Ewing's Sarcoma/PNET of the Talus - Report of a Case

Ewing's sarcoma (ES)/PNET is common in both axial and appendicular skeletons, but is extremely rare in the talus. Here, we report a case of ES/PNET of the left talus in a 29-year-old male patient diagnosed by fine needle aspiration cytology, and review the literature on similar cases. The cytological smears were composed of individually dispersed small round cells and occasional clusters of loosely cohesive cells. The tumor cells were fragile, frequently exhibiting naked nuclei. Two distinct types of cells were observed. The light (chief) cells displayed round or slightly oval nuclei with frequent indentations, generally inconspicuous nucleoli, and a thin rim of cytoplasm, which sometimes harbored small vacuoles. The dark cells were smaller, displaying scanty cytoplasm with dense hyperchromatic nuclei, intermixed with chief cells, and often manifesting as small molded groups. However, no significant nuclear pleomorphisms or mitoses were noted. Tumor cells in the ceil block revealed positive cytoplasmic glycogen, as determined by a PAS stain with diastase control, and also exhibited positive immunoreactivity for CD99.