Membranous fat necrosis in appendices epiploicae. A clinicopathological study.

Membranous fat necrosis (MFN) is a degenerative process involving mature systemic adipose tissue. It is characterised by the presence of membranocystic foci surrounded by a lipophagic fibro-inflammatory reaction typical of fat necrosis. Membranocystic foci are cysts lined by an eosinophilic membrane with pseudopapillary infoldings having the histochemical staining profile of ceroid. Although MFN is described in an increasing number of adipose tissue sites, it has not been described as a distinct entity in appendices epiploicae (AE). Macroscopically, MFN in AE mimics nodal tuberculosis or metastatic tumour with necrosis and cystic change. Ischaemia, which can be secondary to physiological or pathologic processes, is crucial in the pathogenesis of MFN in AE. Heightened awareness of MFN as a distinct entity in AE is essential for accurate diagnosis and establishment of the pathogenesis of this enigmatic pathological process.