Bone marrow lesions related to bone marrow edema syndromes and osteonecrosis.

Bone marrow lesions (BML) are abnormalities in the bone marrow identified on magnetic resonance imaging (MRI) and can generally be classified as traumatic or atraumatic. This review focuses on atraumatic bone marrow edema syndromes (BMES) and their imaging evaluation. The MRI remains the modality of choice for assessing BMES, particularly using fluid-sensitive sequences although other sequences such as Dixon and T1-weighted imaging can be of further assistance. Emerging evidence supports dual-energy CT (DECT) as a reliable alternative, with high sensitivity and specificity for detecting bone marrow edema. The term BMES is a collective term for conditions, such as transient osteoporosis (TO) and regional migratory osteoporosis (RMO), predominantly affect weight-bearing bones in middle-aged individuals and pregnant or postpartum females. Subchondral insufficiency fractures of the knee (SIFK) are a key subset of BMES. These fractures most commonly involve the medial femoral condyle (MFC) and are associated with risk factors, such as meniscal root tears and extrusion of the meniscal body. The MRI findings typically include bone marrow edema-like signals and subchondral fracture lines, with additional features, such as secondary osteonecrosis in advanced cases. Prognostic indicators are crucial for stratifying patients and guiding management. Low-grade or reversible lesions often resolve with conservative treatment, whereas high-grade or irreversible lesions may require surgical intervention.Avascular necrosis, another atraumatic BML entity, differs from BMES by its association with systemic factors, such as steroid use or alcohol abuse. Accurate imaging, particularly in the early stages, is vital to distinguish between reversible and irreversible lesions, facilitating timely and appropriate management.