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) do not automatically cause death. 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 side effects that cause 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.
Primary brain tumors
Primary neoplasms of the brain are tumors that originate in the intracranial sphere or the central spinal canal, based on the organic tissues that make up the brain and the spinal cord. From the brain-lemma we can learn a lot of things about the composition of the brain from different types of organic tissues. For the purpose of this article we will discuss only some types.
The brain itself is composed of neurons and glia (that function primarily as the physical support for neurons). The neuron itself is rarely the basis for a tumor, though tumors of the glial cells are glioma and often are of the cancerous type.
The brain is surrounded by a system of connective tissue membranes called meninges that separate the skull from the brain. Tumors of the meninges are meningioma and are often benign neoplasms.
Below the brain is pituitary and pineal gland which could be the basis for its own -albeit rare- kind of benign glandular neoplasms.
Secondary brain tumors
Secondary tumors of the brain are metastatic tumors that invaded the intracranial sphere from cancers primarily located in other organs. This means that a (malignant) cancerous neoplasm has developed in another organ elsewhere in the body and that cancer cells leak from that primary tumor. The leaked cells enter the lymphatic system and blood vessels, circulate through the bloodstream, and are deposited (stranded in the small blood vessels in the brain) within normal tissue elsewhere in the body, in this case in the brain. There these cells continue growing & dividing and become another invasive neoplasm of the primary cancers tissue. Secondary tumors of the brain are very common in the terminal phases of patients with an incurable metastased cancer , most common types of cancers that bring about secondary tumors of the brain are lung cancer, breast cancer and malignant melanoma (skin cancer), kidney cancer and cancer of the colon (in decreasing order of frequency).
Unfortunately enough this is the most common cause of neoplasms in the intracranial cavity.
The skull bone structure can also be subject to a neoplasm that by it very nature reduces the volume of the intracranial cavity, and can damage the brain.
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