The anal canal is 3–4 cm long in males and slightly shorter in females. It consists of two concentric muscle layers known as the internal and external sphincters (Fig. 17.1). The internal sphincter is a condensation of the circular smooth muscle of the rectum and is a continuation of the circular muscle of the gastrointestinal tract. It is controlled by the autonomic nervous system with fibres from the pelvic sympathetic nerves, the lower lumbar ganglia and the pre-aortic/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, so 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. 17.2). 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.

Fig. 17.1 Musculature of the anorectum.

Fig. 17.2 The puborectalis sling establishing the anorectal angle.

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 epithelium of the anal canal is specialized and contains three distinct zones. The external zone (from dentate line to anal verge) is keratinized, stratified squamous epithelium. There is a short, modified, anal transitional zone of non-keratinized squamous epithelium, which lies immediately proximal to the dentate line, separated from the columnar epithelial 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 mid-anal canal (Fig. 17.3). 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 so conditions affecting this region, such as abscess, anal fissure or tumour, result in anal pain.

Fig. 17.3 The lining of the anorectal canal.

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 non-keratinized 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 4–8 specialized 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 mid-anal canal; these glands have ducts that open directly on to the dentate line (Fig. 17.4). They are involved in the aetiology of perianal abscess and fistula-in-ano. The function of the anal glands is to secrete mucus, lubricating and protecting the delicate epithelium of the anal transition zone. The ducts from these glands open into the folds of mucosa at the dentate line. The relevance of these glands lies in the fact that they are the source of most perianal abscesses. When an anal gland duct becomes occluded, the obstructed gland may become infected with gut organisms such as coliforms, and anaerobic bacteria such as Bacteroides.

Fig. 17.4 Principal anorectal spaces in relation to the anal sphincters and rectum.

The anal (haemorrhoidal) cushions

Although the internal and external sphincters, the pubo- rectalis sling and the anorectal angle play important roles in maintaining anal continence, fine control is aided by the anal ‘cushions’ that lie in the submucosa within the anal canal, above the dentate line. The anal cushions are specialized vascular structures comprised of 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 because there are three terminal branches of the artery (left, right posterior and right anterior, corresponding with 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 specialized anal cushions; indeed, haemorrhoids are uncommon in patients with portal hypertension, despite the fact that the anal canal represents a potential portosystemic anastomosis.

Summary Box 17.1 Factors maintaining anal continence

• Intact anorectal and pelvic floor sensation

• Intact anal sphincters and levator ani

• Preservation of the anorectal angle

• The bulk provided by the anal haemorrhoidal ‘cushions’.

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 anatomical 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 metastasizes to inguinal lymph nodes, whereas rectal cancer metastasizes upwards to the mesorectum and onwards to the para-aortic chain. Thus, radiotherapy fields for anal squamous cancer normally incorporate the inguinal nodes.

Summary Box 17.2 Causes of severe acute anal pain

• Perianal abscess

• Anal fissure

• Thrombosed haemorrhoids

• Perianal haematoma

• Anorectal cancer.

Anorectal disorders

Haemorrhoids

Despite haemorrhoids (colloquially known as piles) being very common, the aetiology remains obscure. Almost all haemorrhoids are primary, with only a tiny proportion due to other factors, such as a cancer in the distal rectum. Haemorrhoids are enlarged, prolapsed anal cushions and the pathophysiology involves degeneration of the supporting fibroelastic tissue and smooth muscle, with enlargement and protrusion of the cushions at the 3, 7 and 11 o’clock position. As the cushions prolapse, there is keratinization and hypertrophy of the overlying anal transitional zone and eventually prolapse of the columnar epithelial component in advanced stages. However, the underlying cause of the stretching of the fibroelastic support is unknown. Constipation and straining at stool are common features. 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 due to 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 aetiological factor. However, as with other putative aetiological factors, there is no real evidence for cause and effect.

piles, it is important to consider that the haemorrhoidal cushions contribute to fine control of continence. Hence, an element of anal incontinence can be one of the long-term sequelae of any haemorrhoidectomy. Surgery should not be considered lightly.

Fissure-in-ano

Fissure-in-ano is a common condition characterized by a linear anal ulcer, often with the internal sphincter visible in the base, affecting the anal canal below the dentate line from the anal transition zone to the anal verge (Fig. 17.7). There is often little in the way of granulation tissue in the ulcer base. Owing to failed attempts at healing, there may be a tag of skin at the lowermost extent of the fissure, known as a ‘sentinel pile’. At the proximal extent of the fissure there may be a hypertrophied anal papilla. Sometimes fissures will heal incompletely and mucosa will bridge the edges of the fissure. This results in a low perianal fistula and may present years later. Fissures are most frequently observed in the posterior midline of the anal canal, although anterior fissures may occur in women following childbirth; they are rarely seen in males.

Fig. 17.7 Anal fissure.

A The fissure (arrow) comprises a linear ulcer at the typical 6 o’clock position (arrow). B Explanatory diagram.

The condition most commonly affects people in their twenties and thirties, with a slight male preponderance. Most fissures are idiopathic, but it is clear that 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 circle of anal pain and sphincter spasm that causes further trauma to the anal mucosa during defaecation. Fissures may be acute and settle spontaneously, but chronic anal fissure is defined as an ulcer that has been present for at least 6 weeks. 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. Fissure is an uncommon complication of haemorrhoidectomy and results from a non-healing wound combined with anal spasm.

Fissure-in-ano is one of the most common causes of constipation in infants and children. The pain associated with the fissure leads to a pattern of behaviour in which the child tries to avoid 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 and diagnosis

The most common symptoms are pain on defaecation in a young patient. There is often associated rectal bleeding of the outlet type, with blood on the paper or dripping into the pan after passing the motion. The amount of bleeding is usually minor and there may be some staining or mucous discharge in the underwear. Patients often report that it is painful to wipe the anus after moving the bowels. Pain is the predominant symptom and may be burning, tearing or sharp in nature. It may last a few hours after defaecation. There may be a history of constipation, which could be aetiologically responsible for the tear, but is more likely a response to the pain.

The diagnosis should be suspected from the history alone and is confirmed by gently parting the superficial part of the anal sphincter with the 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 (Fig. 17.7). It is often too painful to perform a digital rectal examination or a proctoscopy, and so this is best left until after treatment is instigated. However, it is important to complete clinical assessment with rigid sigmoidoscopy at a later date. A full history is important to exclude previous perianal surgery, perianal abscess, trauma during childbirth or symptoms consistent with Crohn’s disease.

Management

Many acute fissures resolve spontaneously and so treatment should be reserved for chronic symptoms of 6 weeks’ or more duration. Having established that the fissure is primary, treatment is aimed at alleviating pain and anal spasm in order to break out of the vicious circle. It is important to document reproductive history for females, as surgery may have implications for future anal continence.

The optimal approach is conservative in the first instance. Stool softeners may help, but rarely effect a cure as the sole treatment. Chemical sphincter relaxation is first-line treatment of choice using topical 0.5% diltiazem or nitrates (glyceryl trinitrate 0.2–0.5%) as a cream applied 12-hourly to the anal canal. Headaches can be a dose-limiting side effect especially with topical nitrates, but healing can be achieved in 50–70% of chronic fissures. Other means of reduction in sphincter tone include direct injection of the sphincter with botulinum toxin, which temporarily paralyses the sphincter.

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 has been abandoned, as it is associated with significant sphincter damage and the risk of incontinence (EBM 17.2). Lateral sphincterotomy is the most common operation for anal fissure and involves controlled division of the lower half of the internal sphincter 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 have had birth-related anal sphincter damage. In women, it may therefore be more appropriate to avoid further division of any sphincter muscle, and this can be achieved using an anal advancement flap or a rotation flap to cover the ulcerated base of the fissure and allow new, well-vascularized skin to heal the ulcer and reduce the associated anal spasm.

17.2 Anal fissure

‘A step-wise hierarchical approach to treatment is optimal comprising medical therapy (diltiazem cream then botulinum toxin), internal sphincterotomy or anal advancement flap. Anal stretch is an outdated surgical treatment and is associated with a significant excess risk of faecal incontinence.’

Nelson RL. Non surgical therapy for anal fissure. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD003431. DOI: 10.1002/14651858.CD003431.pub2.

Nelson RL, Chattopadhyay A, Brooks W, Platt I, Paavana T, Earl S. Operative procedures for fissure in ano. Cochrane Database of Systematic Reviews 2011, Issue 11. Art. No.: CD002199.DOI: 10.1002/14651858.CD002199.pub4.

Perianal abscess

Perianal abscess is a nonspecific term encompassing abscesses in the perianal, intersphincteric, ischiorectal or pelvirectal spaces (Fig. 17.8). Perianal suppuration is common, affecting men three times more frequently than women.

Fig. 17.8 Spread of infection from the anal gland to the anorectal spaces and resultant abscess formation.

Conditions that predispose to perianal abscess include Crohn’s disease and ulcerative colitis, as well as any cause of immunosuppression such as haematological disease, diabetes mellitus, chemotherapy and human immunodeficiency virus (HIV) infection. Most patients who present with perianal abscess have no predisposing factors and most abscesses are cryptoglandular, initiated by blockage of the anal gland ducts (see Fig. 17.3). The obstructed anal gland becomes secondarily infected with large bowel organisms such as Bacteroides, Streptococcus faecalis and coliforms. The fact that the anal glands are situated in the intersphincteric space (see Fig. 17.4) explains the routes that the infection may take as pus tracks along the line of least resistance through the tissue spaces. Rarely, patients with established sepsis elsewhere may develop metastatic suppuration in the perianal region.

Clinical features

In cases where the abscess remains localized within the intersphincteric space, the patient presents with acute anal pain and tenderness. There is usually no evidence of suppuration on inspection of the perianal region. Pain often prevents digital examination, and so general anaesthetic is required. The main differential diagnosis is acute anal fissure. The diagnosis is confirmed by demonstration of a localized pea-sized lump in the intersphincteric space. True perianal abscess is the most common type, in which pus tracks inferiorly to appear at the perianal margin between the internal and external sphincters (Fig. 17.8). Symptoms are usually of 2–3 days’ duration and the abscess may have discharged spontaneously. Systemic upset is minimal and anal pain is the predominant presenting complaint.

Infection may extend into the ischiorectal space resulting in ischiorectal abscess, which is a relatively uncommon but serious problem. Poorly controlled diabetes is a common underlying correlate and should be excluded in all cases. As the ischiorectal space is horseshoe-shaped and there are no fascial barriers within it, infection can track extensively, including posteriorly around the anus to affect the contra-lateral space. In such cases, the patient is toxic and pyrexial with a large, painful, fluctuant, brawny swelling affecting both buttocks, due to large volumes of pus. There is a history of perianal pain for several days, associated with difficulty in sitting.

Infection tracking upwards from the infected anal gland through the upper part of the intersphincteric space may result in a high intersphincteric (high intermuscular) abscess or a pelvirectal abscess. As these spaces encircle the anorectum above the levator muscles, abscesses can be bilateral and often present with a major systemic upset. These are complex problems meriting specialist management. With high abscesses, it is also important to consider intra-abdominal sepsis from Crohn’s or diverticular abscess.

Management

An established abscess will not respond to antibiotics alone and requires surgical drainage. Treatment of perianal abscess is usually straightforward and involves drainage of the pus under general anaesthetic. Most cases are adequately dealt with by incising and deroofing the abscess at the point of maximal fluctuance. However, anatomical considerations are important, as inappropriate incision of sphincter muscle can result in incontinence in the long term. Furthermore, drainage of pus through the wrong space will create a perianal fistula (see below). At operation, pus should be sent for bacteriological assessment to determine the causative organism(s). In uncomplicated cases, antibiotics have no place after incision and drainage. Where there is extensive cellulitis, as is often the case with ischiorectal abscess, parenteral antibiotics, such as broad-spectrum cephalosporins and metronidazole, should be administered. Parenteral antibiotics are mandatory for diabetic patients with peri-anal sepsis. Unusually complex perianal sepsis or recurrent abscess should raise suspicion of underlying Crohn’s disease. Sigmoidoscopy and rectal biopsy should be performed and the roof of the abscess sent for histology.

Summary Box 17.5 Anorectal sepsis

• Most anorectal sepsis is cryptoglandular

• Perianal and ischiorectal abscesses most common anorectal abscesses

• Recurrent abscess should raise suspicion of fistula and Crohn’s disease

• Abscess requires incision and drainage.

Fistula-in-ano

The underlying pathogenesis of the vast majority of cases of perianal abscess or anal fistula is obstruction of the anal gland duct. This results in stasis and infection of the anal gland (cryptoglandular infection). Abscess precedes all such cases of fistula, although the sepsis is often subclinical. Inappropriate surgical drainage of perianal abscess is responsible for a small but significant proportion of fistulae. Figure 17.9 is a simplified diagram showing the classification of fistula-in-ano. A fistulous tract should be suspected in all patients with recurrent perianal abscess. Typically the patient presents repeatedly with an abscess that intermittently points and discharges pus on to the perianal skin. However, there is no need to search routinely for a fistula when draining straightforward perianal abscesses. Inexpert probing may inadvertently induce a fistula.

Fig. 17.9 Categories of fistula-in-ano.

A Low intersphincteric and trans-sphinteric. B Ischiorectal and suprasphincteric.

In addition to cryptoglandular aetiology, perianal fistula may be due to Crohn’s disease, anal trauma, inexpert surgical drainage and anorectal carcinoma. Other rare causes include ulcerative colitis, tuberculosis and actinomycosis. Around 10% of patients with small intestinal Crohn’s disease without colorectal involvement, have perianal disease. Hence, it is important to exclude Crohn’s disease in patients with recurrent perianal fistula or sepsis resistant to treatment.

Clinical features and assessment

In most cases, the patient presents with a chronically discharging opening in the perianal skin, associated with pruritus and perianal discomfort. A detailed clinical history is essential to determine any predisposing medical conditions or previous surgery. Investigation requires examination under anaesthetic (EUA) by a colorectal specialist when the fistula should be probed to trace the tract from external to the internal openings. Goodsall’s Law is a rough rule of thumb as to the likely course of fistulous tracts. Thus, when the fistula opens on the perianal skin of the anterior anus, the tract usually passes radially directly to the anal canal. However, when the opening is posterior to a line drawn between the 3 o’clock and 9 o’clock positions (Fig. 17.10), then the tract usually passes circumferentially backwards and enters the anal canal in the midline (6 o’clock position). It is essential to avoid inducing further fistulae by ill-advised probing of the region. It is important to determine whether the fistula is low or high (Fig. 17.9), as the prognosis and treatment are different for each. Most fistulae can be delineated and treated at EUA, but complex cases may merit magnetic resonance imaging (MRI). MRI of a complex high fistula involving the pelvirectal space is shown in Figure 17.11. Endoanal ultrasound may be useful. Further investigation to exclude Crohn’s disease may be appropriate, involving colonoscopy, small bowel MRI or small bowel follow-through.

Fig. 17.10 Goodsall’s rule.

Fig. 17.11 Coronal MRI scan of complex pelvirectal fistula (arrow).

Management

Treatment is determined by the course of the fistula tract. Usually, low fistulae can simply be laid open and allowed to heal. However, where a significant proportion of the internal and/or external sphincter is involved, then laying open the tract will result in faecal incontinence. In such complex cases, the fistula tract can be probed and a seton passed along its length (Fig. 17.12) to allow the fistula to drain. Once it is drained, a tighter seton can be applied that will gradually cut out through the sphincters, allowing them to heal behind the seton. Applying such a cutting seton maintains the ends of the sphincters together and minimizes the risk of incontinence. High fistulae may be treated by an anorectal advancement flap. This involves raising a flap of rectal wall and upper internal sphincter. The flap is advanced distally to close the internal opening. The external opening and superficial part of the tract heals as there is no faecal stream to maintain the sepsis. In some complex cases, a defunctioning colostomy may be necessary.

Fig. 17.12 A seton encircling a trans-sphincteric fistula.

A seton is a piece of surgical thread, suture material or specialized tie that is passed through the fistula. It is tied in a loop to allow the fistula to drain (loose seton) and/or to cut slowly through the sphincter muscle, with the muscle healing behind the advancing seton (tight seton).

Miscellaneous benign perianal lumps

Perianal haematoma

Perianal haematoma is a painful condition caused by subcutaneous haemorrhage and formation of thrombus in the superficial space between the anoderm and the anal sphincter. A localized lump forms at the anal verge, due to blood tracking subcutaneously from haemorrhoids after the passage of a hard bowel motion. It can also arise in patients with a bleeding diathesis or those on anticoagulants. It is important to recognize the condition because it is readily treated by surgical drainage under local anaesthetic, with almost instantaneous relief. The condition will settle eventually without surgical intervention, but recognizing the haematoma will spare the patient many days of an exquisitely tender anus.

Perianal haematoma is easily recognized by the presence of a well-circumscribed, bluish dome-shaped lump under the perianal skin. The main differential diagnosis is prolapsed, thrombosed haemorrhoids, and so it is essential to make an accurate diagnosis. Inappropriate incision of haemorrhoids will result in considerable bleeding. Perianal haematoma should be readily differentiated from perianal abscess by nature of the colour and by the surrounding erythema and induration.

Anal warts

Anal warts cause discomfort, pain, pruritus ani and difficulty with perianal hygiene. Warts are also associated with an increased risk of squamous carcinoma because they are usually associated with human papillomavirus (HPV). The lesions may be very extensive or relatively sparse.

After viral infection and the development of an initial crop of warts, they may be spread extensively by scratching, which is provoked by the associated pruritus ani. Many cases resolve spontaneously, but those requiring treatment can usually be managed effectively by the application of podophyllin. More extensive cases may require surgical excision, and very extensive cases associated with dysplasia may require excision and skin grafting, combined with a temporary colostomy.

Fibroepithelial anal polyp

Fibroepithelial anal polyp it is not a neoplasm, but hypertrophic epithelium arising on a stalk from the anal canal itself. Histologically, it comprises of keratinized squamous epithelium supported by scarred, fibrotic subcutaneous tissue. The clinical history may suggest haemorrhoids as the main differential diagnosis, but this is easily discounted by digital examination and proctoscopy, which reveals the polyp on a stalk. The main differential diagnosis is of a prolapsing rectal adenomatous polyp on a long stalk. However, rectal polyps arise above the dentate line. Excision biopsy confirms the nature of the polyp.

Patients with a fibroepithelial polyp may present with a prolapsing anal lesion, discomfort on defaecation, or pruritus ani associated with faecal-stained mucus causing irritation to the delicate perianal skin. Anal polyps are usually associated with a current or previous history of perianal disease, including haemorrhoids or fissure-in-ano. Treatment of symptomatic polyps is by simple excision under general anaesthetic.

Anal skin tags

Prolapse of haemorrhoids is usually followed by a degree of regression, and may leave irregular skin at the anal verge, known as anal skin tags. Haemorrhoids often present with minor anal skin tags, but it is important to stress that the tags themselves are not haemorrhoids. Although the anus may not look particularly tidy, there is no indication to operate unless the patient is having significant problems with perianal hygiene or the lesions are causing pruritus. Anal tags associated with haemorrhoids that merit surgery can be removed at the same time as haemorrhoidectomy.

Anal cancer

Anal cancer is rare in comparison with colorectal cancer. There are around 600 new cases annually in the UK. Over 85% of anal cancers are squamous in origin and arise from the keratinized squamous epithelium of the anal margin or from the non-keratinized squamous epithelium of the anal transitional zone immediately above the dentate line. Anal verge tumours often present earlier than canal tumours because the patient becomes aware of a mass or irregular area at the anal margin. Around 5% of tumours are adenocarcinomas and these arise from the glandular epithelium of the upper anal canal or rarely from the anal glands located in the intersphincteric space. These are distinct from low anorectal adenocarcinoma. Most patients with anal cancer present in the sixth or seventh decade, but younger cases are well recognized, particularly in those with HIV and high risk activities. Other rarer tumours include melanoma, lymphoma and sarcoma.

There is a strong association between anal cancer and infection with HPV types 16 and 18. HPV infection is responsible for the majority of anal carcinomas. Smoking is a risk factor and likely interacts with viral infection. Anogenital warts are also a risk factor, as is anoreceptive intercourse. HIV infection is also a predisposing factor, owing to im-munosuppression and susceptibility to viral infection. The premalignant lesion, anal intraepithelial neoplasia (AIN), is probably the precursor of most anal carcinomas and is analogous to cervical intraepithelial neoplasia (CIN), the precursor lesion of cervical cancer. The level of AIN (1–3) is dependent on the degree of cytological atypia and the depth of that atypia in the epidermis. A high proportion of AIN 3 progresses to carcinoma and is shown in Figure 17.13. It is important to perform a cervical smear in patients with proven anal cancer. There is also an association with vulval intraepithelial neoplasia (VIN), which also has a common HPV aetiology.

Fig. 17.13 The most severe degree of anal intraepithelial neoplasia (AIN 3), the precursor of most anal squamous cancer.

Clinical features and assessment

Anal cancer is frequently misdiagnosed in the early stages because of its rarity and because symptoms of benign anal conditions are highly prevalent. Early cancer may be confused with fissures, piles and warts. Nevertheless, because of accessibility, anal tumours are readily detectable by careful clinical examination; anal pain/discomfort, bleeding or discharge into the underwear, and pruritus ani should be sought. Advanced tumours that have spread to the anal sphincters may present with incontinence. Clinical examination of anal cancer at the margin reveals an ulcerated discoid lesion at the anal verge (Fig. 17.14). Cancer of the anal canal may not be visible, although extensive lesions may protrude to the anal verge by direct spread. Careful examination under anaesthetic is required to allow tumour biopsy and sigmoidoscopy. Biopsy is essential to confirm the diagnosis, but also to determine the tissue of origin, as the treatment for squamous carcinoma varies from that for adenocarcinoma.

Fig. 17.14 Squamous carcinoma of the anal verge.

Staging

Staging is important for prognosis and also guides treatment approaches. The TNM staging system for anal cancer is shown in Table 17.1. The lymph nodes most commonly involved are the inguinal groups, particularly for anal verge cancers. Canal tumours may spread proximally to the mesorectal nodes or to the internal iliac nodes via the middle rectal lymph nodes. Lymphadenopathy alone is not sufficient to confirm lymph node spread, and accessible nodes should be biopsied because reactive changes due to infection are common. Examination under anaesthetic is an important part of clinical staging, as the tumour is often painful and the anus tender to digital examination. CT and MRI are essential; endoanal ultrasound may be helpful but usually needs to be performed under anaesthetic.

Table 17.1 TNM staging of anal cancer

T (Tumour)

• TX Primary tumour cannot be assessed

• T0 No evidence of primary tumour

• T1 < 2 cm

• T2 2–5 cm

• T3 > 5 cm

• T4a Invading vaginal mucosa

• T4b Invading structures other than skin, or rectal or vaginal mucosa (i.e. local spread to muscle or bone)

N (node)

• NX Regional lymph nodes cannot be assessed

• N0 No regional lymph node metastasis

• N1 Metastasis in perirectal lymph node(s)

• N2 Metastasis in unilateral internal iliac and/or inguinal lymph node(s)

• N3 Metastasis in perirectal and inguinal lymph nodes and/or bilateral internal iliac and/or inguinal lymph nodes

M (Metastases)

• MX Distant metastasis cannot be assessed

• M0 No distant metastasis

• M1 Distant metastasis

Management

It is important to detect anal cancer at an early stage, as extensive local invasion and metastatic disease are associated with a poor outcome. Multidisciplinary treatment of anal cancer is essential with surgeon and radiotherapist involved in assessment and treatment.

For early, well-circumscribed superficial (T₁N₀) carcinomas, wide surgical excision is the optimal treatment, as it avoids the morbidity of chemoradiotherapy. However, for T₂, T₃ and T₄ tumours, treatment comprises radiotherapy to the anal canal and inguinal lymph nodes, combined with 5-fluorouracil (5-FU) (recently capecitabine is preferred) and mitomycin C (EBM 17.3). Newer regimens of radiotherapy, combined with capecitabine and cisplatinum, are also being introduced. The usual approach is external beam radiotherapy, but radioactive implants such as selectron wires are also used in selected cases. Surgery has a limited role in the primary treatment of these lesions but does play an important part in the management of advanced disease. Surgery is reserved for radiotherapy treatment failures, when ‘salvage’ abdominoperineal excision of the anus and rectum may afford a cure in some cases and alleviate symptoms in others.

17.3 Anal cancer

‘Combination chemoradiation is the primary treatment modality for anal canal and T2, T3 and T4 tumours. Abdominoperineal resection is reserved for salvage procedures in cases of relapse after chemoradiation.’

Anal Cancer. Position Statement of the Association of Coloproctology of Great Britain and Ireland. http://www.acpgbi.org.uk/assets/documents/Anal_Cancer_Position_Statement.pdf

Glynne-Jones R, Northover JM, Cervantes A; ESMO Guidelines Working Group. Anal cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Ann Oncol. 2010 May;21 Suppl 5:v87-92. PubMed PMID: 20555110. http://annonc.oxfordjournals.org/content/20/suppl_4/iv57.full

Modern multimodality approaches involving tailored surgery and chemoradiation have radically improved the morbidity of treatment by avoiding abdominoperineal resection and permanent colostomy for many patients; the 5-year survival rate is now around 65%.

Summary Box 17.7 Anal carcinoma

• Anal carcinoma is associated with human papillomavirus types 16 and 18

• Anal intraepithelial neoplasia (AIN) is a malignant precursor

• Local surgical excision is the treatment of choice for T1N0 lesions

• Chemoradiotherapy is treatment of choice for T2, T3, or T4 lesions

• Chemoradiotherapy is mandatory for those with involved lymph nodes

• Abdominoperineal resection is reserved for failures of chemoradiation.

Rectal prolapse

Rectal prolapse is a distressing condition that can affect young and older adults, as well as children. The term rectal prolapse encompasses three types of abnormal protrusion of all, or part of, the rectal wall:

• A full-thickness rectal prolapse (procidentia) includes the mucosa and the muscular layers.

• Mucosal prolapse, as the name suggests, involves only the mucosal lining of the rectum.

• Occult rectal prolapse refers to intussusception of the rectal wall but without the prolapse protruding through the anal canal. This term also refers to the much rarer condition of solitary rectal ulcer syndrome. This consists of a prolapse of the full thickness of the anterior rectal wall only, although the terms occult rectal prolapse and solitary rectal ulcer syndrome are not synonymous.

The pathological process that results in rectal prolapse is incompletely understood. However, certain factors are clearly implicated in predisposing to the condition. Mucosal prolapse should not be confused with full-thickness prolapse. It is often associated with a degree of haemorrhoids, but whether these are causal or simply the result of a common aetiology is not understood. The majority of cases of full-thickness rectal prolapse occur in elderly women, with no obvious aetiological basis. Weight loss in the elderly with loss of fat supporting the rectum, combined with degeneration of collagen fibres and weakness of the musculature of the pelvic floor, results in loss of the anorectal angle and laxity of the rectal wall (see Fig. 17.2). In many cases, there is a deep rectovaginal pouch with a long loop of sigmoid colon that pushes down into the rectovaginal pouch and contributes to the prolapse. Occasionally, there is a clear history of obstetric injury but most patients are nulliparous.

Chronic constipation and straining at stool are the most common aetiological factors in young adults, although spinal injury, psychiatric illness, multiple sclerosis, spinal injuries and spinal tumour are predisposing factors. In children, the lack of a sacral hollow, combined with constipation and excessive straining at stool, is responsible for evagination of the rectum and protrusion of the prolapse through the anus. In children with cystic fibrosis, excessive coughing contributes to elevated intra-abdominal pressure.

Clinical features and assessment

Patients present with an uncomfortable sensation of ‘something coming down’ the back passage. Initially, this is only on defaecation, but eventually the rectum remains constantly prolapsed and will not reduce spontaneously. The patient may be able to reduce the prolapse digitally. Constipation is usually an accompanying feature. There is often a degree of faecal incontinence and there may be mucous discharge into the underwear. Blood-stained mucus is also common when the rectum remains prolapsed. The prolapse may become ulcerated and may become strangulated. In extreme cases, there may be associated uterine prolapse, alluding to the fact that the underlying aetiology relates to weakness of the entire pelvic floor.

Examination confirms the diagnosis in most cases. If the prolapse is not apparent, it will usually appear when the patient strains on a commode. A typical example of a full-thickness rectal prolapse is shown in Figure 17.15. Digital examination reveals a patulous anus, poor sphincter tone and evidence of a weak pelvic floor on straining. Rigid sigmoidoscopy will reveal cases of occult prolapse. If the history is of short duration, consideration should be given to the presence of a spinal tumour, a spinal stenosis or a prolapsed intervertebral disc. In occult rectal prolapse, radiological assessment using a defaecating proctogram or dynamic MRI may help secure the diagnosis. Conditions that might be mistaken for a rectal prolapse include large fourth-degree haemorrhoids, prolapsing rectal neoplasia, anal warts, anal skin tags and fibroepithelial anal polyp. On the basis of symptoms alone, the differential diagnosis of rectal prolapse includes rectal cancer and inflammatory bowel disease, and these should be excluded by appropriate investigations.

Fig. 17.15 Full-thickness rectal prolapse at operation prior to repair.

Management

Childhood rectal prolapse

Rectal prolapse in children is usually treated effectively by attention to maintaining a regular bowel habit with stool softeners, combined with digital reduction of the prolapse by the parents. The condition is self-limiting and surgery is rarely indicated.

Mucosal rectal prolapse

In adults, mucosal rectal prolapse can be treated by submucosal injection of sclerosant, by photocoagulation or by applying Barron’s bands to the prolapsed area. In resistant cases, a limited excision of the area, similar to a haemorrhoidectomy, is effective. Stapled anorectal rectopexy has gained favour in some centres.

Full-thickness rectal prolapse

Surgery is the only effective treatment for established full-thickness rectal prolapse. However, none of the available surgical options is wholly satisfactory. The aim of surgery is to treat the prolapse and improve any associated incontinence. Operations for rectal prolapse can be undertaken employing perineal or abdominal approaches:

• Perineal approaches aim to fixate or excise the prolapse surgically from below. ‘Delorme’s procedure’ involves the excision of the mucosa lining the prolapse, with plication of the muscle tube, and ‘perineal rectosigmoidectomy’ entails excision through the anus of the prolapsed rectum and lower part of the sigmoid. The latter may be combined with a repair of the pelvic floor (Altmeier procedure)

• Abdominal approaches aim to fix the rectum to the bony pelvis using sutures or foreign material. Increasingly these procedures are performed laparoscopically. The abdominal approach may also include resection of the redundant sigmoid colon, particularly when constipation is a predominant feature, because rectal fixation usually aggravates the constipation.

Solitary rectal ulcer syndrome

This rare condition is difficult to treat effectively because the main aetiology is behavioural and there may be a psychological overlay. The peak age-group affected is 20–40 years. The condition is associated with an introspective and anxious personality. Patients with this condition spend an inordinate amount of time in the toilet attempting to defaecate. The diagnosis is confirmed by visualizing the anterior ulcer in the low rectum, and biopsy shows the typical features of submucosal fibrosis, hypertrophy of the muscularis mucosae and overlying ulceration. Management involves the use of stool softeners and other conservative measures, along with input from a psychologist. Biofeedback may have a place in suitable patients who are compliant. Various surgical procedures have been attempted including anterior or posterior rectopexy, and even low anterior resection. However, the results are usually poor and surgery should be avoided if at all possible.

Summary Box 17.8 Rectal prolapse

• Rectal prolapse may occur at any age but most common in the elderly

• Diagnosis is clinical

• Defaecating proctogram may be required to confirm the diagnosis in a minority

• Dynamic MRI delineates the extent of the entire pelvic floor problem.

• Treatment is usually surgical: either perineal or transabdominal.

Anal incontinence

Several factors are involved in maintaining anal continence (see Box 17.1) and these may be adversely affected by any combination of structural damage to the musculature, disruption of the nerve supply, and marked intestinal hurry with defaecatory urgency (such as in ulcerative colitis). Damage to the internal or external sphincters may occur during childbirth. Peripartum nerve injury due to a prolonged 2nd stage of delivery due to pressure effects from the baby’s head or due to forceps can affect the pudendal nerves, eventually leading to denervation and atrophy of the striated muscle of the external sphincter, the puborectalis sling and the levator ani. Neurodegenerative disease is also a recognized aetiological factor. Perianal sepsis or the surgery required to treat it, may result in structural damage to the sphincter complex.

Faecal incontinence is both distressing and socially disabling, but patients are often reluctant to discuss the issue with relatives or with medical professionals due to social stigma and embarrassment. Hence, the population prevalence of incontinence is probably underestimated. Nevertheless, it has been variously estimated at 2–5% in the general population and 10% of adult females. There are a variety of specific aetiological factors but the majority of cases are ‘idiopathic’, most commonly affecting older parous women. Aetiological factors associated with anal incontinence are listed in Table 17.2.

Table 17.2 Aetiology of anal incontinence

Trauma

• Obstetric sphincter injury (including episiotomy)

• Accidental trauma (e.g. road traffic accident, bicycle injury)

• Surgical trauma (injudicious fistula surgery, drainage of perianal abscess or haemorrhoidectomy)

• Perianal sepsis

Congenital

• Anorectal atresia (usually treated surgically in childhood)

• Spinal dysraphism (spina bifida)

Neurological

• Denervation of pelvic floor following childbirth

• Multiple sclerosis

• Low spinal or sacral tumour

Miscellaneous

• Rectal cancer invading sphincter

• Perianal Crohn’s disease

• Faecal impaction

• Relative incontinence due to intestinal hurry (e.g. inflammatory bowel disease)

• Psychiatric or behavioural disorders (including encopresis)

The majority of patients are women with a past history of obstetric problems and difficult deliveries. The underlying mechanism of subsequent incontinence in such cases is complex. Although full-thickness obstetric tears are rare, significant sphincter defects have been observed to occur in 10–30% of women after vaginal delivery. As well as structural sphincter defects, prolonged labour may lead to internal pudendal nerve damage. Denervation of the pelvic floor results in atrophy of the sphincter complex and the levator ani in later life. Most cases of incontinence involve a combination of sphincter muscle damage and the secondary effects of denervation.

Clinical features and assessment

A full history is essential, with particular reference to obstetric history and any past perianal operations. Incontinence should be graded using established scoring systems, such as the Cleveland Clinic Incontinence Score, which incorporate frequency and severity of episodes of incontinence to gas, liquid or solid stool. Such scores enable more objective assessment of any improvement or deterioration in incontinence. Coexisting disease should be documented and neurological symptoms sought. A defaecation history should be sought, including the degree of defaecatory urgency. It is important to enquire about co-existing urinary incontinence. Examination to determine sphincter tone, the presence of previous scars and the state of the rectovaginal septum should be undertaken. Poor anal sensation suggests a neurogenic basis for the incontinence. Other anorectal causes of incontinence, as listed in Table 17.2, should be excluded where possible, and by rigid sigmoidoscopy in all cases. It is important to remember that any cause of intestinal hurry (such as colonic cancer, inflammatory bowel disease or even infective diarrhoea) can render incontinent a patient who had previously been coping with a more formed stool. Hence, colonoscopy is an important part of assessment. Endoanal ultrasound scanning of the sphincters delineates the presence and extent of any sphincter defect. Anorectal physiology studies document resting and squeeze anal sphincter pressures, and also define whether there is a predominant neurogenic element. Where there is any concern from the history or clinical examination regarding a spinal lesion, MRI should be performed.

Conservative management

Any remedial causes of incontinence (Table 17.2) should be addressed appropriately. However, women with ‘idiopathic’ faecal incontinence constitute the majority of cases. In older women, who almost universally have a combination of sphincter and nerve damage, conservative measures should be instigated in the first instance. Dietary advice is important to avoid exacerbating factors in the diet, such as caffeine, spicy foods and excessive alcohol. Stool-bulking agents such as Fybogel should be combined with loperamide to reduce the propulsive activity of the GI tract and induce a degree of constipation. In cases with a predominant neurogenic basis, rectal irritability resulting in faecal urgency may respond to therapy with amitriptyline (25–50 mg at night). Conservative measures should be combined with regular emptying of the rectum using stimulant suppositories or enemas. In many cases, these measures have a dramatic beneficial effect on quality of life even when minor degrees of incontinence persist.