Rectal neoplasia: pre-operative evaluation and surgical planning

Rectal tumors are uncommonly encountered in small animal surgical practice but can be challenging to treat depending on their type, location and extent. In dogs, adenomatous polyps, adenocarcinomas, plasma cell tumors, lymphoma, mast cell tumors and hemangiosarcomas occur within the rectum. In cats the most common tumors are lymphoma and adenocarcinoma. Adenomatous polyps in dogs are well known to be precancerous lesions that have the potential to undergo malignant transformation.^1-3 Benign neglect of these tumors is therefore not recommended. Once invasion into the lamina propria and submucosa has occurred they are generally termed carcinoma in situ and once the basement membrane has been penetrated they are termed adenocarcinoma and at that stage are much more likely to metastasize. Carcinoma in situ, exhibits histologic atypia which can progress to invasive malignancy in 17 to 50% of dogs.^1-3

Most rectal tumors are either diagnosed due to the detection of hematochezia or fecal tenesmus or after a rectal examination has been performed. Less commonly, rectal masses may be evident after prolapsing out of the rectum. Other clinical signs seen in these patients can include dyschezia and weight loss. On rectal examination a palpable mass will be obvious in up to 60% of canine cases. Many epithelial tumors will ulcerate easily and so blood may be evident on rectal examination. Some cases with annular lesions may have a stricture-like area palpable. [...]