Factors in adipogenesis

Perirenal lipoma versus renal cell carcinoma

Pure renal and perirenal lipomas are rare. They arise from renal cortex, capsule, or perirenal tissue, and may be difficult to distinguish from renal adenocarcinomas. We report on a patient who presented with a renal mass that had the radiologic findings suggestive of a renal cell carcinoma, but proved to be a simple lipoma.

Hibernoma: distinctive light and electron microscopic features and relationship to brown adipose tissue

Four hibernomas and samples of developing human brown and white adipose tissue were observed. Distinctive features of hibernomas were 1) lobules of closely apposed large polygonal cells and capillaries; 2) three principal cell types (granular eosinophilic, multivacuolated, and univacuolated) varying in prominence from case to case; 3) investment of each tumor cell by basal lamina; 4) an inverse relationship between lipid droplet size and the number of mitochondria per unit of cytoplasm; 5) pleomorphic mitochondria with dense matrixes or large, round mitochondria with transverse lamellar cristae; 6) undulating plasmalemmal invaginations; 7) micropinocytotic vesicles; 8) periodic short plasmalemmal densities; and 9) a conspicuous lack of cytoplasmic membrane systems. The frequent association of micropinocytotic vesicles and undulating plasmalemmal invaginations in proximity to capillaries strongly suggests that the invaginations represent a localized cell membrane adaptation for efficient endocytosis. In human fetal brown adipose tissue, which is first recognizable in fetuses of 21 weeks' gestational age, the most characteristic cell was the polygonal multivacuolated cell. Univacuolated cells were present in brown adipose tissue of older fetuses, and in infants and adults entire lobules containing univacuolated cells coexisted with lobules of multivacuolated cells and granular eosinophilic cells. The ultrastructure of human brown adipose tissue resembled that of hibernomas and was similar to previously described features of this tissue in animals. Developing white adipose tissue differed from brown adipose tissue by its loose plexiform arrangement of capillaries and spindle-shaped cells in less circumscribed lobules and by the absence of polygonal multivacuolated cells. The authors did not identify centripetal lobular maturation in white adipose tissue, but peripheral growth "caps" were a common finding in maturing brown adipose tissue. They consider brown adipose tissue to be a special form of adipose tissue, the variable cytologic composition of which is reflected in the histologic spectrum of hibernomas.

Lipoma of the superior medullary velum with Schwann cells --report of a case and review of the literature

A large intracranial lipoma, located on the superior medullary velum is reported. Histologically, the tumor consisted of adult adipose tissue. The right trochlear nerve was involved within the tumor, and the scattered nests of Schwann cells and some larger vessels were also present. Lipoma of the dorsal region of the mid-brain is rare and has not been reported from Japan. Schwann cell proliferation in the lipoma is another unusual feature in this case. The histogenesis of this tumor is discussed, and the literature on lipomas of the dorsal region of the mid-brain is reviewed.