What is a Brain Tumor?

A brain tumor is any intracranial mass created by an abnormal and uncontrolled growth of cells either normally found in the brain itself: neurons, glial cells (astrocytes, oligodendrocytes, ependymal cells), lymphatic tissue, blood vessels), in the cranial nerves (myelin producing Schwann cells), in the brain envelopes (meninges), skull, pituitary and pineal gland, or spread from cancers primarily located in other organs (metastatic tumors).

Primary (true) brain tumors are commonly located in the posterior cranial fossa in children and in the anterior two-thirds of the cerebral hemispheres in adults, although they can affect any part of the brain.

In the United States in the year 2000, it was estimated that there were 16,500 new cases of brain tumors1, which accounted for 1.4% of all cancers, 2.4% of all cancer deaths2, and 20%?25% of pediatric cancers2,3. Ultimately, it is estimated that there are 13,000 deaths/year as a result of brain tumors.

Causes

Aside from exposure to vinyl chloride or ionizing radiation, there are no known environmental factors associated with brain tumors. Mutations and deletions of so-called tumor supressor genes are incriminated in some forms of brain tumors. Patients with various inherited diseases, such as Von Hippel-Lindau syndrome, multiple endocrine neoplasia, neurofibromatosis type 2 are at high risk of developing brain tumors.

Symptoms

The kind of symptoms brain tumors may cause depend on two factors: tumor size (volume) and tumor location. The time point of symptom onset in the course of disease correlates in many cases with the nature of the tumor (enign, i.e. slow-growing/late symptom onset, or malignant, i.e. fast growing/early symptom onset).

Many low-grade (benign) tumors can remain asymptomatic (symptom-free) for years and they may accidentally be discovered by imaging exams for unrelated reasons (such as a minor trauma)

New onset of epilepsy4 is a frequent reason for seeking medical attention in brain tumor cases.

Large tumors or tumors with extensive perifocal swelling edema inevitably lead to elevated intracranial pressure (intracranial hypertension), which translates clinically into headaches, vomiting (sometimes without nausea), altered state of consciousness (somnolence, coma), dilatation of the pupil on the side of the lesion (anisocoria), papilledema (prominent optic disc at the funduscopic examination). However, even small tumors obstructing the passage of cerebrospinal fluid (CSF) may cause early signs of intracranial hypertension. Intracranial hypertension may result in herniation (i.e. displacement) of certain parts of the brain, such as the cerebellar tonsils or the temporal uncus, resulting in lethal brainstem compression. In young children, elevated intracranial pressure may cause an increase in the diameter of the skull and bulging of the fontanelles.

Depending on the tumor location and the damage it may have caused to surrounding brain structures, either through compression or infiltration, any type of focal neurologic symptoms may occur, such as cognitive and behavioral impairment, personality changes, hemiparesis, (hemi)hypesthesia, aphasia, ataxia, visual field impairment, facial paralysis, double vision, tremor etc. It cannot be stressed enough that these symptoms are not specific for brain tumors - they may be caused by a large variety of neurologic conditions (e.g. stroke, traumatic brain injury). What counts, however, is the location of the lesion and the functional systems (e.g. motor, sensory, visual, etc.) it affects.

A bilateral temporal visual field defect (bitemporal hemianopia?due to compression of the optic chiasm), often associated with endocrine disfunction?either hypopituitarism or hyperproduction of pituitary hormones and hyperprolactinemia is suggestive of a pituitary tumor.

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