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