Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Internal Hernias: Congenital and Acquired
Intestinal obstruction is a commonly encountered surgical condition. The diagnosis is made with a history of nausea, vomiting, abdominal pain, signs of abdominal distention and tenderness, and imaging displaying dilated bowel with air-fluid levels. Adhesive disease is the etiology of approximately 50% to 75% of small bowel obstructions, with Crohn obstruction, neoplasm, and abdominal wall hernia completing the differential diagnosis in most cases. Internal hernias, defined as a protrusion of viscus through an intraabdominal aperture without traversing fascial planes, cause 0.6% to 5.8% of small bowel obstructions. The aperture can be acquired or congenital and often presents with symptoms of intermittent small bowel obstruction or vague abdominal pain. The diagnosis may be elusive, even in its acute state.
Mortality associated with acute internal hernia is reported to be as high as 31% to 50%, which may be an overestimation because the increasing use of Roux-en-Y gastric bypass (RYGB) to treat morbid obesity has heightened the awareness of this condition. Appropriate management of small bowel obstruction is consistent with appropriate internal hernia management; high suspicion, early diagnosis, and early operative intervention are key in limiting morbidity and mortality. This chapter will discuss acquired and congenital forms of internal hernias, their diagnosis, and management.
Acquired Internal Hernia
An acquired internal hernia requires the formation of an intraabdominal aperture through which bowel and other viscera may pass. Any rearrangement of intraabdominal organs creates a potential space through which bowel may herniate. These include the mesenteric defect created in a bowel anastomosis, hepaticojejunostomy during liver transplantation or Whipple procedures, and even ostomy formation. The most common site for internal hernia after liver transplantation is through the transverse mesocolon. Most notably, and more common, are the multiple defects formed during an RYGB. Due to the remarkable increase in the use of bariatric surgery for weight loss, and the importance of this complication, this chapter highlights the procedure's propensity for internal hernia, subsequent work-up, and management.
Roux-en-Y Gastric Bypass
With the increasing incidence of morbid obesity in developed countries, its surgical management has increased steadily over the last 50 years. Although multiple restriction and malabsorption operations have been devised and implemented, the RYGB provides profound lasting excess weight loss of 65% to 85%. The nadir in patient weight is typically between 18 and 24 months, with an average of 20% weight regain between 2 and 6 years postoperatively. From a public health perspective, the resolution of significant comorbidities associated with obesity is more important than the weight loss itself. Comorbidities, including degenerative joint disease (DJD), hypercholesterolemia, hypertension, gastroesophageal reflux disease (GERD), depression, hypertriglyceridemia, sleep apnea and obesity-related hypoventilation, fatty liver disease, urinary stress incontinence, type 2 diabetes mellitus, cholelithiasis, and asthma, are resolved in as many as 96% of patients. Most importantly, large retrospective and prospective trials of bariatric surgery have shown approximately 35% decreased overall death rate and decreased obesity-related risk of death in long-term follow-up. These effects are even more pronounced in patients with a body mass index (BMI) greater than 45.
In 1994, the laparoscopic Roux-en-Y gastric bypass (LRYGB) was introduced with the advantages of fewer wound infections, incisional hernias, splenic injuries, and clinically significant adhesions, as well as lower mortality and less postoperative pain. The disadvantage of the laparoscopic approach is the increased incidence of gastrojejunal anastomotic stricture and internal hernia. The increased incidence of internal hernia after laparoscopic bypass is due to the lack of adhesion formation and the resulting mobility of the bowel. A similar increased incidence of internal hernia is seen in immunosuppressed patients, and is also thought to be due to decreased adhesion formation.
The reoperation rate after LRYGB has been reported at 6.9% to 13%, with early studies showing reoperation rates as high as 42%. The most common secondary operations are cholecystectomy, lysis of adhesions, liver biopsies, and umbilical hernia repairs. Reoperations may be classified as early or late reoperations. Early operation, defined as within 90 days of the initial operation, accounts for 18% of all reoperations. The most common indication for early reoperation is bowel obstruction or obstructive symptoms due to gastrojejunal stricture, obstruction at the jejunojejunal (JJ) anastomosis, malorientation, or adhesive disease. Late reoperation, occurring after 90 days, is most commonly done for exploration secondary to pain, nausea, or vomiting of unclear etiology, but can also be due to adhesive obstruction or internal hernia. Although studies vary, the incidence of internal hernia after LRYGB is somewhere between 1.8% and 7.6%. Internal hernia is the indication for less than half of reoperations after LRYGB. The median time to reoperation for internal hernia ranges from 15 to 33.5 months. The drastic weight loss leading up to this time frame results in increased intraabdominal space, bowel mobility, and widening of previous mesenteric defects due to mesenteric fat loss. The average excess weight loss at time of reoperation is 54% to 90%. Due to this relatively delayed complication after surgery, studies reporting internal hernia rates prior to at least 2 years' median follow-up may have a misleadingly low incidence.
Presentation
As with abdominal wall hernias, symptoms of obstruction predominate with internal hernia. The lack of overt visual cues makes the diagnosis difficult, so suspicion must be high. In LRYGB, there are three potential segments of bowel that may become obstructed, and it is important to understand the complex anatomy defining an RYGB to understand variance in presentation. Roux limb obstruction most commonly results in ill-defined epigastric and left upper quadrant pain temporarily relieved with emesis. Signs of high-grade obstruction will be present in 50% of patients, and 40% of patients will have abdominal pain. Common channel obstruction presents in much the same fashion; however, bilious emesis indicates that obstruction is beyond the JJ anastomosis. Finally, herniation of the biliopancreatic limb, a rare event, may result in pain, remnant gastric distention, tachycardia, and hiccoughs.
Physical exam findings are generally nonspecific; however warning signs of bowel ischemia include tachycardia, fever, and tenderness to palpation. Laboratory examinations are generally nondiagnostic, but patients with internal hernia may present with amylasemia and leukocytosis. Leukocytosis, accompanying the physical exam findings described earlier, necessitates early diagnostic laparoscopy if an alternative diagnosis is not clear by imaging. The lack of a hernia sac in LRYGB, which may be present in some forms of congenital internal hernia, allows herniation of long segments of bowel and may lead to catastrophic ischemia.
Anatomy of the Roux-en-Y
Before attempting interpretation of imaging or operative exploration, it is paramount to thoroughly understand the anatomy of an RYGB. Knowledge of the specifics of a patient's index operation is as important here as for any other operation. The typical RYGB has a 100- to 150-cm Roux limb anastomosed to a 15-mL gastric pouch. The Roux limb may be passed anterior or posterior to the transverse mesocolon (antecolic or retrocolic, respectively) and remnant stomach ( Fig. 74.1 ). Distally, the Roux limb will be anastomosed to the biliary limb, commonly called the JJ anastomosis. Distal to the anastomosis, the bowel is called the common channel or limb. The biliary limb includes the length of the duodenum and approximately 30 cm of jejunum measured from the ligament of Treitz. There are two potential sites of herniation in any RYGB. A defect in the mesentery at the JJ anastomosis (Brolin space) may occur. When the Roux limb traverses the transverse colon, the aperture created by the crossing of the two bowels' mesenteries creates what is known as a Petersen defect. Retrocolic passage of the Roux limb at the index operation creates a third potential aperture in the transverse mesocolon, where bowel may herniate alongside the Roux limb. Closure or nonclosure of all of these defects at the index operation has been described. There is evidence of decreased incidence of internal hernia with closure of every defect at initial operation. This is preferably performed with nonabsorbable suture in a running fashion. Reported closure of the defects does not rule out the potential for internal hernia in these locations because closure breakdown or massive weight loss can widen spaces that were once thought to be obliterated.
Most closely studied with regard to internal hernia is the antecolic versus the retrocolic approach to LRYGB. The retrocolic approach was originally favored due to fear of excess stretch on the gastrojejunal anastomosis with an antecolic approach. Most studies report an increased incidence of internal hernia in the retrocolic approach compared to the antecolic approach of 2.3% to 8.5% versus 0.3% to 3.8%, respectively. The variability in these studies is likely due to the variability in time to follow-up. Studies with shorter follow-up time report a lower incidence of internal hernia. This is likely due to mesenteric fat loss that is inadequate to significantly widen mesenteric defects. The increased incidence of internal hernia with the retrocolic approach appears to be due to herniation through the transverse mesocolic defect. Routine closure of this defect significantly reduces the occurrence of herniation to 0.2% to 0.7%, with recent studies showing internal hernia rates similar to the antecolic approach. Because closure of the mesentery at the JJ anastomosis has become standard, the Petersen defect is the most common site of herniation in the antecolic approach to gastric bypass. Data are conflicting, but there appears to be a trend toward decreased incidence of internal hernia with routine closure of the Petersen space as well.
Imaging
Contrast-enhanced computed tomography (CT) has largely replaced any form of plain film studies with oral contrast due to its availability, speed, and multiplanar formatting capabilities. Although small bowel follow-through studies and ultrasound may aid in diagnosis, this section will focus on the CT diagnosis of internal hernia. Because internal hernias often spontaneously reduce, it is important to image the symptomatic patient with signs of internal hernia. Oral contrast may help elucidate the etiology of obstruction; however, internal hernias in this setting are typically proximal obstructions without a pylorus to slow filling of the small bowel. Thus, small amounts of oral contrast are sufficient if the patient cannot tolerate the typical dosage. Simply having the patient swallow a tolerable amount of contrast on the table immediately before scanning is adequate.
The diagnosis of any form of internal hernia on CT scan requires experience and high suspicion. Medical centers with experienced radiologists with a suspicion for internal hernia will be unable to diagnose internal hernia on imaging in 16% to 20% of cases. Despite a reportedly normal CT, concerning signs and symptoms in a patient with history of RYGB requires diagnostic laparoscopy. Generally speaking, the CT findings indicating potential internal hernia include aberrant vascular arrangement, clustering of bowel loops, and signs of obstruction. A swirl sign occurs when tension on the small bowel mesentery causes the mesenteric vessels to twist around in a whorl-like fashion and occurs in 55% of patients with internal hernia. This may be a sign of intestinal volvulus and is concerning for ischemia. Any abrupt changes in the direction of mesenteric vessels or vascular engorgement are also concerning findings. When possible, attempting to trace bypass anatomy from its origin will uncover the etiology of the patient's symptoms. Specifically, clustering of bowel loops in aberrant locations is indicative of obstruction. Lateral clustering with displacement of the colon, mass effect on the stomach, or abnormal location of the omentum (if it is known where its ultimate location was at the end of the index operation) are all signs of potential internal hernia. CT signs of obstruction in a patient with potential for internal hernia necessitate diagnostic laparoscopy. Small bowel dilation is found in 25% of patients, and mesenteric edema and free fluid are found in 11%.
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here