Osteomyelitis with subperiosteal abscess and soft tissue extension
osteomyelitis subperiosteal abscess soft tissue infection MRI
Publication Date: 2008-04-17
There is increased T2 signal throughout the bone marrow of the proximal right humerus. This abnormal increased T2 signal extends through the physis into the proximal humeral epiphysis. There is abnormal hyperintense T2 signal in the subperiosteal region, extending through the periosteum into the subcutaneous tissue anteriorly and posteriorly.
The post-contrast images demonstrate heterogeneous enhancement within the humerus. There are focal nonenhancing regions as well.
Osteomyelitis involving the majority of the right humerus, with subperiosteal abscess and extension into soft tissues. The patient was taken to the operating room the following date for debridement. The cultures were positive for MRSA.
Osteomyelitis can occur via 3 different mechanisms. The most common in the pediatric population is via hematogeneous spread. This occurs via the metaphysis. It is thought that the change in flow dynamics and sharp curves at the transition from arterioles to the venous sinusoids allows for infection to take root. Also, there are a lack of macrophages in this region. Hematogenous spread commonly affects the growing ends of long bones. this is most often seen in the distal and proximal femur, proximal tibia, distal humerus, and distal radius. Osteomyelitis can also occur due to a secondary infection from trauma or surgery, or least likely, from vascular insufficiency.
The majority of infections in children is due to Staph aureus (70-90%). MRSA is increasingly more common. Overall, recurrence of osteomyelitis occurs in approximately 5%. Diagnosis and treatment is key, as long term complications can include bone growth abnormalities, limb-length discrepancies, arthritis, gait abnormalities, and pathologic fractures.
MRI has a major role in defining the extent of infection and bony involvement. MRI can assess for joint effusion, cartilage, involvement, and abscess. It therefore can guide debridement or drainage. It is also useful in determining other etiologies of the patient’s symptoms, such as cellulitis, avascular necrosis, infarction, septic arthritis, occult fracture, or osteoid osteoma.
On MRI, acute osteomyelitis has low bone marrow signal on T1 and increased bone marrow signal on T2 weighted images. The margins of signal abnormality are ill-defined. There is enhancement in the vascularized areas of inflammation. The nonenhancing regions are felt to represent necrosis. There can be periosteal elevation due to pus, with or without periosteal disruption. Of note, the abnormal bone marrow signal is not necessarily specific for osteomyelitis. Subperiosteal and soft tissue abscesses have low T1 and high T2 signal, and are variable in demonstrating rim enhancement.
Chronic osteomyelitis has low T1 and T2 signal due to areas of fibrosis. There are areas of cortical thickening. There may be a sequestrum, which has low T1 and T2 signal and does not enhance. There may be a sinus tract, which has high T2 signal and enhances
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