Neoplasms Overview

(central as well as the newly described extraventricular

variant), dysembryoplastic neuroepithelial tumor, papillary

glioneuronal tumor, rosette-forming glioneuronal tumor (of

the 4th ventricle), and cerebellar liponeuroblastoma are

included.

Pineal region tumors: Pineal region neoplasms account for <

1% of all intracranial neoplasms and can be germ cell tumors

or pineal parenchymal tumors. Pineal parenchymal tumors are

less common than germ cell tumors. Because germ cell

neoplasms occur in other intracranial sites as well as the pineal

gland, they are considered separately.

Pineocytoma is a very slowly growing, well-delineated tumor

that is usually found in adults. Pineocytomas are WHO grade I.

Pineoblastoma is a highly malignant primitive embryonal

tumor mostly found in children. Highly aggressive and

associated with early CSF dissemination, pineoblastomas are

WHO grade IV neoplasms.

Pineal parenchymal tumor of intermediate differentiation

(PPTID) is intermediate in malignancy, probably WHO grade II

or III. Many so-called aggressive pineocytomas would probably

be reclassified as PPTIDs. A newly described neoplasm,

papillary tumor of the pineal region, is a rare neuroepithelia

tumor of adults. No WHO grade has been assigned.

Embryonal tumors: This group includes medulloblastoma

(MB), CNS primitive neuroectodermal tumors, and atypical

teratoid-rhabdoid tumors (AT/RT). SMARCB1 (INI1/hSNF5)

mutation is diagnostic of AT/RT even in the absence of overtly

rhabdoid cells.

MB, which has 1 classic and 3 histologic variants, is now

divided into 4 groups based on molecular profiling (the 1st

step in risk stratifying MB patients for therapy). Although all 4

groups are designated as WHO IV tumors, they behave quite

differently, and 1 specific subgroup (Wnt) is associated with an

especially favorable prognosis.

Meningeal Tumors

Overview: Meningeal tumors are the 2nd largest category of

primary CNS neoplasms. They are divided into meningiomas

and mesenchymal, nonmeningothelial tumors (i.e., tumors

that are not meningiomas). Hemangiopericytomas (HPCs),

hemangioblastomas (HGBLs), and melanocytic lesions are also

considered part of the meningeal tumor grouping.

Meningiomas: Meningiomas arise from meningothelial

(arachnoid cap) cells. Most are attached to the dura but can

occur in other locations (e.g., choroid plexus of the lateral

ventricles). Although meningiomas have many histologic

subtypes (e.g., meningothelial, fibrous, psammomatous, etc.),