Differential diagnosis of pedal osteomyelitis and diabetic neuroarthropathy: MR Imaging

Almost all diabetic foot infections originate from a foot ulcer. Decreased pain perception and structural deformities such as previous partial foot amputation, Charcot joints, and toe deformity in combination with chronic ischemia lead to a propensity for skin breakdown and subsequent infection. Magnetic resonance (MR) imaging is increasingly performed to evaluate for potential bone infection, but diagnosis of osteomyelitis can be complicated because signal changes from acute Charcot arthropathy, fractures, and postoperative residues may be mistaken for infection. Signal alterations of bone infection may be atypical in sclerosing osteomyelitis and gangrene. Differentiation between osteomyelitis and acute or subacute neuroarthropathy requires careful analysis of the location of bone signal alterations, their distribution, and pattern because qualitative changes are often identical. Presence of secondary signs such as adjacent ulcer, cellulitis, and sinus tract is indicative of osteomyelitis. Differentiation of noninfected neuroarthropathy from infected neuroarthropathy based on MR examinations is difficult. Presence of a sinus tract, disappearance of subchondral cysts, diffuse bone marrow abnormality, and bone erosions are in favor of infection.     

Transient bone marrow edema of the hip

Transient bone marrow edema of the hip is characterized by moderate homogeneous low MR signal intensity with ill-defined margins that involves at least a portion of the femoral head. Spin echo T1-weighted images are helpful to exclude other underlying diseases (tumor, infection, necrosis from systemic origin…), for which marrow edema is secondary or no epiphyseal in location. High-resolution fat-suppressed T2-weighted or proton density images allow evaluation of the articular cartilage, subchondral bone and subchondal marrow: if the articular cartilage is abnormal, the lesion is irreversible (arthrosis or necrosis); if the subchondral bone is focally interrupted and/or if the femoral is no longer spherical, the lesion is irreversible (necrosis); if a focal linear fluid collection is present under the subchondral bone, the lesion is irreversible (necrosis). Finally, subchondral changes may provide useful prognostic information: the absence of any abnormality other than marrow edema typically indicates that complete resolution is likely; the presence of a focal T2-weighted hypointense lesion immediately next to the subchondral bone suggests an irreversible lesion, especially if it is equal to or thicker than 4mm or the joint space. In some instances, prognosis cannot be reliably determined requiring the need for follow-up imaging.     

Bone marrow edema patterns in the ankle and hindfoot: distinguishing MRI features

OBJECTIVE: Many disorders produce similar or overlapping patterns of bone marrow edema in the ankle. Bone marrow edema may present in a few hindfoot bones simultaneously or in a single bone. The purpose of this pictorial essay is to provide guidelines based on clinical history and specific MRI patterns and locations to accurately identify the cause of ankle bone marrow edema. We will first focus on bone marrow edema in general disease categories involving multiple bones, such as reactive processes, trauma, neuroarthropathy, and arthritides. A discussion of bone marrow edema in individual bones of the ankle and hindfoot including the tibia, fibula, talus, and calcaneus will follow. Helpful hints for arriving at the correct diagnosis will be provided in each section. CONCLUSION: After review of this article, radiologists should be able to use their knowledge of clinical history and specific MRI patterns and locations to accurately distinguish between the various causes of bone marrow edema in the ankle and hindfoot.     

Idiopathic bone marrow edema lesions of the femoral head: predictive value of MR imaging findings.

PURPOSE: To determine the frequency of several subchondral magnetic resonance (MR) imaging features observed in bone marrow edema lesions of the femoral head and to determine their value for differentiation of irreversible from transient lesions. MATERIALS AND METHODS: The authors reviewed MR images of 72 femoral head lesions in 42 men and 25 women (median age, 48 years) with equivocal radiographic findings and bone marrow edema seen at MR imaging (T1- and T2-weighted images in all patients and contrast material-enhanced T1-weighted images in 39 patients). Follow-up MR images showed 57 lesions to be transient and 15 to be irreversible. The presence and size of subtle subchondral features observed on initial MR images were compared for both types of lesion. RESULTS: Lack of any additional subchondral change on T2-weighted or contrast-enhanced T1-weighted images had 100% positive predictive value for transient lesions. For irreversible lesions, presence of a subchondral area of low signal intensity at least 4 mm thick or 12.5 mm long had positive predictive values of 85% and 73%, respectively, on T2-weighted images and 87% and 86%, respectively, on contrast-enhanced T1-weighted images. CONCLUSION: Careful assessment of subchondral changes enables confident differentiation between early irreversible lesions and transient bone marrow edema lesions.     

MRI findings of septic arthritis and associated osteomyelitis in adults

OBJECTIVE: The purpose of this study was to describe the soft-tissue, synovial, and osseous MRI findings of septic arthritis. MATERIALS AND METHODS: At 1.5 T (T1-weighted, T2-weighted or STIR, and contrast-enhanced images), 50 consecutive cases of septic arthritis were evaluated by two observers for synovial enhancement, perisynovial edema, joint effusion, fluid outpouching, fluid enhancement, and synovial thickening. The marrow was assessed for abnormal signal on T1- and T2-weighted images or after contrast enhancement. We noted whether the marrow signal was diffuse or abnormal in bare areas. MRI findings were compared with microbiologic, clinical, and surgical data and diagnoses. RESULTS: The frequency of MRI findings in septic joints was as follows: synovial enhancement (98%), perisynovial edema (84%), joint effusions (70%), fluid outpouching (53%), fluid enhancement (30%), and synovial thickening (22%). The marrow showed bare area changes (86%), abnormal T2 signal (84%), abnormal gadolinium enhancement (81%), and abnormal T1 signal (66%). Associated osteomyelitis more often showed T1 signal abnormalities and was diffuse. CONCLUSION: Synovial enhancement, perisynovial edema, and joint effusion had the highest correlation with the clinical diagnosis of a septic joint. However, almost a third of patients with septic arthritis lacked an effusion. Abnormal marrow signal-particularly if it was diffuse and seen on T1-weighted images-had the highest association with concomitant osteomyelitis.     

MR features of tuberculous osteomyelitis

OBJECTIVE: To describe the MR imaging features of tuberculous osteomyelitis. DESIGN AND PATIENTS: MR imaging features of 11 patients (14-65 years) with proven extra-spinal tuberculous osteomyelitis were reviewed. Osseous and adjacent soft-tissue changes were analyzed. RESULTS: On the basis of the signal intensity characteristics compared with the normal marrow fat, two kinds of lesions were observed: (a) predominantly intermediate to low signal intensity lesions on T2-weighted images with low signal intensity on T1-weighted images, and (b) lesions which had a discrete peripheral zone of marginally higher signal intensity than the center on T1-weighted images and surrounding edema and lower signal intensity than the fatty bone marrow with variable signal intensity on T2-weighted images. Soft-tissue abscesses and marrow edema were each noted in eight cases. Soft-tissue edema was noted in most cases. CONCLUSION: An osseous lesion with intermediate to low signal intensity on T2-weighted images and associated soft-tissue abscess may be suggestive of tuberculous osteomyelitis. Lesions with a rim of mildly increased signal intensity on T1-weighted images, a non-specific indicator of an infective process, may also be seen.     

The diabetic foot: magnetic resonance imaging evaluation

Fourteen diabetic patients with suspected foot infection and/or neuropathic joint (Charcot Joint) were evaluated with magnetic resonance imaging (MRI) in an attempt to assess the extent of the infection and also to distinguish infection from the changes seen with neuroarthropathy. The majority of patients with infection had more than one site of involvement and the following diagnoses were made by MRI evaluation: osteomyelitis (n = 8), abscess (n = 7), neuropathic joint (n = 5), septic arthritis (n = 4), and tenosynovitis (n = 4). Clinical or surgical/pathological confirmation of the MRI diagnoses was obtained in all but nine sites of infection or cases of neuropathic joint. If the two diagnostic categories of septic arthritis and tenosynovitis are excluded, all but four of the MRI diagnoses were confirmed. A distinctive pattern for neuroarthropathy was identified in five cases, consisting of low signal intensity on T1- and T2-weighted images within the bone marrow space adjacent to the involved joint. We conclude that MRI is a valuable adjunct in the evaluation of the diabetic foot, and that it provides accurate information regarding the presence and extent of infection in this subset of patients. MRI has proven particularly helpful in differentiating neuroarthropathy from osteomyelitis.     

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.     

Eosinophilic granuloma: MRI manifestations

The appearance on magnetic resonance imaging (MRI) of 16 cases of pathologically proven eosinophilic granuloma were reviewed retrospectively and correlated with the radiographic appearance of the lesion. The most common MR appearance (ten cases) was a focal lesion, surrounded by an extensive, ill-defined bone marrow and soft tissue reaction with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, considered to represent bone marrow and soft tissue edema (the flare phenomenon). The MRI manifestations of eosinophilic granuloma, especially during the early stages, are nonspecific, and may simulate an aggressive lesion such as osteomyelitis or Ewings sarcoma, or other benign bone tumors such as osteoid osteoma or chrondroblastoma.     

Bone marrow edema pattern in osteoarthritic knees: correlation between MR imaging and histologic findings

PURPOSE: To correlate magnetic resonance (MR) images of a bone marrow edema pattern with histologic findings in osteoarthritic knees. MATERIALS AND METHODS: Sixteen consecutive patients (age range, 43-79 years; mean, 67 years) referred for total knee replacement were examined with sagittal short inversion time inversion-recovery (STIR) and T1- and T2-weighted turbo spin-echo MR imaging 1-4 days before surgery. Tibial plateau abnormalities on MR images were compared quantitatively with those on histologic maps. RESULTS: The bone marrow edema pattern zone (ill-defined and hyperintense on STIR images and hypointense on T1-weighted MR images) mainly consisted of normal tissue (53% of the area was fatty marrow, 16% was intact trabeculae, and 2% was blood vessels) and a smaller proportion of several abnormalities (bone marrow necrosis [11% of area], abnormal [necrotic or remodeled] trabeculae [8%], bone marrow fibrosis [4%], bone marrow edema [4%], and bone marrow bleeding [2%]). The bone marrow edema pattern zone and the zone with a normal MR imaging appearance differed significantly in the presence of bone marrow necrosis (P =.021), bone marrow fibrosis (P =.014), and abnormal trabeculae (P =.011) but not in the prevalence of bone marrow edema (P =.069). Bone marrow edema also was found in zones with an unremarkable MR appearance (perifocal zone, 5% edema; control zone, 2% edema). CONCLUSION: A bone marrow edema pattern in osteoarthritic knees represents a number of noncharacteristic histologic abnormalities. Edema is not a major constituent of MR imaging signal intensity abnormalities in such knees.     

Subchondral insufficiency fracture of the femoral head: histopathologic correlation with MRI

Objective. To correlate the magnetic resonance imaging (MRI) features with the histopathologic findings in subchondral insufficiency fracture (SIF) of the femoral head. Design and patients. This study was based on a retrospective review of the MRI features and histopathologic findings in seven patients with SIF who had had total hip replacement. Results. In all seven cases, MRI showed a bone marrow edema pattern in the femoral head, and a focal low-intensity band beneath the articular cartilage on some slices (not all) on the T1-weighted images. The shape of the low-intensity band varied: it was irregular and serpentine in four cases, well-delineated, smooth, and a mirror image to the articular surface in two cases, and parallel to the articular surface in one case. On histologic examination, the low-intensity band on MRI corresponded to a fracture line and its associated repair tissue. In all but one case, the band was not visible on T2-weighted or fat suppression images, and the proximal subchondral portion of the lesion had a homogeneous high signal intensity. This region of high signal intensity corresponded histopathologically to viable bone and marrow tissue with associated callus, edema, and vascular granulation tissue. Conclusions. SIF of the femoral head characteristically demonstrates a low-intensity band on T1-weighted images that corresponds, histopathologically, to a linear subchondral fracture and its associated repair tissue. In most cases, the subchondral portion of the lesion appears on T2-weighted images as an area of homogeneously high signal intensity. Received: 1 June 2000 Revision requested: 17 August 2000 Revision received: 11 October 2000 Accepted: 9 January 2001     

膝关节骨关节炎MRI表现

目的：评价MRI在膝关节骨关节炎临床诊治中的价值。方法：对127例184个受累膝关节骨关节炎MRI各序列图像进行分析。结果：所有膝关节均表现不同程度MRI异常信号改变,15个仅表现为单纯软骨下骨质水肿．27个表现为I级软骨损伤,35个表现为Ⅱ级软骨损伤,40个表现为Ⅲ级软骨损伤,67个表现为Ⅳ级软骨损伤,82个关节间隙不均匀变窄,103个膝关节存在轻一中等度滑膜增厚,少一中等量关节腔积液。软骨损伤MRI分别表现为高信号软骨内异常低信号影．软骨面毛糙、缺损、完全缺失、骨赘形成。软骨下骨单纯水肿在T1wI上表现为片状低信号,FS-T1WI-FLASH上呈高信号,骨质吸收破坏呈斑片状长T1长T2影,境界清晰,骨质增生硬化在MRI各序列上均呈片状、条状、环状及分隔状低信号。结论：MRI能准确反映膝关节骨关节炎损伤的程度、范围,为临床对骨关节炎的诊治提供了可靠、直接的依据。     

Subtle bone marrow edema assessed by frequency selective chemical shift MRI.

Subtle edema in yellow bone marrow from tumors (14 subjects) and osteomyelitis (9 subjects) were examined by selective nonexcitation (SENEX) water imaging using a short five pulse frequency selective excitation with lipid suppression greater than 96%. Standard spin-echo (SE) proton density-, T1- and T2-weighted images, and fat suppression methods such as short inversion time inversion recovery and also the chemical shift selective Dixon method are discussed in comparison with SENEX. Application of the SENEX method is described and images from four typical cases are demonstrated. Sensitivity to edema is obviously better using the SENEX chemical shift selective method than using other imaging techniques. Improved delineation of abnormal areas in yellow bone marrow is provided by SENEX water imaging in one slice after multislice standard imaging. After shimming, only one SE scan with frequency selective excitation is necessary to get a pure water image.     

MR imaging of epiphyseal lesions of the knee: current concepts, challenges, and controversies

This article focuses on spontaneous painful conditions involving the subchondral bone and marrow of mature knee epiphyses. MR imaging is the technique of choice for the work-up of these lesions and enables distinction of two main categories of lesions on the basis of T1-weighted images: avascular necrosis, and lesions presenting the bone marrow edema pattern. This latter category encompasses spontaneous osteonecrosis of the knee, and a variety of self-resolving conditions that may be differentiated by the study of the subchondral bone marrow area on T2-weighted images. Behind definite appellation of lesions, the challenge for the radiologist is to provide a prognosis: the distinction between self-resolving lesions from those that may evolve to epiphyseal collapse and joint impairment should be possible in most cases.     

Bone marrow edema pattern around the knee on magnetic resonance imaging excluding acute traumatic lesions

Magnetic resonance imaging (MRI) is very sensitive for the detection of marrow abnormalities. Bone marrow edema on MRI has been defined as an area of low signal intensity on T1-weighted images, associated with intermediate or high signal intensity findings on T2-weighted images. The bone marrow edema pattern is a nonspecific finding with multiple etiologies. The knee is a common place for bone marrow signal abnormalities to appear on MRI. Besides contusions and fractures from acute trauma, there are a variety of other causes of the bone marrow edema pattern. It is important for the interpreter of the study to be aware of the different etiologies responsible for producing these changes and to be able to narrow the differential diagnosis without mistaking such a pattern for acute trauma or infiltrative tumor. This article concentrates on those entities that produce a bone marrow edema pattern not related to acute trauma including red marrow proliferation, stress, osteochondral lesions, osteonecrosis, bone marrow edema syndrome, arthropathy, infection, Paget's disease, and marrow replacement disorders.     

Linear signal hyperintensity adjacent to the subchondral bone plate at the knee on T2-weighted fat-saturated sequences: imaging aspects and association with structural lesions

Objective

To describe the association between linear T2 signal abnormalities in the subchondral bone and structural knee lesions.

Materials and methods

MR studies of patients referred for the evaluation of knee pain were retrospectively evaluated and 133 of these patients presented bone marrow edema pattern (BMEP) (study group) and while 61 did not (control group). The presence of linear anomalies of the subchondral bone on T2-weighted fat-saturated sequences was evaluated. The findings were correlated to the presence of structural knee lesions and to the duration of the patient’s symptoms. Histologic analysis of a cadaveric specimen was used for anatomic correlation.

Results

Linear T2 hyperintensities at the subchondral bone were present in 41 % of patients with BMEP. None of the patients in the control group presented this sign. When a subchondral linear hyperintensity was present, the prevalence of radial or root tears was high and that of horizontal tears was low (71.4 and 4.8 %, respectively). Sixty-nine percent of the patients with a subchondral insufficiency fracture presented a subchondral linear hyperintensity. It was significantly more prevalent in patients with acute or sub-acute symptoms (p?Conclusions The studied linear T2 hyperintensity is located at the subchondral spongiosa and can be secondary to local or distant joint injuries. Its presence should evoke acute and sub-acute knee injuries. This sign is closely related to subchondral insufficiency fractures and meniscal tears with a compromise in meniscal function.     

Diagnosis of osteomyelitis by MR imaging

Bone scans are highly sensitive for the diagnosis of acute osteomyelitis, but the difficulty of separating bone-marrow processes from soft-tissue disease limits the specificity and accuracy. A diagnostic technique capable of distinguishing bone-marrow processes from soft-tissue disease would improve the diagnostic accuracy of osteomyelitis. To evaluate the use of MR in the diagnosis of osteomyelitis, MR examinations were performed in 35 patients with suspected acute osteomyelitis. Twelve of these were proved to have osteomyelitis either by surgery (nine patients) or by clinical follow-up (three patients). In the other 23, osteomyelitis was excluded by surgery (12 patients) or by the clinical course (11 patients). Evidence of osteomyelitis on MR consisted of abnormalities of the bone marrow with decreased signal intensity on the T1-weighted images and increased signal intensity on the T2-weighted or short-T1 inversion recovery (STIR) images. MR and bone scintigraphy were interpreted by two radiologists who were given no clinical information other than to rule out osteomyelitis. The sensitivities of MR and static bone scan were 100% for bone-marrow abnormality. Because bone-marrow abnormality in osteomyelitis associated with healing fractures was incorrectly diagnosed by MR (one case) and bone scintigraphy (two cases), the sensitivities of MR and scintigraphy for the diagnosis of osteomyelitis were 92% and 82%, respectively. The specificities of MR and scintigraphy were 96% and 65%, respectively (p less than .05). The overall accuracy for the diagnosis of osteomyelitis was 94% for MR and 71% for bone scan (p less than .05). Because of its ability to separate soft-tissue disease from underlying bone marrow, MR may be used to evaluate patients with positive bone scintigraphy to improve the specificity and accuracy of diagnosis for osteomyelitis.     

A subchondral fracture in transient osteoporosis of the hip

Although subchondral changes are reported to be associated with transient osteoporosis of the hip (TOH), the etiology of this disorder is unknown.In this paper, we describe a 45-year-old man with TOH who underwent both MRI and CT examinations. Plain radiographs obtained 2 months after the onset of hip pain showed a focal loss of radiodensity in the left femoral head. MRI revealed a bone marrow edema pattern in the left femoral head and neck with an associated subchondral serpiginous low signal intensity line on the T1-weighted images. A CT scan showed a subchondral fracture in the corresponding area. The hip pain and imaging abnormalities resolved spontaneously following conservative treatment.This case study demonstrated that a subchondral fracture of the femoral head was associated with TOH using MRI and CT examinations, and suggests that the presence of a subchondral fracture may be important for the pathophysiology of TOH.     

MR imaging features of foot involvement in ankylosing spondylitis

OBJECTIVE: To determine alterations of the soft tissue, tendon, cartilage, joint space, and bone of the foot using magnetic resonance (MR) imaging in ankylosing spondylitis (AS) patients. MATERIALS AND METHOD: Clinical and MR examination of the foot was performed in 23 AS patients (46 feet). Ten asymptomatic volunteers (20 feet) were studied on MR imaging, as a control group. MR imaging protocol included; T1-weighted spin-echo, T2-weighted fast-field echo (FFE) and fat-suppressed short tau inversion recovery (STIR) sequences in sagittal, sagittal oblique, and coronal planes using a head coil. Specifically, we examined: bone erosions, tendinitis (acute and chronic), para-articular enthesophyte, joint effusion, plantar fasciitis, joint space narrowing, soft tissue edema, bone marrow edema, enthesopathy in the Achilles tendon and plantar fascia attachment, subchondral signal intensity abnormalities (edema and sclerosis), tenosynovitis, retrocalcaneal bursitis, subchondral cysts, subchondral fissures, and bony ankylosis. Midfoot, hindfoot, and ankle were included in examined anatomic regions. RESULTS: Clinical signs and symptoms (pain and swelling) due to foot involvement were present in 3 (13%) of the patients while frequency of involvement was 21 (91%) with MR imaging assessment. The MR imaging findings were bone erosions (65%), Achilles tendinitis (acute and chronic) (61%), para-articular enthesophyte (48%), joint effusion (43%), plantar fasciitis (40%), joint space narrowing (40%), subchondral sclerosis (35%), soft tissue edema (30%), bone marrow edema (30%), enthesopathy of the Achilles attachment (30%), subchondral edema (26%), enthesopathy in the plantar fascia attachment (22%), retrocalcaneal bursitis (22%), subchondral cysts (17%), subchondral fissures (17%), tendinitis and enthesopathy of the plantar ligament (13%), and bony ankylosis (9%). The most common involved anatomical region was the hindfoot (83%) following by midfoot (69% ) and ankle (22%). CONCLUSION: In our experience, MR imaging may detect inflammatory and/or erosive bone, soft tissue, cartilage, tendon, and joint abnormalities in AS patients, even if AS patients did not have clinical signs and symptoms of foot involvement. If these data prove to be confirmed in further MR studies, MR imaging may be of importance especially in early diagnosis of inflammatory changes in the foot.     

Treatable chondral injuries in the knee: frequency of associated focal subchondral edema

OBJECTIVE: In the knee, chondral flaps and fractures are radiographically occult articular cartilage injuries that can mimic meniscal tears clinically; once correctly diagnosed, these injuries can be treated surgically. We investigated an associated MR imaging finding--focal subchondral bone edema--in a series of surgically proven lesions. MATERIALS AND METHODS: Two musculoskeletal radiologists retrospectively reviewed the MR studies of 18 knees with arthroscopically proven treatable cartilage infractions, noting articular surface defects and associated subchondral bone edema; subchondral edema was defined as focal regions of high signal intensity in the bone immediately underlying an articular surface defect on a T2-weighted or short inversion time inversion recovery (STIR) image. RESULTS: The first observer saw focal subchondral edema deep relative to a cartilage surface defect in 15 (83%) of the 18 cases; in two additional cases a surface defect was seen without underlying edema. The second observer identified 13 knees (72%) with surface defects and associated subchondral edema and three with chondral surface defects and no associated edema. Subchondral edema was seen more frequently on fat-suppressed images and on STIR images than non-fat-suppressed images. CONCLUSION: Focal subchondral edema is commonly visible on MR images of treatable, traumatic cartilage defects in the knee; this MR finding may prove to be an important clue to assist in the detection of these traumatic chondral lesions.