Answer: Cystic schwannoma

Histology: H&E sections show a cystic encapsulated cellular tumor with large thick walled blood vessels. The cellular areas are composed of bland spindle cells that are arranged in broad bundles and interfacing fascicles. These areas are mixed with areas that exhibit a loose textured, cobweb like meshwork of cells with multiple processes in a myxoid matrix. A central cystic areas is noted which is lined by the same spindle cells thar are surrounded by hemosiderin laden macrophages and scattered lymphocytes. Immunohistochemistry demonstrates that the tumor cells are S100 positive (not shown) and CD34 negative (not shown).

Discussion: Schwannomas are benign, usually encapsulated, non-melanotic nerve sheath tumors that are composed entirely of cells exhibiting a Schwann cell phenotype. They are usually detected adjacent to a nerve and are typically composed of a more cellular (Antoni A) and a less cellular myxoid components (Antoni B). Schwannomas are benign tumors that often undergo degenerative changes which can be represented by cystic degeneration or by degenerative nuclear atypia that lack significant mitotic activity.