Infection: musculoskeletal

Intramedullary fat globules related to bone trauma: a new MR imaging finding

OBJECTIVE

The purpose of this study is to describe intraosseous fat globules related to bone trauma that are detectable with magnetic resonance imaging (MRI), to define the relationship of this finding to fracture and bone contusion, to establish the frequency and associated findings. A proposed pathogenesis is presented.

MATERIALS AND METHODS

We retrospectively reviewed 419 knee MRI examinations in patients with a history of recent injury and MRI findings of fracture or bone contusion. As a control population, 268 knee MRI examinations in patients without MRI findings of recent bone injury were also reviewed.

RESULTS

Eight of 419 (1.9%) patients with acute or subacute knee injury with positive findings of osseous trauma on MRI demonstrated intraosseous fat globules. The mean age of patients with fat globules was greater than that of those without fat globules, and the finding was more commonly seen in women. Fat globules were hyperintense to the normal fatty marrow present elsewhere in the bone on TI-weighted imaging and had a surrounding halo of high signal intensity on fluid-sensitive imaging.

CONCLUSIONS

Intramedullary fat globules related to bone injury visible on MRI are thought to be due to coalesced fat released by the necrosis of fatty marrow cells. The pathogenesis is supported by histologic studies of fat globules related to osteomyelitis, bone contusions and fractures. As the medullary cavity of long bones in older patients contains more fat than hematopoetic bone marrow, it is likely that this finding is more common with advancing age.

Dynamic gadolinium-enhanced MRI of the proximal femur: preliminary experience in healthy children

OBJECTIVE

The purpose of this study is to use dynamic contrast-enhanced MRI to evaluate the perfusion characteristics of the proximal femur in the growing skeleton.

MATERIALS AND METHODS

We evaluated 159 subjects (mean age, 5.67 years) who underwent a well-controlled protocol of contrast-enhanced MRI of the abdomen and hips. Perfusion and permeability parameters (enhancement ratio peak, AUC, time to peak, and rate of extraction) for six regions of the proximal femur were calculated.

RESULTS

A decrease with age was found for all contrast kinetics parameters in all regions (p < 0.001). Perfusion parameters differed between the regions (p < 0.001). The highest perfusion and permeability parameters were found in the metaphyseal spongiosa, metaphyseal marrow, and periosteum. The metaphyseal spongiosa had a highly vascular pattern of enhancement and showed the highest enhancement ratio peak, AUC, and rate of extraction and the lowest time to peak. The metaphyseal marrow showed a vascular pattern of enhancement with a lower peak compared with the metaphyseal spongiosa. The periosteum showed prompt nonvascular contrast enhancement that reached a plateau that remained elevated.

CONCLUSION

The highest enhancement was seen in areas involved with growth: the metaphyseal spongiosa, which is related to endochondral ossification, and the periosteal cambium, which is related to membranous ossification. The enhancement characteristics are radically different: in the spongiosa; enhancement is brisk and declines, with a vascular pattern, whereas contrast uptake increases with time in the periosteum. Recognition of normal enhancement patterns of the proximal femur is important for distinguishing normal development from pathologic processes.

Role of MRI in the diagnosis and treatment of osteomyelitis in pediatric patients

Osteomyelitis is a significant cause of morbidity in children throughout the world. Multiple imaging modalities can be used to evaluate for suspected osteomyelitis, however magnetic resonance imaging (MRI) has distinct advantages over other modalities given its ability to detect early changes related to osteomyelitis, evaluate the true extent of disease, depict extraosseous spread of infection, and help guide surgical management. MRI has assumed a greater role in the evaluation of osteomyelitis with the increase in musculoskeletal infections caused by methicillin-resistant Staphylococcus aureus which have unique imaging features that are well-demonstrated with MRI. This review focuses primarily on the use of MRI in the evaluation of osteomyelitis in children and will include a discussion of the clinically important and characteristic findings on MRI of acute bacterial osteomyelitis and related conditions.

MR imaging of the paediatric foot and ankle

Radiography is the mainstay for initial evaluation of paediatric foot and ankle pathology. MRI is the preferred exam for further characterisation of the majority of these conditions. The modality features high sensitivity and specificity for this purpose with few exceptions. Findings on MRI will often dictate patient referral and further management, and are frequently required for surgical planning. This article will provide an overview of a variety of pathologies that afflict the foot and ankle in children. These include tarsal coalition, osteochondral lesions, osteonecrosis, osteochondroses, stress fractures, osteomyelitis, inflammatory arthritis, neoplasms of bone and soft tissue, and foreign bodies. Their respective imaging manifestations on MRI are the focus of the paper. Technical parameters and marrow signal variation are also discussed.

Childhood osteomyelitis: imaging characteristics

Background

The purpose of this review is to illustrate the imaging findings of childhood osteomyelitis. The diagnosis of childhood osteomyelitis can be challenging. Clinical presentation and laboratory results can differ and are relatively unreliable. To date, its role in the assessment of treatment efficacy is not yet clear.

Methods

This review article provides an overview of the different imaging modalities and imaging characteristics of childhood osteomyelitis. Levels of evidence for different modalities are presented.

Results

Paediatric radiology plays a pivotal role in the diagnosis of childhood osteomyelitis and can also be used to guide therapy and intervention.

Conclusion

Although imaging is essential in the diagnostic process, cooperation between the physician and radiologist remains the cornerstone in accurately diagnosing childhood osteomyelitis.

Main Messages

• Imaging plays a pivotal role in the diagnosis of childhood osteomyelitis.

• Cooperation between the clinician and radiologist is a very important aspect of making the diagnosis.

• The initial imaging modality in childhood osteomyelitis is conventional imaging.

• Normal conventional imaging does not exclude osteomyelitis.

Taking the stress out of evaluating stress injuries in children

Pediatric stress injuries result from a mismatch between (a) the burden of activity on growing bone and cartilage and (b) their intrinsic biomechanical properties. Although the presentation of stress injuries varies with the specific physical activity and the site of injury, in children it varies primarily with the degree of skeletal maturation. During the past several years, there has been a substantial increase in the incidence of pediatric stress injuries. The differential diagnosis of a stress injury in a child or adolescent can be challenging because the injury sometimes can appear aggressive at imaging assessment. Awareness of the spectrum of imaging features of stress injuries can help the radiologist to reach the correct diagnosis and prevent unnecessary anxiety. This review depicts the range of stress injuries in children and adolescents in various anatomic locations, with emphasis on their appearances at magnetic resonance imaging.

Limb infections in children and adults

Infections of the bone and soft tissue of the limbs need to be diagnosed and treated urgently regardless of the patient's age. Clinical features are often non-specific. MRI and, in some cases, sonography investigations lead to early diagnosis and appropriate management. Computed tomography has limited value. Needle aspiration and biopsy need not be routine. In children, anatomical particularities explain the different morphological manifestations, which vary with age. It is important to both know when to propose the diagnosis of infection, so that appropriate imaging investigations are carried out, and to be aware of the symptomatology of limb infections in children and adults and understand the differential diagnoses for each age group. Clinicians should also be aware of the specific characteristics in children.