Small cell carcinoma of the urinary bladder: CT and MR imaging findings

Objective: Primary small cell carcinoma (SCC) is a rare aggressive malignancy of the urinary bladder, with identical histopathology to that of the lung. The treatment and prognosis of bladder SCC are somewhat different from those of more frequent transitional cell carcinoma. The purpose of this study was to analyze the CT and MR imaging findings of bladder SCC. Materials and Methods: Six adult patients (five males and one female) with pathologically proven SCC of the urinary bladder who had undergone pelvic CT and/or MR imaging were included in this study. The radiologic findings were retrospectively evaluated in terms of tumor location, texture, calcification, depth of invasion, perivesical extension, lymph node involvement, and local or distant metastasis, by two radiologists, who established a consensus. Results: CT and MR images depicted all tumors as large, ill-defined, relatively well enhancing, broad-based polypoid intramural masses with (n=3) or without (n=3) cystic portions. Their frequent location was posterior and trigonal (n=3). Calcification was found within one tumor, and lymphadenopathy in four. At T2-weighted MR images, the solid portion of the tumor was relatively hypointense. The stage at the time of diagnosis was C in three patients, and D1 in three. Follow-up imaging showed brain metastasis in one patient and liver metastasis in two. Conclusion: On CT and MR images, SCC of the urinary bladder appeared as a large, enhancing, broad-based polypoid mass. It was stage C or higher, and lymph nodes and distant metastasis were frequent. T2-weighted MR images showed that the solid portion of the tumor was relatively hypointense. When radiologic examinations demonstrate a bladder tumor of this kind in adults, SCC of the urinary bladder should be included in the differential diagnosis.