Lipomembranous fat necrosis: A distinctive and unique morphology (Review)

Abstract

Lipomembranous fat necrosis (LFN) is an uncommon but distinct form of fat necrosis, which is characterized by eosinophilic, crenulated and/or serpiginous membranes. LFN exhibits macrocystic, microcystic and/or crushed features. LFN is routinely detectable on hematoxylin and eosin (H&E)-stained sections, and is present both in the acute phase and in the later or fibrous stage of necrotic fatty lesions. Smaller crushed LFN embedded within fibrous tissues may be difficult to recognize on H&E-stained sections, but can be highlighted by some staining techniques, including Masson trichrome, periodic acid-Schiff, orcein, long Ziehl-Neelsen stain, silver impregnation, phosphotungstic acid-hematoxylin and luxol fast blue staining. LFN was initially considered a specific feature of Nasu-Hakola disease, but has since been identified in various subcutaneous or intraabdominal lesions related to ischemic conditions or venous insufficiency. In addition, LFN is detectable in intra-articular loose bodies and aortic valves with or without dysfunction, suggesting that LFN is also associated with ischemia-like hypoxic conditions or malnutrition. LFN is considered to be a histological hallmark of hidden ischemic or hypoxic/malnourished conditions in various diseases; however, the exact mechanisms of LFN remain poorly understood. The present review described the clinicopathological features of this interesting, but poorly characterized, condition.

Keywords: LFN; Nasu-Hakola disease; aortic valve; intraarticular loose body; ischemia; lipomembranous changes; membranocystic changes; membranous fat necrosis; soft tissue tumor.

Figure 1

LFN. (A-C) Microcystic LFNs are characterized by (A) eosinophilic, crenulated membranes on H&E staining, stained (B) red by Masson trichrome stain, and (C) enhanced by the periodic acid-Schiff reaction (A, bar=50 µm; B and C, bar=10 µm). (D and E) Crushed LFNs (D, arrows) within fibrous tissues adjacent to microcystic LFN (D, asterisk) on H&E-stained sections are challenging to detect, but Masson trichrome stain highlights LFNs in red (E, arrows and an asterisk) on a bluish fibrous background (D and E, bar=50 µm). Insets in (D and E) represent high-power views of crushed LFN (bar=10 µm). LFN, lipomembranous fat necrosis; H&E, hematoxylin and eosin.

Figure 2

Hematoxylin and eosin-stained macrocystic and microcystic LFN. (A) Macrocystic LFNs (asterisks) and microcystic LFNs are found in subcutaneous tissues (bar=200 µm). (B) High-power views of aggregated small LFNs localized near macrocystic LFNs (bar=50 µm). (C) High-power views of the macrocystic wall of LFN showing septa-like hyaline, crenulated membranes transformed from cohesive LFNs (bar=50 µm). LFN, lipomembranous fat necrosis.

Figure 3

Ultrastructural features of LFN. LFN composed of serpiginous membranes and focally adherent to a mononuclear phagocyte (bar=10 µm). Inset depicting a high-power view of the microtubular structures of membranes (bar=1 µm). LFN, lipomembranous fat necrosis.

Figure 4

LFN in aortic valves embedded within aortic valves. (A and C) Low-power views (bar=200 µm) of (A) hematoxylin and eosin and (C) Masson trichrome staining demonstrating calcified and fibrously thickened aortic valves. (B) High-power views of the area indicated by the arrow in (A), showing an eosinophilic, crenulated LFN (bar=10 µm). (D) High-power views of the area indicated by the arrow in (C), clearly demonstrating reddish LFN by Masson trichrome staining (bar=10 µm). LFN, lipomembranous fat necrosis.

Figure 5

Hematoxylin and eosin-stained LFN associated with a soft tissue tumor. Scattered LFNs (arrows) in subcutaneous fatty tissues adjacent to invading high-grade sarcoma are shown in the lower field. The artery and vein in the left-sided central field are open and well-preserved. Small lipogranulomas are also multifocally present in these fatty tissues (not shown; bar=200 µm). LFN, lipomembranous fat necrosis.