Definition
Brodie's abscess, a chronic abscess of bone surrounded by
dense fibrous tissue and sclerotic bone.
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Radiographic Appearance
There is quite a well demarcated lucent area in the
metaphysis of the humorous of the tibia. This lucent area lies
immediately underneath the epiphyseal plate. There is no evidence of
infiltrative type destruction of the bone adjacent to it and there
is no periosteal reaction. The appearances are relatively
non-specific, although this is a typical location for a Brodies
abscess.
In the early stages of osteomyelitis the x-rays are normal or may
show some minor soft tissue changes. A nuclear bone scan is a much
more sensitive test for detecting early disease. Generally
osteomyelitis has to be present for at least 4 to 7 days before
there are significant radiological changes. If there are
radiological changes, the most common appearance is irregular bone
destruction. Later periosteal reaction is seen, and even later this
much better defined stage, known as a Brodies Abscess, is seen often
when the osteomyelitis is inadequately or only partially treated.
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Pathology
Acute hematogenous osteomyelitis is most commonly seen in children
and characterized by accumulation of the pathogenic organisms in the
terminal arterioles and capillars of the bone metaphysis. In
children a boy to girl ratio of 3/1 is seen. As edema and
granulation occur, the intraosseous pressure may increase and result
in bone necrosis due to compression of the vascular structures.
These may lead to formation of a Brodie's abscess. In adults other
pathogenic mechanisms of osteomyelitis are more common and include
traumatic inoculation and spread from a nearby infected focus.
Brodie's abscess as located form of chronic osteomyelitis is very
common in children, due to high vascularity of the metaphysis and
growth plates. Metaphyseal locations are most common before closure
of the growth plates. After closure, a metaepiphyseal abscess is
most frequent. When not hematogeneous in etiology, they occur most
frequently in young adults at the long bones of the lower
extremities. Pathologically, the wall of the abscess contains large
amounts of granulation tissue, accounting for pronounced rim
enhancement on contrast-enhanced MRI or CT scans. The central
portions are mainly constituted by necrotic fluid and pathologic
organisms. Staphylococcus aureus is cultured in half of the cases.
The abscess is commonly surrounded by inflammatory changes and edema
of adjacent bone marrow. Transcortical fistulization may lead to
soft tissue spread. Until recently, early detection of bone
abscedation was only possible by bone scintigraphy. This technique
however is non-specific, as neoplastic changes or avascular necrosis
revealed similar changes. MRI is considered more specific and
furthermore allows better anatomical and topographical evaluation of
disease extent. Only advanced stages of bone abscess are seen on
conventional radiographs as areas of bone sclerosis with central
radiolucency and eventually periosteal reaction and bone
sequestration within the abscess
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Treatment:
Patients are initially treated with two days of intravenous
antibiotics and then were switched to oral antibiotics to complete a
six week course. |
Image 1
Image 2 MRI Knee (http://www.rbrs.org)
A cortical fistula (arrow) is clearly demonstrated. Axial
TSE T2-weighted MR-image
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Useful Link
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