Choroid plexus papilloma of the cerebellopontine angle.

Choroid plexus papillomas are rare tumors, representing less than 1% of all intracranial neoplasms in our review of the English literature. Derived from the neuroepithelial cells of the choroid plexus, these tumors recapitulate the structure of the normal choroid plexus, often demonstrating a well-developed papillary architecture. This tumor most commonly affects children and typically arises in the lateral ventricles. Before 1992, 26 cases have been reported arising in the cerebellopontine angle. We describe an example of choroid plexus papilloma of the cerebellopontine angle that was initially diagnosed as metastatic papillary carcinoma. A metastatic disease workup revealed a right thyroid lobe nodule. Fine needle aspiration biopsy of this nodule yielded a few atypical cells, but no evidence of papillary carcinoma. We performed additional laboratory investigations to rule out the possibility of a primary papillary carcinoma of the thyroid gland and to make a definitive diagnosis of a choroid plexus papilloma. This article reviews choroid plexus papilloma of the cerebellopontine angle and demonstrates the use of immunohistochemistry to differentiate this benign primary neoplasm from well-differentiated metastatic papillary carcinoma.