Primary tibial adamantinoma diagnosed by fine needle aspiration

Adamantinoma is one of the rarest primary bone tumors and is almost exclusively found in the tibia. Because of its scarcity, there are only a handful of reported cases of adamantinoma diagnosed by fine needle aspiration (FNA). We report a case of a 30-year-old woman seen at The Johns Hopkins Hospital for a 2.5-cm lytic lesion in the distal diaphysis of the tibia. A computed tomography-guided FNA of the lesion revealed a moderately cellular lesion consisting of a biphasic admixture of epithelioid cells seen singly and in fragments. These cells had round to oval nuclei with pale chromatin and well-formed nuclear grooves. The other population had more elongated nuclei and spindled appearance. An immunostain for cytokeratin was positive, supporting the diagnosis of adamantinoma. Due primarily to its rarity, the diagnosis of adamantinoma on FNA can be challenging and must be made in the context of its characteristic clinical and radiographic setting.