CNS tumor
General
Glioma overview


Topic Completed: 1 March 2012

Minor changes: 11 July 2020

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PubMed Search: Glioma [title] CNS [title]


Eman Abdelzaher, M.D., Ph.D.
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Cite this page: Abdelzaher E. Glioma overview. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/cnstumorgliomageneral.html. Accessed August 11th, 2020.
Definition / general
  • Most common CNS tumor
  • Includes astrocytoma, ependymoma, glioblastoma, oligodendroglioma and various subtypes / combinations
  • Diagnosis of "glioma" may be used for frozen section but is not a final diagnosis
  • Important to identify oligodendroglial component, due to effectiveness of chemotherapy for these gliomas
  • Presence of thrombosed vessels in tumors may predict postoperative systemic thromboses (J Neurosurg 1998;89:200)
  • The etiology of gliomas is not entirely understood, but a known risk factor is radiation therapy to the cranium, and gliomas in this setting usually arise 5-25 years after exposure
Terminology
  • Intra-axial: within brain and spinal cord
  • Intramedullary: within spinal cord
  • Extra-axial: not within brain and spinal cord (such as meningioma)
  • Extramedullary: not within spinal cord
  • Supratentorial: above tentorial membrane - cerebrum
  • Infratentorial: below tentorial membrane - cerebellum, brainstem or spinal cord
  • Clinical features
    • 13K deaths in US annually (2% of cancer deaths)
    • Peaks in childhood, then declines to age 25 years, then increases with age
    • Childhood tumors: 33% in anterior fossa (supratentorial), 67% in posterior fossa (astrocytoma - 26%, medulloblastoma / PNET - 24%, ependymoma - 14%)
    • Adults: metastases are more common than primary brain tumors but are usually not biopsied; of biopsied tumors, 67% arise in anterior fossa (glioma - 33%, meningioma - 13%, metastases - 12%, pituitary adenoma - 5%), 33% in posterior fossa (schwannoma - 8%, misc. - 33%)
    • Most common spinal cord tumors are schwannoma, meningioma and ependymoma
    • Metastasis of primary CNS tumors outside CNS is rare, usually occurs along brain and spinal cord via subarachnoid space or due to surgery related implantation of tumor cells into vessels
    • Benign appearing tumors may still be infiltrative and difficult to resect
    • Tumors may arise from neural stem cells, precursors of neurons and glial cells, recently discovered in mature brain
    • Symptoms: focal deficits, seizures, increased intracranial pressure (due to mass effect, hydrocephalus, cerebral edema), herniation
    • Labeling index / proliferation index: percentage of MIB1+ or PCNA+ nuclei (compared to all nuclei), usually in regions of highest proliferation; useful prognostic indicator (high values associated with poorer prognosis)
    Classification
    • Benign: does not recur; applies to pilocytic astrocytomas, certain gangliogliomas and ependymomas; may still have poor prognosis due to location that makes it difficult to resect completely
    • Low grade: may recur as high grade and kill patient
    • Gliomatosis cerebri: diffuse and extensive involvement of CNS associated rarely with glioma; MRI and biopsy helpful for diagnosis
    Microscopic (histologic) description
    • Biopsies of tumor epicenter have cellularity greater than surrounding brain
    • Biopsies of margin only are difficult to grade; often contain granular calcifications among hypercellular glia
    • Also microcysts and mitotic figures (depending on tumor grade)
    • May have uneven distribution of cellular density that obscures gray white junction or spawns secondary structures of Scherer (subpial and perineuronal neoplastic glia)
    Positive stains

    Exceptions:
    • Oligodendroglioma cells have variable GFAP and are Leu7+ and S100+
    • Xanthoastrocytomas are reticulin+
    Negative stains
    Differential diagnosis
    • Gliosis: even distribution of cellular density, contracts instead of expanding near hypercellular glia; usually less pleomorphism, no nuclear hyperchromasia, no nuclear cluster formation, no nuclear molding, no mitotic figures, no calcifications
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