Clinical imaging characteristics of herniation pits of the femoral neck

Abstract

To discuss imaging features of radiographs, computed tomography (CT), magnetic resonance imaging (MRI) and radionuclide imaging of the herniation pit of the femoral neck and their implications for pathogenesis. Twenty-seven patients with 31 herniation pits of the femoral neck were analyzed. All patients were examined by plain radiographs, 18 by CT, 16 by MRI, and 8 by radionuclide imaging. Thirty-one herniation pits located in the anterior part of the femoral neck or the base of the femoral head were round, oval or '8'-shaped subcortical defects. The pits were usually seen as mild radiolucent areas on radiographs, soft-tissue attenuation with a thin sclerotic rim and a focal cortical perforation on CT and three different signal intensities on MRI. Only one of eight pits revealed mild focal increased uptake on bone radionuclide scans. The occurrence of a herniation pit of the femoral neck correlates closely with the particulars of the structure of the hip joint and corresponding mechanical forces. Round or oval subcortical defects surrounded by a thin sclerotic rim in the superior lateral part of the femoral neck or the anterior lateral base of the femoral head, which are usually normal on radionuclide imaging and have focal cortical perforations on CT, are specific signs for diagnosing herniation pits of the femoral neck.