A case of pleomorphic adenoma of the parotid gland metastasizing to a mediastinal lymph node

Pleomorphic adenomas are the most common salivary gland tumors and are typically cured with complete surgical excision. There are rare reports, however, in which these histologically benign tumors have inexplicably metastasized to distant sites. We present a case of a patient who presented, 27 years after excision of a parotid pleomorphic adenoma, with a recurrence in the parotid bed and a mediastinal metastasis.

Case report.

A 43-year-old woman presented with a mass in the right parotid bed 27 years after excision of a pleomorphic adenoma of the parotid. The patient's presentation, workup, and final diagnosis of benign metastasizing pleomorphic adenoma will be discussed, along with a pertinent review of the literature.

A diagnosis of recurrent pleomorphic adenoma was made from a fine needle aspiration biopsy of the right parotid mass. On subsequent computed tomographic scan, chest images revealed an incidental left mediastinal mass, which also proved to be a pleomorphic adenoma on computed tomography-guided fine needle aspiration biopsy. The patient underwent a completion parotidectomy and sternotomy with excision of the mediastinal mass. Examination of the pathology specimens confirmed a diagnosis of pleomorphic adenoma in both the parotid bed and the mediastinum. No histologic characteristics of malignancy were seen in either specimen; therefore, a diagnosis of benign metastasizing mixed tumor was rendered.

Benign metastasizing pleomorphic adenoma is a rare and controversial but distinct clinical entity. Although the definition of the term benign precludes metastatic disease, these tumors do not demonstrate any malignant features yet metastasize to distant sites. It remains to be determined whether these benign metastasizing pleomorphic adenomas are really low-grade salivary malignancies.