Name: 小兒腦腫瘤--病因、症狀、診斷、治療、病理。 (Pediatric brain tumors - causes, symptoms, diagnosis, treatment, pathology)
Uploaded: 2021-01-14T08:12:24.000Z
Duration: 11 min 50 s
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Pediatric brain tumors are masses of abnormal
cells that generally occur in children, 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

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 it to the fourth

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
the spine.

So this makes it possible for cerebrospinal
fluid to also flow through the central canal

Now, focusing in on cells within the brain
- there are many different types with specialized

For example, neurons communicate neurologic
information through neurotransmitter regulated

Then there are cells that secrete hormones
into circulation and regulate the functions

These cells are found in glands, like the
supratentorial pineal gland which is located

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,

These include astrocytes which have cellular
processes coming off their cell body, giving

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.

Ependymal cells are also neuroglial cells,
and they're cuboidal-to-columnar - so square

to rectangular shaped - ciliated cells that
line the ventricles and central canal.

One of their main roles is to regulate the
circulation of cerebrospinal fluid.

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

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

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

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 for example an astrocytoma is

But their severity is classified, or graded
by the World Health Organization's (WHO)

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,

So let's start with tumor types that are
generally infratentorial tumors, because they

make up the majority of pediatric brain tumors.

Overall, the most common malignant tumor is
a medulloblastoma, which typically forms in

or around the cerebellum, adjacent to the
fourth ventricle.

Medulloblastomas originate from embryonic
stem cells and they tend to be extremely aggressive.

One relatively unique feature is that they
metastasize through the cerebrospinal fluid

in a process called drop metastasis where
the tumor spreads to the base of the spine.

Because of this, medulloblastomas are typically
only classified as grade IV.

Histologically, medulloblastomas often have
a feature called Homer-Wright rosettes, which

are dense tangles of neurons and neuroglial
cells, surrounded by ring-like structures

Now, while medulloblastoma may be the most
common malignant tumor, the most common primary

pediatric tumor is a type of astrocytoma called
a juvenile pilocytic astrocytoma.

Because astrocytes are found through the brain
and spinal cord, astrocytomas can form throughout

those locations, but juvenile pilocytic astrocytomas
are mostly infratentorial tumors in the cerebellum

And while astrocytomas can be graded I through
IV, juvenile pilocytic astrocytomas are only

grade I because they are generally benign
and slow-growing.

Histologically, they can have cysts, or sacs
filled with fluid; bodies of granular material;

and Rosenthal fibers, which are fibers that
clump together in the cytoplasm of the astrocyte

and look a bit like a worm or a corkscrew.

Among the fibers is the structural protein
glial fibrillary acidic protein that is typically

Finally, another common infratentorial tumor
is an ependymoma.

Now, again, they can form in the brain and
spinal cord because that's where ependymal

cells are found, but pediatric ependymomas
tend to form in the fourth ventricle.

Now, there are a few types of ependymomas
and they're WHO graded I through III.

In grade II, classic ependymomas, tumor cells
have a regular, round to oval nucleus.

Histologically, a prominent feature are their
perivascular pseudorosettes, which are ring-like

structures formed by tumors cells with rod-shaped
ependymal processes, like cilia, surrounding