NEUROPATHOLOGY- TUMORS OF THE CNS

---

[ CATS Home | About CATS | CATS Teaching Modules | Course Outline | Neuropathology | UVM Department of Pathology | Other Pathology Sites | UVM College of Medicine | UVM ]

---

I. KEY POINTS FOR MAJOR CNS TUMORS
II. CLASSIFICATION
III. ADDITIONAL GENERAL POINTS
IV. TUMORS IN THE ADULT
V. TUMORS IN CHILDREN (<15 YEARS)

VOCABULARY
Terms you should be familiar with:

Primary brain tumor
Metastatic brain tumor
Radiation therapy
Chemotherapy
Meningioma
Schwannoma
Glioma
Astrocytoma
Anaplastic astrocytoma
Glioblastoma multiforme
Oligodendroglioma
Ependymoma
Medulloblastoma
Pleomorphism
Tumor giant cell
Endothelial proliferation
Psammoma body
Primary brain lymphoma
Pontine (brain stem) glioma
Leukemia
Well differentiated astrocytoma

OBJECTIVES: The objectives of these two hours are to establish general principles by which to consider tumors of the CNS, to distinguish the features of adult vs childhood tumors, to consider the important pathologic and clinical details of a few CNS tumors in both age groups, and to discuss the relevance of metastatic (secondary) brain tumors.

I. KEY POINTS FOR MAJOR CNS TUMORS

There are only a few CNS tumors with which you should be familiar, since these few account for the vast majority of CNS tumors you will see in clinical practice. Key points to keep in mind concerning all of these are:

• Autopsy Series (FAHC) 1976-1986: 50% of all CNS tumors were primary and 50% metastatic (secondary).
  
  
• Childhood: 75% of primary brain tumors located below tentorium and solid metastatic tumors are rare.
  
  
• Adults: 75% of primary brain tumors located above the tentorium, and solid metastatic tumors are common with increasing age.
  
  
• Signs and symptoms related to both local tumor growth and secondary effects of edema (vasogenic).
  
  
• Treatment tends to be tumor specific and consists of various combinations of surgery and radiation therapy. Chemotherapy less commonly used.
  
  
• The term "benign" has to be used with caution with regard to primary brain tumors.

II. CLASSIFICATION

Tumors of the CNS can be classified according to five fundamental origins.

• The neuroectoderm (principally gliomas)
  
  
• Mesenchymal structures (notably meningiomas and schwannomas, and primary brain lymphoma)
  
  
• Tissues and cells that have been ectopically displaced intracranially during embryonic development
  
  
• Retained embryonal structures
  
  
• Metastases

Back to Top

III. ADDITIONAL GENERAL POINTS

• Intracranial tumors are second only to leukemia as a cause of childhood cancer, and are the most common solid tumor of childhood.
  
  
• In adults, 50% of all primary brain tumors are astrocytomas (well differentiated astrocytoma, anaplastic astrocytoma, glioblastoma multiforme), and half of these are glioblastoma multiforme.
  
  
• In adults, 20% of all primary brain tumors are meningiomas.
  
  
• Although malignant primary brain tumors tend to grow very aggressively and long term survival is rare, they rarely metastasize to systemic organs.
  
  
• Some tumors, notably medulloblastomas and ependymomas, tend to seed the neuraxis via CSF pathways.
  
  
• As stated above, location of primary brain tumors is very age specific. As an example, tumors of the astrocyte tend to occur in the cerebral hemispheres in middle life and old age, in the cerebellum and pons in children, and in the spinal cord in young adults.
  
  
• The exact histology of primary brain tumors, e.g. of the astrocytic line, is modified by its location.
  
  
• Signs and Symptoms
  
  
  • Infiltration with destruction of neural tissue causes specific functional deficit.
  • Irritation of a functional area causes seizures.
  • Secondary effects of edema and raised intracranial pressure cause headache, vomiting, and may lead to herniation.

Back to Top

IV. TUMORS IN THE ADULT

• Astrocytomas are the most common type of glioma and are classified into three different subtypes.
  
  
  • Well differentiated astrocytoma (sometimes modified by the terms low grade or benign): composed of well-differentiated astrocytes. Varieties include fibrillary, pilocytic, and gemistocytic.
    • Most commonly found in cerebral hemispheres
    • Accounts for 15-20% of primary brain tumors in the adult
    • May contain microcysts and calcium
    • Grossly, the tumor has poorly defined margins and is infiltrative.
    • Microscopically, relatively uniform appearing nuclei occur in fibrillary background or matrix
    • Life expectancy 5 years, but much longer survivals have been reported.
    • Astrocytomas have a bad habit of dedifferentiating to more malignant forms.
  • Anaplastic astrocytoma: greater degree of cellularity and pleomorphism
    • Distribution parallels the astrocytoma
    • Accounts for 3-5% of primary brain tumors in the adult
    • Life expectancy 3 years
  • Glioblastoma multiforme
    • Accounts for 25% of all primary brain tumors in the adult.
    • Extreme expression of astrocytic anaplasia
    • Microscopic features include marked cellularity with pleomorphism, mitoses, tumor giant cells, areas of necrosis and endothelial proliferation
    • Grossly, usually located in white matter of cerebral hemispheres and often show hemorrhage and necrosis. Borders are relatively well defined but very irregular.
    • Life expectancy: mean survival 1 year with surgery and radiation. Experimental protocols under investigation may prolong life.
      
      
• Other, Less Common Gliomas
  
  
  • Oligodendroglioma
    • Slow growing hemispheric tumor allows for 5-10 year survivals.
    • Seizures a prominent 1st complaint
    • Calcium and fried egg appearance are classic microscopic features.
    • White matter of hemispheres most common location
    • Anaplastic variety mimics the natural history of anaplastic astrocytoma
  • Ependymoma
    • Occurs most commonly in the 4th ventricle, and in that location may lead to obstructive hydrocephalus.
    • May also occur in the spinal cord and filum terminale
    • Only rarely involves the 3rd and lateral ventricles
    • Propensity to seed CSF pathways
    • Anaplastic variety much more aggressive
      
      
• Mesenchymal Origin
  
  
  • Meningiomas ("tumor of the meninges")
    • Accounts for 20% of primary adult brain tumors
    • Occurs in later decades of life; 60:40 F to M ratio in brain; 80:20 F to M ratio in spinal cord
    • Important: This tumor, unlike the previous tumors we have discussed, is extra axial and does not invade the brain
    • They arise from arachnoid villi and are most common in the parasagittal region
    • Can be cured surgically
    • Extremely slow growing and benign, with histologic variants having essentially the same natural history and prognosis
    • Histologic features include meningothelial cells and psammoma bodies
    • Common presenting symptoms include headache, seizures and dementia
  • Schwannoma ("tumor of the nerve root")
    • Most commonly affects the 8th cranial nerve and presents as a cerebellopontine angle mass. Here called an acoustic neuroma.
    • Benign, surgically curable lesion. Malignant transformation very rare
    • Together with meningiomas, constitute the largest proportion of intradural extramedullary neoplasms
    • Classic histologic appearance includes Antoni A, Antoni B, and Verocay bodies
  • Primary brain lymphoma
    • Usually located deep in cerebral hemispheres and often multicentric
    • Constituent cells usually large, uncleaved B cells
    • Close association with immunosuppression, particularly AIDS
    • Sensitive to radiation therapy, although survival longer than 2 years is rare
    • Does not tend to metastasize to systemic organs
      
      
• Metastatic Tumors
  
  
  • Account for 50% of all brain tumors in adults
  • In order of propensity to metastasize: lung, breast, melanoma, unknown, kidney, thyroid
  • Carcinomas of the GI tract, bladder, prostate, ovaries, and uterus rarely go to brain
  • Grossly, tend to occur at gray and white matter junction and to be round with well defined borders. Necrosis and hemorrhage frequent. Usually multiple
  • Treatment is by radiation, prognosis is very poor
  • Lymphomas (systemic) rarely metastasize to brain parenchyma, but do go to meninges and as extradural implants

V. TUMORS IN CHILDREN (<15 YEARS)

• Neuroectodermal Origin
  
  
  • Medulloblastoma: Common intracranial tumor of childhood, accounting for 20-25%. This tumor may arise after the 1st decade, but much less frequently.
    • Tends to be midline, affecting the vermis, and presents with gait instability, headache and vomiting. Cerebellar tumor.
    • Proximity to CSF makes seeding frequent
    • Composed of round, blue cells with scanty cytoplasm and pleomorphism. Mitoses are frequent
    • Treated with surgery, radiation and chemotherapy. 5 year survival now about 40%.
  • Astrocytoma
    • In children, this tends to be located in the cerebellar hemisphere and tends to be cystic and pilocytic.
    • Account for 20-25% of all childhood tumors.
    • treated with combined surgery and radiation, and 5 year survivals are very common.
  • Pontine (brain stem) gliomas
    • Accounts for 10% of childhood brain tumors.
    • Prognosis tends to be bad since
      • They are not surgically accessible.
      • They eventually dedifferentiate and become anaplastic.
    • CT scan diagnosis
    • MRI scan diagnosis
  • Other tumors of children of some interest, but much less common.
    
    
• Metastatic Tumor: Leukemia only one to think about, and usually goes to brain as meningeal infiltration.

Back to Top

Go Back to Course Outline

Go Back to Neuropathology

[ Introduction and Objectives | Basic Reactions of the CNS | Vascular Disease | Trauma to the CNS | Alcohol and the CNS | Infections of the CNS | Tumors of the CNS | Diseases of the Myelin Sheath | Spinal Cord Disease | Muscle Disease | Congenital Anomalies of the CNS | Neuropathology of AIDS | Degenerative Diseases of the CNS | Dementia and Related Issues | Unconventional Transmissible Agent (Prion) Diseases ]

---

[ CATS Home | About CATS | CATS Teaching Modules | UVM Department of Pathology | Other Pathology Sites | UVM College of Medicine | UVM ]

---

Questions? Comments? Send a message to the CATS guru: jkessler@salus.uvm.edu