Brodie abscess is an intraosseous abscess related to a focus of subacute or chronic pyogenic osteomyelitis. Unfortunately, there is no reliable way to radiographically exclude a focus of osteomyelitis. It has a protean radiographic appearance and can occur at any location and in a patient of any age. It might or might not be expansile, have a sclerotic or nonsclerotic border, or have associated periostitis.
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Epidemiology
Typically a Brodie abscess will present in children with unfused epiphyseal plates, more frequently in boys.
Pathology
Aetiology
S. aureus (most common); cultures often negative 5
Location
It has a predilection for ends (metaphysis) of tubular bones:
proximal/distal tibial metaphysis (most common)
femur
carpal and tarsal bones
It may rarely traverse the open growth plate and extend to the epiphysis (in children and infants).
Markers
inflammatory markers (e.g. CRP, ESR) are often normal 5
Radiographic features
Plain radiograph
lytic lesion often in an oval configuration that is orientated along the long axis of the bone
surrounded by a thick dense rim of reactive sclerosis that fades imperceptibly into surrounding bone
lucent tortuous channel extending toward growth plate prior to physeal closure (pathognomonic)
periosteal new bone formation +/- adjacent soft tissue swelling
may persist for many months
CT
central intramedullary hypodense cystic lesion with thick rim ossification
extensive thick well-circumscribed periosteal reaction and bone sclerosis around the lesion could be seen
MRI
The “penumbra sign” on magnetic resonance (MR) imaging is useful for discriminating subacute osteomyelitis from other bone lesions. The penumbra sign is a rim lining of an abscess cavity with higher signal intensity than that of the main abscess on T1-weighted images which strongly and rapidly enhances after contrast.
Differential diagnosis
-
osteoid osteoma 4,5 :
often cortical in location
nocturnal pain relieved by aspirin
-
sarcoma 5 :
more aggressive
associated soft tissue mass
History and etymology
The lesion is named after Sir Benjamin Collins Brodie (1783-1862), who initially described a chronic inflammatory process affecting the tibia without acute precipitating factors in the 1830s.