General Considerations

•benign and malignant tumors occur with equal frequency in the rectum of dogs

•benign tumors include adenomatous polyps which are described as sessile, raised, pedunculated, single, or multiple

•malignant rectal tumors in cats and dogs include ADC and LSA

•rectal ADC in dogs is described as infiltrative, ulcerative, or proliferative


•mean age 8.5 years (range, 2-14 years)

•sex predilection: 60%-70% male

•sites: large intestine and mid-to-distal rectum

•gross appearance is variable:

•nodular (single or multiple)

•pedunculated (mid-to-distal rectum)

•annular constriction or obstruction (colon to mid-rectum)

•metastatic rate is highly variable depending on the study


•site: distal rectum

•80% are single lesions and 20% are multiple

•0%-41% local tumor recurrence rate after surgical resection

•18% rectal polyps undergo malignant transformation

•tenesmus, hematochezia, dyschezia, rectal bleeding unassociated with defecation, and polyp prolapse

•other signs can include vomiting, diarrhea and weight loss


Physical Examination

•cachexia is common

•abdominal mass is frequently palpable via either abdomen and rectal palpation

•other findings include dehydration and abdominal pain

Laboratory Tests

•anemia and leukocytosis reported but occur less commonly than small intestinal tumors

•paraneoplastic leukocytosis reported with adenomatous rectal polyp


•endoscopy is recommended prior to definitive treatment

•biopsy samples should be interpreted histologically as cytologic misdiagnosis is common with intestinal ADC being misdiagnosed as either septic inflammation or LSA

•biopsy samples are often small and superficial resulting in false-negative diagnosis if lesion is either submucosal or associated with surface ulceration and necrosis



Surgical Techniques

•surgical approaches: rectal eversion, rectal pull-through, or resection and end-to-end anastomosis

•fecal incontinence is uncommon if rectal resection < 4 cm

•however, fecal incontinence and incisional dehiscence is common if > 4 cm rectum is resected with rectal pull-through surgery

•transanal endoscopic resection of benign rectal tumors has been described in 6 dogs

•incontinent end-on colostomy has been described in the management of 1 dog with rectal ADC


•cryosurgery has been used in 1 dog rectal leiomyosarcoma complications include rectal prolapse, perineal hernia, and stricture formation

•cryosurgery of pedunculated stalk can be considered with rectal polyps


•multiagent protocols recommended for LSA as either adjuvant therapy or sole treatment for diffuse disease

•chemotherapy is also recommended for cats with intestinal plasmacytoma and MCT

•no effective chemotherapy for ADC, but combination of 5-fluorouracil and cisplatin may be effective

•piroxicam (suppository or oral) for rectal tubulopapillary polyps with significant PR or CR in 88% (7/8)


Rectal Polyp

•0%-41% local tumor recurrence rate after surgical resection or cryosurgery

•18% rectal polyps undergo malignant transformation

•survival time > 1 year with few deaths related to polyp

•survival time for polyps diagnosed as carcinoma in situ 5-24 months

Benign Rectal Tumors

•5 dogs alive between 5-20 months after surgery

•3 local recurrence with recurrence as carcinoma in one dog

Rectal Carcinoma

•mean survival time 22 months following surgery

•radical surgery associated with high complication rate and poor survival (< 1 week)

•local appearance may be predictive of survival:

•mean survival time 32 months if pedunculated

•mean survival time 12 months if nodular or cobblestone

•mean survival time 1.6 months if annular

•mean survival time 24 months following cryosurgery

•survival times following electrocautery are reported between 18-29 months

•MST 7 months following intraoperative orthovoltage radiation therapy with 12-month survival rate 67%, local tumor recurrence in 54%, and median DFI 6 months







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