Diffuse Serous Atrophy of Bone Marrow in the Ankle and Hindfoot with Focal Acute Lateral Malleolar Osteomyelitis: A Magnetic Resonance Imaging–Based Case Report

Serous atrophy of bone marrow (SABM) is a rare marrow disorder associated with severe chronic illness and malnutrition. It results in characteristic magnetic resonance imaging (MRI) signal due to atrophy of fat cells and loss of hematopoietic cells with deposition of gelatinous material. This may be misinterpreted as a technical error from the MRI scanner or mimic infiltrative or infectious processes. We report a case of a 71-year-old severely malnourished and immunosuppressed man with a full-thickness ulcer over the right lateral malleolus who underwent an MRI of the right ankle without and with intravenous gadolinium contrast for evaluation of suspected osteomyelitis. Pre-contrast MRI images demonstrated diffuse abnormal marrow signal throughout the ankle and hindfoot consistent with SABM, given his profound cachexia and malnutrition. Post-contrast images demonstrated a small focus of enhancement at the lateral malleolus beneath the patient’s ulcer, suggesting an additional diagnosis of acute osteomyelitis without cortical destruction. The marrow signal in SABM and osteomyelitis can be indistinguishable on non-contrast MRI sequences; post-contrast imaging and correlation with clinical examination are essential, as SABM does not demonstrate contrast enhancement and acute osteomyelitis demonstrates enhancement. Given the patient’s frailty and poor healing capacity, conservative management was pursued. Recognizing SABM and osteomyelitis in the ankle and foot requires integration of the clinical context with MRI findings, in which invasive procedures and misdiagnosis can be avoided.