Glycogen-rich adenoma of the parotid gland. An uncommon benign clear-cell tumor resembling certain clear-cell carcinomas of salivary origin

Abstract

An instance of glycogen-rich adenoma of the parotid gland is presented. This lesion contains conspicuous numbers of clear cells, causing confusion with certain clear-cell salivary carcinomas. In the glycogen-rich adenoma, the clear cells form a peripheral mantle within tubular complexes and contain abundant glycogen, whereas similar appearing clear cells within acinic cell and mucoepidermoid carcinomas occur in nests and trabeculae, and lack glycogen. Although the precise nosologic position of this lesion is speculative, the admixture of epithelial and clear-celled myoepithelial elements may justify placing this lesion in the broad category of mixed tumors, particularly those variants lacking a prominent stromal component elaborated by such myoepithelium. The presence of areas of cytologically atypical, locally invasive growth in the recurrent tumor are interpreted as evidence of malignant degeneration, and may have been related to prior radiotherapy.