oncocytosis

Oncocytosis is a histopathological term referring to the diffuse or multifocal proliferation of oncocytes, specialized epithelial cells characterized by abundant eosinophilic, granular cytoplasm due to a large number of mitochondria. Oncocytes appear in various organs, and oncocytosis is generally considered a change or reaction rather than a single disease. The cells typically have a large, central nucleus and prominent cytoplasmic granularity on light microscopy, with mitochondria visible on electron microscopy.

Common sites include the salivary glands, thyroid, kidney, and, less commonly, the pancreas or liver. In the thyroid, oncocytic (Hurthle) changes may occur in chronic inflammatory conditions or in neoplasms such as Hurthle cell adenomas or carcinomas. In the salivary glands, oncocytic metaplasia or oncocytosis can accompany chronic sialadenitis and is a feature of certain tumors such as Warthin tumor, which contains oncocytic epithelium with lymphoid stroma. In the kidney, diffuse or multifocal oncocytic change can be seen in renal oncocytosis, and renal oncocytoma is a benign tumor composed predominantly of oncocytes; this lesion can mimic other renal carcinomas on imaging.

Clinical significance varies by organ and context. Oncocytosis itself is often an incidental histologic finding, but it can be associated with benign or malignant neoplasms depending on the organ involved. Diagnosis relies on histopathological examination and, when necessary, immunohistochemical or ultrastructural studies to distinguish oncocytic changes from other eosinophilic or granular cell lesions. Treatment is organ-specific and guided by the underlying condition, ranging from observation for incidental changes to surgical management for associated tumors.