Ultrasound of Pleomorphic Adenoma of the Parotid Gland

In this radiology lecture, we review the ultrasound appearance of pleomorphic adenoma of the parotid gland!

Key teaching points include:

Pleomorphic adenoma AKA benign mixed tumor.
Most common salivary gland tumor, most common benign salivary gland tumor, and most common in the parotid gland.
Most common in patients aged 40-50, slightly more common in females.
For salivary gland masses in adults, the larger the gland, the more likely the tumor is benign: Parotid gland: 80%, submandibular gland: 50%, sublingual glands: 20%.
Parotid Gland 80% Rule: 80% of all salivary tumors are in the parotid, 80% of benign parotid gland tumors are pleomorphic adenomas, 80% of pleomorphic adenomas occur in the parotid gland, 80% of pleomorphic adenomas occur in the superficial lobe, and 80% of untreated pleomorphic adenomas stay benign, but 20% can undergo malignant degeneration.
On ultrasound, appears as a well-defined mass with lobulated borders, hypoechoic with posterior acoustic enhancement, and with homogeneity of internal echoes common.
When large, may have cystic degeneration and internal heterogeneity mimicking malignancy.
Vascularity is variable.
Describe lesion location, image-guided biopsy planning, evaluate for cervical lymphadenopathy.
Superficial and deep parotid lobes divided by facial nerve traveling through gland. Nerve not readily seen, but passes just superficial to adjacent retromandibular vein, which can be seen = Use as a landmark. Inferior to the retromandibular vein, may see branches of the external carotid artery.
Treatment is typically excision due to risk of malignant degeneration carcinoma ex pleomorphic adenoma if not completely excised.
DDx includes Warthin tumor: Second most common benign parotid tumor, bilateral in 20%, often exhibit cystic components, most common in elderly.
Malignant parotid tumors are also in the DDx and may appear with ill-defined margins, irregular shape, heterogeneous internal architecture, extraglandular extension, and adjacent lymphadenopathy.
Mucoepidermoid carcinoma: Most common salivary gland malignancy, most common in parotid gland.
Adenoid cystic carcinoma: Second most common parotid malignancy, but most common submandibular and minor salivary gland malignancy.
Higher risk of perineural spread: Patients may present with facial pain and facial nerve paralysis.