Spectrum of pathologic features in neuroendocrine neoplasms of the mediastinum

Neuroendocrine tumors arising in the mediastinum are rare. They all share in common the consistent expression of certain morphologic, immunohistochemical, and ultrastructural features indicative of their neuroendocrine lineage. Although some of them may share very similar morphologic characteristics, differences in biologic behavior among some of these tumors mandate careful assessment and specific diagnosis. A number of unusual morphologic variants of neuroendocrine neoplasms have been described in recent years in the mediastinum. The present review highlights some important pitfalls in their interpretation and offers some insights for their separation into specific entities. In addition, issues and controversies regarding the current classification of primary neuroendocrine carcinomas of the thymus are also discussed.