Brodie abscess

Lytic lesion with internal septations in the medullary cavity of the distal tibial diaphysis with slight medial eccentric location. Size is 18 x 19 x 36 mm (AP x transverse x craniocaudal). It is well-circumscribed, and is mildly expansile, associated with marked smooth cortical thickening with overlying smooth periosteal reaction over the medial tibial cortex.  

The favored diagnosis is multifocal Brodie abscess secondary to chronic osteomyelitis. Less likely differentials include aneurysmal bone cyst or eosinophilic granuloma.

Further evaluation via contrast-enhanced MRI is recommended, as well as orthopedic opinion.

Findings:

• as demonstrated on the prior radiograph there is a multiloculated cystic lesion involving the distal tibial diaphysis which demonstrates peripheral enhancement and is associated with smooth periosteal reaction and endosteal scalloping

• the cortex surrounding this lesion appears expanded and thickened relative to the normal appearing cortex more cranial to the lesion

• additionally there is marrow edema extending from the midshaft of the tibia to the tibial metaphysis  

• the overlying soft tissues demonstrate mild subcutaneous edema and fluid tracking along the fascial plane of the anterior compartment which extends along the length of the mid to distal shaft of the tibia

• the flexor and extensor tendons appear to be grossly intact and uninvolved  

Impression:

Findings most consistent with a Brodie abscess. 

Radiographic and MRI follow-up may be considered following appropriate clinical therapy in or to exclude more sinister pathology such as sarcoma. 

Other differential considerations less likely include osteoid osteoma, aneurysmal bone cyst, adamantinoma and chondromyxoid fibroma.