Histologic sections of a parotid gland tumor that is found to be infiltrating along the facial nerve are most likely to reveal

The salivary glands give rise to a wide variety of tumors, the majority of which are of epithelial origin and benign. Most tumors occur in adults and have a slight female predominance. Approximately 75 to 85% occur in the parotids, 10 to 20% in the submandibular glands, and the remainder in the minor glands. In the parotid the vast majority are benign, whereas in the minor glands 35 to 50% are malignant. Clinically, most tumors of the salivary glands present as palpable masses, regardless of histologic type. The most common neoplasm of the parotid gland is the pleomorphic adenoma (mixed tumor), which histologically reveals epithelial structures embedded within a mesenchyme-like stroma consisting of mucoid, myxoid, or chondroid tissue. A malignant tumor may develop from a pleomorphic adenoma, in which case it is called a carcinoma ex pleomorphic adenoma. The second most common tumor is Wahin's tumor (papillary cystadenoma lymphomatosum), which histologically reveals cleftlike spaces lined by oncocytic epithelial cells overlying a stroma with a dense lymphocytic infiltrate. The epithelial cells are oncocytic because their pink cytoplasm is packed with mitochondria Three malignant tumors of the salivary glands are mucoepidermoid carcinoma, adenoid cystic carcinoma, and acinic cell carcinoma. Mucoepidermoid carcinomas consist of a mixture of squamous epithelial cells and mucus-secreting cells. The mucus-secreting cells of a mucoepidermoid carcinoma can demonstrate intracellular mucin with a special mucicarmine stain. Adenoid cystic carcinomas form tubular or cribriform patterns histologically and have a tendency to invade along perineural spaces, especially the facial nerve. Acinic cell carcinomas contain glands with cleared or vacuolated epithelial cells. Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition