Non-specific clinical manifestations, absence of characteristic radiological and scintigraphic findings may cause a delay in diagnosis and treatment. Intra-articular OO of the hip located in subchondral bone of the acetabulum

Osteoid osteoma (OO) is a relatively common benign skeletal neoplasm of unknown etiology that is composed of osteoid and woven bone. Although, the clinical, radiological and scintigraphic features of OO have been well described, these features may be misleading or altered in the cases of intra-articular involvement. The acetabulum is a relatively uncommon location for OO with a few number of cases reported up to date. We reported a case of a 28-year-old man with intra-articular OO of the hip, located beneath the acetebular rim. Computed tomography, magnetic resonance imaging and bone scans were all nonspecific and confusing. We could show the nidus with the help of PET/CT. The final diagnosis and surgical excision can be made 6 months after the first on set of complaints. Intraarticular OO can mimic lots of pathologic entities related to the affected joint, and presents a diagnostic challenge and cause a delay in the diagnosis. The delays in the diagnosis and treatment can be avoided with a high index of suspicion. Furthermore, PET/CT is a useful imaging modality to demonstrate the tumor especially in the intraarticular location even in the absence of a characteristic nidus. Treatment should be individualized according to the surgeon’s preference and the characteristics of the case.