A brain tumor (or brain tumour) is an intracranial solid neoplasm, a tumor (defined as an abnormal growth of cells) within the brain or the central spinal canal.
Brain tumors include all tumors inside the cranium or in the central spinal canal. They are created by an abnormal and uncontrolled cell division, normally either in the brain itself (neurons, glial cells (astrocytes, oligodendrocytes, ependymal cells, myelin-producing Schwann cells), lymphatic tissue, blood vessels), in the cranial nerves, in the brain envelopes (meninges), skull, pituitary and pineal gland, or spread from cancers primarily located in other organs (metastatic tumors).
Any brain tumor is inherently serious and life-threatening because of its invasive and infiltrative character in the limited space of the intracranial cavity. However, brain tumors (even malignant ones) are not invariably fatal. Brain tumors or intracranial neoplasms can be cancerous (malignant) or non-cancerous (benign); however, the definitions of malignant or benign neoplasms differs from those commonly used in other types of cancerous or non-cancerous neoplasms in the body. Its threat level depends on the combination of factors like the type of tumor, its location, its size and its state of development. Because the brain is well protected by the skull, the early detection of a brain tumor only occurs when diagnostic tools are directed at the intracranial cavity. Usually detection occurs in advanced stages when the presence of the tumor has caused unexplained symptoms.
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.
The prognosis of brain cancer varies based on the type of cancer. Medulloblastoma has a good prognosis with chemotherapy, radiotherapy, and surgical resection while glioblastoma multiforme has a median survival of only 12 months even with aggressive chemoradiotherapy and surgery. Brainstem gliomas have the poorest prognosis of any form of brain cancer, with most patients dying within one year, even with therapy that typically consists of radiation to the tumor along with corticosteroids. However, one type of brainstem glioma, a focal seems open to exceptional prognosis and long-term survival has frequently been reported.
Tumors have characteristics that allow pathologists to determine how dangerous a tumor is/was for the patient, how it will evolve and it will allow the medical team to determine the management plan for the patient.
Anaplasia: or dedifferentiation; loss of differentiation of cells and of their orientation to one another and blood vessels, a characteristic of anaplastic tumor tissue. Anaplastic cells have lost total control of their normal functions and many have deteriorated cell structures. Anaplastic cells often have abnormally high nuclear-to-cytoplasmic ratios, and many are multinucleated. Additionally, the nuclei of anaplastic cells are usually unnaturally shaped or oversized nuclei. Cells can become anaplastic in two ways: neoplastic tumor cells can dedifferentiate to become anaplasias (the dedifferentiation causes the cells to lose all of their normal structure/function), or cancer stem cells can increase in their capacity to multiply (i.e., uncontrollable growth due to failure of differentiation).
Atypia: is an indication of abnormality of a cell (which may be indicative for malignancy). Significance of the abnormality is highly dependent on context.
Neoplasia: is the (uncontrolled) division of cells; as such neoplasia is not problematic but its consequences are: the uncontrolled division of cells means that the mass of a neoplasm increases in size, and in a confined space such as the intracranial cavity this quickly becomes problematic because the mass invades the space of the brain pushing it aside, leading to compression of the brain tissue and increased intracranial pressure and destruction of brain parenchyma. Increased Intracranial pressure (ICP) may be attributable to the direct mass effect of the tumor, increased blood volume, or increased cerebrospinal fluid (CSF) volume may in turn have secondary symptoms
Necrosis: is the (premature) death of cells, caused by external factors such as infection, toxin or trauma. Necrotic cells send the wrong chemical signals which prevents phagocytes from disposing of the dead cells, leading to a build up of dead tissue, cell debris and toxins at or near the site of the necrotic cells.
Arterial and venous hypoxia, or the deprivation of adequate oxygen supply to certain areas of the brain, occurs when a tumor makes use of nearby blood vessels for its supply of blood and the neoplasm enters into competition for nutrients with the surrounding brain tissue.
More generally a neoplasm may cause release of metabolic end products (e.g., free radicals, altered electrolytes, neurotransmitters), and release and recruitment of cellular mediators (e.g., cytokines) that disrupt normal parenchymal function.
The visibility of signs and symptoms of brain tumors mainly depends on two factors: tumor size (volume) and tumor location. The moment that symptoms will become apparent, either to the person or people around him (symptom onset) is an important milestone in the course of the diagnosis and treatment of the tumor. The symptom onset - in the timeline of the development of the neoplasm - depends in many cases on the nature of the tumor but in many cases is also related to the change of the neoplasm from "benign" (i.e. slow-growing/late symptom onset) to more malignant (fast growing/early symptom onset).
Symptoms of solid neoplasms of the brain (primary brain tumors and secondary tumors alike) can be divided in 3 main categories :
- Consequences of intracranial hypertension : The symptoms that often occur first are those that are the consequences of increased intracranial pressure: 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 eye examination). However, even small tumors obstructing the passage of cerebrospinal fluid (CSF) may cause early signs of increased intracranial pressure. Increased intracranial pressure 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 very young children, elevated intracranial pressure may cause an increase in the diameter of the skull and bulging of the fontanelles.
- Dysfunction : 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 (including impaired judgment, memory loss, lack of recognition, spatial orientation disorders), personality or emotional changes, hemiparesis, hypoesthesia, aphasia, ataxia, visual field impairment, impaired sense of smell, impaired hearing, facial paralysis, double vision, dizziness, but more severe symptoms might occur too such as: paralysis on one side of the body hemiplegia or impairment to swallow . 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.
- Irritation : abnormal fatigue, weariness, absences and tremors, but also epileptic seizures.
The above symptoms are true for ALL types of neoplasm of the brain (including secondary tumors). It is common that a person carry a primary benign neoplasm for several years and have no visible symptoms at all. Many present some vague and intermittent symptoms like headaches and occasional vomiting or weariness, which can be easily mistaken for gastritis or gastroenteritis. It might seem strange that despite having a mass in his skull exercising pressure on the brain the patient feels no pain, but as anyone who has suffered a concussion can attest, pain is felt on the outside of the skull and not in the brain itself. The brain has no nerve sensors in the meninges (outer surface) with which to feel or transmit pain to the brain's pain center; it cannot signal pain without a sensory input. That is why secondary symptoms like those described above should alert doctors to the possible diagnosis of a neoplasm of the brain.
Although there is no specific or singular clinical symptom or sign for any brain tumors, the presence of a combination of symptoms and the lack of corresponding clinical indications of infections or other causes can be an indicator to redirect diagnostic investigation towards the possibility of an intracranial neoplasm.
The diagnosis will often start with an interrogation of the patient to get a clear view of his medical antecedents, and his current symptoms. Clinical and laboratory investigations will serve to exclude infections as the cause of the symptoms. Examinations in this stage may include ophtamological, otolaryngological (or ENT) and/or electrophysiological exams. The use of electroencephalography (EEG) often plays a role in the diagnosis of brain tumors.
Swelling, or obstruction of the passage of cerebrospinal fluid (CSF) from the brain may cause (early) signs of increased intracranial pressure which translates clinically into headaches, vomiting, or an altered state of consciousness, and in children changes to the diameter of the skull and bulging of the fontanelles. More complex symptoms such as endocrine dysfunctions should alarm doctors not to exclude brain tumors.
A bilateral temporal visual field defect (due to compression of the optic chiasm) or dilatation of the pupil, and the occurrence of either slowly evolving or the sudden onset of focal neurologic symptoms, such as cognitive and behavioral impairment (including impaired judgment, memory loss, lack of recognition, spatial orientation disorders), personality or emotional changes, hemiparesis, hypoesthesia, aphasia, ataxia, visual field impairment, impaired sense of smell, impaired hearing, facial paralysis, double vision, or more severe symptoms such as tremors, paralysis on one side of the body hemiplegia, or (epileptic) seizures in a patient with a negative history for epilepsy, should raise the possibility of a brain tumor.
The goal of radiation therapy is to selectively kill tumor cells while leaving normal brain tissue unharmed. In standard external beam radiation therapy, multiple treatments of standard-dose "fractions" of radiation are applied to the brain. This process is repeated for a total of 10 to 30 treatments, depending on the type of tumor. This additional treatment provides some patients with improved outcomes and longer survival rates.
Radiosurgery is a treatment method that uses computerized calculations to focus radiation at the site of the tumor while minimizing the radiation dose to the surrounding brain. Radiosurgery may be an adjunct to other treatments, or it may represent the primary treatment technique for some tumors.
Radiotherapy may be used following, or in some cases in place of, resection of the tumor. Forms of radiotherapy used for brain cancer include external beam radiation therapy, brachytherapy, and in more difficult cases, stereotactic radiosurgery, such as Gamma knife, Cyberknife or Novalis Tx radiosurgery.
Radiotherapy is the most common treatment for secondary brain tumors. The amount of radiotherapy depends on the size of the area of the brain affected by cancer. Conventional external beam 'whole brain radiotherapy treatment' (WBRT) or 'whole brain irradiation' may be suggested if there is a risk that other secondary tumors will develop in the future. Stereotactic radiotherapy is usually recommended in cases involving fewer than three small secondary brain tumors.
Occurrence of Brain Tumors
The incidence of low-grade astrocytoma has not been shown to vary significantly with nationality. However, studies examining the incidence of malignant CNS tumors have shown some variation with national origin. Since some of these high-grade lesions arise from low-grade tumors, these trends are worth mentioning. Specifically, the incidence of CNS tumors in the United States, Israel, and the Nordic countries is relatively high, while Japan and Asian countries have a lower incidence. These differences probably reflect some biological differences as well as differences in pathologic diagnosis and reporting.
Worldwide data on incidence of cancer can be found at the WHO (world health organisation) and is handled by the AIRC (Agency for Interanctional Research on Cancer) located in France.
Figures for incidences of cancers of the brain show a significant difference between more and less developed countries (i.e. the lesser developed countries have less incidences of tumors of the brain) this could be explained by undiagnosed tumor-related deaths (patient in extreme poor situations don't get diagnosed simply because they don't have access to the modern diagnostic facilities required to diagnose a brain tumor) and by deaths caused by other poverty related causes that preempt a patients life before tumors develop or tumors become life threatening. Nevertheless studies have been made that certain forms of primary brain tumors are more prevalent among certain groups of the population.
