Pleomorphic Adenoma

Ariane Staub Neish, MD
Amir Zamani, MD

July 12, 1995

Presentation

A 43-year-old woman presented with an enlarging left cheek mass.

Imaging Findings

T1-weighted MRI

T2-weighted MRI

T1-weighted MR image through the parotid gland reveals a 3.5 x 3 cm intermediate-to-low signal mass within the left parotid gland (arrow). Both medial and lateral to this mass, the left parotid gland appears normal. The right parotid gland also appears normal; there are likely two right retromandibular veins, a common normal variant.

On the T2-weighted images this mass has heterogeneous but high signal intensity over all (arrows).

Diagnosis

pleomorphic adenoma

Discussion

This left parotid mass has no distinguishing radiologic features that allow it to be categorized as being either malignant or benign. However, the most common parotid gland tumor is a pleomorphic adenoma, and these represent 70-80% of all benign parotid tumors. Over 84% of pleomorphic adenomas occur in the parotid gland, 8% occur in the submandibular gland, and 6.4% occur in the minor salivary glands. A full 90% of pleomorphic adenomas arise lateral to the facial nerve (the facial nerve is not clearly visible on these images). Pleomorphic adenomas are typically seen in middle aged women and present as a painless slowly growing mass. These masses are typically solitary and well demarcated. They may appear heterogeneous secondary to hemorrhage, calcification, and necrosis. Sarcomatous transformation is seen in only 2-5% of cases and is usually associated with tumors that have been present for 10-15 years.

Other benign adenomas also occur in the parotid gland. Unlike pleomorphic adenomas, these tumors are characterized by the absence of condromyxoidstroma and the presence of uniform epithelium. These tumors include the Warthin's tumor, oncocytoma, basal cell adenoma, clear cell adenoma, and sebaceous lymphadenoma. Of these, the Warthin's tumor is the second most common benign lesion in the parotid gland. This tumor is also known as adenolymphoma. These represent 2-10% of all parotid gland tumors. Unlike the pleomorphic adenomas, they are more common in men and also present in the 40-70-year-old age group. They are more common in whites than blacks. Of all the parotid gland tumors, Warthin's tumors are most likely to be bilateral (although only 10% are). An unusual feature of Warthin's tumor is that it accumulates technetium-99m pertechnetate.

Of malignant parotid gland tumors, the mucoepidermoid tumor is the most common and represents 10% of all parotid gland tumors. Adenoid cystic carcinoma is the second most common malignant tumor of the parotid gland. Adenoid cystic carcinoma represents 2-6% of all parotid gland tumors, 15% of submandibular tumors, 30% of minor salivary gland tumors, and 50% of lacrimal gland tumors. A distinctive feature of adenoid cystic carcinoma is its tendency to grow and extend along nerves.

References

1. Som PR, Bergeron RT. Head and neck imaging. St Louis: Mosby Yearbook, 1991:320-340.

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