osteonecrosis ( RID5180 ) Osteonecrosis of the medial sesamoid. Medial > lateral. F > M. Precipitating factors: microtrauma, sporting activities, cavus deformity. Imaging: fragmentation into two or more pieces, patchy increased density, areas of demineralization, or heterogeneous sclerosis: time lag of up to 6 months. Nonspecific (T1 low, T2 high) then sclerotic change (T2 low); rare classic double line sign. Cyst formation in late stage: differentiated from OA by lack of kissing lesion or adjacent articular change. Variable enhancement.