Salivary Gland Neoplasms: Pleomorphic Adenoma

• The most common location of occurrence is the parotid (85%) followed by the minor salivary glands (10%), in which the palate, upper lip and buccal mucosa are most commonly affected.
  
• These tumors are most often diagnosed in the 4^th to 6^th decades of life and are uncommon in children although they are second only to hemangiomas in this population.
  
• They are seen more frequently in women with a female-to-male ratio of 3-4:1.

The typical clinical presentation of a pleomorphic adenoma is a slow-growing, painless and firm mass. In the parotid, 90% occur in the superficial lobe and most commonly are seen in the tail of the gland. Minor salivary gland pleomorphic adenomas most commonly occur on the lateral palate and are covered with normal appearing mucosa. In all locations, they are typically nontender to palpation and tend to be mobile when small but may become fixed with advanced growth.

These tumors are nearly always solitary although rare cases of synchronous or metachronous salivary neoplasms have been reported- either involving a second mixed tumor or a distinct lesion, most commonly Warthin’s tumor.

Facial nerve paralysis in association with pleomorphic adenomas almost never occurs, even with extremely large tumors.

The gross pathologic appearance of a pleomorphic adenoma is a smooth or lobulated, well-encapsulated tumor that is clearly demarcated from the surrounding normal salivary gland. They are typically solid tumors and may have areas of gelationous myxoid stroma. Cystic degeneration or tumor infarction and necrosis are rarely seen except in large, long-standing lesions. Microscopically, these tumors are composed of varying proportions of gland-like epithelium and mesenchymal stroma. The epithelial cells may display several different patterns of growth—small nests, solid sheets, ductal structures or anastamosing trabeculae. The stroma is just as variable and may be myxoid, chondroid, fibroid or osteoid. Also on microscopic examination, the incomplete encapsulation and transcapsular growth of tumor pseudopods characteristic of pleomorphic adenoma are demonstrated.

Treatment of pleomorphic adenomas is complete surgical excision with a surrounding margin of normal tissue, i.e., superficial parotidectomy with facial nerve preservation, submandibular gland excision or wide local excision for a minor salivary gland. Simple enucleation of these tumors is what is believed to have led to high local recurrence rates in the past and should be avoided. Rupture of the capsule and tumor spillage in the wound is also believed to increase the risk of recurrence, so meticulous dissection is paramount.

Category: Pathology Notes