management of colon atresia is surgical.

Distal Ileal Atresia

Distal ileal atresia is part of the jejuno-ileal atresia spectrum. It is thought to occur secondary to a vascular event in late gestation. If the atresia is in the distal ileum, then the infant will present with abdominal distension and delayed passage of meconium. The plain radiograph will show a low obstruction with multiple dilated loops of bowel. On enema, contrast medium cannot be refluxed into the dilated small bowel, the colon is usually a microcolon, but depending on how late in gestation the vascular insult occurs, there may be some colonic contents owing to succus entericus passing into the colon before the insult. The condition is managed surgically.

Anorectal and Cloacal Malformations

Anorectal malformations (ARMs) are a congenital abnormality of the terminal hindgut, known as the primitive cloaca. In the first trimester, the cloaca is divided into ventral (GU) and dorsal (rectal/anal) compartments by progressive descent of a structure known as the urorectal septum. ARMs are caused by the incomplete development of the urorectal septum and consist of an anorectal atresia/stenosis with or without a fistula between the distal colon and the GU tract. The degree of severity will depend on the point at which failure of the septum occurs. The cloacal malformation represents a very complex form of ARM and occurs exclusively in girls.

ARMs occur in approximately 1 : 5000 live births and are more frequent in males. Associated congenital anomalies are very common and occur in up to 70% of patients born with an ARM. Amongst the commonest associated anomalies, the VACTERL sequence occurs in approximately 45% of patients. Between 2% and 8% of patients have Down syndrome, with the vast majority of these patients having imperforate anus without a fistula. Currarino triad is the association between an anorectal malformation, bony sacral anomalies and a presacral mass lesion.

ARMs can be classified using either the Wingspread or Krickenbeck classification, and each classification has separate male and female sections. The Wingspread classification describes ARMs as low, intermediate, or high depending on the position of the rectal pouch relative to the levator sling. The Krickenbeck classification is concerned with the presence or absence of a fistula and it defines five types of fistula according to location. The Krickenbeck classification tends to be preferred in modern practice because it gives information regarding the localisation of the atretic anorectum and has an important bearing upon surgical planning. In male patients, the fistula may be to the prostatic or bulbar urethra or bladder neck. In females, the fistula may be to the vaginal vestibule, with true posterior vaginal wall fistulae being extremely rare. Perineal fistulae may be present in infants of either sex, as may imperforate anus and rectal atresia or stenosis, the latter groups being without fistulae.

The diagnosis should be made clinically during the baby check immediately following delivery, and immediate referral to the local paediatric surgery team is merited. Imaging at this stage is likely to be focused on assessment of any associated anomalies. In cases with an obvious perineal fistula, the child may proceed to surgery without imaging of the ARM.

The traditional cross-table lateral radiograph, with the infant in the prone position and the buttocks elevated, has been demonstrated to be inaccurate and should be interpreted with caution, especially if the child was crying or straining at the time of imaging. It is not recommended as a standard imaging test in ARM. Similarly, ultrasound has been described as a method of measuring the pouch–perineum distance in ARM, but has also been shown to be inaccurate for the same reasons as the lateral radiograph and is not considered as a standard investigation.

Infants who have a perineal fistula usually undergo a posterior sagittal anoplasty within the first 24 to 48 hours of life. All other children with ARMs will have a defunctioning colostomy performed, with the aim of surgery being to separate the GI and GU tracts and stop faecal contamination of the latter. Definitive surgery is postponed until a later stage, when the infant has grown and all other imaging investigations are complete.

Imaging evaluation of associated abnormalities is of greater importance in the newborn than is a detailed anatomical imaging assessment of the ARM. A detailed abdominal and pelvic ultrasound should be performed with particular attention to the kidneys and the pelvic structures. A chest radiograph and echocardiogram are recommended, as is a spinal ultrasound. Up to 50% of children with ARM will also have spinal cord problems, most commonly a tethered cord. Spinal ultrasound is an important screening tool, but MRI will be required to further define any abnormality.

In complex ARM, definitive surgery is planned for several months after birth. A diverting colostomy and, potentially, a vesicostomy (in the case of a cloacal malformation) are performed initially to allow time for the patient to grow. Imaging assessment is complex and multimodality. In terms of defining the precise anatomy of the fistulous tract, the most useful investigation remains the augmented pressure colostogram. A Foley catheter is inserted into the distal segment of the colon and its balloon gently inflated so that it seals the stoma ( Fig. 71.16 ). With the patient in the lateral position, water-soluble contrast medium is hand-injected under mild pressure to distend the distal colon and define the fistulous tract. Interpretation of the images is made easier if there is a bladder catheter in situ, through which some contrast medium has been instilled; this gives anatomical markers for the bladder neck and the course of the urethra. It is also useful to place a skin marker at the expected site of the anus. This is important for the surgeon to assess the distance between the skin and the distal colon.

The cloacal malformation only occurs in female patients. It is a complex anorectal malformation that results in one common channel draining the urethra, vagina and rectum. Examination of the perineum reveals a single opening. Defining the anatomy of these lesions is difficult, but ultrasound, pelvic MRI examinations and contrast studies of the cloaca all play a role. These girls are all managed with an initial colostomy, following which combined fluoroscopic studies are performed. These include an augmented pressure colostogram, micturating cystourethrogram and a ‘cloacogram’, with images obtained in both the lateral and anteroposterior positions. This can also be achieved with MRI using saline or dilute gadolinium to outline the structures of the cloaca and the common channel. It is useful to make an assessment of the length of the common channel on imaging but this is challenging given the small size of the structures. It may be better assessed on cystoscopy. As for all ARMs, ancillary radiological investigations, as described above, are mandatory for assessment of associated anomalies in cloaca.

Acute Appendicitis

Appendicitis is the most common cause for acute surgery in childhood. Between 30% and 40% of children do not present with the typical clinical presentation of appendicitis and, in particular, preschool patients often present with atypical features, more rapid progression and higher incidence of complications. Very young children often have a diagnostic delay and hence they have a higher risk of perforation at presentation. Consequently, imaging is often necessary to confirm, suggest or refute the clinical diagnosis and the use of imaging has dramatically reduced the false-positive appendectomy rates. Ultrasound should be the primary imaging investigation and performing a comprehensive ultrasound examination will make CT redundant in most cases. The ultrasound should be performed with a high-frequency linear transducer using a graded compression technique. The primary criteria of acute appendicitis are typically a tubular, blind-ending, non-compressible structure with maximal outer diameter over 6 mm. Other findings include wall hyperaemia or hypoperfusion (depending on the degree of inflammation/necrosis), surrounding hyperechoic mesenteric fat and the presence of an appendicolith ( Fig. 71.17 ).

CT is rarely necessary but can be an important diagnostic tool in difficult cases where ultrasound is unable to clarify and the clinical situation enforces acute surgery. CT is also often performed when complicated periappendicular abscess formation is suspected. Note that the appendix may be retrocaecal and an inflamed retrocaecal appendix may cause subcapsular liver abscesses ( Fig. 71.18 ).

Sonographic mimics of acute appendicitis may be acute salpingitis in teenage girls or terminal ileitis (see below) ( Fig. 71.19 ).

Mesenteric Lymphadenitis

Mesenteric lymphadenitis is a common cause of abdominal pain in childhood and may present as subacute or acute abdomen. The symptoms are caused by swelling of mesenteric lymph nodes, as a reaction to a trivial, often asymptomatic viral infection. On ultrasonography (US), multiple enlarged lymph nodes are seen in the root of the mesentery. The hyperechoic, fatty hilum is preserved and there is normal Doppler signal within the lymph nodes ( Fig. 71.20 ). Mesenteric lymphadenitis is a diagnosis of exclusion and should be established based on US findings in the absence of any other plausible explanations for the abdominal pain.

Inflammatory Bowel Disease

The diagnosis inflammatory bowel disease (IBD) encompasses Crohn disease, ulcerative colitis and unclassified IBD. IBD is thought to develop from dysregulation of the immune response to gut flora in a genetically susceptible host. The most common symptoms of IBD are chronic diarrhoea, fever and weight loss, but it may also present as acute or subacute abdominal pain. In very small children, the colon is often affected, even in Crohn disease. The imaging features are quite striking with an inflamed colon surrounded by very hyperechoic fat and enlarged lymph nodes and, sometimes, micro abscesses. There is no rectal sparing. These young children often present with fistulating disease.

The gold standard for diagnosing IBD is ileocoloscopy with biopsy. Imaging plays a role in establishing the extent of the disease, to assess possible complications and to select candidates for surgery.

Ultrasonography.

In children, ultrasound is the first imaging tool, especially if the diagnosis is unknown. The sensitivity and specificity for ultrasound depends greatly on the assessment of bowel wall thickness (BWT); much depends on the threshold used. A small BWT greater than 1.5 to 3 mm and a colonic wall thickness more than 2 to 3 mm is generally considered to be abnormal. Colour Doppler US may reveal hyperaemia of the inflamed bowel and this finding may further influence the diagnosis ( Fig. 71.21 ). Other signs of IBD on US include lack of bowel stratification, altered echogenicity of the bowel wall, hyperechoic mesenteric fat and enlarged lymph nodes. One should always look for complications of the disease, such as abscesses and fistulas, but the sensitivity for these features on US is low. US is a quick, radiation-free and readily available investigation but is highly operator dependent and the findings are not necessarily reproducible. Furthermore, some studies show that the sensitivity of detecting terminal ileitis is limited. The technique also has limited value in obese children and with the presence of bowel gas.

Magnetic resonance imaging.

The preferred technique for small bowel assessment on MRI is MR enterography. A comprehensive MRI has a high specificity and sensitivity for bowel inflammation and does not involve ionising radiation. This technique is normally well tolerated by children from 6 to 7 years and older. Sufficient bowel distension is important for a proper assessment of the bowel wall. MR enteroclysis may be an alternative if the child is unable to drink the relatively large amount of fluid required to distend the small bowel. A low-residue diet should be given 3 days before the examination, with no food per mouth from 24 hours before the examination.

MR enteroclysis can estimate the length and localisation of the affected bowel and detect both intra- and extraluminal disease; however, if there is clinical suspicion of a perianla fistula and/or abscess, dedicated pelvic MR fistulography may be required for detection and delineation of the fistula. A dynamic MRI sequence should be included to assess possible bowel strictures because this may change the treatment approach from medical to surgical. Controversies exist regarding MRI's ability to determine disease activity, both owing to the lack of gold standard and because acute and chronic disease may coexist in the same bowel loop. Diffusion-weighted imaging has been shown to increase the sensitivity and specificity of both intraluminal and extraluminal disease in IBD ( Fig. 71.22 ) and may be even more sensitive than contrast-enhanced sequences, therefore making the latter superfluous in many cases. MRI signs of IBD are listed in Table 71.5 .

TABLE 71.5

Magnetic Resonance Imaging Signs of Inflammatory Bowel Disease

Bowel Loop Appearance

Fixed

Dilated

Pseudo-sacculation appearance

Strictures

Bowel Wall

Thickness

Focal lesions (ulceration, pseudo-polyps, mural abscess)

Enhancement pattern after gadolinium injection (mucosal alone, layered, global, serosal hypervascularity)

Restricted diffusion

Extramural signs: fibro-fatty proliferation, distended and enhancing mesenteric vessels fistula, abscess, enlarged lymph nodes

Intussusception

Intussusception is a common surgical emergency in infants and young children and consists of a telescoping of a segment of bowel (intussusceptum) into a more distal segment (intussuscipiens). This condition usually occurs in children under 1, with a peak incidence between 5 and 9 months of age; however, it may occur up to school age. Ileocolic intussusceptions are the most common type. Ileoileocolic, ileo-ileal, and colocolic are much less common. Most (more than 90%) have no focal lead point and are caused by lymphoid hypertrophy, usually following a viral infection. Secondary lead points (which include nasojejunal tubes, Meckel diverticulum, intestinal polyp, duplication cyst and lymphoma) are present in 5% to 10% of patients. In young infants or children more than 6 to 7 years of age, intussusception is more likely to be caused by a secondary lead point. The clinical presentation of intussusception varies. The classical clinical signs are of colicky abdominal pain and bloody stools; a palpable abdominal mass appears in less than 50% of the children. Intussusception must be treated as a surgical emergency. The clinical situation may deteriorate rapidly, particularly in infants, and may become life threatening with hypovolemia and shock. Prolonged symptom duration will reduce the likelihood of successful reduction. Intussusception is now diagnosed by US, with a sensitivity and specificity of 100% in several reported studies, even when performed by less-experienced radiologists, if properly trained. The characteristic appearance of intussusception makes diagnosis or exclusion very easy.

The intussusceptum is usually found just deep to the anterior abdominal wall, most often on the right side of the midline. The sonography must be performed with a high-frequency, linear array transducer. The intussusception forms a mass of 3 to 5 cm in diameter with a ‘target appearance’ in the transverse plane, and a ‘sandwich appearance’ in the longitudinal plane. The characteristic ‘crescent in doughnut’ sign—a hyperechoic semilunar structure, caused by the mesenteric fat pulled into the intussceptum—facilitates the differentiation from mimickers of intussusception, such as bowel wall thickening, faeces and the psoas muscle ( Fig. 71.23 ). Lymph nodes and fluid may be seen within the intussuceptum and, in some studies, have been found to be associated with decreased hydrostatic-reduction rate. Bowel necrosis is difficult to assess by US, even with power Doppler examination of the bowel wall. Free intraperitoneal fluid is commonly seen in patients with intussusception and is, therefore, an unreliable indirect sign of bowel ischaemia. US should not only be performed to establish the diagnosis but also to look for secondary lead points and other intra-abdominal problems unrelated to the intussusception ( Fig. 71.24 ); however, no sonographic features, including the presence of a secondary lead point, should preclude an attempt of reduction. In a well-hydrated, haemodynamically stable child the only contraindications for hydrostatic or pneumatic reduction are the presence of free intraperitoneal air or clinical signs of peritonitis.

The role of plain radiography in the diagnosis of intussusception is controversial. The radiographic features of intussusception include a soft-tissue mass contrasting an air-filled bowel loop, the so-called ‘meniscus sign’ ( Fig. 71.25 ). There may be dilated, gas-filled bowel loops proximal of the intussusceptum and the absence of gas within the caecum may suggest a ileocaecal intussuception; however, the caecum may be difficult to localise in a child, and the sigmoid is located on the left side of the abdomen in almost 50% of children and may be indistinguishable from the caecum on a plain radiograph. Abdominal radiographs should therefore not be routinely used in intussusception. The presence of free intraperitoneal gas is extremely rare in children with intussusception, and may be assessed by a quick fluoroscopy performed before the fluoroscopically guided reduction.

In intussusception involving the colon, image-guided reduction is the first-line therapy of choice and can be performed using a pneumatic technique or by contrast enema, under fluoroscopy or ultrasound guidance ( Fig. 71.26 ). Most centres in the UK use pneumatic reduction under fluoroscopy guidance, but the choice of technique varies across Europe and should be based on the experience and expertise of the radiologist who performs the reduction. The use of sedation is also controversial; however, a prospective clinical study found an increased success rate and no difference in complications when using deep sedation in pneumatic reduction of intussusception in children. Regardless of the technique used, one should aim at a reduction rate of more than 80%.

Small bowel intussusception.

The reported frequency of small bowel intussusception varies. It may be seen as an incidental finding and will usually reduce spontaneously; however, small bowel intussusception sometimes causes ileus and must be treated surgically because this condition is not suited for enema reduction. It may be challenging to differentiate small bowel from ileocolic intussusception on ultrasound; however, this is crucial to choose the right treatment. Small bowel intussuceptum diameter tends to be smaller than that of ileocolic, but measurements of lesion diameter alone cannot enable reliable differentiation between ileocolic and small bowel intussusception. Some authors have found that the presence of a fatty core in the lesion, in combination with lesion diameter and wall thickness, and especially the ratio between the diameter of the fatty core to the thickness of the outer wall, can be used to differentiate between the types of intussusception. Lymph nodes are rarely seen within small bowel intussusceptums. If the bowel wall is oedematous the small bowel intussusception is less likely to reduce spontaneously ( Fig. 71.27 ).

Constipation

Constipation is probably the most common GI problem in infants and children. Childhood functional constipation has an estimated prevalence of 3% in the Western world. The symptoms are typically infrequent painful defecation, faecal incontinence and abdominal pain. This can lead to encopresis or faecal soiling and, occasionally, can cause acute, severe abdominal pain. Less than 5% of children with constipation have an underlying disease. The diagnosis of constipation is essentially clinical and radiological investigations play a very limited role in the work-up of constipation and should not routinely be performed in children with functional constipation. The plain abdominal radiograph will demonstrate the degree of faecal loading and dilatation of the large bowel; however, the presence of faecal loading on the plain radiograph does not necessarily indicate constipation and several studies show that plain radiographs have a low sensitivity and specificity for diagnosing constipation, and may even lead to misdiagnosis. Radiological investigations should only be performed in a carefully selected group of patients where an underlying cause is suspected.

US should be the first imaging tool in chronic abdominal pain when radiological work-up is indicated. It gives a good overview over the bowel and intra-abdominal organs and can help differentiate a faecal mass from a true mass. Other imaging techniques described for the evaluation of constipation include the measurement of colonic transit time using radiopaque markers, fluoroscopy and MRI defaecography. These are only indicated in highly selected cases.

Intestinal Motility Disorders

Intestinal motility disorder is a term used to describe a variety of abnormalities that have reduced motility of the bowel and no organic occlusion of the bowel lumen in common. They can be divided into acute and chronic disorders.

Acute dysmotility includes paralytic ileus in which there is temporary cessation of peristalsis in the gut. This simulates intestinal obstruction because there is failure of propagation of intestinal contents. Acute gastroenteritis can simulate small bowel obstruction by causing a local paralytic ileus, with dilatation of the affected segment of bowel and multiple fluid levels on an erect plain radiograph of the abdomen.

Chronic motility disorders include primary abnormalities of the bowel—Hirschsprung disease (aganglionosis) and neuronal intestinal dysplasia, which is a defect of autonomic neurogenesis characterised by an absent or rudimentary sympathetic ganglion innervation of the gut, or by hyperplasia of cholinergic nerve fibres and hyperplasia of neuronal bodies in intramural nerve plexuses.

The definitive diagnosis of Hirschsprung is based on rectal biopsy. A positive contrast enema portends a high probability of Hirschsprung disease, but inconclusive or negative studies do not exclude the disease and neither positive nor negative barium enemas make rectal biopsy superfluous if there is clinical suspicion of Hirschsprung disease. The main role of barium enema in this disease is to find the transitions zone to assess the length of the aganglionic segment in children with a positive rectal biopsy, which is important in order to choose the correct surgical technique ( Fig. 71.28 ).

Most children with neuronal dysplasia present with severe constipation but tend to spontaneously recover colonic motility between 6 and 12 months of age. Plain radiographs of the abdomen may show signs of obstruction of bowel and the barium enema may show dilatation of the bowel. Diagnosis is by biopsy and barium enema may be performed to establish the level of obstruction in order to plan surgery.

Chronic intestinal pseudo-obstruction (CIP) is rare and represents a spectrum of diseases that have in common clinical manifestations consisting of recurrent symptoms mimicking bowel obstruction over weeks or years. The age of presentation varies from newborn to adulthood. The condition is caused by a visceral neuropathy or myopathy, which can be familial or non-familial, resulting in a lack of coordinated intestinal motility. Megacystis–microcolon–intestinal hypoperistalsis syndrome is the most severe form of CIP and is usually fatal in the first year of life. Plain radiographs of the bowel will show loops of bowel with pronounced dilatation. The diagnosis is made by intestinal manometry and biopsy. A contrast medium enema can exclude mechanical obstruction in children with acute symptoms.