Brain Tumor

A brain tumor is an abnormal growth that develops within the skull. Brain tumors are classified as primary or metastatic (secondary) depending on their origin. Primary brain tumors arise from the cells of the brain and its surrounding structures. Metastatic brain tumors occur when cancer cells spread to the brain from other parts of the body (e.g., lung, kidney, breast, skin).

Primary brain tumors comprise many entities, named for the cell of origin. For example, astrocytomas arise from astrocytes—supporting cells for neurons. Tumors are also graded under the microscope to predict behavior over time: lower-grade (“benign,” slower-growing) versus higher-grade (“malignant,” more aggressive). While this distinction is helpful, location and involvement of nearby blood vessels or cranial nerves may limit curative treatment even for tumors considered “benign.” Primary brain tumors rarely spread outside the central nervous system, whereas metastatic brain tumors—originating from cancers such as lung, breast, or melanoma—account for more than half of all brain tumors.

Below are brief descriptions of several common brain tumors:

Meningioma

Meningioma is the most common extra-axial primary brain tumor, representing 15–20% of primary brain tumors. It is typically benign and often curable with surgery alone. Meningiomas arise from arachnoid cap cells of the meninges and can occur wherever these cells are present—frequently near the superior sagittal sinus, convexity, skull base, and posterior fossa. Symptoms vary with location because the tumor compresses adjacent structures. These tumors are usually firm and highly vascular, occur more often with increasing age, grow slowly, and may be quite large at diagnosis or found incidentally on imaging. Incidence is roughly 2.3 per 100,000; peak age is 45-year-old; women are affected about twice as often as men.

Pituitary Adenoma

Pituitary adenomas account for 10–15% of intracranial tumors. With advances in MRI/CT and serum hormone testing, even microadenomas (<10 mm) can be accurately diagnosed. Treatment outcomes have improved substantially with medical therapy, surgery, and stereotactic radiosurgery. By size, they are classified as microadenomas (<10 mm), macroadenomas (≥10 mm), and giant adenomas (≥40 mm).

Vestibular Schwannoma (Acoustic Neuroma)

A benign tumor arising from Schwann cells around the vestibular nerve. It often originates within the internal auditory canal, then enlarges to involve adjacent cranial nerves, brainstem, and cerebellum. It typically presents in adults over 30 years; women are affected about twice as often as men. In patients under 20, bilateral tumors suggest neurofibromatosis type 2.

Glioma

Gliomas arise from glial cells (astrocytes, oligodendrocytes, ependymal cells). More than half are malignant, and even low-grade differentiated gliomas tend to undergo malignant transformation over time. Many infiltrate normal brain, grow rapidly due to loss of growth control, and are difficult to completely remove surgically. Despite aggressive multimodal therapy (surgery, radiation, chemotherapy), recurrence is common and prognosis remains guarded.

Symptoms depend on the tumor’s location:

• Frontal lobe: personality change, mood disorders, weakness or paralysis, gait disturbance, reduced motor initiation.
• Parietal lobe: impaired sensation and perception; difficulty with light/pressure recognition, left–right disorientation, visuospatial deficits.
• Occipital lobe: partial or complete visual field loss.
• Temporal lobe: language problems, auditory changes, memory impairment, behavioral change or aggression.
• Brainstem: cranial nerve syndromes (abnormal eye movements, motor/sensory deficits); involvement of vital functions (heart rate, breathing, vasomotor control).
• Cerebellum: nausea/vomiting, imbalance, diplopia, gait ataxia, fine motor incoordination.

The exact cause of primary brain tumors is unknown, and they are not contagious. Several factors are associated with increased risk:

• Sex: overall, brain tumors are more common in men; meningiomas are more common in women.
• Race/Ethnicity: some primary brain tumors occur more often in White populations.
• Age: many primary brain tumors occur in adults ≥70; in children, brain tumors are the second most common cancers (after leukemia), with higher incidence under age 8.
• Family history: a family history of glioma may increase risk in some individuals.
• Occupational exposures:
  - Ionizing radiation (e.g., nuclear industry) is linked to higher risk.
  - Formaldehyde exposure has been associated with increased risk among certain workers (e.g., embalmers, some pathologists), though findings are mixed for other occupations.
  - Vinyl chloride (plastics industry) and acrylonitrile (textiles/plastics) exposures have been implicated in some studies.
• Under investigation: large epidemiologic studies to date have not demonstrated a clear increase in brain tumor risk from cell phone use or from head injury.

There is no proven way to prevent brain tumors. Early evaluation is crucial because symptoms are diverse and may be misattributed (e.g., to dementia, psychiatric illness, ophthalmologic or urologic conditions, or gastrointestinal disorders). Individuals with concerning symptoms should seek prompt specialty consultation and appropriate imaging to facilitate early diagnosis.