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.     

Role of scintigraphy in musculoskeletal and spinal infections

Clinical findings are still the mainstay for suspecting the diagnosis of musculoskeletal infections, especially osteomyelitis. No single complementary imaging technique has 100% specificity and sensitivity for every case of musculoskeletal infection. Depending on the age of the patient, presence of orthopedic hardware, location of infection, underlying bone, and systemic conditions, the choice of imaging modalities must be tailored to the patient's condition. Plain radiographs are performed first and may be sufficient. In children, bone scan is highly accurate to diagnose osteomyelitis. Labeled leukocytes with complementary bone or bone marrow studies are recommended for orthopedic hardware or diabetic foot. Finally, gallium scanning is useful for the diagnosis of vertebral osteomyelitis. Current radiopharmaceuticals used for diagnosing infection also label inflammation. Newer products, as Infecton, should in the future allow better differentiation between infection and sterile inflammation.     

Extramedullary fat fluid level on MRI as a specific sign for osteomyelitis

The role of MR in the early diagnosis of acute osteomyelitis is well known. In the context of florid cellulitis, abnormalities of marrow signal are not uncommon, although they are often non-specific. Marrow oedema and enhancement in the context of deep cellulitis might reflect either reactive marrow oedema or true osteomyelitis. More specific signs lend favour to the diagnosis of osteomyelitis: these include focal bone destruction, periosteal reaction and sequestra. The observation of an extramedullary fat-fluid sign is also a specific sign for osteomyelitis, as illustrated in the following case report. This sign is an indication of cortical breach and, thus, in the setting of infection and in the absence of trauma confirms the presence of osteomyelitis. To our knowledge, this additional specific sign of osteomyelitis has not been previously reported on MR.     

Chronische Infektionen des Skelettsystems Bildgebende Diagnostik

The diagnosis of chronic osteomyelitis is made on the basis of clinical, radiologic and histologic findings. The role of imaging in patients with known chronic osteomyelitis is to detect and to delineate areas of active infection. To correctly interpret the imaging findings, it is essential to take both the individual clinical findings and previous imaging studies into account. Reliable signs of active infection are bone marrow abscess, sequestra and sinus tract formation. Only the combined evaluation of bony changes together with alterations of the adjacent soft tissues provides good diagnostic accuracy. Projection radiography gives an overview of the condition of the bone, which provides the basis for follow-up and the selection of further imaging modalities. Computed tomography can be used to evaluate even discrete or complex bony alterations and to guide percutaneous biopsy or drainage. Magnetic resonance imaging achieves the best diagnostic sensitivity and specificity and provides superior contrast as well as anatomical resolution in both bone marrow and soft tissues. In this paper the features and clinical relevance of imaging in primary chronic osteomyelitis, posttraumatic osteomyelitis, tuberculous spondylitis and osteomyelitis of the diabetic foot are reviewed, with particular respect to MRI.     

A longitudinal insufficiency fracture of the tibia in association with a healed chronic osteomyelitis

Longitudinal stress fracture of the tibia often present with an atypical clinical presentation which can be mistaken for osseous tumor or osteomyelitis. We present a case of longitudinal stress fracture of the tibia which occurred in a patient with healed chronic osteomyelitis of the tibia. Magnetic resonance imaging failed to make the correct diagnosis. Accurate diagnosis was only obtained by helical CT which showed the longitudinal fracture line. Magnetic resonance imaging showed only non-specific signs of bone marrow edema, suggesting recurrence of osteomyelitis. Magnetic resonance imaging can be misleading in the absence of direct visualization of the fracture line. Received: 30 September 1999; Revised: 26 April 2000; Accepted: 2 May 2000     

Intramedullary and extramedullary fat globules on magnetic resonance imaging as a diagnostic sign for osteomyelitis

We retrospectively studied the frequency of persistent foci of fat signal on magnetic resonance (MR) imaging in osteomyelitis to assess its frequency, cause and diagnostic value. The radiographs and MR scans of 100 patients with a final diagnosis of osteomyelitis referred to a specialist orthopaedic oncology service with the presumptive diagnosis of a bone tumour were reviewed. The MR signal and morphological characteristics were recorded with particular attention to the presence of persistent fat signal within the infected area, which was classified as diffuse or focal. Seventeen cases were classified on radiographic grounds as acute, 63 as subacute and 20 as chronic osteomyelitis. In the acute group 12 (70%) showed replacement of the marrow with fluid containing residual fatty signal, diffuse in seven and focal in five cases. Two cases showed predominantly fatty marrow with very early marrow oedema and three cases (18%) showed replacement of marrow fat with fluid and no residual fatty foci. None of the subacute group showed foci of fatty signal and two cases of inactive sclerosing osyeomyelitis in the chronic group showed restoration of normal marrow. Persistent fatty signal within the bone as well as soft tissues on MR imaging is a frequent finding in acute osteomyelitis. Radiological–pathological correlation suggests that the increasing intramedullary pressure leads to septic necrosis with death of the lipocytes and release of free fatty globules. This characteristic, but not pathognomonic, MR finding supports the diagnosis of osteomyelitis and may help to exclude the presence of a tumour.     

骨髓炎的MRI诊断

目的:探讨MRI在骨髓炎诊断中的价值。方法:回顾分析20例骨髓炎的X线、MRI平扫及Gd-DTPA增强扫描资料。结果:MRI最早可在发病第3天发现骨髓信号异常,骨髓炎在MRI上表现出T1WI为低或稍低信号,在T2WI上呈高信号,以STIR或FFE序列最明显,Gd-DTPA扫描病变不均匀强化,骨髓炎多有脓肿和脓肿壁环状强化。结论:MRI对骨髓炎的诊断具有重要价值,尤其在显示早期病变及病变范围方面明显优于X线。     

Abnormal bone marrow distribution following unsuccessful hip replacement: a potential confusion on white cell scanning

A case is presented in which a grossly abnormal distribution of bone marrow following failed hip replacement would have led to the false diagnosis of osteomyelitis. The value of combining bone marrow scanning with indium white cell scanning in possible osteomyelitis is emphasised.     

The diabetic foot

Foot complications in diabetics often lead to amputation. Ulceration is the most common complication in the diabetic forefoot and underlies more than 90% of cases of pedal osteomyelitis. The diagnosis of osteomyelitis is, nevertheless, difficult, and imaging is an important part of the work-up. Plain radiographs, although useful for anatomical information, are neither sensitive nor specific. Three-phase bone scintigraphy is sensitive but not specific. Labelled leucocyte scintigraphy and MRI are both useful and are complementary to one another. Labelled leucocyte scintigraphy is valuable for diagnosis as well as follow-up of pedal osteomyelitis. MRI offers exquisite anatomical detail, which is invaluable for guiding surgical management. The principal complication in the mid and hind foot is the neuropathic or Charcot joint. Although infection of the neuropathic joint is infrequent, its diagnosis is difficult. The extensive bony changes that accompany this disorder severely diminish the value of radiography and bone scintigraphy. It is not always possible to distinguish the marrow oedema of neuropathy from that of osteomyelitis and the role of MRI in the evaluation of this entity is still uncertain. Uptake of labelled leucocytes in the absence of infection may occur and is owing, at least in part, to haematopoietically active marrow. Combined leucocyte/marrow scintigraphy holds considerable promise for identifying the infected Charcot joint.     

Multimodality imaging of osteomyelitis

Early diagnosis of osteomyelitis continues to be a clinical problem. Multiple imaging modalities are being used for the diagnosis of osteomyelitis, but none of them is ideal for all cases. The choice of modality depends on several factors based on an understanding of the pathophysiologic aspects of different forms of osteomyelitis. After a brief introduction outlining some basic principles regarding the diagnosis of osteomyelitis, pathophysiologic aspects are reviewed. Advantages and disadvantages of each imaging modality and their applications in different forms of osteomyelitis are discussed. The use of different imaging modalities in the diagnosis of special forms of osteomyelitis, including chronic, diabetic foot, and vertebral osteomyelitis, and osteomyelitis associated with orthopedic appliances and sickle cell disease is reviewed. Taking into account the site of suspected osteomyelitis and the presence or absence of underlying pathologic changes and their nature, an algorithm summarizing the use of various imaging modalities in the diagnosis of osteomyelitis is presented.     

Acute bone crises in sickle cell disease: the T1 fat-saturated sequence in differentiation of acute bone infarcts from acute osteomyelitis

AIM: To prove the hypothesis that acute bone infarcts in sickle cell disease are caused by sequestration of red blood cells (RBCs) in bone marrow, and to evaluate the unenhanced T1 fat-saturated (fs) sequence in the differentiation of acute bone infarction from acute osteomyelitis in patients with sickle-cell disease. MATERIALS AND METHODS: Two studies were undertaken: an experimental study using in-vitro packed red blood cells and normal volunteers, and a retrospective clinical study of 86 magnetic resonance imaging (MRI) studies. For the experimental study containers of packed RBCs were placed between the knees of four healthy volunteers with a saline bag under the containers as an additional control, and were scanned with the pre-contrast T1-fs sequence. Signal intensity (SI) ratios were obtained for packed RBCs:skeletal muscle and packed RBCs:saline. For the clinical study, the SIs of normal bone marrow, packed RBCs, bone and/or soft-tissue lesions, and normal skeletal muscle of 74 patients (86 MRI studies) were measured using unenhanced, T1 fat-saturated MRI. The ratios of the above SIs to normal skeletal muscle were calculated and subjected to statistical analysis. RESULTS: Fifty-one of 86 MRI studies were included in the final analysis. The ratios of SIs for normal bone marrow, packed red cells, bone infarction, acute osteomyelitis, and soft-tissue lesions associated with bone infarct, compared with normal skeletal muscle were (mean+/-SD) 0.9+/-0.2, 2.1+/-0.7, 1.7+/-0.5, 1.0+/-0.3, and 2.2+/-0.7, respectively. The difference in the ratio of SIs of bone infarcts and osteomyelitis was significant (p=0.003). The final diagnoses were bone infarction (n=50), acute osteomyelitis (n=1), and co-existent bone infarction and osteomyelitis (n=2). Seven patients who had suspected osteomyelitis underwent image-guided aspiration. CONCLUSION: Acute bone infarcts in sickle cell disease are caused by sequestration of red blood cells in the bone marrow. The unenhanced, T1-fat-saturated sequence alone is diagnostic for acute bone infarcts. Contrast enhancement aids in the diagnosis of acute osteomyelitis. MRI can thus help in early diagnosis, specific treatment, and preventing empirical antibiotic therapy.     

MRI evaluation of bone marrow changes in the diabetic foot: a practical approach

One of the most important roles of magnetic resonance (MR) in imaging of the diabetic foot is to differentiate between the common and often comorbid pathologies that present with abnormal bone marrow signal. The primary diagnostic challenges in this setting are to distinguish osteomyelitis from reactive bone marrow edema, neuroarthropathy from osteomyelitis, and the sterile from the superinfected neuropathic joint. Whereas both osteomyelitis and reactive marrow edema share increased T2 signal, osteomyelitis is confirmed by T1 hypointensity in the bone marrow and reactive edema demonstrates isolated T2 signal hyperintensity. In distinguishing osteomyelitis from neuroarthropathy, a localized or contiguously spreading forefoot focus of abnormal bone marrow away from the subchondral surface and adjacent to a skin ulcer, cellulitis, abscess, or sinus tract would be indicative of osteomyelitis. A midfoot, subchondral, periarticular, or polyarticular distribution of findings in the absence of a contiguous focus of skin disruption would strongly support neuroarthropathy. Parameters that have been successfully correlated with acute infection superimposed on neuroarthropathy include diffuse bone marrow signal abnormality, progressive subarticular enhancement, loss of subchondral cysts, and the presence of the MRI "ghost sign."     

Central skull base osteomyelitis in patients without otitis externa: imaging findings

BACKGROUND AND PURPOSE: Skull base osteomyelitis typically arises as a complication of ear infection in older diabetic patients, involves the temporal bone, and has Pseudomonas aeruginosa as the usual pathogen. Atypical skull base osteomyelitis arising from the sphenoid or occipital bones without associated external otitis occurs much less frequently and initially may have headache as the only symptom. The purpose of this study was to review the clinical and MR imaging features of central skull base osteomyelitis. METHODS: We retrospectively reviewed MR images obtained in six patients with central skull base osteomyelitis. No patient had predisposing external otitis or osteomyelitis of the temporal bone. RESULTS: All of our patients presented with headache, no external ear pain, and cranial nerve deficits. Five of six patients had a predisposition to infection, and the erythrocyte sedimentation rate was elevated in the five patients in whom it was checked. In each case, the diagnosis was delayed until MR imaging demonstrated central skull base abnormality, and the diagnosis was then confirmed with tissue sampling. The most consistent imaging findings were clival bone marrow T1 hypointensity and preclival soft tissue infiltration. Five of six patients were cured with no recurrence of skull base infection over a 2-4-year follow-up period. CONCLUSION: In the setting of headache, cranial neuropathy, elevated erythrocyte sedimentation rate, and abnormal clival imaging findings, central skull base osteomyelitis should be considered as the likely diagnosis. Early tissue sampling and appropriate treatment may prevent or limit further complications such as intracranial extension, empyema, or death.     

Imaging features of musculoskeletal tuberculosis

The purpose of this article is to review the imaging characteristics of musculoskeletal tuberculosis. Skeletal tuberculosis represents one-third of all cases of tuberculosis occurring in extrapulmonary sites. Hematogenous spread from a distant focus elsewhere in the body is the cornerstone in the understanding of imaging features of musculoskeletal tuberculosis. The most common presentations are tuberculous spondylitis, arthritis, osteomyelitis, and soft tissue involvement. The diagnostic value of the different imaging techniques, which include conventional radiography, CT, and MR imaging, are emphasized. Whereas conventional radiography is the mainstay in the diagnosis of tuberculous arthritis and osteomyelitis, MR imaging may detect associated bone marrow and soft tissue abnormalities. MR imaging is generally accepted as the imaging modality of choice for diagnosis, demonstration of the extent of the disease of tuberculous spondylitis, and soft tissue tuberculosis. Moreover, it may be very helpful in the differential diagnosis with pyogenic spondylodiscitis, as it may easily demonstrate anterior corner destruction, the relative preservation of the intervertebral disk, multilevel involvement with or without skip lesions, and a large soft tissue abscess, as these are all arguments in favor of a tuberculous spondylitis. On the other hand, CT is still superior in the demonstration of calcifications, which are found in chronic tuberculous abscesses.     

Abnormal bone marrow distribution following unsuccessful hip replacement: a potential confusion on white cell scanning

A case is presented in which a grossly abnormal distribution of bone morrow following failed hip replacement would have led to the false diagnosis of osteomyelitis. The value of combining bone marrow scanning with indium white cell scanning in possible osteomyelitis is emphasised.     

Cold defects in in-111 labeled leukocyte imaging of osteomyelitis in the axial skeleton

Use of In-111 oxine labeled leukocytes in the detection of osteomyelitis of the peripheral skeleton usually presents few problems. However, the diagnosis of osteomyelitis is more difficult in marrow-bearing areas because uptake of indium is normal. Sixty-one In-111 labeled leukocyte scans, that had been performed to exclude osteomyelitis of the axial skeleton, pelvis, and proximal long bones, were reviewed. Eight cold defects were identified at sites of suspected osteomyelitis. Five of these were surgically proven osteomyelitis. Nineteen percent of all cases of osteomyelitis in these areas (5 of 26) presented as cold defects. This incidence of osteomyelitis presenting as cold defects is higher than previously reported. Therefore, the possibility of osteomyelitis should be strongly considered when a cold defect is identified in red marrow areas.     

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.     

Infection of the appendicular skeleton

In relation to the clinical course, infection in bone can be divided into acute, subacute and chronic osteomyelitis. The diagnosis of acute osteomyelitis is often challenging but can best be made by correlating radiography, bone scintigraphy and MRI with clinical information. Radiography should routinely be supplemented by sonography in the newborns and infants, if applicable. Brodie's abscess, which is clinically a subacute form of osteomyelitis, is best diagnosed by the combination of radiography and MRI. Chronic osteomyelitis is divided into primary haematogenous forms and exogenous, mostly post-traumatic, osteomyelitis. In the majority of patients, post-traumatic osteomyelitis is a clinical diagnosis; however, in a number of patients only the correlation of clinical findings, blood tests and imaging reveals the correct diagnosis. Often, MRI and scintigraphic methods, such as scanning with labeled leucocytes, together establish the diagnosis. Chronic recurrent multifocal osteomyelitis may mimic bacterial osteomyelitis but is a distinct disease probably associated with the SAPHO syndrome.     

Infection of the appendicular skeleton

In relation to the clinical course, infection in bone can be divided into acute, subacute and chronic osteomyelitis. The diagnosis of acute osteomyelitis is often challenging but can best be made by correlating radiography, bone scintigraphy and MRI with clinical information. Radiography should routinely be supplemented by sonography in the newborns and infants, if applicable. Brodie’s abscess, which is clinically a subacute form of osteomyelitis, is best diagnosed by the combination of radiography and MRI. Chronic osteomyelitis is divided into primary haematogenous forms and exogenous, mostly post-traumatic, osteomyelitis. In the majority of patients, post-traumatic osteomyelitis is a clinical diagnosis; however, in a number of patients only the correlation of clinical findings, blood tests and imaging reveals the correct diagnosis. Often, MRI and scintigraphic methods, such as scanning with labeled leucocytes, together establish the diagnosis. Chronic recurrent multifocal osteomyelitis may mimic bacterial osteomyelitis but is a distinct disease probably associated with the SAPHO syndrome.     

Comparison of the diagnosis of plain radiography ultrasonography and magnetic resonance imaging in early diagnosis of acute osteomyelitis experimentally formed on rabbits

PURPOSE: We have compared the sensitivities of MRI, US and radiography which are some of the radiologic modalities used in the early diagnosis of acute osteomyelitis. MATERIALS AND METHODS: After 1 week care and research on 20 New Zealand rabbits (average weight: 2.5 kg) in animal laboratory, study was begun. Six rabbits died after anesthesia and surgical procedure. There were 14 rabbits remaining and 10 of them formed the study group. Four of them were used as the control group. Fresh mouse feces was inoculated into the bone marrow of 20 tibia under general anesthesia and during the following 15 days, MRI, US and radiographic researches were made everyday. RESULTS: According to the results that we got at the end of the 15-day period, MRI was found as the most sensitive method in describing early diagnosis of infection in the bone marrow and also in showing the extension of the infection to the soft tissue. Although US showed the findings later than MRI, it was determined that its sensitivity was less than but near MRI's in detecting subperiosteal fluid in short term period. Radiographic research gives acute osteomyelitis diagnosis latest, so it was determined as the modality that has the lowest sensitivity. CONCLUSION: MRI which is one of the radiologic modalities among other diagnostic radiologic modalities that can be used in early diagnosis of acute osteomyelitis, has the highest sensitivity. Ultrasonography is the second most sensitive modality. Radiographic analysis has the least sensitivity among other modalities. As a result, first MRI then US and after that plain radiography should be used for the early diagnosis of acute osteomyelitis.