ANORECTAL DISEASES

The presenting signs of anorectal disease may include any of the following: dyschezia, hema- tochezia, constipation, anal discomfort (licking, scooting), ribbonlike feces, fecal incontinence, anal discharge, foul perianal odor, matting of perianal hair, and perianal dermatitis.

Anorectal Prolapse

Anorectal prolapse is usually a consequence of an underlying disorder that produces persistent straining; thus it is associated with (1) intestinal diseases that cause diarrhea and tenesmus,

(2) anorectal diseases that cause dyschezia,

(3) lower urinary tract and prostatic diseases that cause stranguria, and (4) dystocia. Partial prolapse involves only the rectal mucosa and appears as a red, swollen, donut-shaped ring of prolapsed mucosa. Complete prolapse involves all layers of the rectal wall and appears as an edematous cylindric-shaped mass. The prolapsed tissue may be viable (pink or red and moist) or necrotic (blackened and dry). A thermometer or finger should be inserted in the space between the pro­lapsed tissue and the anal sphincter to probe for a cul-de-sac. If there is none and resistance is not met, the prolapsed tissue is an intussusception of ileum or colon rather than an anorectal prolapse.

Management of anorectal prolapse involves both repair of the prolapse and treatment of the underlying cause. Minor prolapses in which the tissue is viable are treated by reduction and med­ical therapy to reduce tenesmus and prevent repro­lapse, such as an anticholinergic-antispasmodic drug, hydrocortisone retention enema, mesalamine enema, or mild sedation. See Table 8-2 for dosages. A temporary (2 to 3 days) anal purse-string suture may be required in patients with persistent straining that produces recurrence of the prolapse.

Perineal Hernia

Perineal hernia occurs when weakness of the pelvic diaphragm muscles fails to support the rec­tal wall, resulting in persistent rectal distention and impaired defecation. The pathogenesis of the weakened pelvic diaphragm is poorly under­stood. Older male dogs are almost exclusively affected, although perineal hernia has also been reported in cats. The hernia usually contains out­pouched rectum and can be either unilateral or bilateral; unilateral hernias are predominantly right-sided. The rectal defects associated with perineal hernia have been classified as (1) saccu­lation, when unilateral loss of support allows expansion of the rectal wall to one side; (2) dila­tion, when bilateral loss of support allows gener­alized distention of the rectum; (3) deviation or flexure, when the rectum curves or bends to one side within the hernia sac; and (4) diverticulum, when there is an outpouching of mucosa through a defect in the rectal wall. The hernia sac may also contain retroperitoneal fat, prostate gland, or rarely abdominal organs such as the urinary bladder.

The clinical signs of perineal hernia include constipation, obstipation, dyschezia, and tenesmus. Stranguria may occur with herniation of the uri­nary bladder and associated urethral obstruction. The diagnosis is based on palpation of a reducible swelling ventrolateral to the anus and rectal palpa­tion of the weakened pelvic diaphragm and rectal dilation.

Initial treatment is aimed at evacuating retained feces from the rectum as described in the section on constipation and dyschezia. Urethral catheteri­zation or cystocentesis also may be necessary ini­tially to relieve urinary obstruction.

Anorectal Foreign Bodies and Fecoliths

Ingested foreign bodies such as bones, toys, sticks, or sewing needles can sometimes pass unobtrusively through the GI tract and become lodged transversely within the rectum or at the anal sphincter. In addi­tion, foreign objects are occasionally inserted into the anus of an animal by a malicious or deranged person. Older cats are sometimes presented for inability to pass a firm lump of feces (fecolith) that lodges in the anal canal between the internal and the external sphincter. Whenever a foreign body or fecolith is lodged in the anal canal or rectum, defe­cation becomes painful or impossible and signs of dyschezia, tenesmus, and secondary fecal impaction occur.

Most anorectal foreign bodies and fecoliths can be detected and removed by rectal palpation, although sedation or anesthesia is often necessary. In some cases a proctoscope may facilitate foreign body extraction. There are two potentially serious complications of anorectal foreign bodies: rectal laceration, resulting in retroperitoneal cellulitis, and anorectal stricture.

Anorectal Stricture (Stenosis)

Strictures of the anus or rectum may result from the trauma caused by passage of sharp foreign bod­ies (especially bones), from postsurgical scarring after anorectal surgery, and from the chronic inflammation of anal sac disease, perianal fistulae, or proctitis. Anorectal strictures cause dyschezia, tenesmus, hematochezia, and secondary constipa­tion. The stricture can usually be identified by digital rectal palpation, proctoscopy, or barium enema contrast radiography. Surgical correction is usually required.

Anal Spasm

Some authors report a rare form of severe dyschezia, in which the anal sphincter appears to contract in spasm when the patient attempts to defecate; the patient may cry out in pain, move about frantically before stopping to make another attempt to defecate, turn and stare at its hindquar­ters, and appear extremely anxious.

Congenital Defects of the Anus and Rectum

Imperforate Anus and Rectal Agenesis Imperforate anus and rectal agenesis are uncom­mon congenital malformations of cloacal develop­ment that result in an absence of a patent anal opening for defecation. Consequently, within days or weeks of birth the affected puppy or kitten shows signs of abdominal distention and discom­fort, tenesmus, restlessness, vomiting, and loss of appetite. The diagnosis is established by absence of an anal opening. The variations in the malforma­tion range from an imperforate anal mem­brane covering the anal opening (atresia ani) to varying degrees of rectal agenesis (rectal atresia), in which the rectum ends in a blind pouch at some distance cranial to the anus. The terminal end of the rectum can be delineated radiographi­cally by the intraluminal air when a lateral ra­diograph is exposed with the patient's hind end slightly elevated. In some patients, imperforate anus is associated with genitourinary defects such as rectovaginal fistula.

The treatment for atresia ani is surgical opening and removal of the retained anal membrane, usu­ally producing favorable results.

Rectovaginal Fistula

Rectovaginal fistula is a rare congenital malforma­tion of females characterized by passage of fecal material from the vaginal opening. In many cases there also is an imperforate anus. Persistent fecal incontinence through the vagina leads to perivulvar dermatitis. Colonic distention usually occurs once the puppy or kitten begins eating solid food. The defect can be surgically corrected, but the progno­sis is guarded. Other related anorectal anomalies that are very rare include rectovestibular fistula, anovagi- nal cleft, and rectourethral fistula.

Anal Sac Disease

Disorders of the anal sacs are the most common problem of the anal area in small animals, espe­cially in dogs. Anal sac disease has been classified into impaction, inflammation (sacculitis), infec­tion, abscess, and rupture. These probably repre­sent a continuum such that impacted anal sacs tend to become inflamed and infected, which may then lead to abscessation and finally to rupture or fistulation. All breeds of dogs can be affected. Anal sac disease is uncommon in cats and usually involves only impaction.

The specific cause of anal sac disease is poorly understood. It is believed to be associated with conditions that promote inadequate emptying of the sacs, which should normally occur during defecation when feces of normal consistency are forced through a normally functioning anal sphincter. It is therefore the abnormal retention of anal sac secretions that leads to the impaction­inflammation-infection cycle.

The most frequent clinical signs of anal sac dis­ease are related to anal discomfort and include scooting the hind end on the floor, tenesmus, and licking and biting the anal area, perineum, or base of the tail. Chewing and licking may result in areas of self-inflicted (pyotraumatic) dermatitis.

The diagnosis of anal sac disease is based on historical signs and examination of the anal sacs. The anal sacs are best examined by palpation with a gloved index finger inserted in the rectum and a thumb compressed against the skin ventro­lateral to the anus. Impaction is usually bilateral and indicated by sacs that are distended, mildly painful on palpation, and not readily expressed. The impacted contents are usually thick and pasty and dark brown or grayish brown. Anal sacculitis is associated with moderate to severe pain on palpation, and the sacs contain a thinner-than- normal, yellowish or blood-tinged purulent fluid. Anal sac abscess is usually unilateral and charac­terized by marked distention of the sac with pus, cellulitis of surrounding tissues, erythema of the overlying skin, and fever. Abscessed anal sacs may rupture through the adjacent skin, producing a draining fistulous tract.

Treatment of anal sac impaction and anal sac- culitis by manual evacuation of the sac contents to reestablish drainage may be all that is required in many patients. Follow-up examination and expression of the anal sacs again in 1 to 2 weeks are advisable. A high-fiber diet may help to pre­vent recurrences. For recurrence of impaction or sacculitis, irrigation with povidone-iodine solu­tion with a lacrimal needle and instillation of an antibiotic (e.g., an otic or ophthalmic antibiotic ointment) into the sac may be helpful, along with follow-up expression of the sacs every 3 to 4 days. Culture and sensitivity testing of the sac contents also should be considered for patients with trou­blesome recurrences. Anal sac abscesses are drained, irrigated with povidone-iodine solution, and treated with systemic antibiotics. Recurrent anal sacculitis or abscess is treated by surgical exci­sion of the sacs. Chemical cautery and cryosurgery also have been used as alternatives to surgical excision for ablation of the sacs.

Perianal Fistulae

Perianal fistulae is a chronic progressive disease characterized by deep ulcerating fistulous tracts and suppuration in the perianal tissues. The dis­ease occurs primarily in the German shepherd, although it has been reported sporadically in Irish setters, Labrador retrievers, and various other breeds. The proposed pathogenesis involves infec­tion and abscessation of the various glandular ele­ments in and around the anus as promoted by the moist contaminated environment of the area and a broad-based, low-slung tail conformation.

Dogs with perianal fistulae usually have signs of anal discomfort (licking the anal area, scoot­ing, dyschezia, tenesmus) along with any of the following: hematochezia, constipation, fecal incontinence, or foul-smelling purulent perianal discharge. Examination of the perianal area estab­lishes the diagnosis. The fistulas usually first appear as small draining puncture holes in the perianal skin with inflammation and hyperpigmentation of the surrounding skin. These small tracts then enlarge and coalesce to form large, interconnect­ing fistulas and areas of ulceration and granulation tissue. The fistulous tracts may extend deep into the perirectal tissues, and the anal sacs may also be infected or ruptured. Histopathologically, there is hidradenitis, chronic necrotizing pyogranuloma- tous inflammation of skin and hair follicles, cellulitis, necrosis, and fibrosis.

Surgery is the traditional method of treatment for perianal fistulae. Numerous surgical tech­niques have been advocated, including varying degrees of excision and debridement of diseased tissue, chemical cautery and electrocautery, and cryosurgery. It is advisable to tailor the aggressive­ness of the technique to the extensiveness of the lesions and to preserve as much normal tissue and anal function as possible. Postoperative complica­tions such as fecal incontinence, anal stenosis, and recurrence of the lesions can lead to an unaccept­able outcome. Recent studies have shown that medical therapy using cyclosporine (Sandimmune, 0.8 mg to 1.4 mg/lb orally every 12 hours) pro­duces a high rate of healing within 16 weeks, although the recurrence rate is 40%, necessitating additional treatment or surgery. In general, early diagnosis and medical or surgical intervention allows a less radical excision than is required in advanced disease, which in turn means less risk of postoperative complications and a better prognosis.

Pseudocoprostasis

Pseudocoprostasis is a condition of obstruction of the anal opening when the surrounding hair becomes densely matted with feces. It occurs most often in long-haired breeds of dogs and cats, espe­cially during bouts of diarrhea. The anal obstruc­tion leads to anal irritation, inability to pass feces, and constipation. The patient is usually restless and attempts to bite or lick at the anal region. The owner may complain of an unexplained foul odor from the patient. In addition, the matted hair often results in an underlying dermatitis and in warm weather attracts flies that may produce a maggot infestation (myiasis) of the anal area. Examination of the anal region is sufficient for diagnosis. For treatment the hair mats are clipped away and the underlying irritated skin is cleansed and treated topically. Once the obstructing hair mats are removed, defecation should occur normally; how­ever, if the patient has severe colonic impaction of feces, measures to evacuate the colon, as discussed in the Constipation and Dyschezia section may be required.

Perianal Dermatitis

Anal irritation, a common consequence of anal sac disease and other anorectal disorders, often causes licking and biting at the anal area, which may lead to perianal dermatitis. Any pruritic skin condition, most notably fleas, also may cause local dermatitis in this area. Finally, the mucocutaneous junction where the perianal skin and anal mucosa join may be severely inflamed and ulcerated similarly to other mucocutaneous junctions of the body in any of the systemic mucocutaneous dermatologic disorders such as pemphigus vulgaris, bullous pemphigoid, systemic lupus, candidiasis, and cutaneous drug eruption. Eosinophilic granuloma complex of cats also may involve the perianal region. Perianal der­matitis itself can often be treated topically, but the key is to recognize that it is usually secondary to some other anorectal or dermatologic disorder that must be identified and treated.

Anal and Perianal Tumors

The most common tumor of the anal region is the perianal (circumanal) gland adenoma of dogs. These androgen-dependent tumors occur most often in older intact male dogs, and they usually appear as small, firm, well-circumscribed nodules in the skin surrounding the anus. Perianal gland adenomas may be incidental findings unassociated with clinical signs or they may cause anal irritation with scooting and licking at the anal area. In addi­tion, they sometimes ulcerate and periodically bleed. The treatment of choice is excisional or cryosurgical removal and adjunctive castration because of their hormone dependency. Castration alone can produce regression of these tumors; however, excisional biopsy at the time of castration is the only way to rule out malignancy. Estrogens also are inhibitory for perianal gland adenomas; however, they cannot be recommended for pro­longed use because of their myelotoxic effects. Other benign tumors of the anal area are rare but include lipoma and leiomyoma.

The two most important anal malignancies are the perianal (circumanal) gland adenocarcinoma and the apocrine gland (anal sac, anal gland) ade­nocarcinoma. Perianal gland adenocarcinomas occur most often in older male dogs and may resemble an ulcerated perianal gland adenoma, except they are locally invasive and may cause diffuse thickening of surrounding tissues. They eventually metastasize to regional lymph nodes (sublumbar) and beyond. Their appearance can also be confused with a perianal fistula lesion or a ruptured anal sac. Apocrine gland adenocarcino­mas arise in the anal sac and most often affect older spayed female dogs. They are unique in that they can be an ectopic source of parathyroid hor­mone—like protein; thus even very small apocrine adenocarcinoma nodules often produce a hyper­calcemia of malignancy syndrome with polyuria and polydipsia. Other malignant tumors of the anal region include squamous cell carcinoma, melanoma, and mast cell neoplasia.

For potentially malignant lesions of the perianal area, excisional biopsy is the diagnostic procedure of choice. Thoracic and abdominal radiography and abdominal ultrasonography of the sublumbar region are indicated to evaluate for metastasis. Early exci­sion of malignant tumors of the anal region can be effective, but once extensive local invasion or regional lymph node metastasis has occurred, the prognosis for a cure is poor. Repeated partial exci­sions, radiation therapy, cryosurgery, and chemother­apy have been used for palliative therapy of inoperative malignancies of the anal region.