Monomorphic adenoma

The term “monomorphic adenoma” refers to a group of rare salivary tumors that includes the basal cell, canalicular, sebaceous, glycogen-rich and clear cell adenoma. Of these, the basal cell adenoma is the most common. It constitutes 1.8% of benign epithelial salivary gland tumors and typically occurs in the 6th decade of life. There are conflicting reports of gender predilection for this tumor but it does seem to occur more frequently among Caucasians than African Americans. The majority of basal cell adenomas occur in the parotid gland where they present as a slowly enlarging firm mass. They are well-encapsulated, smooth tumors on gross inspection and are divided into four subtypes based on their microscopic appearance—solid, trabecular, tubular and membranous.

Epidemiology
The presentation of canalicular adenoma peaks in the 7th decade of life and, like the basal cell adenoma, is more common in whites than blacks. There is a female predominance with a female-to-male ratio of occurrence of 1.8-1.

Signs
This tumor most commonly involves the minor salivary glands of the upper lip (74%) or buccal mucosal (12%).

Symptoms
Clinically it presents as a nonpainful submucosal nodule. On gross pathologic examination, canalicular adenomas may or may not possess a capsule and it is not unusual for there to be multifocal growth. Microscopically there are cords of single-layer columnar or cuboidal cells forming duct-like structures in a background of fibrous stroma (1,2,3,4).

Treatment
The majority of monomorphic adenomas display nonaggressive behavior and are adequately treated with surgical excision.