MRI diagnosis and follow-up of subcutaneous fat necrosis.

The purpose of this report is to present the MRI features of subcutaneous fat necrosis (SFN) and the natural history of this process. We have seen 12 patients with SFN, one case of which was confirmed histopathologically. In six patients, a follow-up MRI study was performed. MRI findings were very similar in all of the cases: small, linear, and spiculated lesions with one or two components: a globular area yielding high signal intensity on T1-weighted images, intermediate to high signal intensity on fast SE T2-weighted images and focal signal void on short-inversion -time inversion recovery (STIR) sequence, corresponding to an area of fat necrosis; and a laminar starred component, with low signal intensity on T1 and fast SE T2-weighted images and high signal intensity on the STIR sequence, corresponding to reactive fibrous tissue. The follow-up MRI study of six patients showed either disappearance (n = 2) or decrease in size (n = 3) of the globular component; in one patient, no change was observed. A less prominent decrease of the laminar component also was seen in five patients. One patient did not present any change in this laminar component. The most characteristic MRI findings of this lesion are the high signal intensity areas on T1-weighted images, their small size (< 3 cm), their linear spiculated shape with both laminar and globular components, and no contrast enhancement after injection of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) injection. We believe that the location, size, morphology, and MRI signal intensity of SFN may allow its differentiation from other types of soft tissue lesions.