The Types of Brain Cancer

 

The Types of Brain Cancer

Brain tumors are broadly classified based on where they originate (primary or metastatic) and the type of cell they arise from.¹ The World Health Organization (WHO) also assigns a grade from I to IV based on how aggressive the cells are.²

Here is an overview of the types of brain cancer and tumors:

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1. Primary Brain Tumors³

These tumors originate within the brain or spinal cord tissue.⁴ They are often named after the cells they resemble.⁵

A. Gliomas (The Most Common Type)

Gliomas arise from glial cells, the supportive cells of the brain.⁶ They are categorized by the specific type of glial cell they develop from:⁷

Type of Glioma	Originating Cell	Common Grade	Key Characteristics
Glioblastoma (GBM)	Astrocytes (or mixed)	Grade IV (Highest)	The most common and most aggressive, malignant (cancerous) primary brain tumor in adults.
Astrocytoma	Astrocytes	Grade II, III, or IV (GBM)	Can occur throughout the brain; often infiltrative (grow into surrounding tissue).
Oligodendroglioma	Oligodendrocytes	Grade II or III	Arise from cells that produce myelin; often have specific genetic markers that can predict treatment response.
Ependymoma	Ependymal cells (lining the ventricles)	Grade I, II, or III	More common in children and often found in the cerebellum or spinal cord.

B. Non-Glial Primary Tumors

These tumors arise from other structures surrounding the brain:

Tumor Type	Originating Tissue	Typical Nature	Key Characteristics
Meningioma	Meninges (membranes covering brain/spinal cord)	Usually Benign (Grade I)	The most common primary brain tumor; typically slow-growing and more common in women. A small number are malignant (Grade II or III).
Medulloblastoma	Embryonal cells in the cerebellum	Malignant (High Grade)	Highly aggressive; one of the most common malignant brain tumors in children.
Pituitary Adenoma	Pituitary gland	Usually Benign	Slow-growing; can affect hormone production.
Schwannoma (Acoustic Neuroma/Vestibular Schwannoma)	Schwann cells (on nerves)	Usually Benign	Develops on the vestibular nerve (balance/hearing); slow-growing.
Primary CNS Lymphoma	Lymphatic cells	Malignant	A rare, aggressive cancer of the immune cells that starts in the brain or spinal cord.

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2. Metastatic (Secondary) Brain Tumors⁸

These are cancers that start in another part of the body (e.g., lung, breast, skin/melanoma, colon) and spread to the brain.⁹

• Key Fact: Metastatic tumors are far more common than primary brain tumors.¹⁰

• The tumor is named and treated according to the tissue of origin (e.g., metastatic lung cancer to the brain).¹¹

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The WHO Brain Tumor Grading System

The World Health Organization (WHO) classifies brain tumors into four grades based on how the cells look under a microscope (histology) and their likely behavior:¹²

WHO Grade	Classification	Characteristics
Grade I	Benign / Low-Grade	Slowest growing; least malignant; often curable with surgery alone.
Grade II	Low-Grade	Grow slowly but may spread into nearby tissue; can potentially recur as a higher grade.
Grade III	Malignant / High-Grade	Faster growing; cells are abnormal (anaplastic); likely to recur.
Grade IV	Malignant / High-Grade	Fastest growing; most aggressive and invasive (e.g., Glioblastoma).

There are over 100 types of cancer that can affect the central nervous system (CNS).16 As mentioned previously, cancers that arise in other locations (breast, lung, etc.) and spread (metastasize) to the brain are not considered brain cancer. They are still treated as the cancers of the original site. Here, we will only discuss primary brain cancers (those that originate in the brain).

Gliomas

Malignant gliomas are the most common and deadly brain cancers. They originate in the glial cells of the central nervous system (CNS). Gliomas can be divided into 3 main types: 

• astrocytomas, 
• oligodendrogliomas, and 
• ependymomas.

The median survival of patients with glioma has improved over the past few years but is still only 15 months, with few patients living more than two years.Research indicates that this type of brain cancer may resist treatment because it contains stem cells that are responsible for driving the formation of blood vessels (angiogenesis), spread of the tumor (metastasis), and resistance to treatments. 

1.     Astrocytomas: 

Astrocytomas are tumors that develop in astrocytes and are found in the cerebrum and the cerebellum. Astrocytomas make up approximately 50% of all primary brain tumors. Glioblastoma multiforme, an astryocytoma subtype, is the most aggressive form of brain cancer and is associated with poor prognosis.

1.     Oligodendrogliomas: 

Oligodendrogliomas are tumors that develop in oligodendrocytes, and more often in the oligodendrocytes that are found in the cerebral hemispheres.  Oligodendrocytes are glial cells that produce myelin, a component of the brain that increases impulse speed. Oligodendrogliomas make up approximately 4% of primary brain tumors. Approximately 55% of all cases of oligodendrogliomas appear in people between the ages of 40 and 64. 

1.    Ependymomas:

 Ependymomas are tumors that develop in the ependymal cells. Ependymal cells are the cells in the brain and where ceribrospinal fluid (CSF) is created and stored. 24Ependymomas account for only 2% to 3% of all primary brain tumors but account for 8% to 10% of brain tumors in children. Ependymoma tumors are usually found in ventricle linings, the spinal cord, or the regions near the cerebellum.

Nongliomas

Nongliomas are tumors that do not arise from glial cells. More prevalent examples of nongliomas include meningiomas and medulloblastomas. Less prevalent examples include medullpituitary adenomas, primary CNS lymphomas, and CNS germ cell tumors. 

Meningiomas: 

Meningiomas are tumors that develop in the meninges, membranes covering the brain and spinal cord. Meningioma tumors are frequently formed from arachnoid cells. These cells are responsible for the absorption of the cerebrospinal fluid (CSF). Meningioma tumors are responsible for 13% to 30% of all tumors arising within the cranium - the bony case surrounding the brain. Tumor arising within the cranium are also called intracranial tumors. Most meningiomas are benign. Malignant meningiomas are extremely rare, with an incidence rate of approximately two out of every million people, per year. The risk for developing meningiomas increases with age and is more prevalent in women. 

Medulloblastomas: 

Medulloblastomas are the most common brain malignancies in children. These cancers arise in the posterior fossa - a specific region of the space inside the skull (intracranial cavity) that contains the brainstem and the cerebellum. The fourth ventricle region is involved in the development of approximately 80% of childhood cases.

The Types of Brain Cancer Video :

GETTING INFORMATION IN AND OUT OF THE BRAIN

GETTING INFORMATION IN AND OUT OF THE BRAIN

Getting information into and out of the brain relies on the Central Nervous System (CNS) and the Peripheral Nervous System (PNS) working together via specialized neural pathways.

The flow of information is categorized into two main directions:

1. Input (Afferent/Sensory): Information coming into the CNS (brain and spinal cord).

2. Output (Efferent/Motor): Information going out of the CNS to the body's effectors (muscles and glands).

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👂 Input: Sensory (Afferent) Pathways

Sensory information from the environment (e.g., sight, touch, pain) travels toward the brain via sensory neurons.

• Peripheral Receptors: Specialized sensory receptors in the skin, eyes, ears, and internal organs detect stimuli (e.g., pressure, light, chemical signals).

• Transmission: This detection generates an electrical impulse (action potential) in a sensory neuron.

• Ascending Tracts: The impulse travels along the nerve fibers (axons) through peripheral nerves and then enters the spinal cord or brainstem. Once inside the spinal cord, it travels toward the brain in organized bundles called ascending tracts.

  • Body Below the Neck: Information ascends through the spinal cord. Major pathways, like the Spinothalamic Tract (for pain and temperature) and the Dorsal Column System (for fine touch and proprioception), carry the signal.

  • Head and Neck: Information is carried directly to the brainstem via the Cranial Nerves (e.g., the Optic Nerve for vision, the Vestibulocochlear Nerve for hearing/balance).

• Processing Centers: The sensory signal is typically relayed in the thalamus (the brain's major relay center) before reaching its final destination in the cerebral cortex (e.g., the Somatosensory Cortex in the parietal lobe for touch, the Visual Cortex in the occipital lobe for sight).

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💪 Output: Motor (Efferent) Pathways

Instructions for movement and gland function travel away from the brain to the body's muscles and glands via motor neurons.

• Initiation: Voluntary movement instructions are typically initiated in the cerebral cortex, mainly the Primary Motor Cortex in the frontal lobe.

• Descending Tracts: The instructions travel down from the cortex as electrical impulses along upper motor neurons through the brainstem and into the spinal cord in bundles called descending tracts. The most famous of these is the Corticospinal Tract, which controls voluntary, skilled movements of the limbs.

• Relay in Spinal Cord: In the spinal cord, the upper motor neuron synapses (communicates) with a lower motor neuron.

• Final Destination: The lower motor neuron's axon exits the spinal cord and travels through peripheral nerves to connect directly with the muscle fiber or gland, causing it to contract or secrete.

This constant, rapid flow of input (sensory) and output (motor) allows the brain to perceive the environment, process the information, and execute appropriate and timely responses.

How does information come into the brain? 

A lot of information comes in through the spinal cord at the base of the brain. Think of a spinal cord as a thick phone cable with thousands of phone lines. If you cut that spinal cord, you won't be able to move or feel anything in your body. Information goes OUT from the brain to make body parts (arms and legs) do their job. 

There is also a great deal of INCOMING information (hot, cold, pain, joint sensation, etc.). Vision and hearing do not go through the spinal cord but go directly into the brain. That’s why people can be completely paralyzed (unable to move their arms and legs) but still see and hear with no problems.

Information enters from the spinal cord and comes up the middle of the brain. It branches out like a tree and goes to the surface of the brain. The surface of the brain is gray due to the color of the cell bodies (that's why it's called the gray matter). The wires or axons have a coating on them that's colored white (called white matter).

GETTING INFORMATION IN AND OUT OF THE BRAIN VIDEO :

IS THE BRAIN ONE BIG COMPUTER?

IS THE BRAIN ONE BIG COMPUTER?

The brain functions as an incredibly sophisticated electrical and chemical machine, using a seamless two-step process to transmit and process information via its fundamental unit, the neuron (nerve cell).¹

The communication within the brain relies on the following cycle:

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⚡ 1. The Electrical Signal (Action Potential)²

Information travels rapidly within a single neuron as an electrical signal called an action potential (or nerve impulse).³

• Basis: The neuron maintains an electrical charge difference, or resting membrane potential, across its cell membrane, established by an unequal distribution of positively and negatively charged ions (primarily Sodium (⁴$Na^+$), Potassium (⁵$K^+$), and Chloride (⁶$Cl^-$)) inside versus outside the cell.⁷

• Firing: When a neuron receives enough stimulation from its neighbors to reach a specific voltage threshold, voltage-gated ion channels rapidly open.⁸

  • This causes a sudden, massive influx of positive ions (⁹$Na^+$) into the cell, which momentarily reverses the electrical charge from negative to positive—this is the action potential.¹⁰

• Propagation: This electrical spike then travels quickly and in an all-or-nothing fashion down the length of the neuron's transmitting fiber, the axon, until it reaches the end terminal.¹¹

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🧪 2. The Chemical Signal (Neurotransmitters)¹²

Once the electrical signal reaches the end of the axon, it must cross a tiny gap, the synapse, to communicate with the next neuron.¹³ This is where the signal converts from electrical to chemical.¹⁴

• Conversion and Release: When the action potential arrives at the axon terminal, it triggers the release of specialized chemical messengers called neurotransmitters into the synaptic cleft (the gap).¹⁵

• Crossing the Synapse: The neurotransmitters quickly diffuse across this gap and bind to receptors on the receiving neuron's dendrites.¹⁶ This binding is specific, like a key fitting a specific lock.¹⁷

• Effect: The action of the neurotransmitter on the receptor determines the next step for the receiving neuron:¹⁸

  • Excitatory Neurotransmitters (e.g., Glutamate) push the receiving neuron's voltage toward its firing threshold, making it more likely to generate its own action potential.¹⁹

  • Inhibitory Neurotransmitters (e.g., GABA) push the voltage away from the firing threshold, making it less likely to fire.²⁰

By constantly integrating thousands of these excitatory and inhibitory chemical inputs, the receiving neuron determines whether to generate its own electrical signal, thereby perpetuating the communication throughout the brain's vast neural circuits.²¹

Key Chemical Messengers

Neurotransmitter	Primary Role(s)
Glutamate	Major Excitatory neurotransmitter; learning and memory.
GABA (Gamma-Aminobutyric Acid)	Major Inhibitory neurotransmitter; calming, anxiety regulation.
Dopamine	Reward, motivation, motor control.
Serotonin	Mood, sleep, appetite.
Acetylcholine	Muscle contraction (PNS), attention, memory (CNS).

Diagram of Brain

Is the brain like a big phone system or is it one big computer with ON or OFF states ? Neither of the above is correct.

Let's look at the brain as an orchestra. In an orchestra, you have different musical sections. There is a percussion section, a string section, a woodwind section, and so on. Each has its own job to do and must work closely with the other sections. When playing music, each section waits for the conductor. The conductor raises a baton and all the members of the orchestra begin playing at the same time playing on the same note. If the drum section hasn't been practicing, they don't play as well as the rest of the orchestra. The overall sound of the music seems "off" or plays poorly at certain times. This is a better model of how the brain works. We used to think of the brain as a big computer, but it's really like millions of little computers all working together. Diagram of Brain

IS THE BRAIN ONE BIG COMPUTER? VIDEO