A Signet Cell Carcinoma of the Ileum: A Rare Differential Diagnosis of Intestinal Pathology with Fistula Mimicking Crohn’s Disease

Colorectal cancer (CRC) is the third most common cancer and the fourth most common cause of cancer-related death in the USA. Primary signet ring cell carcinoma (SRCC) of the colon and rectum is extremely rare with a reported incidence of less than 1%. Here we present the case of a 41-year-old man who presented with abdominal pain, severe microcytic anaemia and a negative faecal occult blood test (FOBT). A CT scan of the abdomen revealed thickening of the terminal ileum and proximal right colon with extensive lymphadenopathy and a fistula tract extending from the terminal ileum to the right buttock. Endoscopic features like cobblestoning of the ileocolic junction along with elevated blood and stool inflammatory markers raised suspicion of Crohn’s disease (CD). However, histopathological study surprisingly revealed primary colorectal signet cell carcinoma (PCRSCC) with no evidence of CD. Cases of simultaneous PCRSCC and CD have been reported, but no clear association has been established. Our case is unique in that it presented with classic clinical features of CD, but PCRSCC without any histological evidence of underlying CD was found on histology. LEARNING POINTS: A rare case of primary colorectal signet cell carcinoma of the colon is described. Primary signet cell carcinoma of the colon can present with severe microcytic anaemia and abdominal pain. Signet cell carcinoma can mimic Crohn’s disease on radiological and endoscopic findings, including the presence of a fistula tract.