MR imaging of avascular necrosis and transient marrow edema of the femoral head.

The value of high spatial resolution and contrast material-enhanced magnetic resonance (MR) imaging was assessed in 69 patients with either femoral head avascular necrosis (AVN) or transient bone marrow edema lesions. An AVN lesion was typically a well-demarcated epiphyseal area of variable signal intensity. A transient bone marrow edema lesion appeared as an ill-delimited low-signal-intensity epiphyseal area on T1-weighted images that converted to a high-signal-intensity area on T2-weighted images. T1- and T2-weighted spin-echo images helped distinguish from AVN lesions some transient lesions apt to simulate the segmental pattern of AVN lesions. T2-weighted images also helped detect necrotic tissue in some unusual AVN lesions that mostly showed ill-delimited edemalike marrow changes. In some cases, contrast-enhanced MR images may increase diagnostic confidence by showing homogeneous hypervascularization in bone marrow edema lesions and by depicting hypovascular marrow areas in AVN lesions. The authors believe sequential MR imaging is valuable in the assessment of equivocal femoral head lesions.