Anal Sac Disease in Dogs and Cats

Anal sacs can become impacted, infected, abscessed, or neoplastic. Decreased manual expression of the sacs during defecation, poor muscle tone in obese dogs, and generalized seborrhea (which produces glandular hypersecretion) lead to retention of sac contents. Such retention may predispose the gland to bacterial overgrowth, infection, and inflammation. Obstruction of the anal sac duct when an infection is present can lead to abscess formation.

Clinical signs of anal sac disease are related to pain and discomfort associated with sitting or defecation. Scooting, licking, biting at the anal area, and painful defecation (dyschezia) with tenesmus may be noted and may lead to constipation. Induration, abscesses, and fistulous tracts are common.

With impaction, hard masses are palpable in the anal sac area. The sacs are packed with a thick, pasty, brown secretion, which can be expressed as a thin ribbon only with a large amount of pressure. When the sacs are infected or abscessed, severe pain and often discoloration of the area are present. Fistulous tracts can form from abscessed sacs and rupture through the skin. Fistulous tracts must be differentiated from perianal fistulas.

Anal sac neoplasms are usually nonpainful and may be associated with perineal edema, erythema, induration, or fistula formation. Apocrine gland anal sac adenocarcinomas typically occur in older dogs. In early studies, female dogs were overrepresented, but subsequent larger studies have not shown a sex predilection. Affected dogs may develop clinical signs secondary to hypercalcemia, such as polyuria and polydipsia, or problems related to the perineal mass, such as constipation or tenesmus.

• Physical examination

• Microscopy, ultrasonography, or biopsy

Diagnosis of impaction, infection, or abscessation is confirmed by digital rectal examination, at which time the anal sacs can be expressed. Microscopic examination of the contents from infected sacs reveals large numbers of polymorphonuclear leukocytes and bacteria. With recurrent infections, culturing the contents may be helpful to guide antimicrobial selection.

A tumor (anal sac apocrine adenocarcinoma) should be suspected in anal sacs that are firm, enlarged, and nonexpressible, even with irrigation. Ultrasonographic evaluation may be useful to determine whether a firm, nonexpressible anal sac is due to infection/abscessation or to neoplasia. If a tumor is suspected, the diagnosis should be confirmed by biopsy. Regional and systemic metastasis should be evaluated, and serum calcium concentration should be measured to check for paraneoplastic hypercalcemia.

• Manual expression and flushing

• Antimicrobials or anti-inflammatory medications

• Anal sacculectomy as needed

Impacted anal sacs should be gently manually expressed. A softening, or ceruminolytic, agent or saline solution (0.9% NaCl) can be infused into the sac if the contents are too dry to express effectively. Infected sacs should be cleaned with antiseptic, followed by local and systemic antimicrobial therapy. Hot compresses, applied every 8–12 hours for 15–20 minutes each, are beneficial for abscesses. Repeated weekly flushing, combined with infusion of a steroid-antimicrobial ointment, may be needed. Adding supplemental fiber to the diet can increase fecal bulk, facilitating anal sac compression and emptying during defecation.

If medical treatment is ineffective or if neoplasia is present, surgical excision of the sac is indicated. The closed technique for excision is preferred and has the lowest complication rate. However, fecal incontinence, a common complication of anal sac surgery, can result from damage to the caudal rectal branch of the pudendal nerve and may be complete if damage is bilateral. Chronic fistula formation may be evident when sac removal is incomplete or when the sac ruptures. Scar formation in the external anal sphincter may result from surgical trauma and result in tenesmus.

• Also see pet owner content regarding anal sac disease in dogs and cats.