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

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 juxtaarticulary, atypical clinical presentation and radiological 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 and operated through anterior ankle arthrotomy. A nodular lesion 1 cm in diameter with hard rubber consistency was removed from the dorsal aspect of the talar neck. The pathological specimens were consistent with subperiosteal osteoid osteoma. The patient's symptoms resolved rapidly in the early postoperative period. The patient remained asymptomatic at the 20th-month follow-up and the control MRI revealed no signs of recurrence. Atypical radiological and clinical presentation of juxtaarticular subperiosteal osteoid osteomas cause misdiagnosis, delay in diagnosis, incomplete resection and recurrence. It is important to keep in mind "juxtaarticular subperiosteal osteoid osteoma" in the differential diagnosis of cases with suspected Pigmented Villonodular Synovitis.