What is a Brain Tumor?
Sometimes cells in the body grow and multiply indiscriminately to produce an abnormal mass of tissue which is known as a tumor. When such a growth occurs in the brain, it is called a brain tumor. The cause of this uncontrolled growth is not always known. The tumor may grow slowly or rapidly but it will interfere with normal brain function by occupying space within the skull.
Some tumors originate in the brain and are known as primary tumors, while others occur as a result of spread of cancer from other sites in the body (metastasis). These are known as secondary tumors or metastatic tumors. However, metastasis of brain tumors to other parts of the body other than the central nervous system (CNS) is extremely rare.
Not all brain tumors are malignant (cancerous). Non-cancerous tumors are known as benign tumors.
Types of Brain Tumors
Brain tumors may be of various types. They may be benign (non-cancerous) or malignant (cancerous) in nature.
Benign Brain Tumors
Benign brain tumors are primary tumors of the brain. These are grade 1 tumors where the cells look mostly normal under the microscope with well-defined margins. These are usually slow-growing tumors which do not invade nearby brain tissue or metastasize to distant sites.
Malignant Brain Tumors
Malignant tumors may be primary brain tumors or metastatic brain tumors. A primary malignant brain tumor is usually confined within the central nervous system and rarely metastasizes to distant sites. A secondary or metastatic brain tumor occurs by spread of cancer cells to the brain from a primary site elsewhere in the body. Metastatic brain tumors are usually multiple, although solitary tumors may sometimes be seen. Malignant brain tumors have a tendency to recur even after treatment.
Both benign as well as malignant brain tumors can produce pressure symptoms on the brain which can lead to a disturbance in brain function and may even be life-threatening. In addition, malignant growths invade surrounding tissue thereby destroying it and is at risk of spreading to distant sites.
Grading of Brain Tumors
Brain tumors are graded from 1 to 4 according to their appearance under the microscope. In general, grade 1 and 2 tumors have more normal-looking and slow-growing cells than those of grade 3 and 4 tumors.
- Grade 1 – the cells look relatively normal and are usually slow-growing. The tissue is benign.
- Grade 2 – the cells look slightly different from normal cells. The tissue is malignant.
- Grade 3 – the cells look very different from normal cells. The malignant tissue is said to be anaplastic or rapid-growing.
- Grade 4 – the cells look extremely abnormal and the malignant tissue grows rapidly.
Primary Brain Tumor
A primary brain tumor originates in the brain and nearby tissues such as the meninges (membranes covering the brain), cranial nerves, pituitary gland, or pineal gland. Genetic mutations of the DNA within the cells usually leads to primary brain cancer. The initial differentiation should be whether the primary brain tumor is benign or a malignant. Primary brain tumors are named according to the type of cells it originated from. These may include :
- Acoustic neuroma or schwannoma.
- Astrocytoma or glioma – anaplastic astrocytoma and glioblastoma fall under this category.
- Germ cell tumor.
- Pineoblastoma – this is a malignant form of pineal tumor.
Of these, gliomas and meningiomas are the most common primary brain tumors in adults.
Gliomas arise from glial cells, such as astrocytes, oligodendrocytes, and ependymal cells. Glial cells form the connective tissues or the supportive tissues of the central nervous system. Gliomas may be of different types :
- Astrocytic tumors arise from the star-shaped glial cells or astrocytes and include the less malignant astrocytoma (grade 1 and 2), as well as the high grade anaplastic astrocytomas (grade 3 tumor), and the most malignant glioblastomas (grade 4 tumor), also known as malignant astrocytic glioma. Astrocytomas commonly arise in the cerebrum in adults, while in children they may arise in the brain stem, cerebrum, and cerebellum.
- Brain stem gliomas arise from the brain stem and are more common in children and young adults.
- Ependymoma arises from cells lining the ventricles or the central canal of the spinal cord. It may be grade 1, 2, or 3 and is common in children and adults.
- Oligodendroglial tumors are rare and are usually slow-growing and less aggressive. It arises from a type of cell of the central nervous system known as oligodendrocytes, which provides support to the nerves and make up the myelin sheath that insulates and protects the nerve fibers. Oligodendrogliomas usually arise in the cerebrum and are more common in middle-aged adults.
- Mixed gliomas are made up of both astrocytic and oligodendrocytic tumors.
- Glioblastomas are the most invasive and rapid growing type of primary brain tumor.
- Optic nerve gliomas are found in or close to the optic nerve and may produce double vision or progressive loss of vision. It can range from low grade to high grade and are seen more often in infants and children but may occur in adults.
These are usually benign tumors (grade 1) but may rarely be cancerous (grade 2 and 3). Meningiomas develop in the meninges, the membranes covering the brain and spinal cord and are usually slow-growing tumors. Even though benign, it is potentially life-threatening and symptoms depend on its size and location. Meningiomas are more common in the 40 to 70 year age group and women are at greater risk than men.
Other Types of Brain Tumors
- Medulloblastoma is the most common type of malignant brain tumor occurring in children and usually arises in the cerebellum. It is also known as primitive neuroectodermal tumor and usually a grade 4 tumor.
- Craniopharyngioma is usually low grade and is more common in children and adults in their 50s and 60s. It occurs at the base of the brain, near the optic nerve and close to the pituitary gland. The symptoms may include headache, vision problems, weight gain, and delayed development in children.
- Schwannomas are benign tumors that arise from cells (Schwann cells) that form a protective sheath around nerve fibers. They are most often seen on the acoustic nerve which is associated with balance and hearing. It may produce symptoms such as hearing loss, loss of balance, dizziness, tinnitus (ringing in the ears), and weakness on one side of the face. A schwannoma is also known as an acoustic neuroma, vestibular schwannomas, or neurilemmoma. This type of tumor is most commonly seen in adults.
- Pituitary tumors or pituitary adenomas are usually benign tumors of the pituitary gland. It is more common in women than in men and may produce symptoms such as amenorrhea (cessation of menstruation), abnormal nipple discharge, gynecomastia or breast enlargement in men, low blood pressure, hypertrichosis (excessive body hair growth), abnormal growth of hands and feet, and weight gain.
- Primary lymphoma of the brain is cancer of the lymph cells that originates in the brain. It is more common between the ages of 45 and 70. People with a weakened immune system are more at risk of developing this type of brain tumor.
- Pinealoma are rare tumors that arise in or close to the pineal gland, which is located between the cerebrum and cerebellum. It occurs more often in children and young adults. Pineoblastoma is a malignant form of a pineal tumor.
- Germ cell tumor of the brain is most commonly seen in young adults. It arises from germ cells, which are cells that develop into sperm or ova. Of the different types of germ cell tumors of the brain, germinoma is the most common.
Common Brain Tumors in Children
The most common types of brain tumors seen in children are :
- Grade 1 and 2 astrocytoma – juvenile pilocytic astrocytoma is the most common type of astrocytoma seen in children.
- Brain cell glioma – diffuse intrinsic pontine glioma is the most common type.
- Optic nerve glioma
- Pineal tumor
- Germ cell tumor of the brain
Secondary or Metastatic Brain Tumor
A tumor that originates in some other region of the body and then spreads (metastasizes) to the brain is known as a secondary or metastatic brain tumor. The cancer cells reach the brain tissue through the blood stream. The original site of cancer is usually already identified but occasionally a secondary brain tumor may present with symptoms prior to the diagnosis of the primary cancer. The abnormal cells found in the metastatic tumors are seen to be of the same type as that of the primary tumor elsewhere. As a rule, metastatic brain tumors are more common than primary brain tumors.
The common sites from where metastasis may occur to the brain are :
The outcome in these cases is not positive since in most people with metastatic brain tumor, the cancer has usually spread to other parts of the body as well.
Symptoms of Brain Tumors
The symptoms produced will depend upon the size, location, and type of tumor. Symptoms of a brain tumor may occur as a result of it taking up space within the skull. This may cause :
- Increased pressure in the brain
- Shifting of the brain
- Pressure on the skull
- Damage to the nerves and blood vessels in the brain
- Damage to the brain tissue
Nerves, blood vessels, and brain tissue may also be affected when they are invaded by cancer cells. The abnormal growth may thus affect brain function. Depending on the site of the growth, symptoms will vary since different areas of the brain are involved with different functions. Symptoms will also depend on the size, as well as the type of tumor and its growth rate. The symptoms that are commonly seen include :
- Headaches – these are often more severe in the mornings. Headaches may occur when a person is sleeping and may be severe enough to wake him up from sleep. The pattern may be different from previous headaches or the headache may be a new symptom. The intensity of headaches may gradually increase and they may come more frequently. A headache associated with one or more of the other symptoms such as nausea, vomiting, vision problems, or seizure may need to be investigated for a possible brain tumor.
- Nausea and vomiting – likely to be most severe in the mornings.
- Personality changes.
- Emotional changes.
- Problem with thinking, speaking, or finding words.
- Loss of concentration.
- Memory loss.
- Vision problems, such as loss of vision in one or both eyes. Peripheral vision is most often affected.
- Uncontrolled eye movements.
- Hearing loss.
- Unsteadiness or loss of balance.
- Weakness, loss of sensation, or paralysis affecting one side of the body.
- Increased size of the head in young children.