MR Imaging Features of Obturator Internus Bursa of the Hip

The authors report two cases with distension of the obturator internus bursa identified on MR images, and describe the location and characteristic features of obturator internus bursitis; the "boomerang"-shaped fluid distension between the obturator internus tendon and the posterior grooved surface of the ischium.

Osteonecrosis of the Femoral Head after Bone Marrow Transplantation

PURPOSE: To retrospectively review finding of osteonecrosis of the femoral head after bone marrow transplantation. MATERIALS AND METHODS: We reviewed the clinical and MR findings of osteonecrosis of the femoral head in 23 of 1112 patients who underwent marrow transplantation during a five-year follow-up period lasting from 1996 to 2000. RESULTS: Mean age at the time of diagnosis was 31 (range, 20-47) years, and the mean time from transplant to diagnosis was 17 months. All patients developed variable graft-versus-host disease and seventeen were treated with high-dose prednisolone and/or cysclosporin for severe acute or extensive chronic graft versus host disease. Osteonecrosis was diagnosed by magnetic resonance (MR) imaging, which allowed early detection of disease assessment of its stage. At the time of diagnosis, 15 hips were at stage I, 28 at stage II, two at stage III, and none at stage IV, according to the international ARCO classification system. Osteonecrosis of femoral diaphyses, the lower lumbar spine, or pelvic bones in the MR field was also found to have occurred in 11 patients. Initial treatment was conservative: 21 hips underwent surgery [core decompression (n=10), vascularized fibular bone graft (n=5), and joint replacement (n=6)]. CONCLUSION: In patients receiving high-dose steroids for the treatment of graft-versus-host disease, MR screening might help detect osteonecrosis at an early stage.

Idiopathic Synovial Osteochondromatosis of the Hip: Radiographic and MR Appearances in 15 Patients

OBJECTIVE: To evaluate the radiographic and MR appearance of idiopathic synovial osteochondromatosis of the hip. MATERIALS AND METHODS: Radiographs and MR images of 15 patients with idiopathic synovial osteochondromatosis of the hip were assessed. The former were analysed in terms of the presence of 1) juxta-articular calcified and/ or ossified bodies, 2) osteophytes, 3) bone erosion, 4) juxta-articular osteopenia, and 5) joint space narrowing, while for the latter, analysis focused on 1) the configuration of intra-articular bodies, 2) bone erosion, 3) synovial thickening, 4) conglomeration of intra-articular bodies, and 5) extra-articular extension. RESULTS: At hip radiography, juxta-articular calcified and/ or ossified bodies were seen in 12 of the 15 patients (80%), bone erosion in eight (53%), osteophytes in seven (47%), juxta-articular osteopenia in five (33%) and joint space narrowing in five (33%). In eight patients (53%), MR imaging depicted intra-articular bodies of focal low signal intensity at all pulse sequences, and areas of isointensity at T1WI and hyperintensity at T2WI. In three (20%), intra-articular bodies of focal low signal intensity and areas of hyperintensity at all pulse sequences were observed, with areas of iso-intensity at T1WI and hyperintensity at T2WI, while in four (27%), intra-articular bodies of only focal low signal intensity at all pulse sequences were apparent. Synovial thickening was present in 13 patients (87%), bone erosion in 11 (73%), conglomeration of the intra-articular bodies in 11 (73%), and an extra-articular herniation sac in six (40%). CONCLUSION: The most common radiographic finding of synovial osteochondromatosis of the hip was the presence of juxta-articular calcified and/ or ossified bodies. MR imaging depicted intra-articular bodies of focal low signal intensity at all pulse sequences, with areas of iso-intensity at T1WI and hyperintensity at T2WI. In addition, the presence of an extra-articular herniation sac was not uncommon.

MR Evaluation of "Metaphyseal" Change in Legg-Calve-Perthes Disease

PURPOSE: To determine the metaphyseal changes occurring in Legg-Calve-Perthes(LCP) disease using MRI. MATERIALS AND METHODS: Between 1992 to 1999, 80 LCP patients (87 hips) underwent MR imaging and plain radiography. All MR images were reviewed, bone marrow signal intensity, the size and location of the metaphyseal cyst and its epiphyseal necrosis grade determined. RESULTS: Metaphyses were abnormal in 43hips (49%), while bone marrow edema was present in 28 (32%) and a metaphyseal cyst in 30 (34%). Metaphyseal cysts were classified as either 'true' (n=9) or 'false' (n=21) according to the enhancement pattern. The maximum diameters of true and false cysts were 1.1+/-0.3 cm and 1.1+/-0.4 cm, respectively. Their most commom location was the anterior column; a true cyst occurred there in 7cases (78%), and false cyst in 16 (76%). Using the Waldenstrom classification, seven of the nine hips wih a true cyst (78%), were found to be at the avascular stage and 15 of the 21 with a false cyst (71%) were at the fragmentation stage. Seven of these nine (78%) and 19 of these 21 (90%) were Catterall grade IV. CONCLUSION: According to the findings of MR imaging, the metaphyseal changes occurring in LCP disease were bone marrow edema and metaphyseal cyst. This latter was visualized mainly in the anterior column and severely affected hip, and was classified as 'true' or 'false'.

Serial MR findings of Metaphyseal Cyst in Legg-Calve'-Perthes Disease: A Case Report

Metaphyseal cysts are common findings in Legg-Calv Perthes(LCP) disease, though usually disappear within 6-12 months. Several studies have described the MR imaging findings of these cysts, though serial MRI findings have not been documented. In this report, therefore, we report the serial MRI results of metaphyseal cyst in LCP patients.

Contrast-Enhanced Fat-Suppression MR Imaging of Avascular Necrosis of Femoral Head

PURPOSE: To evaluate the findings and role of contrast-enhanced fat suppression MR imaging in avascular necrosis(AVN) of the femoral head. MATERIALS AND METHODS: In 15 patients with AVN of the femoral head, MR T1-weighted and T2-weighted images and contrast-enhanced fat-suppression T1-weighted images were obtained, and the findings were re-viewed. Early and advanced groups were classified on the basis of clinical findings and imaging, and the en-hancement pattern was classified as either type I, rim enhancement; type II, surrounding diffuse enhance-ment; type III, intralesional enhancement; or type IV, II + III. RESULTS: Twenty-four cases of AVN of the femoral head were detected; in nine patients, lesions were bilateral. Eight cases occurred in the early group and 16 in the advanced. All eight in the early group showed the "double line sign" on T2-weighted images, with a type-I enhancement pattern. In the advanced goup, type II(8/16) and type IV(8/16) enhancement patterns were seen. Among the cases showing the type-IV pattern, the intrale-sional enhancing area showed low signal intensity on T1-weighted images and isosignal intensity on T2 weighted in one case, and low signal intensity on T1-weighted images and high signal intensity on T2-weight-ed in the other cases. There was no difference in the extent of the disease before and after enhancement. CONCLUSION: Contrast-enhanced fat-suppression MR images may be helpful in evaluating the extent of AVN of the femoral head and predicting the histopathologic findings of the disease

Efficacy of MR Arthrography in the Diagnosis of the Acetabular Labral Tear

PURPOSE: To determine the accuracy of magnetic resonance (MR) arthrography in the detection and staging of lesions of the acetabular labrum. MATERIALS AND METHODS: Fifteen hips of 14 patients with chronic hip pain and clinical suspicion of labral lesions were examined with direct or indirect MR arthrography and underwent subsequent arthroscopic evaluation. The study population consisted of six women and eight men aged between 40 and 59 years. Nine arthrograms were obtained intra-articular administration of gadolinium solution, and six involved articular motion exercise after intravenous administration of gadolinium solution. In 14 cases a phased-array pelvic coil was used, and a shoulder coil in one. Fat-suppressed T1-weighted images were obtained in the coronal, oblique coronal and oblique axial planes, and T1-and T2-weighted images were obtained in the axial plane. Labral lesions were graded according to the Czerny classification and evaluated on the basis of presence or absence of a tear and location (anteroinferior, anterosuperior, superior, posterosuperior, posteroinferior). The findings were then correlated with the arthroscopic findings. RESULTS: After direct and indirect MR arthography, the findings-based on the Czerny classification -were as follows : stage IA:3; IB:1; IIA:8; IIB:1; IIIA:4; IIIB:0. MR arthrography also showed that seven cases were located in the anterosuperior portion of the labrum, seven in the superior portion, and three in the posteroinferior portion. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of MR arthrography for diagnosis of the labral tear was 92%, 75%, 92%, 75 %, and 88 %, respectively. CONCLUSION: In this preliminary study, MR arthrography appears to be a promising imaging modality for accurate diagnosis and useful for screening patients with chronic hip pain.

Early Avascular Necrosis of the Femoral Head: Relationship of the Findings of Preoperative MRI and the Long-Term Results of Core Decompression

PURPOSE: To evaluate potential correlation between the extent and site of avascular necrosis (AVN), as determined by preoperative magnetic resonance (MR) imaging, and the development of femoral head collapse. MATERIALS AND METHODS: Using clinical, radiographic and MR imaging criteria, twenty hips in 15 patients were selected for core decompression. Preoperative MR results were classified into three categories: group A, less than 15% involvement of the weight-bearing portion of the femoral head; group B, 15%-30% involvement; group C, more than 30% involvement, according to ARCO staging. We also established three groups according to site of involvement of the femoral head, namely medial, middle and lateral. RESULTS: Of 20 cases, three were stage Ia; two, Ib; four, Ic; three, IIa; two, IIb; and 6, IIc. Ten cases of Ia, Ib, IIa or IIb showed no femoral head collapse during follow-up of at least 24 months, while ten cases of Ic or IIc showed femoral head collapse. CONCLUSION: The prognosis of core decompression in patients with early AVN is related to the area of lesion in the femoral head.