Plasmacytoid urothelial carcinoma of the urinary bladder with colorectal metastasis and mimicking colitis: A case report.

Plasmacytoid urothelial carcinoma (PUC) is a rare histologic variant of urothelial carcinoma. PUC is characterized by aggressiveness and poor prognosis. Since the first reported case of PUC in 1991, approximately 100 cases have been documented. In patients with PUC, colorectal metastasis is an uncommon presentation that is difficult to diagnose because it can mimic colitis on imaging examination, exhibiting colorectal wall thickening with a preserved vesicorectal fat plane. The pathogenesis of urologic malignancies that metastasize to the colon remains unclear. A 65-year-old Taiwanese man presented to our emergency department with a 3-month history of progressive abdominal fullness. A month before presentation, he had visited our hospital for gross hematuria with hydronephrosis and was subsequently hospitalized in our urology ward for transurethral resection of a bladder tumor. Postoperative histopathologic examination confirmed PUC. Regarding the illness at presentation, abdominal computed tomography revealed diffuse distension of the small and large intestines and long segmental thickening of the rectosigmoid colonic wall. Conservative management-empirical antibiotics, bowel rest, nasogastric tube decompression, and intravenous fluid support-was initiated with a presumptive diagnosis of colitis. Because of the patient's inadequate response to conservative management, a diverting ileostomy was performed, which relieved the abdominal distension. Subsequent colonoscopic and histopathologic examinations with immunohistochemical staining confirmed colorectal metastasis through an atypical metastatic route. Our case highlights diagnostic challenges posed by atypical imaging findings and unusual etiologies of gastrointestinal wall thickening with peripheral infiltration.