Fine needle aspiration cytology of the primitive myxoid mesenchymal tumor of infancy.

Primitive myxoid mesenchymal tumor of infancy (PMMTI) is a recently described entity, previously included under the umbrella of undifferentiated sarcomas. These tumors are notorious for recurrence, chemoresistance and may even metastasize. We describe here, for the first time, the cytomorphology of PMMTI. Further, we discuss the morphological differentials and relevant immunocytochemical markers to reach a correct diagnosis. Knowledge about the distinctive cytomorphological features with characteristic immunocytochemistry is the key to the challenging diagnosis of PMMTI. Establishing the diagnosis on cytology is not difficult in cases of recurrence when such a history is forthcoming. These tumors are a rarity, and awareness of cytomorphology and employment of ancillary techniques is diagnostic, guiding the appropriate therapeutic management.