Overview

Most rectoanal polyps are benign growths located in the distal rectum. Histopathologic evaluation typically reveals adenomas, but lesions may undergo malignant transformation.

Signalment

• Dog and rarely cat
• Middle-aged to old
• No breed or sex predilection

Signs

• Hematochezia with relatively well-formed feces.
• Mucus-covered feces.
• Pencil-thin or ribbon-like feces.
• Tenesmus.
• Dyschezia.
• Soft, well-vascularized, friable, and often ulcerated mass(es) may be seen or palpated rectally.
• Usually single but multiple polyps can occur.
• May be pedunculated or broad-based sessile masses.

Causes & Risk Factors

Unknown

Differential Diagnosis

• Carcinoma in situ and adenocarcinoma.
• Other neoplasias-leiomyoma, lymphoma, papilloma.
• Proctitis.
• Pythiosis.
• Colitis (clinical signs are characterized by diarrhea with a marked increase in frequency, scant volume of feces, increase fecal mucus, and tenesmus. These clinical signs are vastly different to those of dogs with rectoanal polyps which do not cause diarrhea).
• Incomplete rectal prolapse.

CBC/Biochemistry/Urinalysis

Usually unremarkable

Other Laboratory Tests

N/A

Imaging

N/A

Diagnostic Procedures

• Rectal palpation.
• Direct visualization through anus.
• Proctoscopy-viable low-cost procedure that allows one to visualize the descending colon after cleansing the animal's colon. This method is suitable in most dogs and cats because the polyps are usually localized to the rectoanal or colorectal region and tend not to metastasize.
• Colonoscopy-recommended to evaluate the entire rectum and colon for additional polyps.
• Cytologic examination of polyp aspirate or scraping may help the initial diagnosis, although cytology should be interpreted with caution given the inherent challenges of differentiating benign adenomas from adenocarcinomas cytologically.
• Histopathologic examination of excised tissue is required for definitive diagnosis and to assess completeness of the excision.

Pathologic Findings

• Adenomatous polyp
• Adenomatous hyperplasia
• Carcinoma in situ

Drug(s)

• Appropriate perioperative antibiotics are recommended (e.g., cefoxitin sodium 30 mg/kg IV).
• Stool softeners may help decrease tenesmus-docusate sodium (dogs, 50–200 mg PO q8–12h; cats, 50 mg PO q12–24h) or docusate calcium (dogs, 50–100 mg PO q12–24h; cats, 50 mg PO q12–24h).
• Alternative stool softener-lactulose (1 mL/4.5 kg PO q8h to effect).

Contraindications/Possible Interactions

N/A

Patient Monitoring

• Examine the excision site 14 days after surgery and again at 3 and 6 months to ensure absence of recurrence or stricture.
• Twice yearly examination thereafter to assess for recurrence.

Possible Complications

• Recurrence
• Rectal stricture (rare)

Expected Course and Prognosis

• Dogs with focal single adenomas have a good prognosis with a low rate of recurrence.
• Dogs with multiple and/or diffuse lesions (involvement of >50% of circumference of rectal wall) have much higher rates of recurrence.
• Malignant transformation of benign lesions can occur in up to 50% of dogs.
• Excised tissues should be submitted for histopathology even when preoperative biopsies have been performed. The diagnosis may change in up to one-third of the cases in which preoperative endoscopic biopsies are performed.

See Also

• Adenocarcinoma, Anal Sac
• Dyschezia and Hematochezia
• Rectal and Anal Prolapse

Abbreviation

• NSAID = nonsteroidal anti-inflammatory drug

Internet Resources

http://www.jr2.ox.ac.uk/Bandolier/band129/b129–6.html. This site reviews the mixed results of clinical trials using various NSAIDs in humans.

Author Eric R. Pope

Consulting Editor Stanley L. Marks