oncocytic

Oncocytic describes a cell type characterized by abundant granular, eosinophilic cytoplasm, reflecting a high mitochondrial content. Oncocytes can arise in various tissues as a reactive or metaplastic change, or as the predominant cell type in neoplasms. The term is used for both benign and malignant lesions, and the diagnostic context—clinical presentation, imaging, and histology—is important for interpretation.

Histologically, oncocytes are typically polygonal with a large, distinctly stained cytoplasm. The cytoplasm appears finely granular and strongly eosinophilic on light microscopy. Nuclei are usually round to oval and may have prominent nucleoli. Electron microscopy reveals numerous mitochondria, which account for the cytoplasmic appearance.

Oncocytic change occurs in several organs. In the thyroid, Hurthle cells (oncocytes) are seen in Hashimoto’s thyroiditis and in Hurthle cell neoplasms. In the salivary glands, oncocytic metaplasia can occur, and Warthin tumor is a benign neoplasm comprising oncocytic epithelium with lymphoid stroma. In the kidney, renal oncocytoma is a benign neoplasm composed of oncocytic cells; malignant counterparts described as oncocytic carcinoma are rare. Oncocytic features can also appear in tumors of the liver and other tissues, though less commonly.

Diagnosis relies on histopathology and, when helpful, immunohistochemistry and ultrastructural confirmation of mitochondrial abundance. Management is guided by the organ involved and whether the lesion is benign or malignant, and may range from observation to surgical excision.