Ischiorectal fossa metastasis from colon cancer: Case report of a rare entity and review of literature.

Introduction and importance Colorectal cancer is one of the most common cancers both nationally and internationally. It commonly metastases to local lymph nodes, liver and lungs, with few reported cases of rare sites of metastasis such as adrenal glands, breast and skin. Case presentation We report a 55-year-old-female admitted as case of large bowel obstruction and unintentional weight loss. Computed tomography scan of chest, abdomen and pelvis (CT CAP) showed sigmoid colon circumferential thickening with three lesions in the right hemi-liver. A laparoscopic diverting ileostomy followed by a colonoscopy showed a sigmoidal mass consistent with adenocarcinoma on histopathology. Hence, she received neoadjuvant chemotherapy followed by hepatectomy for the liver metastasis. Post-operatively CT CAP showed a newly developed right ischiorectal fossa (IRF) nodule along with newly developed porta hepatis lymph node. PET scan showed uptake in these two new lesions. Therefore, the patient underwent resection of the primary tumor, porta hepatis lymph node and right ischiorectal fossa nodule excision. The histopathology of the primary tumor came as moderately differentiated adenocarcinoma with both ischiorectal lesion and the porta hepatis nodule being positive for metastatic disease. Clinical discussion & conclusion Ischiorectal fossa tumors are extremely rare with the majority being benign in origin. Nevertheless, the possibility of metastasis is there with no clear explanation regarding the pathway of how the metastatic cells can reach the IRF. Pre-operative diagnosis is important to determine the appropriate approach particularly if the mass is thought to be malignant. Further larger studies are needed to understand the pathway of metastasis to IRF.