16 - Epithelial, Neuroendocrine, and Metastatic Lesions

Metastatic lesions are the most common neoplastic lesions of the central nervous system (CNS). Therefore, distinguishing a primary from a metastatic neoplasm is the first critical step in the diagnosis of a CNS tumor. Although in many instances the clinical history of an extracranial neoplasm facilitates the diagnosis, in some cases the intracranial tumor is the initial presentation of a systemic malignancy. In this latter scenario, it becomes the responsibility of the pathologist to determine the organ of origin of a metastatic CNS lesion, usually with the aid of ancillary studies. Although metastatic carcinomas are the most common metastatic CNS lesions, there are several other epithelioid tumors that can also metastasize to the CNS. This chapter discusses metastatic carcinomas, metastatic epithelioid tumors, and important immunohistochemical stains that assist the pathologist in their characterization. Paraganglioma and papillary tumor of the pineal region, two uncommon but important CNS tumors, are also discussed. Cystic lesions (which generally cause symptoms due to mass effect) are also frequently encountered in surgical neuropathology and are presented in this chapter. Neuroimaging studies provide vital information and constitute a critical aspect of surgical neuropathology; therefore, relevant neuroimaging studies have been included alongside the corresponding entities.