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General Pediatric Brain Tumor

 

 

Types of Tumor

Brain tumors can be subcategorized into different "types."

They can be thought of in terms of:

  • Location
    • Supratentorial versus infratentorial
    • Intra-axial versus extra-axial
  • Origin
    • Primary vs secondary
  • Tumor pathology
    • Primary tumors may be benign vs malignant
    • Different histology and origins
    • Grade (high grade versus low grade)

 

Location

Most (60%) of childhood brain tumors arise in the posterior fossa and are infratentorial:

In the diagram below:

  • S = Supratentorial
  • I = Infratentorial
  • T = Tentorium

The tentorium is an extension of the dura mater that covers the cerebellum and separates the cerebellum from the inferior occipital lobes.

INFRA-tentorial means below the tentorium and applies to tumors arising in the posterior fossa. Brain stem tumors are usually included in this definition.

SUPRA-tentorial means above the tentorium and applies to tumors arising above the tentorium.

 

Summary Table of Infratentorial Tumors:

Tumor

Relative

Frequency

Brief Description

Astrocytoma

35%
  • Commonly occurs in posterior fossa and arises from the cerebellar hemisphere

 

  • Has nodular and cystic components.

 

  • Usually low grade (pilocytic) and does well with surgery alone

 

Medulloblastoma

35%

  • Usually a midline lesion arising from the vermis

 

  • Highly malignant small round blue cell tumor (Primitive Neuro-Ectodermal Tumor - PNET)

 

  • By defintion a PNET arising in the posterior fossa

 

  • Needs aggressive multimodality therapy

 

Ependymoma

20%

  • More common in the posterior fossa.

 

  • Arises from the ependymal lining, most commonly from the roof of the fourth ventricle

 

  • Generally a high risk of local recurrence after surgery alone
Other

10%

 

  • Ganglioglioma

 

 

 

Summary Table of Supratentorial Tumors:

Tumor

Relative

Frequency

Brief Description

Hemispheric Astrocytoma

 40 %
  • Low grade tumors commoner than high grade tumors

 

Ependymoma

 
  • Supratentorial tumors may do well with surgery alone

 

Supratentorial PNET

 
  • Same histology as medulloblastoma, but different location

 

Optic Nerve Glioma

5%
  • Slow growing

 
Craniopharyngioma 5%
  • Slow growing and cystic

 
Pineal Tumors 2 - 5%
  • Pathology and therefore behavior can differ - many types of tumor.
Ganglioglioma 4% or so
  • Mixed neuronal glial tumor

 

  • Commonly supratentorial

 

Pleomorphic Xanthoastrocytoma

(PXA)

 
  • Solid and cystic tumors attached to the leptomeninges
Oligodendroglioma  
  • Very rare in children

 

Dysembryoplastic

Neuroepithelial

Tumor (DNET)

 
  • Benign mixed neuronal-glial tumors

 

  • Often in the temporal lobes

 

  • Do well with surgery alone

 

 

Tumors can also be thought of in terms of the location of the tissue that they arise from in relation to the leptomeninges:

  • Tumors arising inside the pia-arachnoid are called intra-axial
  • Tumors arisng outside the pia-arachnoid are called extra-axial

The pia-arachnoid:

  • both the pia mater and arachnoid layers of the meninges covering the brain and spinal cord
  • the pia mater and arachnoid are considered together as one functional unit; the leptomeninges.

 

Summary Table of Intra-axial versus Extra-axial Tumors:

Intra-axial

Extra-axial
Arise inside the pia arachnoid layer Arise outside the pia arachnoid
From brain parenchyma From meninges and nerve sheath

Tumor differential diagnosis:

  • Glioma
  • Medulloblastoma
  • Hemangioblastoma (very rare in children)
  • Metastatic disease

Tumor differential diagnosis:

  • Meningioma
  • Pituitary adenoma(adult)
  • Craniopharyngioma
  • Schwannoma
  • Metastatic disease

Other conditions that can lead to masses in this region:

  • Abscess/infection
  • Congental malformation
  • AVM
  • Infarct

 

Other conditions that can lead to masses in this region:

  • Infection
  • Dermoid cyst
  • Epidermoid cyst
  • Hematoma

 

This Uniformed Services University of the Health Sciences, Bethesda website has a great program to study the differential diagnosis of any brain lesion by location:

Brain Lesion Locator™: Differential Diagnosis by Location

 

Basic Pathology (tumor grade)

Tumors can also be thought of in terms of benign versus malignant. Low grade tumors are more common than high grade.

 

Summary Table of Benign versus Malignant Tumors:

Benign

Malignant

Slow-growing with long clinical history

Rapidly growing with short clinical history

 

Distinct borders

Invasion of surrounding brain tissue

Rarely spreads to other parts of brain or spine.

 

No spread outside CNS

Local invasion and often spreads to other locations in brain and spinal cord

 

Spread outside the CNS can sometimes occur but is very rare

Life threatening secondary to location in critical area of the brain

Significantly worse prognosis and invariably life threatening

Often requires only craniotomy for tumor resection

Multiple modality therapy:

  • craniotomy for tumor resection
  • chemotherapy
  • radiation

 

 

 

 

 

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