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The anorectum
Introduction
Anorectal complaints are extremely common; 2% to 3% of the population has anorectal symptoms at any given time. Pain, bleeding, discharge, itching and the presence of a lump are common presenting symptoms. Symptoms are often ignored, attributed to ‘haemorrhoids’ or hidden by the patient from relatives and doctors. It is important that perianal symptoms are elicited without embarrassment, and because these overlap with conditions affecting the large bowel, a full gastrointestinal (GI) history is essential. Basic clinical skills such as history taking and rectal examination differentiate patients who merit specialist assessment from those who can be treated symptomatically in the first instance. Misdiagnosis of perianal conditions is common and leads to delay in initiating management, with associated resource implications. Importantly, surgical management should be carefully considered, given the potential for poor long-term functional outcomes.
Applied Surgical Anatomy
The anus enables the passage of stool or flatus (when socially convenient) but is also essential in maintaining continence to gas, fluids and solids at almost all other times in healthy individuals.
Anal musculature and innervation
The anal canal is 3 to 4 cm long in males and slightly shorter in females. It consists of two concentric muscle layers known as the internal and external sphincters ( Fig. 18.1 ). The internal sphincter is a condensation of the circular smooth muscle of the rectum and is a continuation of the circular muscle of the GI tract. It is controlled by the autonomic nervous system with fibres from the pelvic sympathetic nerves, the lower lumbar ganglia and the preaortic/inferior mesenteric plexus. Parasympathetic fibres arise from the sacral plexus. The smooth muscle of the internal sphincter maintains tone and contributes to resting pressure within the anal canal, playing an important role in maintaining continence. The longitudinal muscle of the gut ends at the anus as a series of fibrous bands that radiate to the perianal skin and is of little consequence to perianal disease. The striated muscle of the external sphincter is under voluntary control, being innervated bilaterally by the internal pudendal nerves and the fourth branch of the sacral plexus. The circular muscle tube of the external sphincter blends with the lower part of the levator ani, known as the puborectalis sling ( Fig. 18.2 ). The puborectalis fibres of the levator ani originate from the posterior aspect of the pubic symphysis and pass posteriorly to join the external sphincter. The levator ani muscles themselves are also important in maintaining the relationship of the anus and rectum during defaecation.
Anal canal epithelium
The cell type of the anal canal epithelium determines why certain diseases, such as tumours and viral infections, affect only particular levels of the canal. The anal canal epithelium is specialised and contains three distinct zones. The external zone (from dentate line to anal verge) is keratinised, stratified squamous epithelium. The short, modified anal transitional zone of nonkeratinised squamous epithelium lies immediately proximal to the dentate line, separated from the columnar epithelium of the anal canal but continuous with the rectal epithelium. The anal valves are crescentic mucosal folds that form a serrated or dentate line on the luminal aspect of the midanal canal ( Fig. 18.3 ). The dentate line represents the line of fusion between the endoderm of the embryonic hindgut and the ectoderm of the anal pit. Thus the epithelium is innervated by the autonomic nervous system and is insensate with respect to somatic sensation. The canal lining below the dentate line is innervated by the peripheral nervous system, and pathology affecting this area, such as abscess, anal fissure or tumour, causes anal pain.
The composition of the epithelium of the anorectum determines the type of tumour that affects the region. Thus squamous cell carcinoma of the anal canal arises from the epithelium below the dentate line or in the transitional zone of nonkeratinised squamous epithelium. Because the canal above the anal transition zone contains columnar glandular epithelium, tumours of the upper anal canal are adenocarcinoma; they are best considered as a low rectal cancer and treated accordingly.
There are four to eight specialised anal glands located within the substance of the internal sphincter or in the space between the internal and external sphincters at the level of the midanal canal; these glands have ducts that open directly onto the dentate line ( Fig. 18.4 ). The ducts from these glands open into the mucosal folds at the dentate line. The function of the anal glands is mucus secretion, which lubricates and protects the delicate anal transition-zone epithelium. The glands are clinically relevant because they are the source of most perianal abscesses and fistula-in-ano.
The anal (haemorrhoidal) cushions
Although the internal and external sphincters, the puborectalis sling and anorectal angle play important roles in maintaining anal continence, fine control is aided by the submucosal anal ‘cushions’ above the dentate line. The anal cushions are specialised vascular structures comprising fibroconnective tissue containing arteriovenous communications, fed by the terminal branches of the superior rectal artery with inconstant anastomoses to the middle and inferior rectal arteries. There are usually three anal cushions corresponding to the three terminal branches of the artery (left, right posterior and right anterior, corresponding to the 3, 7 and 11 o’clock positions when the patient is in the lithotomy position). These positions determine the position of haemorrhoids, which are caused by distension and prolapse of the anal cushions. Haemorrhoids are not ‘varicose veins’ of the anal canal but prolapse of the specialised anal cushions; indeed, haemorrhoids are uncommon in patients with portal hypertension, despite the fact that the anal canal represents a potential portosystemic anastomosis. FLOAT NOT FOUND
Lymphatic drainage of the anal canal
Lymphatic drainage of the anus below the dentate line is to the inguinal lymph nodes. This contrasts with the lower rectum, where lymphatic drainage passes superiorly through the mesorectum to follow the superior rectal artery and on to the inferior mesenteric and aortic chains. There are also some lymphatic channels that follow the course of the middle rectal arteries to drain to the nodes around the internal iliac arteries. This anatomic distinction between the lymphatic drainage of the anus and the rectum has important implications for the management of tumours of the rectum and anus. Anal cancer frequently metastasises to the inguinal lymph nodes, whereas rectal cancer metastasises upwards to the mesorectum and onwards to the paraaortic chain. Thus anal squamous cancer radiotherapy fields incorporate the inguinal nodes. FLOAT NOT FOUND
Haemorrhoids
Haemorrhoids (colloquially known as piles ) are very common; however, the aetiology remains obscure. Almost all haemorrhoids are primary, with only a tiny proportion attributable to other factors, such as a cancer in the distal rectum.
Definition
Haemorrhoids are enlarged, prolapsed anal cushions arising from arteriovenous communications within connective tissues.
Pathogenesis
The pathophysiology involves degeneration of the supporting fibroelastic tissue and smooth muscle, with enlargement of anal cushions and protrusion at the 3, 7 and 11 o’clock positions. As the cushions prolapse, there is keratinisation and hypertrophy of the overlying anal transitional zone and, eventually, prolapse of the columnar epithelial component in later stages.
Risk factors
The underlying cause of the stretching of the fibroelastic support is unknown. Constipation and straining at stool are common features, often with associated low fibre intake. These may be aggravated by a high anal sphincter pressure, with further entrapment of prolapsed piles. Haemorrhoids during pregnancy are very common and are probably a result of hormonal effects inducing connective tissue laxity, combined with constipation and pressure from the baby’s head. Sitting on the toilet for long periods, such as when reading, is also held to be an associated aetiologic factor. However, as with other presumed aetiologic factors, there is no real evidence for cause and effect.
Clinical features
Bleeding and prolapse are the cardinal features and may occur in isolation or together. The bleeding is typically intermittent ‘outlet-type’ bright-red bleeding, separate from the stool and evident in the pan or only on wiping. Bleeding may often be painless, but there may also be aching or dragging discomfort on defaecation. Severe, constant pain is unusual, and in such cases, other pathology should be suspected. Patients may self-reduce their piles to obtain relief after each bowel motion. In the later stages, haemorrhoids remain prolapsed at all times, and there is staining of the underwear with mucus and faecal fluid. It is very unusual for patients to present with incontinence of solid faeces, and a sphincter defect should be suspected in such cases. In cases of constant prolapse, pruritus occurs as a result of discharge, with irritation of the perianal skin.
Classification
-
First-degree piles are those that bleed, are visible on proctoscopy but do not prolapse.
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Second-degree piles are those that prolapse during defaecation but reduce spontaneously.
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Third-degree piles are prolapsed constantly but can be reduced manually ( Fig. 18.5 ).
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Fourth-degree piles are irreducibly prolapsed.
Key point: Although staged according to the degree of prolapse, it is important to note that this classification is not necessarily proportional to symptoms and distress.
Acute presentation
Patients may present as an emergency with a complication of haemorrhoids.
- 1.
Thrombosis: Prolapsing haemorrhoids may acutely thrombose, and there is associated marked sphincter spasm. Thrombosed haemorrhoids are large, swollen and irreducible. They may be dark blue or even black as a result of necrosis and submucosal haemorrhage, and diagnosis is easily made on inspection. Acute pain and tenderness usually render rectal examination impossible.
- 2.
Major haemorrhage: Haemorrhoids rarely cause massive lower GI haemorrhage but should be excluded in patients presenting with a major fresh rectal bleed resulting in significant hypovolaemia and anaemia.
History
Haemorrhoids may occur at the same time as more serious pathology. Because the symptoms of piles and colorectal cancer can be very similar, a careful history is essential to guide clinical assessment and investigation. However, piles are very common, so it is important to avoid indiscriminate large bowel investigation for such a common complaint as fresh rectal bleeding. ‘Outlet-type’ bleeding comprises fresh red blood, dripping in the pan, on wiping and separate from the bowel motion. If the bleeding is outlet type, there is no alteration in bowel habit and the patient is under 50 years of age, then the chance of rectal cancer is remote. In such cases, digital rectal examination, combined with proctoscopy and rigid sigmoidoscopy, should secure the diagnosis. If piles are confirmed, then management can be instigated without recourse to imaging the rest of the colon by colonoscopy. Notably, prescriptions for topical haemorrhoidal creams increase in the year before rectal cancer is diagnosed. Hence, if no demonstrable cause of rectal bleeding is identified on examination or in older patients (>50 years) with a change of bowel habit, further colonic investigation is essential.
Examination
Following abdominal examination in the supine position, perianal examination should be performed in the left lateral position with a chaperone (all patients). Inspection may reveal prolapsed piles, associated anal skin tags or evidence of perianal excoriation from scratching. Digital rectal examination is essential to assess sphincter tone and to exclude other anal conditions. First- or second-degree piles are rarely palpable because they compress on pressure, and diagnosis is made by proctoscopy. The proctoscope should be gently inserted to the hilt and withdrawn; bulging haemorrhoids will be visible at the right anterior, right posterior and left lateral positions. Rigid sigmoidoscopy should be performed to exclude other rectal pathology.
Management
Reassurance after appropriate evaluation is all that many patients require. Specific treatment is not required for most cases because symptoms are minor and intermittent. A high-fibre diet with plenty of vegetables is commonly recommended, although there is no good evidence that this actually provides any benefit at all. However, if constipation is a feature, it does seem reasonable advice; in some cases, bulk laxatives or stool softeners may be indicated. Patients often self-medicate with proprietary ointments containing local anaesthetic. There is no good evidence from controlled trials that these are effective, but if patients find that they help, then it seems reasonable to advise their intermittent use.
Nonoperative approaches
Nonoperative management aims to cause fibrosis and shrinkage of the protruding haemorrhoidal cushion to prevent bleeding and prolapse. Current outpatient clinic approaches include the application of small rubber bands to strangulate the pile (using a special Barron bander) or heat application by infrared photocoagulation. Submucosal injection of a sclerosant (e.g., 5% phenol in almond oil) has been abandoned because of the potential severe side effects (intraprostatic injection). There is no strong evidence that any of these approaches is significantly better than doing nothing at all. In the long term, the symptoms of untreated piles tend to wax and wane, and symptom recurrence after any of these procedures is much the same as without any treatment. Rubber band ligation may be the most effective in the short term but does carry risks of bleeding and pain postprocedure ( Fig. 18.6 ). Where there is a significant cutaneous component to the piles, any of the outpatient treatments is likely to be painful because of the cutaneous nerve supply and is also unlikely to succeed. In these circumstances, the decision should be to do nothing but reassure the patient or offer an operation.
Operative approaches
Standard haemorrhoidectomy
The principle of haemorrhoidectomy involves total removal of the haemorrhoidal mass and securing of haemostasis of the feeding vessel. The wound can be left open (Milligan–Morgan) or can be closed (Ferguson), but there are rarely problems with healing or infection. In some cases, there are secondary haemorrhoids between the main right anterior, right posterior and left lateral positions, and these are also removed as part of the operation.
Stapled haemorrhoidectomy/haemorrhoidopexy/anopexy
The stapled haemorrhoidectomy technique, using a circular stapler, aims to divide the mucosa and haemorrhoidal cushions above the dentate line to transect the feeding vessels and hitch up the stretched supporting fibroelastic tissue, rather than whole haemorrhoidal mass excision in the standard haemorrhoidectomy. Stapled haemorrhoidopexy has now used extensively for symptomatic second-degree piles and the majority of third- and fourth-degree piles ( EBM 18.1 ). With all surgical approaches to treating piles, it is important to consider that the haemorrhoidal cushions contribute to fine control of continence. Hence, a degree of anal incontinence may be one of the long-term sequelae of any haemorrhoidopexy. Surgery should not be considered lightly. Staple line bleeding is the most important early complication and requires intervention to control bleeding vessels. Pain can occur if the staple line involves the sensitive anal mucosa. A randomised
Acheson AG, Scholefield JH. BMJ. 2008;336:380–383; Aly EH. Ann R Coll Surg Engl. 2015;97:490–493; Hollingshead J, Phillips R. Postgrad Med J. 2016;92:4–8; Lumb KJ, Colquhoun PH, Malthaner R, Jayaraman S. Cochrane Database Syst Rev. 2006;(4):CD005393; Simillis C, Thoukididou S, Slesser A, et al. Br J Surg. 2015;102:1603–1618.
EBM 18.1
Haemorrhoids
Anal cancer
‘Non-operative treatment is preferable wherever possible but surgery may be required for a small proportion of cases. Open haemorrhoidectomy is superior to stapled haemorrhoidectomy both in terms of symptom control and recurrence; rubber band ligation has similar efficacy to haemorrhoidectomy.’
controlled trial has shown that those who had the stapled operation had less short-term pain, but after 6 weeks, the recurrence rates, symptoms, reinterventions and quality-of-life measures favoured open haemorrhoidectomy. Given that the instrument is expensive, open haemorrhoidectomy remains a good option when surgery is indicated. FLOAT NOT FOUND
Haemorrhoidal artery ligation operation
Haemorrhoidal artery ligation operation (HALO) involves suture-ligating the feeding blood vessels to the haemorrhoid with (or without) the aid of a Doppler ultrasound probe to identify the vessels. Although the haemorrhoidal mass is not excised, the operation may be combined with procedures aimed at reducing associated prolapsed tissue (rectoanal repair, mucopexy). A recent meta-analysis comparing the clinical outcomes and effectiveness of surgical treatments for haemorrhoids revealed that traditional haemorrhoidectomy had greater complications and lengthier recovery but fewer recurrences. HALO and stapled haemorrhoidectomies were associated with less pain and faster recovery but higher recurrence rates. A randomised controlled trial suggested that both rubber band ligation and HALO had high recurrence rates. As with any operation, informed consent and discussion with the patient are essential.
Fissure-in-ano
Fissure-in-ano is common and usually affects people in their twenties and thirties, with a slight male preponderance. Fissures are most frequently observed in the posterior midline of the anal canal. Anterior fissures may occur in women following childbirth; they are rarely seen in males.
Definition
An anal fissure is a linear ulcer below the dentate line, often exposing the internal sphincter at its base, affecting the anal canal from the anal transition zone to the anal verge ( Fig. 18.7 ). There is often minimal granulation tissue in the ulcer base. Failed attempts at healing may lead to a skin tag, or ‘sentinel pile’, at the lowermost extent of the fissure. At the proximal extent of the fissure, there may be a hypertrophied anal papilla. Incomplete fissure healing, where mucosa bridges the fissure edges, may result in a low perianal fistula that can present years later.
Pathogenesis
A fissure develops when the anal mucosa is excessively stretched or traumatised. The pathophysiology involves ischaemia in the base of the ulcer, associated with marked anal spasm and a significantly raised resting anal pressure. Successive bowel motions provoke further trauma, pain and anal spasm, resulting in a vicious cycle of pain and sphincter spasm leading to further anal mucosa trauma during defaecation. Fissures may be acute and settle spontaneously. Chronic anal fissure is defined as an ulcer that has been present for at least 6 weeks.
Aetiology
Most fissures are idiopathic. Recurrent, multiple or unusually extensive fissures affecting areas other than the midline should raise the suspicion of Crohn’s disease, which can occasionally present with anal fissure as the sole initial complaint. Occasionally, anal fissure may be associated with ulcerative colitis. A fissure is an uncommon complication of haemorrhoidectomy and results from a nonhealing wound combined with anal spasm.
Paediatric
Fissure-in-ano is one of the commonest causes of constipation in infants and children. The associated pain leads to a behaviour pattern in which the child avoids defaecation. This results in stool retention and rectal stool bolus formation. The rectum becomes overdistended, and the child becomes unaware of the need to pass stool. Overflow incontinence and soiling result.
Clinical features
History
The typical presentation is severe pain on defaecation in a young patient. Pain is the predominant symptom and may be burning, tearing or sharp in nature. It is usually painful to wipe the anus, and pain may last for a few hours after defaecation. There is often associated outlet-type rectal bleeding, with blood on the paper or dripping into the pan postdefaecation, or blood streaking of the stools. The amount of bleeding is usually minor, and there may be some staining or mucous discharge in the underwear. There may be a history of constipation, which could be responsible for the tear, but it is more likely secondary to the pain. A full history is important to exclude previous perianal surgery, perianal abscess, trauma during childbirth or symptoms consistent with Crohn’s disease. It is important to remember that fissures can follow an acute attack of diarrhoea. It is important to document reproductive history for females because surgery may have implications for future anal continence.
Examination
The diagnosis should be suspected from the history alone and is confirmed by gently parting the superficial part of the anal sphincter with gloved fingers to reveal the characteristic linear ulcer. There may be an associated ‘sentinel pile’, which consists of heaped-up skin at the lowermost extent of the linear ulcer (see Fig. 18.7 ). It is often too painful to perform a digital rectal examination or a proctoscopy, so this is best left until after treatment is started. However, it is important to complete the clinical assessment with rigid sigmoidoscopy at a later date.
Management
Nonoperative
Many acute fissures resolve spontaneously, so treatment should be reserved for chronic symptoms with a duration of 6 weeks or more. Having established that the fissure is primary, treatment is aimed at alleviating pain and anal spasm to break the vicious cycle. The optimal approach is conservative in the first instance. Stool softeners may help, but they rarely effect a cure as the sole treatment. Chemical sphincter relaxation is the first-line treatment of choice using topical 2% diltiazem or nitrates (glyceryl trinitrate 0.2–0.5%) as a cream applied every 12 hours to the anal canal. Headaches can be a dose-limiting side effect, especially with topical nitrates, but healing can be achieved in about 80% of acute fissures. Other means of reduction in sphincter tone include direct injection of the sphincter with botulinum toxin, which temporarily paralyses the sphincter, but this is no better or worse compared with other topical measures. Anaesthetising the pain-sensitive anoderm using topical 5% lignocaine acts as an adjunct to the treatment and provides immediate symptomatic relief.
Operative approach
Until the relatively recent advent of chemical sphincterotomy as first-line treatment, surgery was the only option. Surgery still has a major role in the management of patients who have fissures resistant to medical treatment or who have recurrence. Anal stretching (Lord procedure) has been abandoned because it is associated with significant sphincter damage and incontinence ( EBM 18.2 ). Lateral (internal) sphincterotomy (Notara procedure) is the commonest operation for anal fissure and involves controlled division of the lower half of the internal sphincter, either to the level of the dentate line or to the length of the fissure at the lateral position (3 o’clock or 9 o’clock with the patient in the lithotomy position). There is a small but appreciable risk of late anal incontinence following lateral sphincterotomy. This is usually only to gas, but occasionally faecal incontinence to liquid or solid can occur, particularly in women who
Nelson RL, Thomas K, Morgan J, Jones A. Cochrane Database Syst Rev. 2012;(2):CD003431; Nelson RL, Chattopadhyay A, Brooks W, et al. Cochrane Database Syst Rev. 2011;(11):CD002199.
EBM 18.2
Anal fissure
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