Primitive neuroectodermal tumor of the kidney. Report of a case initially diagnosed by fine needle aspiration cytology.

Background: Primitive neuroectodermal tumor (PNET) is a malignant small round cell tumor that exhibits neuroepithelial differentiation, most often presenting as a bone or soft tissue mass in the trunk or axial skeleton in adolescents and young adults. Isolated cases of PNET have been observed at visceral sites, such as the ovary, testis, uterus, bladder and pancreas. We present a case of PNET in the kidney initially diagnosed by fine needle aspiration (FNA).

Case: A 21-year-old woman presented with microhematuria. Urine cytology was negative for malignant cells. Physical examination was without abnormal findings. Computerized tomography revealed a partially cystic tumor in the left kidney. FNA showed monotonous-appearing small round tumor cells with occasional rosette formation. The differential diagnoses include other primitive small round cell tumors. The tumor cells were immunoreactive for neuron specific enolase and O13 (CD99). A cytologic diagnosis of PNET was suggested and subsequently confirmed on histopathology.

Conclusion: To our knowledge, this is the first description of PNET of the kidney initially diagnosed by FNA. This nerve tumor must be included in the differential diagnosis of small cell malignant tumors of the kidney and adjacent organs.