Presentation
The patient presented with limping and chronic left leg pain for one month.
Patient Data
Evidence of three cystic lesions in the lower third of the tibia, including intramedullary metaphyseal and meta-diaphyseal regions. The lesions are lytic and display the following characteristics:
centrally hypointense on T1, with hyperintensity on T2 and STIR sequences
the inner ring of the lytic lesion hyperintense on T1, probably due to granulation tissue giving a penumbra sign, and is also hyperintense on T2 and STIR sequences
the outer ring shows a reactive rim of sclerosis, which is hypointense on all sequences
the lesions are surrounded by bone marrow oedema extending to the involved metaphysis, most of the epiphysis, and the proximal diaphysis
The largest lesion measures 1.6 x 1.4 x 1.8 cm (width x AP x CC) in the metaphysis, intramedullary, and is slightly eccentric to the medial aspect. It abuts the physis with minimal extension to the epiphysis but does not reach the articular surface. The lesion extends medially through the cortex, above the medial condyle anteriorly, forming a tunnel surrounded by sclerosis to the outer aspect in peri-tibial fat with a thin rim of fluid in the surrounding tissue.
The other two lesions are proximal, located in the metaphysis and meta-diaphysis, with the same characteristics, and are connected by small tunnels of extension.
Mild joint effusion of the ankle is also noted.
Case Discussion
The imaging finding of MRI and radiograph with clinical presentation in favour of subacute osteomyelitis.
Subacute osteomyelitis can be difficult to diagnose clinically, by conventional radiograph, and by MRI. However, specific signs on MRI, like the penumbra sign, help diagnose the condition and its complications, and aid in differentiating subacute osteomyelitis from other bone lesions. a Brodie abscess is a subtype of subacute osteomyelitis.
At a clinical follow-up visit, the patient reported a marked improvement in symptoms, particularly in pain and swelling of the ankle with antibiotic therapy, which was continued.
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