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Neoplasms Of The Nervous System

Introduction

Primary (3/4) or metastatic

2%of deaths from malignancySecond most common neoplasm in children (20%) after leukemia

(more likely arise in posterior fossa(

CNS neoplasms are different from neoplasms of otherorgans:

Criteria of malignancy are different & less evident

Patten of growth of low-grade tumors may still include

infiltration of large regions of brain serious clinical effects &

poor prognosis

Even benign ones may cause death due to compression of vital

structures Location of the tumor is important

Malignant neoplasms rarely metastasize outside of CNSThe subarachinoid space provides a pathway for spread

Ability to surgically resect infiltrating glial tumors without

compromising neurologic functions is limited

Classification of Primary CNS Tumors

A. Gliomas derived from glial cells:1.Astrocytoma:

Can be classified as:1.Pilocytic astrocytoma (WHO- I(

2.Fibrillary infiltrating or diffuse astrocytomas:Low grade astrocytoma (WHO- II(

Anaplastic astrocytoma (WHO- III(High grade glioblastoma multiforme (WHO- IV(

1.Pilocytic AstrocytomaTypically occur in children & young adults

Common sites: cerebellum, 3rd ventricle & optic nerve

Relatively benign & have excellent prognosis if resectable

Gross:Well-definedOften cystic with small mural nodule in wall

Microscopic:Bipolar cells with hairlike processes pilocytic

GFAP +veRosenthal fibers

Eosinophilic granular bodies

Microcystic areasNo mitosis or necrosis

1.Fibrillary AstrocytomasAccount for 80% of adult 1ry brain tumors

Most frequent in 4th-6th decades

Mainly in cerebral hemispheres

Most common presenting symptoms: seizures, headaches & focal

neurologic deficitsThey have tendency to become less well differentiated over time

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In adults:

Occurs most commonly in spinal cordMainly in setting of

neurofibromatosis type2CSF dissemination is common

The clinical outcome of completely resected supratentorial & spinalones is better than for those in posterior fossaGross:In 4th ventricle they are typically solid or papillary masses

extending from the ventricluar floorMicroscopic:

Perivascular pseudorosettes: Processes of cells are radiating around

blood vesselsEpendymal rosettes: Processes of cells are radiating around lumina

B. Primitive Neuroepithelial Neoplasms PNET: Are composed of embryonal primitive cells

Occur predominantly, but not exclusively in children

They include:

Medulloblastomas* Pineoblastoma

Ependymoblastoma Medulloepithelioma

Neuroblastoma*

MedulloblastomaIs derived from primitive neuroectodermal cells (undifferentiated(

Accounts for 20% of pediatric brain tumorsOccurs predominantly in children (in first 2 decades) and exclusively

in the cerebellum (midline vermis(In adults rare is often found in lateral cerebellar hemispheres

May lead to hydrocephalus if obstructing ventricles

Frequently disseminate through CSF

Highly malignant with poor prognosis if untreated, but with

multimodality therapy "radiosensitive 5ys survival rate may reach75%

Gross:Well circumscribed

Friable & grayMicro:Extremely cellular with sheets of anaplastic small blue primitive

cells with small Homer Wright rosettes cells are arranged around acentral fibrillary core. Mitoses are abundant

C. Neuronal Neoplasms:They include:

Gangliocytoma Ganglioglioma

Dysembryoplastic neuroepithelial tumor (DNT( Central Neurocytoma

Occur mainly in children & young adults

Almost all are low-grade

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Important causes of seizures

D. Meningiomas:Are predominantly benign

Are derived form meningothelial cells that invest arachnoid

Are usually attached to dura & are outside brain parenchyma

May occur in cranial vault or spinal cordOccur mainly in adults, F > M

Multiple meningiomas, especially in association with 8th nerve

schwannomas or glial tumors should raise suspicion of NF-2~50%of meningiomas not associated with NF2 still have mutations

in NF2 gene on long arm of chromosome 22 (22q(Gross:Well-defined, firm & lobulatedAttached to dura mater

Sharp interface with adjacent brain / spinal cord , easily separated

Extension into overlying bone maybe present

Microscopic: 1.Syncytial meningiomas = composed of compact cellular whorls2.Fibroblastic meningiomas = composed of elongated cells with

interspersed collagen3.Transitional meningiomas = share features of syncytial &

fibroblastic types4.Secretory meningiomas = has PAS +ve intracytoplasmic droplets &

intracellular lumina byEM5.Microcystic meningiomas = Has loose & spongy appearance6.Psammomatous meningioma = numerous psammoma bodies

E. Germ Cell Tumors (GCTs:(

Teratomas* & other germinomasOccur along midline, most commonly in pineal & suprasellar region

90%occur during 1st two decades

Tumors in pineal region show a strong male predominance

Histologic classification is the similar to testicular tumors. However,

CNS germinoma is the counterpart of testicular seminoma

F. Primary Brain Lymphoma (PBL:(Account for 2% of extranodal lymphomas & 1% of intracranial

tumorsMajority are diffuse large B-cell lymphomas

It is the most common CNS neoplasm in immunosuppressed (AIDS &transplant) patients. In these pts lymphomas are nearly all caused

by EBVIn nonimmunosupressed populations the incidence increases after

60 years of ageOften multifocal within CNS

Nodal, extranodal & BM involvement is rare & late complication

Is an aggressive disease with relatively poor response to chemoRx

as compared with peripheral lymphomas

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