Unusual presentation of a giant cell tumor of the tendon sheath in the foot.

Giant cell tumor of the tendon sheath has frequently been described in the hand, but it is much less common in the foot. The case report presents an apparent cystic bony lesion of the proximal phalanx of the second toe of the foot. The operative findings and histological examination revealed a giant cell tumor of the tendon sheath that had eroded the phalanx. The case demonstrates that in the differential diagnosis of a cystic lesion of bone, extrinsic soft-tissue lesions should be considered.