Bone marrow edema of the hip: MR findings after core decompression.

Magnetic resonance imaging is an extremely sensitive technique for evaluation of bone marrow changes at an early stage of avascular necrosis (AVN) of the hip. We therefore examined 11 painful hips whose clinical symptoms led us to suspect idiopathic AVN. The radiographs of all of these either were normal or demonstrated a minimal decrease in radiodensity. Magnetic resonance demonstrated diffuse signal loss of the bone marrow at short TR/TE images of the femoral head in all hips, with various extensions in the head, neck, and intertrochanteric area. These regions turned iso- to hyperintense on long TR/TE images compatible with bone marrow edema (BME). Focal abnormalities characteristic for AVN were not seen in any of the cases. Radionuclide studies performed in six cases were positive. All patients underwent core decompression treatment. Hydrostatic bone marrow pressure measurement and intraosseous venography were positive in five cases when measured. Histology available in eight cases confirmed the presence of BME. Furthermore, the bone changes corresponded to those of early AVN. Follow-up examinations after core decompression with MR showed normal signal intensity in all cases. Magnetic resonance represents a viable diagnostic tool for BME and can monitor the therapeutic success of core decompression. Whether BME of the femoral head constitutes a distinct transient syndrome or represents an early form of AVN is controversial at present. Our findings support those who believe that BME may represent an initial stage of idiopathic AVN.     

MR imaging of bone marrow edema and joint effusion in patients with osteonecrosis of the femoral head: relationship to pain

OBJECTIVE: Our aim was to determine the occurrence of bone marrow edema and joint effusion and their relationship to pain in patients with osteonecrosis of the femoral head on the basis of MR imaging. MATERIALS AND METHODS: There were 71 patients with osteonecrosis of the femoral head based on characteristic radiographic and MR imaging findings. All patients had surgical confirmation of the disease. Both hips were affected with osteonecrosis in 39 patients, whereas only one hip was involved in 31 patients. The last patient underwent an arthroplasty of one hip during the study and had only one hip imaged. We evaluated a total of 110 hips in this study, of which 98 were painful. We staged osteonecrosis of the femoral head, using the classification of Steinberg et al. The 31 unaffected hips served as controls. Bone marrow edema and joint fluid were evaluated on MR images. Bone marrow edema was defined as an ill-defined area of low signal intensity on T1-weighted images with corresponding high signal intensity on T2-weighted or inversion recovery images localizing to the femoral head, neck, and intertrochanteric region. The amount of joint fluid was graded from 0 to 3. RESULTS: The peak of bone marrow edema occurred in stage III disease (72%); its odds ratio was seven times greater than that for stage I osteonecrotic hips. Effusions of a grade greater than or equal to 2 were seen most often in stage III disease (92%), compared with 10% in the control hips. With an effusion, bone marrow edema was 12.6 times greater when the hip was painful than when it was not. CONCLUSION: Both bone marrow edema and joint effusions existed with a peak occurrence in stage III disease. Bone marrow edema seems to have a stronger association with pain than does joint effusion in osteonecrosis of the femoral head.     

MRI of joint fluid in femoral head osteonecrosis

OBJECTIVE: To evaluate the relationship between joint fluid, intramedullary pressure (IMP), bone marrow edema, and stages of osteonecrosis of the femoral head (ONFH). MATERIAL AND METHODS: We reviewed the magnetic resonance (MR) images of 28 patients with 40 documented ONFHs. IMP was measured in 16 symptomatic hips. The amount of joint fluid was graded as 0 (no fluid), 1 (fluid <5 mm in width), or 2 (fluid > or = 5 mm in width) adjacent to the entire length of the femoral neck. Associated focal and diffuse bone marrow abnormalities were evaluated. A control group of 29 recruited individuals without symptoms related to hip disease were examined. Follow-up MR images were obtained in four patients (five affected hips) 6-10 months after core decompression. RESULTS:Of the 40 affected hips, the severity of ONFH was divided into stages 0 (n=4), I (n=28), and II (n=8 hips) on MR findings. The correlation of joint fluid to IMP and to the presence of bone marrow edema was poor. The amount of joint fluid correlated significantly with the stage of ONFH. None of the five affected hips showed decreased joint fluid on follow-up MR images. CONCLUSION:The amount of joint fluid correlates well with the stage of ONFH. The amount of joint fluid does not correlate with IMP or bone marrow edema.     

Detection of acute avascular necrosis of the femoral head in dogs: dynamic contrast-enhanced MR imaging vs spin-echo and STIR sequences.

OBJECTIVE. Spin-echo MR imaging has been shown to be highly sensitive in the detection of avascular necrosis. Very early avascular necrosis can, however, appear normal on MR images. We compared dynamic contrast-enhanced MR imaging with conventional spin-echo and short Tl inversion-recovery (STIR) sequences for detecting acute osteonecrosis in an animal model. MATERIALS AND METHODS. Avascular necrosis was induced unilaterally in the femoral heads of five dogs that were imaged with a 1.5-T system within 3 hr of devascularization. After standard T1-weighted, T2-weighted, and STIR images, gradient-recalled echo images, 28/5 (TR/TE) with a 45 degrees flip angle, were obtained at 6-sec intervals for 90 sec synchronous with the IV administration of 0.2 mmol of gadoteridol per kilogram of body weight at a rate of 2 ml/sec via an automated injector. Two animals were reimaged after 7 days. RESULTS. Spin-echo and STIR images did not show any acute changes in the ischemic femoral heads. In contrast, significant differences were present in the enhancement profiles of the marrow spaces in the normal and ischemic femoral heads (p = .005). Normal marrow was characterized by rapid enhancement, with an average signal intensity increase of 83% peaking at 36 sec; no measurable enhancement was seen in the marrow of the ischemic femoral head. Spin-echo images, obtained 7 days after devascularization (n = 2), showed changes characteristic of avascular necrosis. Dynamic contrast-enhanced MR images showed persistent lack of enhancement in the avascular marrow of the ischemic femoral head. A junctional zone, characterized by rapid contrast enhancement in excess of 120% without early washout, was identified at the interface between normal and avascular marrow. CONCLUSION. In this experimental model, dynamic contrast-enhanced MR imaging proved significantly more sensitive than conventional spin-echo and STIR imaging in the detection of acute avascular necrosis.     

Contrast-enhanced fat saturation magnetic resonance imaging for studying the pathophysiology of osteonecrosis of the hips

We imaged 75 hips in 40 patients using fat saturation technique before and after intravenous injection of contrast (0.1 mmol/kg gadolinium diethylene triamine penta-acetic acid, Gd-DTPA). Eighteen hips in 11 patients were determined to be osteonecrotic, either by pathologic or clinical examination. In the osteonecrotic hips, three distinct patterns of enhancement were found: (I) focal area outlined by brightly enhancing rim (7 hips); (II) diffuse enhancement in the femoral head and neck extending into the femoral shaft (3 hips); and (III) a combination of patterns I and II (8 hips). Our data support the hypothesis that early nontraumatic osteonecrosis is associated with hyperemia and/or an increase in capillary permeability rather than acute devascularization, and that diffuse marrow edema is the initial finding in early nontraumatic osteonecrosis.     

Radiographically negative avascular necrosis: detection with MR imaging

To correlate the morphologic appearance on magnetic resonance (MR) images of radiographically negative avascular necrosis (AVN) of the femoral head with that on computed tomographic (CT) and radionuclide scans, the radiographic and clinical records of 24 patients were reviewed retrospectively. In 18 patients the MR signal intensity features were monitored by means of serial imaging. All MR studies included T1-weighted (short repetition time [TR], short echo delay time [TE] ) imaging and T2-weighted imaging (long TR, long TE). Thirty-one hips were determined with MR to be involved by AVN; 27 were staged on the basis of signal intensity characteristics within the low-intensity rim. Core decompression was performed on 18 hips. Afterward, progression of disease occurred in only one hip. Fourteen of the 16 asymptomatic patients (88%) had early-stage focal lesions. CT scans were obtained in 15 patients and radionuclide scans in 21. Ten hips at radionuclide imaging and five at CT appeared normal when MR results were distinctly abnormal. MR can depict early radiographically negative AVN in asymptomatic individuals. At this early stage, the lesions in this series appear to be nonprogressive after treatment.     

Correlation between baseline femoral neck marrow status and the development of femoral head osteonecrosis in corticosteroid-treated patients: a longitudinal study by MR imaging

OBJECTIVE: To test the hypothesis that the development of corticosteroid (CS)-associated femoral head osteonecrosis (ON) is influenced by baseline femoral neck marrow status. PATIENTS AND METHODS: The population consisted of 20 untreated patients with a newly diagnosed rheumatic disease in whom a standardized CS regimen was planned. Before CS treatment, baseline femoral neck marrow status was determined by magnetic resonance (MR) imaging on T1-weighted images (proportion of surface area of femoral neck and intertrochanteric area occupied by fatty marrow; index of marrow conversion [IMC]) and on a quantitative MR sequence (bulk T1 values of femoral head and neck). The presence of ON was assessed by coronal T1-weighted MR images of the hips at 6 and 12 months. RESULTS: None of the patients suffered from ON at baseline. Four patients (20%) developed bilateral femoral head ON at 6 months. The mean percentage of fat marrow in the femoral neck before treatment was significantly higher in ON-positive than in ON-negative patients (p=0.0025). The mean baseline femoral neck IMC value, which parallels the degree of red to yellow marrow conversion, was higher in ON-positive than in ON-negative patients (p=0.089). The mean baseline bulk T1 value of the femoral neck (but not of the femoral head), which inversely correlates with the amount of fat marrow, was significantly shorter in ON-positive than in ON-negative patients (p=0.0298). CONCLUSION: The development of CS-associated femoral head ON is correlated with a high fat content in the proximal femur before CS therapy.     

Correlation between bone marrow edema and collapse of the femoral head in steroid-induced osteonecrosis

OBJECTIVE: The purpose of this study was to clarify whether bone marrow edema is detectable on initial MR imaging of steroid-induced osteonecrosis of the femoral head. SUBJECTS AND METHODS: Forty-eight hips with osteonecrosis were examined consecutively with MR imaging and radiography. In a previously reported screening program, osteonecrosis was diagnosed on MR imaging when subchondral bands of abnormal signals were present. In the screening program, the MR images of 200 hips of 100 patients receiving high-dose steroid therapy were examined prospectively. Subchondral bands were detected in 48 hips at a mean of 14 weeks after the initiation of steroid therapy. RESULTS: On follow-up MR imaging of 47 hips (one hip excluded) bone marrow edema was initially observed in 13 hips after the onset of hip pain. MR imaging of the remaining 34 hips did not reveal bone marrow edema and the patients were all asymptomatic. MR imaging of 31 of the 34 hips continued to show subchondral bands and MR imaging of the other three hips indicated that the subchondral bands had disappeared. When bone marrow edema was detectable, abnormal findings on radiography were slight but 11 (85%) of the 13 hips progressed to advanced osteonecrosis. Bone marrow edema was highly correlated with the subsequent collapse of the femoral head (p<0.0001). CONCLUSION: Bone marrow edema was not present on initial MR imaging of osteonecrosis. Bone marrow edema should be considered a marker for potential progression to advanced osteonecrosis, and careful examinations for osteonecrosis are necessary when bone marrow edema is seen.     

Painful sickle cell crisis: bone marrow patterns observed with MR imaging

Eleven patients with homozygous sickle cell anemia (SCA) undergoing painful crisis were studied with magnetic resonance (MR) imaging. The signal intensity of bone marrow was diffusely decreased in the axial and peripheral skeleton on short repetition time (TR)/echo time (TE) images and long TR/TE images, which suggested hematopoietic marrow hyperplasia and was confirmed by isotope marrow scans in five patients. Focal areas of further decrease in signal intensity were seen on short TR/TE images in 12 of the 14 (86%) painful joints and three of the five (60%) painless joints. In the painful joints, these focal areas converted to high signal intensity on long TR/TE images, presumably due to edema, which suggested acute marrow infarction. In the painless joints, these low-intensity focal areas remained as low signal on long TR/TE images, which suggested absence of edema and thus areas of old infarction or fibrosis. These results indicate that MR imaging may enable differentiation between acute and chronic marrow infarcts in patients with SCA and serve as a useful guide in monitoring and directing therapy.     

严重急性呼吸综合征康复者髋、膝关节骨坏死与激素治疗的关系

目的了解严重急性呼吸综合征（SARS）康复者下肢骨缺血与激素治疗的关系。资料与方法对来自广州市5所医院的148例SARS康复医务人员下肢骨包括双侧髋关节及膝关节进行MRI检查。148例中42例未使用激素治疗,106例使用不同剂量的激素治疗。MRI检查分为筛查与详查。筛查包括T1WI及短反转时间反转恢复序列（STIR）冠状位成像。筛查有阳性发现者则进行详查,在筛查的基础上加用横断位、冠状位T2WI及STIR成像。结果42例未使用激素治疗者未发现下肢骨坏死。106例使用激素治疗康复者中,共发现8例骨缺血改变,其中1例为双侧股骨头缺血坏死,2例为单侧股骨头缺血坏死,1例为双侧股骨头、胫骨髁及单侧股骨髁缺血坏死,1例单侧股骨髁缺血坏死,1例单侧股骨颈骨梗死并钙化,2例双侧股骨、胫骨骨髓水肿。多因素Logistic回归分析显示激素累积剂量是骨缺血性坏死最重要的危险因素（P=0．001）。结论使用激素治疗的SARS康复者中,少数发生下肢骨缺血坏死,而激素累积剂量与骨缺血性坏死关系密切。     

低场强MR对股骨头缺血坏死的诊断价值

目的研究低场强成人股骨头缺血坏死的MRI表现。方法对35例经病理或临床随访证实的股骨头缺血坏死的MRI表现进行分析总结。结果35例患者58个坏死股骨头中出现线样征56个,包括单线18个,双线38个,无线样征2个;骨髓水肿26个。A级信号15个;B级信号21个;C级信号13个;D级信号9个。结论低场强MRI对股骨头缺血坏死的早期诊断具有重要意义。     

MR imaging of marrow changes adjacent to end plates in degenerative lumbar disk disease

MR studies of the lumbar spine in 41 patients were analyzed at 203 disk interspaces to assess the appearance and frequency of bone marrow signal changes in the vertebral bodies adjacent to normal and degenerated disks. Degenerative changes were found at 58 interspaces; an abnormal bone marrow signal was identified in 29 (50%) of these. On spin-echo pulse sequences with short and long repetition times (TRs) and echo times (TEs), an area of relative increased signal intensity was seen in the vertebral body adjacent to the disk in 24 cases (17 were bandlike on both sides of the disk, four were focal on one side of the disk, and three were bandlike and focal on one or both sides of the disk). In one patient decreased signal was noted on both short and long TR/TE imaging. In the other four patients decreased signal was noted on short TR/TE pulse sequences and increased signal was evident on long TR/TE. These marrow changes were not present adjacent to normal disks. The relatively high signal intensity on both short and long TR/TE pulse sequences suggests that the increased signal resulted from the conversion of normal hemopoietic bone marrow to fatty marrow. We conclude that bandlike or focal areas of high signal intensity in the bone marrow adjacent to degenerated intervertebral disks occur commonly on MR images of the spine and must not be confused with signal changes from tumors or infections involving the disk space and adjacent vertebral end plates.     

暂时性骨质疏松的MRI表现

目的 分析暂时性骨质疏松的MR表现。方法 回顾性复习8例暂时性骨质疏松的MR表现。8例均行常规MR轴面和冠状面T1、T2WI。8例中男5例，女3例，年龄范围12-70岁。3例女性患病时均不在妊娠期。结果 双侧髋部病变7例，左肩部病变1例。于T1WI呈低信号8例；T2WI呈正常信号2例，中-高信号3例，高信号3例。这种骨髓水肿征象涉及髋臼1例、股骨头5例，T2WI示双侧髋关节少量关节渗液。结论 MRI有利于明确暂时性骨质疏松的诊断、病变部位和范围。     

Hepatic focal nodular hyperplasia: MR imaging at 1.0 and 1.5 T.

Ten cases of hepatic focal nodular hyperplasia (FNH) were studied with magnetic resonance (MR) imaging. Proof of diagnosis was by needle biopsy or follow-up of as long as 5 years. Both short TR/TE and long TR/TE images were obtained. The most common finding was isointensity of the lesion relative to liver parenchyma with all pulse sequences. A central scar was seen in only one patient and was hyperintense on long TR/TE images. Slight hyperintensity of the lesion on short TR/TE and long TR/TE images was seen in two cases. Textural heterogeneity was present in only one of these. The most common presentation in our series was a visually isointense lesion relative to liver on short TR/TE images and an isointense or slightly hyperintense lesion on long TR/TE images. A review of the literature and the present findings suggest that FNH has a variable appearance on MR images.     

Segmental patterns of avascular necrosis of the femoral heads: early detection with MR imaging

Thirty-two patients (64 hips) in whom avascular necrosis (AVN) of the femoral heads was highly suspected clinically were studied by magnetic resonance (MR) imaging, radionuclide bone scintigraphy, and conventional radiography. MR studies were positive for AVN in 37 hips, compared with 30 positive scintigraphic studies. In all cases in which scintigraphy and radiography were positive, MR imaging demonstrated decreased signal from the affected femoral heads, indicative of bone marrow disease. Imaging results were confirmed by biopsy or subsequent imaging appearances. In patients with negative initial scintigraphic and radiographic studies, the MR imaging criterion for a positive study was a moderately decreased bone marrow signal displaying segmental patterns within an otherwise normal-appearing femoral head on relatively T1-weighted images. In this series of high-risk patients, radionuclide scintigraphy had a sensitivity of 81%, compared with 100% for MR imaging. MR imaging should be the imaging modality of choice for early evaluation of bone marrow changes indicative of AVN.     

股骨头缺血性坏死的MRI表现

目的：探讨常规MRI平扫及增强扫描对股骨头缺血性坏死的诊断价值。方法：对30例确诊为股骨头缺血性坏死患者进行常规MRI平扫检查（共51个缺血性坏死股骨头）、其中10例加做增强MRI检查（共15个缺血性坏死股骨头）。结果：按股骨头缺血性坏死MRI分期,I期见于13个股骨头,Ⅱ期见于19个股骨头,Ⅲ期见于8个股骨头,Ⅳ期见于11个股骨头。增强MRI强化表现为：无强化（n=2）;轻微强化为主（n=10）和强化较明显（n=3）。骨髓水肿10例。髋关节积液48例。结论：常规MRI与增强MRI检查相结合可更好的反映病理改变过程,评估组织活性,有利于临床医师判断病程分期,选择治疗方案。     

Femoral head avascular necrosis: correlation of MR imaging, radiographic staging, radionuclide imaging, and clinical findings

To better correlate the appearance of avascular necrosis (AVN) of the femoral head on magnetic resonance (MR) images with the stage of disease, MR images of 56 proved AVN lesions were compared with staging from corresponding radiographs (n = 56), Tc-99m scans (n = 41), and grade of symptoms (n = 28). Fractures complicating AVN were seen in 28 (50%) of 56 radiographs (radiographic stages III-V). With long repetition (TR) and echo delay (TE) times, a characteristic "double line sign" consisting of high signal intensity inside a low-intensity peripheral rim was seen in 45 lesions (80%). The central region within the rim was isointense with marrow fat on both short and long TR and TE images in 20 (71%) of 28 lesions uncomplicated by fracture (stages I-II) but in only four (14%) of 28 stage III-V lesions (P less than .001). Symptoms were least severe in lesions isointense with fat and most severe in lesions with low-signal central regions at short and long TRs and TEs. The peripheral double line sign on long TR/TE images may add specificity to the diagnosis of AVN by MR imaging. A chronologic pattern of central MR signal features is presented which may allow staging of AVN by MR imaging.     

Early osteonecrosis of the femoral head: detection in high-risk patients with MR imaging

To determine whether magnetic resonance (MR) imaging can demonstrate the early stages of osteonecrosis that are not detectable radiographically, the authors compared radiologic findings with histologic results in seven patients at high risk for osteonecrosis of the femoral head. Radiography and MR imaging were performed, and proximal femoral intramedullary pressures were measured in all patients, even if results from imaging studies were normal. If the pressures were elevated, core decompression with biopsy was performed. Seven patients had elevated pressures in 11 hips. Of 11 hips from which biopsy specimens were taken, all had histologic evidence of osteonecrosis. However, in only five were the MR imaging findings consistent with osteonecrosis. In the remaining six hips with osteonecrosis, MR imaging findings were normal. Sensitivity of MR imaging in detection of osteonecrosis was 46%. The authors conclude that normal MR imaging results in high-risk patients do not rule out the presence of osteonecrosis.     

Bone SPECT is more sensitive than MRI in the detection of early osteonecrosis of the femoral head after renal transplantation.

We compared the diagnostic sensitivity of (99m)Tc-methylene diphosphonate bone SPECT and MRI in the early detection of femoral head osteonecrosis after renal transplantation. METHODS: The patients were 24 renal allograft recipients who underwent both bone SPECT and MRI within 1 mo of each other because of hip pain but normal findings on plain radiography. SPECT was considered positive for osteonecrosis when a cold defect was detected in the femoral head, and the defect was further classified according to the presence of adjacent increased uptake: type 1 = a cold defect with no adjacent increased uptake; type 2 = a cold defect with adjacent increased uptake. MRI was considered positive for osteonecrosis when a focal region with low signal intensity on T1 images was detected in the femoral head. Final diagnoses were made by surgical pathology or clinical and radiologic follow-up of >1 y. RESULTS: A total of 32 femoral heads, including 24 of 29 painful hips and 8 of 19 asymptomatic contralateral hips, were confirmed as having osteonecrosis. SPECT detected osteonecrosis in all 32 of the femoral heads, resulting in a sensitivity of 100% (32/32), whereas MRI detected osteonecrosis in 21 femoral heads, for a sensitivity of 66% (21/32, P < 0.005). SPECT showed the type 1 pattern in 13 and the type 2 in 19. Ten of the 13 femoral heads with the type 1 pattern were false-negative on MRI, whereas only 1 of 19 with the type 2 pattern was normal on MRI (P < 0.001). There were 6 femoral heads with normal MRI findings and abnormal SPECT findings (type 1 pattern) in 3 patients, for whom hip pain decreased and radiographic findings were normal during follow-up. Follow-up bone SPECT showed a decreasing area of cold defect in 4 femoral heads. CONCLUSION: (99m)Tc-methylene diphosphonate SPECT is more sensitive than MRI for the detection of femoral head osteonecrosis in renal transplant recipients. Bone scintigraphy with SPECT is needed to diagnose osteonecrosis in patients with hip pain despite normal radiography results after renal transplantation. The significance of a transient SPECT abnormality needs to be clarified by further natural history studies.     

Preliminary clinical results with low flip angle spin-echo MR imaging of the head and neck

A new approach for producing primarily T2- and proton-density-weighted MR images in less time than the conventional long TR, long TE imaging is to reduce the TR of a double spin-echo pulse sequence and to also reduce the RF excitation flip angle to minimize the resulting T1 sensitivity. In preliminary studies with a human volunteer and five patients with various diseases of the head and neck, conventional long TR, long TE and short TR, short TE images were compared with short TR, long TE images with reduced flip angles (45 degrees, 30 degrees), which required only 40% of the imaging time of the long TR images. The latter images showed a similar contrast pattern to the conventional T2-weighted image, and contrast-to-noise measurements indicated an increase in contrast between the lesion and nearby tissue when the flip angle was reduced. Furthermore, the maximum contrast/noise per unit imaging time on the short TR, long TE image was comparable to that on the long TR, long TE image. Optimization of the flip angle with short TR allows a substantial reduction in imaging time but with a reduction in multislice capability. This technique will be most useful in areas of complex anatomy where two or more orthogonal imaging planes are required, such as the head and neck.