【Abstract】 Objective To investigate the spectrum of CT and MR imaging and surgical operation findings in il iopsoasbursitis in patients with avascular necrosis of femoral head so as to enhance the diagnostic abil ity. Methods A total of 1 415 patients with avascular necrosis of the femoral head were analyzed retrospectively; of them, 15 patients were compl icated by il iopsoas bursitis surgically or aspiration of synovial fluid between May 2005 and May 2007. Fifteen cases were all necrosis of the bilateral femoral head and 17 hips were combined with il iopsoas bursitis. There were 14 males and 1 female, aging 29-58 years. The course of disease was 1 month to 3 years. All 15 patients had l imitation of abil ity of the hips and the “4” type sign was positive. The Harris score of hip’s function was 54-78 (mean 62.7). Five patients of them can be touched a palpable cystic mass and tenderness in the inguinal area, and 3 of them associated with femoral neuropathy and 2 patients presented sl ight atrophy of the thigh muscle in suffering side. All these cases were taken X-ray films of positive and frog-leg lateral position, hel ical CTscan with 5 mm thinness, and MRI was performed in 6 patients with T1WI, T2WI, T2WI and fat-saturated inversion recovery sequence. Results The radiographs were the primary basis evidences for diagnosis and degrees of the avascular necrosis of femoral head. According to the standards of Association Research Circulation Osseuse, there were 2 hips at stage II(II C 2), 6 hips at stage Ⅲ ( Ⅲ B 1, Ⅲ C 5 ) and 9 hips at stage IV. The X-ray films showed the bulging of the fat pad and soft tissue swell ing in 6 patients. CT analysis disclosed that the enlarged il iopsoas bursae appeared as hypodense, well-defined, thin-walled (lt; 2 mm) cystic structures. The content of the examined bursae was homogeneous with a CT density of ranging from 12.7 to 41.2 Hu, showing fluid collection. They were round or oval in shape medial to the il iopsoas, exhibiting inverted water-drop cystic shadow just inferior to the femoral head. Sl ight contrast enhancement of the bursal wall was seen after contrast agent administration in 3 cases. MRI demonstrated that the il iopsoas bursitis presented as low signal on T1WI and water-l ike highsignal on T2WI and markedly higher signal on STIR in 6 cases. The demonstration of the extent, size, mass effects and its relation and subsequent affection to surrounding anatomical structures were clearly shown by MRI, and by the communications between the il iopsoas bursa and the adjacent hip joint. Conclusion In the diagnosis of avascular necrosis of femoral head with imaging approaches, much attention should be paid to the abnormal ities around the articular capsule to early identify il iopsoas bursitis for further management.