The lower intestine consists of the rectum and the anus. Tumors in the rectum are usually benign and appear as polyps or adenomas. They are usually seen singly, but multiple benign tumors might be seen occasionally. Adenocarcinomas are malignant tumors that also form in the rectum. Most dogs affected are middle-aged or older, averaging around 9 years of age, with German Shepherds and Collies more prone to these growths.

Clinical signs

Dogs with lower intestinal growths have difficulty defecating, often times straining or exhibiting pain. In extreme cases, the fecal material is tinged with blood or mucus. Diarrhea or constipation is a common problem. Vomiting tends to occur if the small intestine is also affected. Animals with malignant tumors display cachexia or a progressive loss of weight, decreased appetite and muscle wasting. Abdominal pain and dehydration is also observed. Adenocarcinomas also metastasize to regional lymph nodes, lungs and the liver.

Diagnosis

A diagnosis requires consideration of the changes in excretory habits of the dog as well as a physical exam of the recto-anal area. Abdominal palpation may reveal a mass in the abdominal area. Blood tests are not indicative if tumors are benign; however, hypoproteinemia or anemia might be observed. Abdominal X-rays and ultrasounds can indicate if a tumor is causing intestinal obstruction, irregular small intestinal loops and intestinal constrictions, but they do not accurately predict the existence of tumors. A rectal exam is a good diagnostic method to find polyps. However, polyps situated deeper in the rectum are difficult to palpate, and hence, a colonoscopy may also be considered. A colonoscopy requires for the dog to be under general anesthesia; therefore, his or her physical status must be considered prior. Biopsies are also carried out during colonoscopies, and specimens are sent for histopathological exams.

Treatment

Surgery is recommended for the removal of obstructive polyps and adenomas. Various techniques, such as inducing prolapse of the rectum to expose the polyp, may be employed. Tumors located deeper in the rectum could require more extensive surgery, such as a laparotomy. However, post-surgical complications like rupture of the rectal incision, anal fistulas and bowel strictures are common and may interfere with the dog’s recovery. Non-surgical treatment includes the administration of non-steroidal anti-inflammatory medications, analgesics, stool softeners and antibiotics. Surgical excision, radiation therapy and chemotherapeutics are used to treat adenocarcinomas. However, once metastasis occurs, the probability of survival decreases significantly.

Preventative Measures

Single polyps once excised have a low probability of recurrence unlike multiple masses. Diffused lesions are difficult to surgically excise; thus, preventative measures are used to alleviate symptoms. The prognosis is good if an interfering tumor has been removed by surgery. Dogs with rectal polyps and adenomas that are asymptomatic and do not interfere with defecation are usually considered for treatment. Malignant adenocarcinomas have poor prognosis with survival estimates of up to one year.