Musculoskeletal Imaging

Osteomyelitis

an infection of bone and bone marrow, which may reveal acute, subacute and chronic clinical stages. Not all persons show progression through these phases, however; in some cases chronic osteomyelitis is present at the time of initial evaluation. Occasionally, a sclerotic nonpurulent form of osteomyelitis exists, termed Garrs sclerosing osteomyelitis. Other specific disorders are chronic recurrent multifocal osteomyelitis, tuberculous osteomyelitis and SAPHO syndrome.

Four principal routes of contamination of bones and joints in osteomyelitis are:

  • haematogenous spread;

  • spread from a contiguous source of infection;

  • direct implantation of infectious material; and

  • postoperative spread.

    Owing to differences in vascular anatomy of tubular bones, haematogenous osteomyelitis may have different clinical and radiographic patterns at different ages (infant, child, adult).

    Among the radiographic and pathologic features of osteomyelitis are sequestrum, a segment of necrotic bone separated from living bone by granulation tissue; involucrum, a layer of living bone that has formed around necrotic bone; sinus tract, a tract leading to the skin surface from an infected site in bone; and Brodies abscess a sharply delineated focus of infection in bone.

    It is sometimes difficult to distinguish active from inactive cases of chronic osteomyelitis radiographically. Possible signs of activity are interval changes from preceding radiographs, poorly defined areas of osteolysis, thin linear periostitis and sequestration. Scintigraphy and MR imaging are preferred methods in the early diagnosis of osteomyelitis, but MR imaging lacks specificity and bone abscesses cannot be distinguished from sterile fluid collections without intravenous administration of a gadolinium-containing contrast agent (Fig.1) . Scintigraphy is useful in differentiation of osteolyelitis from cellulitis and in the recognition of renewed activity in chronic osteomyelitis. The extent of bone or soft tissue involvement can be better defined with CT scanning. CT has also been used to identify single or multiple sequestra, bone or soft tissue abscesses, and sinus tracts.

    Complications of osteomyelitis include osteolysis, epiphyseal growth disturbance and neoplasm (epidermoid carcinoma).

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    Fig.1

    Fat-suppressed contrast-enhanced T1-weighted MR image of the legs demonstrates abnormal high signal intensity in the distal portion of the amputated left tibia owing to osteomyelitis. The fluid collection distal to the affected tibia represents an abscess.
    Osteomyelitis, Fig.1