the current WHO schema classifies them rather simply. Most

meningiomas are benign and correspond to WHO grade I.

Atypical meningioma, as well as the chordoid and clear cell

variants, are WHO grade II tumors. Anaplastic (malignant)

meningiomas correspond to WHO grade III.

Mesenchymal, nonmeningothelial tumors: Both benign and

malignant mesenchymal tumors can originate in the CNS.

Most correspond to tumors of soft tissue or bone. Generally,

both a benign and malignant (sarcomatous) type occur.

Lipomas and liposarcomas, chondromas and

chondrosarcomas, osteomas and osteosarcomas are

examples.

HPC is a highly cellular, vascular mesenchymal tumor that is

almost always attached to the dura. HPCs are WHO II or III

neoplasms. HGBL is a WHO grade I neoplasm, consisting of

stromal cells and innumerable small blood vessels. It occurs

both sporadically and as a part of von Hippel-Lindau

syndrome. Primary melanocytic neoplasms of the CNS are

rare. They arise from leptomeningeal melanocytes and can be

diffuse or circumscribed, benign or malignant.

Tumors of Cranial (and Spinal) Nerves

Schwannoma: Schwannomas are benign, encapsulated nerve

sheath tumors that consist of well-differentiated Schwann

cells. They can be solitary or multiple. Multiple schwannomas

are associated with neurofibromatosis type 2 (NF2) and

schwannomatosis, a syndrome characterized by multiple

schwannomas but lacking other features of NF2. Intracranial

schwannomas are almost always associated with cranial

nerves (CN8 is by far the most common) but occasionally

occur as a parenchymal lesion. Schwannomas do not undergo

malignant degeneration and are designated as WHO grade I

neoplasms.