Patient Data
There is a well-defined lucency with surrounding sclerosis observed centrally within the posterior aspect of the tibia, in the proximal third of the diaphysis. A questionable bony sequestration is observed within this lucency. There is prolific, circumferential, solid periosteal new bone formation around the proximal tibial diaphysis, representing an involucrum.
Again noted is the circumferential solid periosteal new bone formation around the proximal tibial diaphysis. There is a focal intramedullary region of low T1, high STIR signal in the proximal third of the tibial diaphysis indicating a focal fluid collection. At this site, there is a collection of heterogenous T1/STIR signal posteriorly which most likely represents evolving late sub-acute and chronic blood and/or proteinaceous cellular debris.
A cloaca extends from this lesion through the involucrum to a draining sinus tract anteromedially.
No definitive sequestrum is identified.
The involucrum, cloaca and sinus are outlined.
Case Discussion
Brodie abscess is most commonly found in the tibia, as is the case here. This focus of chronic osteomyelitis demonstrates the classic features of involucrum formation with a draining cloaca and sinus tract to the skin.
Case images courtesy of Dr. Deborah Forrester