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% |
Brain stem gliomas 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:
|
Tumor differential diagnosis:
|
Other conditions that can lead to masses in this region:
|
Other conditions that can lead to masses in this region:
|
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:
|
