Fine-needle aspiration cytology of primitive neuroectodermal tumor of the urinary bladder: a case report.

Primitive neuroectodermal tumors (PNETs) are malignant small round cell tumors, which exhibit a variable degree of neural differentiation. These tumors are usually found in the extraosseous soft tissue and rarely in bones. Occasional cases of PNETs of the urinary bladder have been reported on histopathology. However, to the best of our knowledge, none have been diagnosed on fine-needle aspiration cytology (FNAC). A patient presented to the out-patient department with complaints of a slowly progressive lump in the lower abdomen, which was diagnosed as PNET on FNAC. The smears showed a dispersed population and sheets of malignant small round cells with focal rosette formation and perivascular arrangement of tumor cells. Periodic acid-Schiff staining showed strong cytoplasmic positivity. Immunocytochemistry of the cytology smears also showed strong membrane positivity for CD99 (MIC-2), which was also confirmed on histopathological examination. PNET of the urinary bladder is a distinct entity, which can be diagnosed on FNAC and confirmed by immunohistochemistry. A diagnosis of PNET should be considered as a differential diagnosis in urinary bladder masses, especially in adolescents and young adults.