Hibernoma (brown lipoma): causes, symptoms, diagnosis, treatment

Hibernoma (syn.: brown lipoma, granular cell tumor of adipose tissue, lipoblast lipoma) develops from lipochrome-rich brown adipose tissue, more often in middle-aged and elderly women, in places where brown fat is localized in the form of rudimentary remnants (along the spine, on the neck, in the armpits, in the groin, lumbar and gluteal regions). Cases of this tumor in children have been described. Clinically, it is a subcutaneous solitary tumor, protruding above the skin surface, with a diameter of 3 to 12 cm, of plastic consistency.

Pathomorphology of hibernoma (brown lipoma). The tumor is encapsulated and divided by connective tissue layers into separate lobules, which are highly vascularized. Most of the cells that make up the tumor are multivacuolar with granular eosinophilic cytoplasm between the vacuoles and small, centrally located nuclei. Their diameter ranges from 20 to 55 μm. Among them, there are intermediate forms - a transition from multivacuolar cells to large, monovacuolar ones. They have a nucleus located on the periphery of the cell, up to 120 μm in size. In some lobules, especially along the periphery of the tumor, there may be only monovacuolar cells. Vacuoles in multivacuolar and monovacuolar cells are stained orange with Sudan III. In addition, there are type 3 cells that do not contain fat and have finely granular eosinophilic cytoplasm. They are smaller in size than multivacuolar cells, with a diameter of about 12 µm.

Histogenesis of hibernoma (brown lipoma). The tumor develops from cells located in the areas of brown fat localization. Although all fat cells go through the stages of multivacuolar and monovacuolar cells in their development, they differ from each other under electron microscopy. Brown fat cells, like hibernoma cells, contain large mitochondria with a complex internal structure and a large number of transversely located tubular cristae, while normal fat cells contain small mitochondria with a poorly expressed internal structure. Some authors believe that the granularity of the cytoplasm of brown fat cells is associated with the presence of large mitochondria. According to O.R. Hornstein and F. Wcidner (1979), the reason for the differentiation of the brown fat cell clone is an enzymatic defect. In their opinion, the brown color is due to phospholipid oxidation products.

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