The brain contains many different kinds of normal cells. Different types of benign (not cancerous) and malignant (cancerous) brain tumors can start in these different cells. These different types of brain tumors vary in prognosis (survival) and the type of treatment (surgery, radiation, radiosurgery, chemotherapy, BCNU polymers) that is recommended.
The neurons carry the signals through the central nervous system. The signals carried by neurons determine thought, memory, emotion, speech and muscle movement. Unlike other types of cells in the brain that can grow and divide, neurons do not divide after birth. This means that damage to the neurons by tumors or treatments that results in death of neurons means the permanent loss of the neurons.
There are three types of glial cells - astrocytes, oligodendrocytes and ependymal cells. Glial cells nourish the neurons, take away the used metabolites and provide an interface between the blood vessels and the neurons. Normal glial cells grow and divide very slowly. The glial cells far outnumber the neurons. Most brain tumors and spinal cord tumors develop from glial cells.
The spaces around the brain are lined by a thin tissue called the meninges. The meninges form a thin, delicate membrane that lies just outside the brain. The meninges can conform to the valleys of the cerebral cortex. The meninges help form the spaces through which cerebrospinal fluid travels.
These cells make myelin. Myelin is a protein that surrounds the nerve "wires" to insulate them. This insulation allows the signal to travel a long way (sometimes several feet). The myelin surrounds and insulates axons that are present in cranial nerves (including the vestibular or acoustic nerve), and other nerves of the body that are outside of the central nervous system.
The choroid plexus is located within the ventricles. The ventricles are cavities in the brain that hold spinal fluid. The choroid plexus makes spinal fluid at the rate of approximately 0.6 cc (ml) per minute.
The pituitary is a gland at the base of the brain. It is located within the "sella turcica" that resides between and behind the eyes. The pituitary gland lies just below the optic nerves and optic chiasm. The pituitary gland makes hormones to stimulate other organs, prolactin, growth hormone, thyroid stimulating hormone (TSH) and others.
The pineal gland is located between the two cerebral hemispheres just above the brainstem and just behind the thalamus. The pineal gland makes melatonin, a hormone that responds to changes in light. The normal pineal gland can "enhance" brightly on the MRI because of absence of the "blood-brain-barrier."
A brain tumor is a space-occupying mass or volume that arises within the brain. Each year more than 17,000 people in the United States have a brain tumor. The American Cancer Society estimates that 17,200 malignant brain tumors or spinal cord tumors (9,800 in men and 7,400 in women) will be diagnosed during 2001 in the United States. Approximately 13,100 people (7,200 men and 5,900 women) will die from these malignant brain tumors or spinal cord tumors. Brain tumors and spinal cord tumors account for approximately 1.4% of all cancers and 2.4% of all cancer-related deaths. Both adults and children are included in these statistics.
The most important distinction for a brain tumor is whether it is benign or malignant. The brain tumors can be "benign" (slowly growing and usually "pushing" on the surrounding normal brain) or "malignant" (rapidly growing and usually invading normal brain).
The benign brain tumors are usually slowly growing, have a fibrous covering (encapsulation), do not usually invade the brain, can often be totally removed by surgery. The benign brain tumors include the meningiomas, acoustic neuromas, pituitary gland tumors, craniopharyngiomas, germinomas, pinealomas, hemangioblastomas and other benign benign brain tumors. Because of the location, however, a benign brain tumor may or may not be able to have complete surgical removal. This means that even a benign brain tumor can be a serious problem if it is in a location that prevents treatment. The location of the brain tumor often determines if surgery can safely remove all of the brain tumor. If a brain tumor is deep in the brain, surgery may not be able to safely remove the tumor in all cases. An example is the "petroclival" or "clival" meningioma that is located at the base of the skull. Many normal cranial nerves may travel through this location, rendering safe removal impossible.
The malignant brain tumors are more rapidly growing, usually lack a covering (no encapsulation), usually invade the brain (have "tentacles" that reach into normal brain) and often cannot be entirely removed surgically. The malignant brain tumors include the glioblastomas, anaplastic astrocytomas, gliosarcomas, malignant meningiomas, chordomas, pineoblastomas, medulloblastomas, primary CNS lymphomas, brain metastases and other malignant brain tumors.
The brain tumors can arise inside the nervous tissue of the brain ("intra-axial" see below) or within the covering of the brain (dura mater or meninges) ("extra-axial but intra-dural"). One implication for this classification is that surgery for intra-axial brain tumors may involve entering and traversing normal brain to reach the brain tumor. For the extra-axial tumors, entry into the brain may not be required to remove the brain tumor. Rather, the brain may be retracted to expose the extra-axial tumor for removal.
The intra-axial brain tumors are tumors that grow within the brain tissue itself. These brain tumors usually arise from the astrocytes, neurons or glia (most often the glia). These brain tumors include the glioblastoma multiforme, anaplastic astrocytoma, fibrillary astrocytoma and pilocytic astrocytoma. Other intrinsic brain tumors include the a hemangioblastoma, choroid plexus adenoma, pineal region tumors and others. One intrinsic brain tumor starts outside of the brain and spreads to the brain. This brain tumor is the brain metastasis, usually arising from lung, breast or colon tumors.
The extra-axial tumors include the tumors of the covering of the brain and include the acoustic neuromas, meningiomas, atypical meningiomas, malignant meingiomas, pituitary tumors (non-secreting, Cushing's disease, growth hormone-secreting, prolactin-secreting) chordomas, chondrosarcomas, and others.
Brain tumors can arise from the uncontrolled division of cells that normally occupy the brain ("intrinsic" or "primary" brain tumors such as the gliomas, for example, that arise from the normal "glial" cells that are present in the brain) or they can arise from growth of cells that arise elsewhere in the body but travel to the brain ("metastatic" or "secondary" that arise from lung carcinoma, for example).
Rare brain tumors can run in families. Neurofibromatosis type 2 is an inherited condition associated with schwannomas of both acoustic (hearing) nerves and in some patients, multiple meningiomas, or spinal cord ependymomas. Patients with tuberous sclerosis may have noninfiltrating subependymal giant cell astrocytomas in addition to benign tumors of the skin, heart, or kidneys. Von Hippel-Lindau disease is associated with hemangioblastomas (blood vessel tumors) of the cerebellum or retina as well as renal cell (kidney) carcinomas.
Brain tumors cause "symptoms" by pressing on, or invading normal brain. These symptoms can result from increased pressure on the brain or destruction of normal nervous tissue. Symptoms can include headache (usually worse in the morning), nausea, vomiting, seizure, and weakness or numbness in the arms and/or legs. Headache is a common symptom of brain tumor, occurring in about 50% of patients. None of these symptoms are specific for brain tumors and they all can be caused by other medical problems. Less than 1% of headaches are caused by brain tumors. Approximately 10% of new seizures in adults are caused by brain tumors.
A "sign" is a finding on the neurological examination by a physician. For the brain tumors, common signs include diminished mental function (inability to concentrate, recall objects or dates, perform arithmetic), increased intracranial pressure ("papilledema" or swelling of the optic nerve head on "funduscopic" examination), weakness, numbness, change in "tone" of the muscles, change in the "reflexes,"loss of co-ordination in the arms or legs, and changes in vision including double vision, blurred vision or "photophobia" (bright lights cause headache). The "signs" on physical examination can help localize the brain tumor and complement the radiographic (MRI) examination.
The treatments of brain tumors depend upon the location in the brain, the size, the number, the presumed type (if surgery has not been performed) and both the severity and the speed of change of the symptoms. For example, for the patient having rapid loss of neurological function and having an MRI that shows a large mass in the brain, surgery has the best chance of restoring normal function. If the tumor is associated with slow progression of symptoms and the MRI shows the tumor is small and deep in the brain, then stereotactic biopsy and non-invasive treatment or non-invasive treatment without biopsy may be indicated (warranted).
Some brain tumors can be observed for months or even years if growth is minimal and symptoms are mild or absent (example: acoustic neuroma and meningioma). For some tumors, growth can be very rapid and the patient has to have treatment right away. These include glioblastomas, anaplastic astrocytomas and brain metastases.
The MRI stands for "Magnetic Resonance Imaging." The patient lies down inside a narrow tube. The tube has a magnetic field. The images are created from "echoes" of the radiofrequency energy that is applied to the brain. The "echoes" are tranformed into images of the brain tumor.
The MRI is very sensitive. The MRI can show very small brain tumors, and can show the effects of brain tumors on the surrounding normal brain. The "gadolinium" is the "contrast" agent that is injected for the second part of the scan. This allows the brain tumor to be even more visible because the "contrast" may leak from the blood vessels into the brain tumor moreso than for the normal brain.
The MRI can often tell what type of brain tumor is in the brain. However, the biopsy or surgery is often needed to make the final "pathologic" diagnosis (examination of the tissue under the microscope).
The name of the brain tumor is derived from the cell of origin. Hence, a glioma is derived from "glial" cells (cells that provide support and nourishment for the neurons of the brain). The meningioma is derived from the "meningeal" cells (lining cells on the outside surface of the brain, the pituitary adenoma is derived from the pituitary cells, the chordoma is derived from notochord cells, and the pinealoma is derived from the pineal cells.
For many tumors the suffix "-oma" simply means "mass" or "space occupying mass."
COMMON BRAIN TUMORS IN ADULTS WITH PERCENTAGE INCIDENCE BY CATEGORY
The meningiomas arise from the "leptomeninges" (lining cells on the outer surface of the brain) or from the "dura mater" (fibrous covering of the brain). The dura is composed of two layers, an outer periosteal (next to bone) layer and an inner layer of dural "border cells." It is widely accepted that the meningiomas arise from the arachnoid "cap cells" and may therefore arise anywhere these cells are located, particularly near the "arachnoid villi" (cells near superior sagittal sinus (large vein at top of brain)).
The meningiomas may be benign or malignant, or in between (atypical). The majority of meningiomas are benign. The benign meningiomas have many histologic subtypes. These include fibrous, transitional, angiomatous and syncytial meningiomas; many other subtypes of meningioma have been described as well. For these subtypes of the benign meningiomas there is no difference in recurrence rates or success of treatments for surgery or radiotherapy.
The diagnosis of meningioma is made by both the neurological examination and the MRI. The meningiomas brightly enhance (take up gadolinium) and are easily discerned on the MRI.
Parasagittal meningiomas arise from arachnoid villi of the superior sagittal sinus. Parasagittal meningiomas grow laterally and downward, displacing but not invading the brain. Forty to 50 per cent of parasagittal meningiomas invade the sinus and 25 per cent are bilateral. The clinical presentation depends on the location. For the frontal location, headache may be present for years, followed by slowly progressive personality change or dementia, apathy, flattened affect and occasionally difficulty walking (ataxia) and urinary incontinence. Seizures can be seen in 25 to 50 per cent of patients having parasagittal meningiomas. The parasagittal meningiomas can become large before diagnosis.
The most common locations for the convexity meningiomas are just off the midline under the curved portion of the skull. The clinical presentation depends on the location: personality change and dementia for frontal meningiomas, sensory seizures or "receptive" aphasia (can speak, but cannot understand words) for parietal meningiomas.
The sphenoid meningiomas are clinoidal, alar and pterional (inner, middle and outer) and each has a different presentation. The inner or medial sphenoid wing meningioma can present with visual loss over several years and optic atrophy on examination. There may be unilateral eye pain.
Olfactory groove meningiomas arise over the "lamina cribrosa" of the "ethmoid bone," approximately 2 cm in front of the pituitary gland. The clinical presentation can be subtle and include anosmia (can't smell), euphoria or inability to concentrate. Seizures can occur in approximately 30 per cent of patients.
Tuberculum Sellae (Suprasellar)
These meningiomas arise from the meninges of the anterior clinoid or tuberculum sellae about 1 cm posterior to the olfactory meningiomas. They can push on the optic chiasm and result in loss of vision.
Cerebellopontine angle meningiomas are 30 to 50 per cent of all posterior fossa meningiomas and can arise anywhere on the posterior surface of the petrous bone. The majority of cerebellopontine meningiomas arise in front of the internal auditory canal. The major symptoms of cerebellopontine angle meningiomas are hearing loss, vertigo, tinnitus (ringing), facial numbness and pain, and headache.
Patients with cavernous sinus meningiomas can complain of pain behind the eye. Patients may develop protrusion of the eye or loss of visual acuity. There can be impairment of the cranial nerves that allow movement of the eye, resulting in double vision.
The primary treatment is surgery for meningiomas that are superficial (near surface of the brain) or radiosurgery for tumors that are difficult to reach (e.g. cavernous sinus) without high risk to the patient. The decision to operate on the meningioma depends upon the nature, magnitude and pace of the symptoms, as well as the size and location of the meningioma. Surgery alone can result in cure or prolonged "disease-free" survival. If the tumor is not completely removed, however, the likelihood of recurrence of the meningioma is high. For such cases postoperative radiotherapy or radiosurgery may be recommended. Fractionation of the radiosurgery for meningioma often results in higher sparing of the surrounding normal tissues.
The acoustic neuroma is a benign tumor of the "vestibular" nerve and is formed by the "Schwann" cells of the vestibular nerve. It is often (and some say should be) called a "vestibular schwannoma."
Acoustic neuromas are the most common tumors of the "cerebellopontine angle" (lateral cerebellar region). Most acoustic neuromas occur unilaterally in a nonhereditary fashion. Bilateral acoustic neuromas are hereditary, associated with neurofibromatosis type II, and account for less than 5 per cent of these tumors.
Rate of Growth
The growth rate of the acoustic neuromas is variable, and can range from 2 to 10 millimeters per year.
In more than 70% of patients having acoustic neuroma, hearing loss is the first symptom. In most patients the loss of hearing is gradual. Sometimes the hearing loss can be abrupt, or can even fluctuate. Other symptoms include:
Difficulty understanding words (loss of speech discrimination)
In patients with large acoustic neuromas additional symptoms may be double vision (due to pressure on the cranial nerves above the tumor), hoarseness or difficulty swallowing, facial pain or numbness, or ataxia (difficulty walking due to imbalance).
Hearing loss is present in the majority of patients who first seek medical attention for the acoustic neuromas. When pure tone audiometry is tested, the most common pattern is a high-frequency hearing loss.
The treatment for acoustic neuroma is surgery or radiosurgery. Surgery for acoustic neuroma is immediate but may have higher risk to the facial nerve. Radiosurgery is non-invasive but takes longer to work. The risk to the facial nerve is higher for single "shot" radiosurgery (gamma knife) but the Fractionated stereotactic radiosurgery (FSR) offers sparing of the facial nerve and preservation of facial strength.
The "gliomas" or "astrocytomas" comprise a spectrum of "glial" or "astrocytic" tumors. They range from the benign "pilocytic" or low grade "fibrillary" gliomas to the "anaplastic" astrocytomas to the most aggressive "glioblastoma multiforme."
Headache, nausea, emesis (vomiting), seizure, weakness of arm and/or leg are common symptoms. The MRI findings are suggestive of the diagnosis. Frequently surgery or biopsy ("open" biopsy via craniotomy or "stereotactic" biopsy are necessary to confirm the diagnosis.
For low grade gliomas, surgery alone or followed by radiotherapy is indicated (recommended). For the anaplastic astrocytoma and glioblastoma, the surgery, postoperative radiotherapy with or without chemotherapy may be recommended.
Pituitary Adenomas arise from the cells of the pituitary gland and can include the prolactin producing cells, the ACTH producing cells, the growth hormone producing cells, and others. Frequently the cells that form the tumor do not make any hormone (nonfunctional pituitary adenoma).
Hormonal overproduction due to functional cells in the tumor is common. The most common functional pituitary tumor is the prolactinoma. Visual change due to pressure on the optic nerve is possible. Frequently the pituitary tumors result in "bitemporal hemianopsia" (loss of peripheral vision on both sides).
The primary treatment is surgery. In some cases radiotherapy or radiosurgery may be the initial treatment. For recurrences the radiation or radiosurgery are useful options.
The brain metastasis is a brain tumor that starts somewhere else in the body but travels to the brain by the bloodstream and starts growing. The most common brain metastases are from tumors of the lung, breast, skin (melanoma) and colon. There are several "prognostic" (foretelling) features of brain metastases including age, "performance status" of the patient (able to care for one's self), control of the primary (tumor outside of the brain) and whether there is spread of the primary tumor to organs outside the brain.
Headache, nausea, emesis, seizure and weakness can occur. The MRI findings can be very characteristic of the brain metastases. These tumors can be single (solitary) or multiple.
The recommended treatment may depend upon symptoms (severity, speed of onset), size of the metastases, and the number of the metastases. Other factors include how sick the patient is. If the patient is well and the tumor is solitary, either surgery or radiosurgery may be given. Postoperative regular radiation may be given as well. If the tumors are multiple and the patient is not doing well, regular radiation may be given with a radiosurgical "boost."