An Unusual Case of Rectal Cancer Presenting as a Cystic Mass in the Cerebellum

Abstract

Purpose: Rectal cancer typically presents with a change in bowel habits, blood in the stool or weight loss. This is an unusual case of rectal cancer presenting in a patient with a cystic mass in the cerebellum. Methods: Case report and literature review. Results: This is a 65-year-old female with a past medical history of hypertension and obesity who was admitted with nausea, vomiting, diffuse abdominal pain and altered mental status. This was her third admission in one month for similar symptoms, although the altered mental status was new on this admission. On her previous two admissions, there was no identified cause for her illness, and her symptoms resolved quickly with supportive care. CT of the abdomen/pelvis was unremarkable with the exception of multiple pulmonary nodules. She was to undergo further evaluation of these nodules as an outpatient. On the third admission, she presented with her prior symptoms and new mental status changes. She was found to have significant metabolic derangements including leukocytosis, hypernatremia and renal failure. CT of the head showed a cystic mass arising in the right cerebellum. A craniectomy with resection of the mass was performed. The pathology was metastatic adenocarcinoma with immunohistochemistry staining positive for CD 20 (antigen expressed on the surface of B lymphocytes) and CDX 20 (positive marker in gastrointestinal malignancies). The gastrointestinal service was consulted for endoscopy. Flexible sigmoidoscopy revealed a 4x3 cm mass in the lower portion of the rectum. Pathology was consistent with rectal adenocarcinoma. Conclusion: Rectal adenocarcinoma rarely metastasizes to the brain. In our review of the literature, 1.9% of metastatic brain tumors are from colorectal cancer and only 0.5% of colorectal cancers have a single metastatic brain lesion. Tumors in the lower third of the rectum can metastasize to the brain and lung without liver involvement. This is due to the venous drainage of the rectum. The middle hemorrhoidal vein drains the lower third of the rectum via the inferior vena cava and thereby, bypasses the liver. This case illustrates the importance of understanding the rectal blood supply and how rectal cancer can present as a metastatic lesion to the brain.