AVASCULAR NECROSIS OF THE FEMORAL-HEAD - MR-IMAGING WITH RADIOLOGICALAND HISTOLOGICAL CORRELATION

Objective To assess the value of MR in the diagnosis of avascular necr osis (AVN) of the femoral head. Methods MR images in 34 consecutive pa tients (26 men and 8 women) with AVN (57 hips) were reviewed. All lesi ons were confirmed by radiographic, radionuclide, computed tomographic , and/or histologic examination. Eleven specimens were obtained after total replacement of the hip. Four hips underwent biopsy. All MR image s were obtained using a 0.35 T superconductive imaging unit with SE se quence. Specimens were cut coronally into 5 mm thick section and radio graphs were obtained. Results There were four types of MR patterns of AVN. Type one appeared liner or patchy low signal area in the superoan terior portion of the femoral head. In type two, a band or ring of low signal intensity was found surrounding a central area of high signal intensity on T1WI and intermediate signal intensity on T2WI. The low s ignal band or ring consisted of thickened trabecular bone, mesenchymal and fibrous tissue, and amorphous acidophilic cellular debris. The ce ntral zones within the ring were composed of necrotic bone and marrow that had not been reached by the repair process. In type three, the fo cal subchondral region showed intermediate signal intensity on T1WI an d high signal on T2WI surrounded by a low signal ring. The low signal ring consisted of thickened trabecular bone and little mesenchymal tis sue. The central area was composed of mesenchymal tissue rich in capil laries and cystic necrotic zones. In type four, the signal intensity o f femoral head was inhomogeneous on both T1WI and T2WI. There were low signal bands in the femoral neck surrounding the necrotic zone. Only limited areas of some lesions had signal intensity isointense with fat on T1WI and T2WI. The inhomogeneous area of low signal intensity cons isted of a mixture of necrotic bone and marrow, amorphous cellular deb ris. The first type of MR pattern corresponded to the early stage of r adiograph, and the third type of MR pattern to stage 5. The second and fourth type of MR patterns correlated less with the radiographic stag e. Conclusions MR imaging plays an important role in the diagnosis of AVN of femoral head especially in the early detection of AVN. The MR p atterns of AVN is not correlated with radiographic stages exactly.