Mobile encapsulated fat necrosis (MEFN) is a rare medical condition featuring the formation of a fibrotic capsule around a small, necrotic mass of fatty tissue.
It is asymptomatic and benign but may be mistaken for other neoplasms due to its typical presentation as a firm nodule beneath the skin that can be moved around within the tissue.
[1][2] MEFN lesions tend to go unnoticed for many years, due to their asymptomatic nature and relatively small size, usually being somewhat flattened and no more than 1–2 cm in diameter.
[1] Once noticed, they are often surgically removed, even in cases where this exceedingly rare condition is successfully identified by a physician familiar with it, because this procedure is minimally invasive and ensures that the MEFN lesion is not a more dangerous tumor.
[2] Nodules of mobile encapsulated fat necrosis are histologically characterized by regions of necrotic adipose tissue, with diffuse infiltration by foamy histiocytes, that are surrounded by fibrous septa.