CT and MR imaging can help characterize changes that are suspicious for PM.

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.

Although the clinical and radiographic features of pigmented villonodular synovitis (PVS) have been well described, diagnosis is often delayed and high rates of recurrence after synovectomy are reported. Magnetic resonance imaging (MRI) has been shown to be useful in the diagnosis of soft tissue masses. Three patients with biopsy-proven PVS and radiographs showing only effusion underwent MRI in the axial, coronal, and sagittal planes. The margins of the diseased synovium were best demonstrated on long TR/TE (T2-weighted) images. The synovium contained areas of void signal intensity felt to be due to hemosiderin, interspersed with increased signal from both inflammation and fat. In all cases, the margins of the diseased synovium were clearly delineated, allowing classification as nodular or diffuse. No appreciable change in signal intensity was seen when comparing nodular and diffuse forms. MRI is useful but not specific for PVS, since rheumatoid synovitis may show a similar signal pattern. However, MRI in patients with suspected PVS may decrease the time until diagnosis, aid in preoperative planning and obtaining adequate margins of resection, and may be a non-invasive method of long-term follow up for possible recurrence.