<p>Plasmacytoid urothelial carcinoma (PUC) is a rare and an aggressive subtype of invasive urothelial carcinoma, often diagnosed at advanced stages with poor prognosis. We report a case of PUC with characteristic radiological findings. A male patient in his 70s presented with nocturnal urinary incontinence; cystoscopy findings suggested cancer. Magnetic resonance imaging (MRI) revealed a 6-mm-sized protruding lesion of the bladder with early contrast enhancement and diffusion restriction, indicative of bladder cancer. Additionally, a diffuse bladder wall thickening, abnormal signal intensity, and contrast enhancement were observed around the bladder. Fluorodeoxyglucose (FDG) positron emission tomography/computed tomography showed no significant FDG uptake in the lesion. The possibility of peritoneal dissemination of gastrointestinal malignancy was considered; however, no obvious primary lesions were identified. PUC was suggested as a differential diagnosis, prompting random bladder biopsies during resection of a protruding lesion in the bladder. Immunohistochemical staining confirmed PUC, with positivity for CD138, CK7, and GATA3 and negativity for CDX-2 and E-cadherin. Following treatment with gemcitabine and cisplatin, the lesion size decreased. Diagnosis of PUC can be difficult because the lesion is not easily detected by cystoscopy, misdiagnosed as peritoneal dissemination of gastrointestinal cancer on CT or MRI, or histopathologically similar to plasmacytoma or malignant lymphoma. PUC may present with pelvic peritoneal spread of the tumor as thick sheets extending along the fascial planes, which may be a characteristic imaging finding. Radiologists must be aware of these typical imaging findings to ensure accurate diagnosis of PUC.</p>