Idiopathic bone marrow edema lesions of the femoral head: Predictive valueof MR imaging findings

PURPOSE: To determine the frequency of several subchondral magnetic resonan ce (MR) imaging features observed in bone marrow edema lesions of the femor al head and to determine their value for differentiation of irreversible fr om transient lesions . MATERIALS AND METHODS: The authors reviewed MR images of 72 femoral head le sions in 42 men and 25 women (median age, 48 years) with equivocal radiogra phic findings and bone marrow edema seen at MR imaging (T1- and T2-weighted images in all patients and contrast material-enhanced T1-weighted images i n 39 patients). Follow-up MR images showed 57 lesions to be transient and 1 5 to be irreversible. The presence and size of subtle subchondral features observed on initial MR images were compared for both types of lesion. RESULTS: Lack of any additional subchondral change on T2-weighted or contra st-enhanced T1-weighted images had 100% positive predictive value for trans ient lesions. For irreversible lesions, presence of a subchondral area of l ow signal intensity at least 4 mm thick or 12.5 mm long had positive predic tive values of 85% and 73%, respectively, on T2-weighted images and 87% and 86%, respectively, on contrast-enhanced T1-weighted images. CONCLUSION: Careful assessment of subchondral changes enables confident dif ferentiation between early irreversible lesions and transient bone marrow e dema lesions.