Herniation pits of the femoral neck: appearance at MR imaging

Herniation pits of the femoral neck are benign lesions recognized because of their characteristic appearance and location on plain radiographs. The appearance of this lesion in seven magnetic resonance (MR) examinations of the hips in five patients is described. MR revealed a well-marginated, round to oval defect in the superior lateral quadrant of the femoral neck with anterior cortical extension in all cases. With T1 weighting the signal intensity within each lesion was uniformly low. All but one case revealed a peripheral margin of absent signal intensity on T2-weighted and out-of-phase images. The MR appearance and location are sufficiently characteristic to allow identification of this lesion and aid in differentiating it from pathologic processes such as avascular necrosis, with which it may be confused.