Intra-articular osteoid osteoma of the hip misdiagnosed by MRI: an unusual cause of unexplained hip pain.

Osteoid osteoma is a common benign bone tumor affecting the young adult with typical clinical and radiographic presentation in its most common locations. However, when arising in unusual intra-articular locations, diagnosis may appear confusing and lead to delayed management. We present the case of a 24-year-old man with intra-articular osteoid osteoma of the hip involving the posteroinferior quarter of the femoral head. This unusual location was at the origin of unexplained pain and delayed diagnosis made 18 months after the onset of symptoms since the initial magnetic resonance imaging (MRI) examination could not identify the lesion whereas it was detected on bone scintigraphy and thin slice CT imaging. Due to the complex location providing difficult access for radioguided techniques, an open surgical management was suggested and performed through a limited posterolateral approach with no hip dislocation, after identification of the circumflex pedicle. Following complete surgical excision of the tumor, the diagnosis could be confirmed after histopathologic analysis. No recurrence was observed.