Background and aim: The role of brown adipose tissue physiology and pathology in humans is debated. A greater knowledge of its developmental aspects could play a pivotal role in devising treatments for obesity and diabetes.
Methods and results: Tissue from a rare case of hibernoma, removed from a 17-year-old boy, was examined by light and electron microscopy, morphometry and immunohistochemistry. The tumour was well vascularised and innervated and contained mature adipocytes with the characteristics of both brown and white adipocytes. Numerous, poorly differentiated cells resembling brown adipocyte precursors were seen in a pericytic position in close association with the capillary wall. On immunohistochemistry mature brown adipocytes were seen to express the marker protein UCP1. On morphometry the intensity of uncoupling protein 1 (UCP1) immunostaining varied in relation to the morphological features of adipocytes: the "whiter" their appearance, the weaker their UCP1 immunoreactivity.
Conclusions: Our data suggest that in humans, as in rodents, brown adipocyte precursors arise in close association with vessel walls and that intermediate forms between white and brown adipocytes can also be documented in human adults.
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