Urachal cancer with direct caecal invasion: differential diagnosis from primary colon cancer

A 56-year-old man who had a history of repeated previous treatment for cystitis was admitted with abdominal distension, dysuria, pollakiuria, nocturia and sensation of urine retention after emptying the bladder. A CT scan showed a 10 cm irregularly shaped soft tissue mass abutting the anterosuperior aspect of the urinary bladder with wall thickening and a soft tissue component in the caecum. Colonoscopy revealed an encircling huge fungating mass on the caecum. The tumour was removed surgically. Histological examination showed moderately differentiated adenocarcinoma extending to the caecal wall and the bladder mucosa, the origin of the mass was consistent with that of a urachal cyst. The epicentre of the tumour was located in the bladder wall, with a distinct margin as a pathological feature. The patient was diagnosed with urachal cancer and concurrent direct caecal invasion.