Osteoid Osteoma of the Talus Mimicking Pigmented Villonodular Synovitis in a 15-Year-Old Male.

Osteoid osteoma is a benign tumor of the bone, which tends to occur in diaphysis or metaphysis of the long bones. The lesion is generally intraosseous with vague clinical symptoms, hence given the name great mimicker. When located subperiosteally and juxta-articulary, atypical clinical presentation and radiographs may lead to a delayed or missed diagnosis. Performing surgery with a misdiagnosis carries the risk of incomplete resection of the lesion and recurrence. We report the case of a 15-year-old male with a subperiosteal osteoid osteoma of the talus, who was misdiagnosed with pigmented villonodular synovitis (PVNS) and operated through anterior ankle arthrotomy. A nodular lesion, 1 cm in diameter, with a hard rubber consistency, was removed from the dorsal aspect of the talar neck. The pathologic specimens were consistent with subperiosteal osteoid osteoma. The patient's symptoms resolved rapidly in the early postoperative period. The patient remained asymptomatic at the 20-month follow-up and the control magnetic resonance imaging revealed no signs of recurrence. Atypical radiographs and clinical presentation of juxta-articular subperiosteal osteoid osteomas cause misdiagnosis, delay in diagnosis, incomplete resection, and recurrence. It is important to keep in mind "juxta-articular subperiosteal osteoid osteoma" in the differential diagnosis of cases with suspected pigmented villonodular synovitis.