Rare Primary Pleomorphic Adenoma in Posterior Fossa

Pleomorphic adenoma is a benign neoplastic tumor of the salivary gland. Salivary gland tumors in the intracranial cavity are generally restricted to the pituitary gland and sellar region. To our knowledge, there has been only 1 previous case report of a primary central nervous system pleomorphic adenoma outside of the sellar region. In that case report of a posterior fossa pleomorphic adenoma, typical myxochondroid stroma was not identified on histology, and its pathogenesis was not explored.

A 71-year-old woman presented with a 6-week history of occipital headache and unsteadiness. Contrast-enhanced computed tomography and magnetic resonance imaging studies revealed a solitary large posterior fossa tumor in the left cerebellopontine angle measuring 47 × 43 × 45 mm. The tumor resulted in moderate hydrocephalus and significant mass effect with compression of the pons and medulla. She underwent a stereotactic right ventriculoperitoneal shunt insertion followed by a stereotactic craniotomy and complete excision of the tumor. The operation went uneventfully, and the patient had an uncomplicated recovery. Histopathologic examination revealed a benign pleomorphic adenoma (benign salivary gland tumor) with a classic appearance comprising an admixture of ductal epithelial cells, myoepithelial elements, and nodules of myxochondroid stroma. No extracranial source has been identified despite extensive investigation and 8 years of follow-up.

This case study illustrates a classic primary central nervous system pleomorphic adenoma in an unusual intracranial site. Its pathogenesis is postulated to involve salivary gland heterotopia.