Benign Salivary Gland Tumors
The benign mixed cell or pleomorphic adenoma comprises about 80% of parotid neoplasms, representing the most common salivary gland neoplasm. They are usually solid, rounded, well defined masses, most commonly found in the superficial lobe of the parotid. On T1 weighted images, they tend to be low signal relative to the gland, and they are generally high signal on T2 weighted images. There may be some fluid containing spaces within the tumor. Unlike a typical cyst, however, they tend to contrast enhance rather brightly with some heterogeneity. There may be calcification within the tumor. A small number can degenerate into carcinomas.
Pleomorphic adenomas can arise from the deep lobe of the parotid and
extend into the parapharyngeal space with an epicenter away from the parotid,
but well centered in the parapharyngeal space. At times, these lesions can
be difficult to differentiate from other parapharyngeal/carotid space lesions
such as schwannomas and glomus tumors. However, lesions that arise from
the parotid tend to have a prestyloid location. They are separated from
the carotid space by the tensor palattini veli fascia. Therefore, a mass
extending into the parapharyngeal space that is of parotid origin will push
the carotid artery and jugular vein posteriorly, whereas those that push
the carotid anteriorly are more likely to be a schwannoma or glomus tumor.
Warthin's tumors are often bilateral and multicentric. Their imaging
features resemble a pleomorphic adenoma in that they tend to have sharp
borders. They also enhance with contrast, however, more centrally and less
peripherally. They tend to be more common in males. They are not infiltrative
and are usually limited to the gland.