Astrocytoma

Astrocytomas account for 70% of neuroglial (non-neuronal macroglial and microglial cells) tumors. They lack capsules which allow them to metastasize.

=Epidemiology=

Lower grade astrocytomas (20-30% of gliomas) tend to occur in younger male patients, usually 20-40 years old.

Higher grade astrocytomas tend to occur in older patients, 40+ years old.

The highest grade astrocytoma (Glioblastoma Multiforme) affects individuals approximately 45-55 years of age.

Location
In children, lower grade astrocytomas tend to occur in the optic tracts, hypothalamus, and along the 3rd ventricle.

In adults, lower grade astrocytomas tend to occur in the cerebral hemispheres.

=Pathology=

Paradoxically, higher grade astrocytomas appear more well-circumscribed than their lower grade astrocytomas counterparts.

Associated Syndromes

 * Basal cell nevus syndrome / Gorlin syndrome
 * Cowden disease
 * Von Hippel Lindau
 * Li-Fraumeni
 * Maffucci
 * Neurofibromatosis 1 and 2
 * Ollier syndrome
 * Tuberous sclerosis
 * Turcot syndrome
 * Colonic familial polyposis, glioblastoma, and rare medulloblastoma

Grading Criteria

 * Cellularity
 * Mitotic activity
 * Pleomorphism
 * Necrosis
 * Endothelial proliferation

Types
Lower grade astrocytomas are separated into categories
 * 1) Grade 1 (well circumscribed): Well-circumscribed on imaging and gross pathologic inspection.
 * 2) Grade 2 (diffuse): Not well-circumscribed. Low degree of cellularity, mitotic activity, and pleomorphism. Lack necrosis and endothelial proliferation.
 * 3) Grade 3 (Anaplastic astrocytoma): Increased mitotic figures, cellularity, and pleomorphism.
 * 4) Grade 4 (Glioblastoma multiforme): Increased mitotic figures, cellularity, pleomorphism, with necrosis and endothelial proliferation.
 * 1) Pilocytic (Grade I)
 * 2) Subependymal giant cell (Grade I)
 * 3) Pleomorphic xanthoastrocytoma (PXA) (Grade I)
 * 4) Fibrillary astrocytoma (Grade II)
 * 5) Protoplasmic astrocytoma (Grade II)
 * 6) Pleomorphic xanthoastrocytoma (Grade II): seen primarily in adolescents and young adults, classically has a heterogeneous mass with a soft tissue component located along the meningocerebral interface.

Metastasis
Spread by four different mechanisms. =Radiology=
 * 1) Via white matter tracts: corona radiata, corticospinal tracts, corpus callosum, hippocampal commissures.
 * 2) Via Virchow-Robin spaces (perivascular pathways)
 * 3) Via subpial, or subependymal pathways.
 * 4) Via meningeal direct spread

An astrocytoma will show features of vascularity, necrosis, and hemorrhage based on its histologic grade.

High grade astrocytomas
Classically, astrocytomas will be expansile masses with central necrosis, ring enhancement, and surrounding vasogenic edema.

Heterogeneous and lobulated with white matter edema.

Calcification infrequently seen.

Necrosis and hemorrhage are common findings. This can cause the cyst like areas of the tumor to be slightly different in intensity compared to CSF.

Vascular proliferation in higher grade tumors can be seen.

Ring enhancement will commonly (~90%) be seen.

Low grade astrocytomas
Fewer than 50% will show enhancement in a portion of the mass.

May not show positive findings in a non-contrast CT or abnormal T2 hyperintensity

No necrosis present

Poorly circumscribed with mass effect

Difficult to distinguish from infarct.

Butterfly Gliomas
CNS lymphoma and GBM both can cause a bihemispheric pattern of invovlement of the corpus callosum centered in the frontal lobes. This can sometimes cause abnormal signal intensity in the corpus callosum fibers due to the neoplams itself, as the fibers are too dense to accomdate vasogenic edema.

T1
T1 weighted images will show prolongation, consequently the tumor area will be dark relative to grey matter.

T2
T2 weighted images will show prolongation, consequently the tumor area will be bright relative to grey matter.

Differential Diagnosis
The differential diagnosis for hemorrhagic neoplasms are:


 * Metastasis


 * Glioblastoma multiforme


 * Oligodendroglioma

The differential diagnosis of ring enhancing lesions are:


 * M: Metastasis


 * A: Abscess


 * G: Glioma


 * I: Infarct (subacute)


 * C: Contusion


 * D: Demyelinating disease


 * R: Resolving hematoma or radiation necrosis

Generally well-circumscribed. Grade 1 and 2 astrocytomas are often cystic but lack necrosis, endothelial proliferation.

Glioblastoma multiforme tends to affect the white matter of the frontal lobe>temporal lobe>basal ganglia

=Treatment=

Treatment is based on tumor grade. Unfortunately, within 1 year tumors frequently recur.

Grade 1 and 2: Treated with surgical resection. Patients live for years.

Grade 3 and 4: Surgical resection, chemotherapy, and radiation.

Patients with GBM typically only have a survival rate of 2% at 3 years.

Treated lesions will show calcification.

Approximately 10% of low grade astrocytomas will advance to higher grade neoplasms.