On the ultrastructure of hibernoma

An electron-microscopic study of hibernoma and a review of the histogenesis, development, and post-natal structural composition of brown and white adipose tissue are presented. The ultrastructural features of hibernoma include multivacuolated and univacuolated cells containing variable numbers of lipid vacuoles, abundant moderately pleomorphic mitochondria with transverse cristae, lysosomes, lipofuscin granules, pinocytotic vesicles, well-formed basal lamina, and prominent subplasmalemmal condensations. The latter have not been previously reported in hibernoma, brown adipose tissue or white adipose tissue, although gap junctions have been observed in brown adipose tissue of newborn mice. It is concluded that the ultrastructural observations support the concept proposed decades ago that hibernoma represents the neoplastic counterpart of brown adipose tissue.