Haemosiderotic fibrohistiocytic lipomatous lesion/tumour of the foot: MRI and histopathology

A 38-year-old woman presented in 2005 with a fatty swelling over the dorsum of her left foot and was subsequently referred to our institution following initial biopsy for further management. MRI was performed before and after surgery. This demonstrated an ill-defined lesion confined to the subcutaneous tissues on the dorsum of the foot with heterogeneous intermediate and high T1 and T2 signal suggesting a complex mixture of fat and fibrous elements. The lesion recurred following initial surgery in the lateral aspect of the hind foot and along the lateral aspect of the ankle. It demonstrated extremely high signal on T2 fat-saturated sequences along the fibrous elements of the lesion and concentrated in a layer just deep to the dermis, which was mirrored on post-contrast images. A histopathological diagnosis of haemosiderotic fibrohistiocytic lipomatous lesion/tumour (HFLL/T) was made. This is a recently described and rare entity that occurs typically in the subcutaneous tissues of the foot or ankle of middle-aged women. To our knowledge this is the first description of the imaging findings in this lesion.