Vasculitis-induced membranous fat necrosis

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

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.

Lipomembranous changes associated with systemic lupus erythematosus

Lipomembranous changes are distinctive histopathological findings, which include the presence of cystic cavities lined by crenulated, hyaline membranes in adipose tissue. It is likely that ischaemia is fundamental to the development of these lesions, and that lipomembranes are formed from the products of degenerating fat cell membranes by some unknown mechanism. Such changes may be seen, although rarely, in many types of subcutaneous inflammatory processes. However, an association with systemic lupus erythematosus (SLE) is rare. We report a patient with SLE who had the histological features of lipomembranous changes associated with vasculopathy.

Extensive cardiac allograft vasculitis and concurrent fat necrosis 6 years after orthotopic heart transplantation

Coronary artery vasculitis has been described as a rare lesion in the spectrum of transplant vasculopathy or as an extension of severe acute cellular rejection. We describe a patient, 6 years after orthotopic cardiac transplantation, who developed rapid heart failure and died despite aggressive treatment, minimal cardiac rejection (ISHLT Grade 1R), and no known transplant vasculopathy. Autopsy showed a diffuse and essentially complete necrotizing vasculitis of the entire coronary vasculature involving small, medium and large vessels, with extensive fat necrosis within the pericardial space. Macrophages of the M2 phenotype were found lining the major coronary vascular lumens and infiltrating their walls. The presence of the M2 macrophage phenotype supports transplant vasculitis as part of the chronic transplant vasculopathy continuum.

Autoimmunity, spontaneous tumourigenesis, and IL-15 insufficiency in mice with a targeted disruption of the tumour suppressor gene Fus1

The Fus1 gene resides in the critical 3p21.3 human chromosomal region deleted in lung and breast cancers. Recently, the tumour suppressor properties of Fus1 were confirmed experimentally by intra-tumoural administration of Fus1 that suppressed experimental lung metastasis in mice. We generated Fus1-deficient mice that were viable, fertile, and demonstrated a complex immunological phenotype. Animals with a disrupted Fus1 gene developed signs of autoimmune disease, such as vasculitis, glomerulonephritis, anaemia, circulating autoantibodies, and showed an increased frequency of spontaneous vascular tumours. Preliminary analysis of immune cell populations revealed a consistent defect in NK cell maturation in Fus1 null mice that correlated with changes in the expression of IL-15. Injection of IL-15 into Fus1 knockout mice completely rescued the NK cell maturation defect. Based on these results, we propose the hypothesis that Fus1 deficiency affects NK cell maturation through the reduction of IL-15 production but does not directly alter their developmental capacity. Since acquired immunity was not affected in Fus1-deficient animals, we suggest a relationship between the Fus1 protein and the regulation of innate immunity via IL-15 production. The increased frequency of spontaneous cancers and the development of an autoimmune syndrome in Fus1 null mice imply that these mice could serve as a model for studying molecular mechanisms of anti-tumour immunity and autoimmunity.

Membranous Fat Necrosis of the Breast: Diagnosis by Minimally Invasive Technique

Clinical and mammographic features of membranous fat necrosis (MFN) may simulate breast malignancy and tissue sampling is essential for accurate diagnosis. The aim of our study was to evaluate the clinical and imaging findings in these patients. Retrospective review of the records of breast biopsies (n = 1200) during the 5-year period 1998 to 2002 revealed eight (0.67%) cases of histologically proven MFN. Seven of the eight patients had a history of breast trauma or surgery. Seven patients underwent mammography: normal in two, a mass with curvilinear calcifications in one, and heterogeneous calcifications in four. Four patients underwent surgical excision of a palpable mass, one patient had complete excision of calcifications with large core biopsy technique, and three patients had stereotactic vacuum-assisted mammotome biopsy (VAMB). MFN should be included in the differential diagnosis of lesions in a breast with previous trauma or surgery. A minimally invasive diagnostic procedure should be considered in order to avoid excessive excisional surgery.

Subcutaneous pseudomembranous fat necrosis: new observations

BACKGROUND

Pseudomembranous fat necrosis is a peculiar manifestation of necrosis of adipose tissue characterized by formation of pseudocystic cavities lined by crenulated membranes. The underlying mechanism for the formation of pseudomembranes is unknown and numerous hypotheses have been proposed. Despite divergent interpretations, most authors consider necrotic fat cells to be the anatomic substrate for the formation of pseudomembranes.

METHODS

A total of 341 panniculitides were reviewed for the presence of pseudomembranous fat necrosis. The specific diagnoses were established after correlation of all available clinical and laboratory data with the histopathology. Special attention was given to the time in the evolution of the disease when the biopsy was taken. Additional immunohistochemical studies were performed in 12 cases.

RESULTS

Thirty of 341 cases of different types of panniculitides were found to show pseudomembranous fat necrosis, namely: 10 of 15 cases of sclerosing panniculitis (lipodermatosclerosis), 6 of 95 cases of erythema nodosum, 7 of 34 cases of traumatic panniculitis, 1 of 7 cases of lupus panniculitis, 1 of 20 cases of erythema induratum Bazin (nodular vasculitis), 1 of 9 cases of necrobiosis lipoidica, 1 of 4 cases of sclerotic lipogranuloma, 1 of 9 cases of infectious panniculitis (erysipelas), 1 of 2 cases of pancreatic panniculitis, and 1 of 4 cases of subcutaneous sarcoidosis. Pseudomembranous fat necrosis labelled strongly for the histiocytic markers CD68 and lysozyme.

CONCLUSIONS

Our series provides data suggesting that pseudomembranous fat necrosis represents a dynamic process that varies according to the evolution of the lesion at the time of the biopsy. In biopsies taken from early foci of panniculitides pseudomembranes show vescicular or picnotic nuclei. Later, pseudomembranes retain their crenulated appearance but lack nuclear elements. Furthermore, we present histopathologic, histochemical, and immunohistochemical evidence that pseudomembranous fat necrosis results from the interaction of residual products of disintegrated fat cells and macrophages. Histiocytic markers such as CD68 and lysozyme may be used as reliable tools in order to detect pseudomembranes in panniculitides.