Incidental lipoma-like hibernoma arising from the adrenal gland: a well-differentiated liposarcoma mimicker.

Hibernomas are uncommon benign lipomatous tumors which show differentiation toward brown fat. To our knowledge, only one case of adrenal hibernoma has been previously reported. We describe a 55-year-old woman showing an incidental, 1.7 cm-hibernoma associated with a 2.6 cm-cortical adenoma producing primary hyperaldosteronism (Conn's syndrome), both in the left adrenal gland. The hibernoma was composed predominantly of univacuolated mature fat cells admixed with small vessels. Scattered areas composed of large multivacuolated pale cells with central or paracentral nuclei, mimicking lipoblasts, accounting for less than 30% of the tumor, were found. These cells lacked nuclear hyperchromasia or marked atypia, were S100-positive, and showed numerous mitochondria reactive with the anti-mitochondrial antibody. A diagnosis of lipoma-like hibernoma was made. Pathologists should be aware of this variant of hibernoma to avoid misdiagnosis and excessive treatment.