Small cell neuroendocrine carcinoma of the urinary bladder: A clinicopathologic study with emphasis on cytologic features

BACKGROUND. Primary small cell neuroendocrine carcinoma (SCNEC) of the urinary bladder is a rare but important entity. The authors have attempted to define the cytopathologic features of this tumor. METHODS. Sixty-one urine specimens (16 with histologic correlation) from 23 patients were studied. Twenty patients were male and 3 were female with an age range of 43 to 86 years (mean age, 68.8 years). Twenty-one cases were pure SCNEC and 2 were high grade undifferentiated carcinoma with neuroendocrine features. There were no false-positive or false-negative urine cytology diagnoses, but several cases of SCNEC were originally diagnosed as high grade transitional cell carcinoma by cytology. RESULTS. Cytologic features of SCNEC included hypercellularity with isolated single cells and clustered cells with naked hyperchromatic nuclei, finely granular nuclear chromatin, rare nucleoli, and a high mitotic karyorrhectic index. Nuclear molding was prominent. No glandular formation or nesting was noted. Half of the cases had a bloody, necrotic, or inflamed background. Histology, when available, was confirmatory in all cases. CONCLUSIONS. Cytologic features of SCNEC are distinct and an accurate urinary cytologic diagnosis can be made. Differential diagnosis is limited and includes metastatic small cell carcinoma, high grade transitional cell carcinoma, and malignant lymphoma.