Osteoid Osteoma Acetabulum-MRI

This is 9 yr old male who came to us with the complaints of pain in left hip.MRI hip was performed. Bone marrow edema of infero-medial wall of acetabulum displaying low signal on T1, high signal on T2 and Stir images is seen along with left hip joint effusion. Axial fat suppressed image shows an irregular low signal focus in acetabular roof suspicious of tumour nidus. Differential diagnosis includes early changes of tubercular osteomyelitis, perthes’s disease (though femoral head involvement is more frequently seen).
Discussion:
Osteoid osteoma is a benign bone tumour constituting about 3% of all primary bone tumours. Males are more commonly affected with M:F = 3:1. Most patients are 5-25 yrs of age and involve long tubular bones of lower extremities. Fusiform sclerosis and central nidus are seen on radiographs, CT and MRI. Soft tissue effusion and bone marrow edema are common accompaniments. Pain is an invariable symptom. CT is more useful diagnostic tool as it well depicts the hypodense nidus with surrounding sclerosis.

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