Cytomorphologic features and differential diagnosis of neoplasms with small cell features in liquid-based urinary tract cytologic specimens

Introduction Urinary tract cytology (UTCy) allows the accurate diagnosis of high grade urothelial carcinoma. Rare malignancies characterized by the presence of small cells may be more difficult to recognize, however. The aim of this study was to review our experience with liquid-based (ThinPrep) UTCy specimens showing small atypical cells and characterize their cytomorphology, potential differences from previously reported morphologic features, and discuss their differential diagnostic considerations. Materials and methods Among 18,859 UTCy specimens reviewed during a 13-year period (2001-2012), we identified 13 cases corresponding to surgical pathology specimens diagnosed as small cell carcinoma (6), melanoma (3), lymphoma (3), and leukemic involvement of the urinary tract (1). We recorded the original diagnoses made on these cases and 10 cytomorphologic features that could aid in their diagnosis. Results We identified 13 cases in UTCy of 7 men and 6 women; 11 of which were diagnosed as positive or suspicious for malignancy. In 8 out of 13 cases (62%) the type of malignancy was correctly reported. Of the 10 recorded features, cellular clustering and nuclear molding were seen only in small cell carcinoma, whereas prominent nucleoli and an inflammatory background or diathesis were noted in lymphoma and melanoma cases. Intracellular pigment and multinucleation were recorded in melanoma cases. Conclusion The presence of small atypical cells in liquid-based UTCy should raise the suspicion of underlying malignancy involving the urinary tract. Cell clustering, nuclear molding, and hyperchromasia are helpful hints for the diagnosis of small cell carcinoma and the presence of small atypical cells with prominent nucleoli raises the possibility of lymphoma or melanoma.