Adult brain tumors are masses of abnormal cells
that generally occur in adults, and result from the uncontrolled growth of those cells
within the brain. OK – let’s start with some basic brain anatomy. First off, there’s the cerebral cortex which
is the part of the brain that’s supratentorial or above the tentorium, and the cerebellum,
which is infratentorial or below the tentorium. And the brain has four interconnected cavities
called ventricles, which are filled with cerebrospinal fluid – a fluid that helps provide buoyancy
and protection, as well as metabolic fuel for the brain. Highest up, are two C-shaped lateral ventricles
that lie deep in each cerebral hemisphere. The two lateral ventricles drain their cerebrospinal
fluid into the third ventricle, which is a narrow, funnel-shaped, cavity at the center
of the brain. The third ventricle makes a bit more cerebrospinal
fluid and then sends all of the cerebrospinal fluid to the fourth ventricle via the cerebral
aqueduct. The fourth ventricle is a tent-shaped cavity
located between the brainstem and the cerebellum. After the fourth ventricle, the cerebrospinal
fluid enters the subarachnoid space, which is the space between the arachnoid and pia
mater, two of the inner linings of the meninges which cover and protect both the brain and
spine. So this makes it possible for cerebrospinal
fluid to also flow through the central canal of the spine. Now, focusing in on cells within the brain
– there are many different types with specialized functions. For example, neurons communicate neurologic
information through neurotransmitter regulated electrical impulses. Then there are cells that secrete hormones
into circulation and regulate the functions of other cells throughout the body. These cells are found in glands, like the
supratentorial pineal gland which is located just behind the third ventricle. Or the infratentorial pituitary gland located
near the front of the third ventricle. There is also a category of cells called neuroglial
cells that help support brain homeostasis, and neuronal functions. These include astrocytes which have cellular
processes coming off their cell body, giving them a star-shaped appearance. Astrocytes are found throughout the brain
and spinal cord, and their main roles include maintaining the blood-brain barrier, providing
nourishment to neurons, and recycling neurotransmitters. Another type of glial cell is the oligodendrocyte,
which has a few cellular processes that look like branches. They are found mostly in the brain though
they are in the spinal cord too. These branches wrap themselves around neurons,
and produce a fatty substance made of lipoproteins called myelin, which helps transmit electrical
impulses along the axons. Some brain cells have a limited ability to
be replaced, especially during injury, and they do it by having undifferentiated stem
cells – called embryonic stem cells – in the brain activate and mature into a specialized
cell. Now, a tumor develops if there’s a DNA mutation
in any of these cell types that leads to uncontrolled cell division. Typically these are mutations in proto-oncogenes
which results in a promotion of cell division, or mutations in tumor suppressor genes which
results in a loss of inhibition of cell division. You can think of proto-oncogenes as the accelerator
or gas pedal and tumor suppressor genes as the brakes. Too much acceleration or an inability to brake
can lead to runaway cell division. As a result, the mutated cells can start piling
up on each other and can become a tumor mass. Some of these tumors are benign and stay well
contained or localized. But some become malignant tumors or cancers,
and these are the ones that break through their basement membrane and invade nearby
tissues. Malignant tumor cells can get into nearby
blood or lymph vessels, and travel from the primary site to establish a secondary site
of tumor growth somewhere else in the body – and that’s called metastasis. Brain tumors can be categorized by their primary
site location as either supratentorial, or infratentorial tumors – though some tumors
can form in either. They are typically named by the cell type
involved, so an astrocytoma is a tumor formed by mutated astrocytes. But their severity is classified, or graded
by the World Health Organization’s (WHO) scale. The scale goes from I to IV based on the morphologic
and functional features of the tumor cells; a grade IV tumor being the most abnormal looking
cells that also tend to be the most aggressive. But not all tumors have all four grades because
some tumors are basically always more benign, whereas others are more aggressive. So let’s start with tumor types that are
generally supratentorial tumors, because they make up the majority of adult brain tumors. A common one is a type of astrocytoma called
a glioblastoma. Because astrocytes are found through the brain
and spinal cord, astrocytomas can form in all of these locations, but glioblastomas
are mostly in the cerebral hemispheres. And while astrocytomas can be graded I through
IV, glioblastomas are only grade IV because they are highly malignant tumors. Because of their quick growth and invasion
of nearby tissues, glioblastomas tend to rapidly cross the corpus callosum. The corpus callosum is the midline structure
that separates the two cerebral hemispheres, that looks like a characteristic “butterfly”
on a cross-section of the brain. Cancer cells typically recruit blood vessels
to provide them nourishment in a process called angiogenesis, but glioblastomas proliferate
so fast that even with angiogenesis their nutrient demand outpaces the blood supply. As a result, because the blood supply serves
the peripheral tumor cells first, the tumor cells at the center of the tumor die first
because they’re the furthest from the blood cell network. Meanwhile the remaining viable tumor cells
collect along the edges of the necrotic regions. Histologically, it appears like the viable
cells are lining up like fence posts against the necrosis in the middle, producing a characteristic
pseudo-palisading pattern. Another common supratentorial tumor is a meningioma. Meningiomas come from cells found in the arachnoid
mater of the meninges, called arachnoid cap cells. They typically form in parasagittal regions
and on the surface of the brain just under the outermost layer of the meninges, the dura
mater. They are graded I through III and tend to
be relatively slow growing. Histologically, they form nests of cells or
a multinuclear syncytium of fused cells, which have an appearance like a wave in the ocean. These tumors may also cause the formation
of calcifications called psammoma bodies. Another common supratentorial tumor in adults
is the pituitary adenoma, which is formed in the pituitary gland by hormone secreting
cells of the anterior pituitary. There are several cell types in the anterior
pituitary that each secrete a tightly regulated level of a particular hormone; for example,
lactotroph cells secrete the hormone prolactin. Pituitary adenomas are typically benign so
they’re classified by the hormone that’s released as the tumor forms, and by the size
of the tumor; rather than using the standard WHO classifications. Histologically, the particular hormone secreting
cell that’s causing the pituitary adenoma will increase in number. Now, a relatively rare supratentorial tumor
is an oligodendroglioma. Because oligodendrocytes are found through
the brain and spinal cord, oligodendrogliomas can form in any of these locations, but adult
oligodendrogliomas typically form in the frontal lobes of the cerebral cortex because those
neurons are the most heavily myelinated. These tumors are categorized as grade II or
III, with an overall tendency to be relatively slow-growing tumors, though they still have
the ability to become malignant. Histologically, prominent features can vary
from fairly small, round nuclei, surrounded by well-defined “halos” or thick white
borders of cytoplasm giving them a “fried egg” appearance in grade II tumors; to having
a “chicken wired” pattern of nearby blood vessels with areas of calcifications in grade
III tumors. Ok, so, now let’s focus on an infratentorial
adult tumors, a hemangioblastoma. These tumors derive from cells with blood
vessel origins, so while they can develop anywhere in the brain they are most often
found in the cerebellum, especially in a middle-aged person.They are slow-growing tumors and are
typically grade I. Histologically, there are often thin-walled capillaries that are arranged
close to one another. Now, the most common symptoms of brain tumors
include headaches, nausea, vomiting, and seizures – and they are a result of the compression
and destruction of healthy brain tissue. In addition, it’s important to consider
the cell type that’s involved. So, for example, a pituitary adenoma causing
an increase in prolactin secretions may lead to amenorrhea in women and infertility in
men. In addition, as the tumor grows in size, it
can compress nearby cells and structures, interrupting their normal functions. For example, as meningiomas enlarge – the
mass of the tumor can compress nearby ventricles blocking the flow of cerebrospinal fluid,
causing swelling which results in hydrocephalus. Generally, the diagnosis of central nervous
system tumors includes medical imaging, like CT scans but more commonly MRIs. But definitive diagnosis needs to be made
based on the histologic and molecular characteristics of a tissue biopsy. Treatments depend on the tumor type, grade,
and symptoms. And can include surgical removal, radiotherapy,
or chemotherapy – frequently in a combination. But specific courses of treatment are guided
by the molecular characteristics of the tumor based on the biopsy. Finally, the chance of recurrence gets higher
in high grade tumors and in tumors that have not been fully removed or destroyed. Ok, quick recap: Adult brain tumors can be
infratentorial and supratentorial and form from a variety of cells. Tumor types are classified using WHO grading
based on morphologic and functional features. Tumor symptoms depend on tumor cell type,
size and location. Diagnosis includes medical imagining, with
a definitive diagnosis being made with a tissue biopsy. Treatments are largely dependent on the molecular
characteristics and tumor grade, and can incorporate surgical removal and a combination of radiotherapy and chemotherapy.

26 thoughts on “Adult brain tumors – causes, symptoms, diagnosis, treatment, pathology”

  1. A YouTube video? What a hell of a way to find out that I have a brain tumor. Better get a second opinion from WebMD. lol!

  2. Hello sir .. I am applying phd can you help me? about my topic thesis I want doing it about brain tumor detection in digital image processing thro matlab but I can't find new topic doesn't use and published before me

  3. Initially u showed pituitary as infratentorial and then described it in supratentorial. Pituitary adenoma is infra or supratentorial???

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