[Basal cell adenoma of the parotid. An ultrastructural study].

The monomorphic basal cell adenoma of parotid gland is a rare tumor of salivary glands. Its diagnosis is difficult with adenoid cystic carcinoma. In the case reported here, a peculiar type named membranous adenoma, the thickness of basement membranes, their penetration inside the epithelial lobules, form true cylinders as in adenoid cystic carcinoma. The histoenzymology and the electron microscopy provide important diagnostic arguments: activity of alkaline phosphatases lower than in cystic adenoid carcinoma; cells of adenoma more differentiated (epidermoid or secretory cells) than those of cystic adenoid carcinoma. The prognosis of the tumor is good, though recurrences may occur.