General Considerations

•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

Diagnosis

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

•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

Treatment

Surgery

•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

Chemotherapy

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

Prognosis

•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