RESIDENT CASE STUDIES

Week 10 June 23 - June 27, 2003: Case 3   

Table of Contents | List of Diagnoses | Case 1 | Case 2 | Case 3

56 year old with persistent painful left parotid mass

Discussion 
Monomorphic adenoma (MA) is a benign epithelial salivary gland tumor which lacks the myxoid, chondroid or other mesenchymal components associated with benign mixed tumor (pleomorphic adenoma). MA most frequently occurs in the parotid gland (70%). The rest of the tumors are seen in the minor glands, especially in the upper lip, the buccal mucosa, and the palate. Other rare sites are in the lower lip, the floor of the mouth and the submandibular salivary gland.¹

Histologically, there are three major growth patterns commonly seen in MA: trabecular, tubular and canalicular. The trabecular pattern consists of nests or cords of cells three or four layers thick and well demarcated by a basal membrane. Stromal component is scant. The tubular pattern resembles the appearance of salivary ducts and forms distinct lumens. The luminal surface is composed of a deeply stained, ductal type of epithelium resembling the intercalated ducts. The outer lining cells are often clear and translucent. The secretion within the lumen is positive for PAS stain. Focal oncocytic or sebaceous cell changes may be present within this type of tumor. The canalicular type most frequently evolves in the glands of the upper lip and is composed of tubules or ducts lined by cuboidal cells, frequently devoid of an outer layer of myoepithelial cells. The unique location of the canalicular type makes some regard it as a distinct entity, distinguishing it from other adenomas. The canalicular adenomas stain positively for cytokeratin, S-100 and focal GFAP.¹ Edwards et al.² reported that c-kit expression is found in monomorphic adenoma as well as adenoid cystic carcinoma and polymorphous low grade adenocarcinoma, therefore it may not be useful in distinguishing them. 

References:

¹Stephen S Sternberg et al. (Eds): Diagnostic surgical pathology, Volume 1, 3rd edition. Lippincott William& Wilkins.

²Edwards PC, Bhuiya T, Kelsch RD. C-kit expression in the salivary gland neoplasms adenoid cystic carcinoma,polymorphous low-grade adenocarcinoma, and monomorphic adenoma. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2003May;95(5):586-93.