Distinct focal lesions of the femoral head: imaging features suggesting an atypical and minimal form of bone necrosis.

Abstract

To document the imaging findings observed in patients with an unusual pattern of abnormality of the femoral head, most likely representing osteonecrosis. The imaging findings in 11 patients (10 men, 1 woman; age range 32-55 years) with a distinct lesion of the femoral head were reviewed with particular attention to the morphologic appearance, location, and extent of the lesion(s) in the proximal femur. The 16 lesions identified in these patients extended to the subchondral area. Articular collapse was not evident in any hip. Radiography and CT showed areas of mixed bone sclerosis and osteolysis surrounded by sclerotic margins. On MR imaging, the signal intensity characteristics of the osseous lesion(s) were most commonly similar to those of fluid. Histopathologic findings, available in two hips, were typical of osteonecrosis. There was evidence of correlation of the site of the lesion with the known general distribution and anastomoses of arteries supplying the femoral head. A distinct, focal lesion of the femoral head is believed to represent an atypical form of bone necrosis. Its restriction to a small portion of the femoral head may relate to localized vascular anatomy. Recognition of the quite characteristic imaging findings can prevent misdiagnosis and may have implications for the prediction of the natural course of the disease.