Brain herniation – causes, symptoms, diagnosis, treatment, pathology

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of pharmacology and clinical reasoning topics. Try it free today. Brain herniation is what it’s called when
some some brain tissue moves outside of the skull, or moves across or into a structure
with the skull. Brain herniation typically happens in response
to increased intracranial pressure, which refers to a high pressure within the skull. An intracranial pressure above 15 mmHg is
considered high. OK – let’s start with some basic brain anatomy. The brain has a few regions – the most obvious
is the cerebrum, which is divided into two cerebral hemispheres, each of which has a
cortex – an outer region – divided into four lobes including the frontal lobe, parietal
lobe, temporal lobe, and the occipital lobe. There are also a number of additional structures
– including the cerebellum, which is down below, as well as the brainstem which connects
to the spinal cord. Now zooming in, the brain and spinal cord
is covered by the meninges, which are three protective layers of the brain. The inner layer of the meninges is the pia
mater, the middle layer is the arachnoid mater, and the outer layer is the dura mater. These first two, the pia and arachnoid maters,
form the subarachnoid space, which houses the cerebrospinal fluid, or CSF. CSF is a clear, watery liquid which is pumped
around the spinal cord and brain, cushioning them from impact and bathing them in nutrients. The outer membrane is the dura mater, which
forms the meningeal folds, such as falx cerebri and tentorium. The falx cerebri is a meningeal fold that
goes down into the longitudinal fissure that separates the hemispheres of the brain. The free edge of the falx cerebri is in close
contact with the central part of the brain called corpus callosum, which connects the
left and right hemisphere. There’s also the tentorium which is a meningeal
fold located in the back of our skull, that separates the cerebrum from the cerebellum. The free edge of the tentorium is in close
contact with the brainstem, which is the region that connects the brain and the spinal cord. The skull has a set volume and the pressure
inside of the skull is kept relatively constant. In other words, the sum of the volumes of
the brain, cerebrospinal fluid, and intracranial venous and arterial blood is always about
the same. So, if there’s an increase in the volume
of any one of these three, there’s a compensatory decrease in the other two. For example, when a high-speeded golf ball
hits you in the head, an artery could rupture within the skull. As the artery bleeds, the blood starts to
pool, it leads to what’s called a mass effect within the skull, and that mass effect increases
the intracranial pressure. To help reduce the volume and pressure back
to normal, there’s less CSF production and more CSF reabsorption. Over time, if the arterial bleed continues,
then it might overwhelm the bodies ability to compensate, and the intracranial pressure
starts to get quite high, and that can lead to brain herniation. So brain herniation can be caused by either
a focal mass effect, like the arterial bleed, or a diffuse mass effect – depending on whether
the problem is in one area or involves the entire brain. In addition to intracranial bleeds, other
causes of focal mass effects are tumors and abscesses. All of these focal masses also create surrounding
inflammation which causes local edema, and that makes the focal mass even larger. Diffuse mass effects are caused by generalized
cerebral edema, which is an excessive buildup of fluid throughout the brain tissue. There’s cytogenic edema which is when there’s
fluid build up within the cells of the brain, due to a retention of sodium and water, and
there’s also vasogenic edema, which is when fluid builds up right outside of the cells,
in the interstitial space. Some causes of cerebral edema are an large
ischemic strokes and meningitis. Depending on the size and location of the
mass effect, there’s a possibility of brain herniations – and it can either be supratentorial
and infratentorial herniation. Supratentorial herniation refers to displacement
of the cerebrum which is above the tentorium, and infratentorial herniation refers to herniation
of the cerebellum which is below the tentorium. Alright, so supratentorial herniations include
four types of displacement and these differ by the exact part of the cerebrum that is
affected. The first type of supratentorial herniation
is uncal herniation, also referred to as transtentorial herniation. In this herniation, the innermost part of
the temporal lobe, called uncus, slips down towards the tentorium and puts pressure on
the brainstem. The uncus can squeeze the oculomotor nerve
resulting in an oculomotor nerve palsy. In oculomotor nerve palsy the eyeball is in
a “down and out” position due to a loss of innervation of muscles controlled by the
nerve. Also, the affected pupil becomes dilated and
fails to constrict in response to light. The posterior cerebral artery can also be
compressed, which results in ischemic stroke of the occipital part of the brain, which
is responsible for processing of visual information. This leads to homonymous hemianopia, which
is a loss of vision in either the left or right halves of the visual fields of both
eyes. The vision is lost in halves that are contralateral
to the posterior cerebral artery that is affected. Although there is a partial loss of vision,
macular function is spared, meaning that central vision is still sharp and detailed. This is because the part of the occipital
lobe in charge of the macula is gets blood from both the posterior cerebral artery as
well as the medial cerebral artery. Uncal herniation stretches and sometimes breaks
branches of the paramedian basilar artery which nourish the brain stem. That causes small linear or flame-shaped hemorrhages
called Duret hemorrhages which can be seen on autopsy. So, let’s say there’s a focal mass effect
on the right side of the skull, which increases intracranial pressure and squeezes the uncus
down onto the brainstem. Now the uncus isn’t only directly compressing
the right side of the brainstem, but indirectly, it’s also pushing the left side of the brainstem
against the free edge of the tentorium forming what’s called a kernohan’s notch. The compressed part of the brainstem is called
the left cerebral peduncle and it’s rich in motor fibers that travel from the cortex
on the left side of your brain to muscles on the right side of your body. Eventually, this injury of the left cerebral
peduncle will result in weakness on the same side of the body as the side of the focal
mass effect, also called ipsilateral weakness. Now, normally damage to brain tissue results
in weakness on the contralateral side, so the Kernohan’s notch causes a false localizing
sign. The second type of supratentorial herniation
is central herniation, and it’s when the diencephalon and parts of the temporal lobes
slip under the free edge of the tentorium. The diencephalon is a part of the brain that
processes sensory information and emotions, as well as regulates hormone production – so
all of these processes can be affected. Central herniation can also cause dilated
and fixed pupils and paralysis of upward eye movement, which leads to the sunset eyes sign. That’s where the eyeballs are in a downward
position, and part of the lower pupil is covered by the lower eyelid. Just like in uncal herniation, duret hemorrhages
can be seen in central herniation. The third type of supratentorial herniation
is cingulate or subfalcine herniation. In this herniation, the innermost part of
the frontal lobe, called the cingulate gyrus, gets squeezed below the free edge of the falx
cerebri to the opposite side of the skull. The displaced part of the brain can compress
the anterior cerebral artery and that can cause an ischemic stroke. Finally, a cingulate herniation is often a
forerunner of other types of supratentorial herniation. The fourth type of supratentorial herniation
is transcalvarial herniation, which is also called an external herniation. In this herniation the brain squeezes out
of the skull through a fracture or surgical site during an operation. Now, the other category of herniations are
infratentorial herniations. There are two types – upward herniation and
tonsillar herniation. In upward herniation there’s a displacement
of the cerebellum upward, through a notch in the tentorium cerebelli. In tonsillar herniation, parts of the cerebellum,
called cerebellar tonsils slip down through an opening in the skull called the foramen
magnum. This is particularly dangerous because the
displaced cerebellum can push onto the brainstem and affect neurons responsible for breathing
and cardiac function. The most common signs of the tonsillar herniation
are headache and neck stiffness. The level of consciousness may also decrease
and give rise to flaccid paralysis where there’s reduced muscle tone. On a physical exam, increased intracranial
pressure should be suspected in individuals with a decreased level of consciousness, focal
neurological signs, and papilledema. Papilledema is the swelling of the optic disc,
which is the point where the optic nerve fibers leave the retina. Also, these individuals may have increased
blood pressure, irregular breathing, and bradycardia. These signs are referred to as a Cushing’s
triad and they represent a physiological response of the central nervous system to increased
intracranial pressure. Lumbar puncture is classified as a relative
contraindication in individuals with suspected increased intracranial pressure due to possible
herniations. In order to confirm the presence of a mass
effect that may be causing increased intracranial pressure, medical imaging such as CT or MRI
can be used. If CT and MRI fails to prove any mass lesions
within the skull, lumbar puncture can be performed. Once the needle is inserted into the spinal
canal, it’s attached to a manometer, which is a device that measures the CSF pressure. Normal opening pressure on lumbar puncture
is 100-180 mm of H2O or 8-15 mmHg, above that is considered increased intracranial pressure Treatment of increased intracranial pressure
and brain herniation is aimed at reducing the pressure within the skull. It may include the treatment of the underlying
cause, such as surgical removal of a tumor, abscess, or hematoma. Furthermore, it may include external ventricular
drain, which requires a placement of a drain through a hole in the skull to get rid of
excessive cerebrospinal fluid or decompressive craniectomy, which is where a part of the
skull is removed to help relieve the pressure. Another way of treating increased intracranial
pressure includes using osmotic therapy, such as mannitol, which helps remove excess water
from the body. All right, as a quick recap. Brain herniation typically results from increased
intracranial pressure. There are two main classes of herniation:
supratentorial, which refers to a displacement of the cerebrum, and infratentorial, which
refers to a herniation of the cerebellum. Furthermore, supratentorial herniations are
subdivided into four types: uncal herniation, also referred to as transtentorial herniation
which affects the innermost part of the temporal lobe – the uncus, central herniation, which
affects the diencephalon and parts of the temporal lobes; cingulate or subfalcine herniation,
which affects the cingulate gyrus; and transcalvarial herniation, which occurs when the brain squeezes
out of the skull. On the other hand, infratentorial herniations
are subdivided into upward herniation and tonsillar herniation. In upward herniation, there’s a displacement
of the cerebellum upward, through a notch in the tentorium cerebelli, while in tonsillar
herniation, parts of the cerebellum slip down through an opening in the skull called the
foramen magnum. Diagnosis is done by a CT or MRI imaging,
and treatment includes a decompressive craniectomy and osmotic therapy.


  1. Thank you so much ! Please also make a video pf Pott’s disease or tuberculosis of the spine thanks! ❤️

  2. Thanks!!! I love your videos. Next time I work in neuro surgical ICU, I'll have a better understanding of what's going on. Keep spreading free knowledge to the world.

  3. Osmosis u guys are really helping me out understand the concept behind all the disease conditions…instead of making me cram up stuff from textbooks..very nice ..thanks a lot
    Could u please add more videos in the ENT section..would be of immense help
    Thanks again

  4. Osmosis keep going up valiabule letreture.. Very good presentation.. Try as much as possible to make new videos.. Thanks

  5. I haven't found one bad osmosis video till this one. It is too much wordy and lacks pictorial description … now, slowly will osmosis begin to suck too ?? please dont let that happen ,,

  6. It's not clear as to how PCA is involved in uncal herniation.Uncus is situated anterolaterally of the Middle cranial fossa whereas PCA is situated away from it, branching off from basilar artery

  7. Can Uncal herniation occur positionally? Let’s say the patient sits or gets into a position that is less conducive to proper flow and csf is pooled due to slow absorbtion can herniation occur temporarily until csf flow is restored by positional change which is more inducive to csf flow?

  8. could you also do anatomy and physiology of the brain and anatomy and physiology of the central nervous systems or just all he nervous systems? 😂

  9. What is the survival rate of a brain herniation after a traumatic brain injury? (Such as Massive Subdermal Hemorrhage GCS 3)

  10. i do not believe that a pt would have flaccid paralysis in brain herniation as said in this video, as flaccidity is a lower motor neuron sign. rather, pts with a brain herniation, if corticospinal tracts were involved, would demonstrate increased tone/spasticity.

  11. I had this question in my exam and due to this explanation, I passed so well. Go Osmosis 💪🏽💪🏽❤️

  12. I have a brain herniation, I have chiari. This video helps me learn, and helps me explain to people what happens with me. Thank you!

  13. hey guys some help please.. first aid says theres early vs late uncal herniation. what does it mean? age maybe? or how much time after herniation?

  14. Med students here really helps. A fun way to remember old topics and to understand the bigger picture of the certain topics

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