Brain herniation is a potentially deadly side effect of very high pressure within the skull that occurs when a part of the

brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...

is squeezed across structures within the

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

. The brain can shift across such structures as the falx cerebri, the

tentorium cerebelli The cerebellar tentorium or tentorium cerebelli ( Latin for "tent of the cerebellum") is an extension of the dura mater that separates the cerebellum from the inferior portion of the occipital lobes. Structure The cerebellar tentorium is an arc ...

, and even through the foramen magnum (the hole in the base of the skull through which the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...

connects with the brain). Herniation can be caused by a number of factors that cause a mass effect and increase

intracranial pressure Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury ( mmHg) and at rest, is normally 7–15 mmHg for a supine adul ...

(ICP): these include traumatic brain injury,

intracranial hemorrhage Intracranial hemorrhage (ICH), also known as intracranial bleed, is bleeding within the skull. Subtypes are intracerebral bleeds (intraventricular bleeds and intraparenchymal bleeds), subarachnoid bleeds, epidural bleeds, and subdural blee ...

, or

brain tumor A brain tumor occurs when abnormal cells form within the brain. There are two main types of tumors: malignant tumors and benign (non-cancerous) tumors. These can be further classified as primary tumors, which start within the brain, and seco ...

. Herniation can also occur in the absence of high ICP when

mass lesion In medicine, a mass effect is the effect of a growing mass that results in secondary pathological effects by pushing on or displacing surrounding tissue. In oncology, the mass typically refers to a tumor. For example, cancer of the thyroid glan ...

s such as

hematoma A hematoma, also spelled haematoma, or blood suffusion is a localized bleeding outside of blood vessels, due to either disease or trauma including injury or surgery and may involve blood continuing to seep from broken capillaries. A hematoma is ...

s occur at the borders of brain compartments. In such cases local pressure is increased at the place where the herniation occurs, but this pressure is not transmitted to the rest of the brain, and therefore does not register as an increase in ICP. Because herniation puts extreme pressure on parts of the brain and thereby cuts off the blood supply to various parts of the brain, it is often fatal. Therefore, extreme measures are taken in hospital settings to prevent the condition by reducing intracranial pressure, or decompressing (draining) a hematoma which is putting local pressure on a part of the brain.

Signs and symptoms

Brain herniation frequently presents with abnormal posturing, a characteristic positioning of the limbs indicative of severe brain damage. These patients have a lowered

level of consciousness An altered level of consciousness is any measure of arousal other than normal. Level of consciousness (LOC) is a measurement of a person's arousability and responsiveness to stimuli from the environment. A mildly depressed level of consciou ...

, with

Glasgow Coma Score The Glasgow Coma Scale (GCS) is a clinical scale used to reliably measure a person's level of consciousness after a brain injury. The GCS assesses a person based on their ability to perform eye movements, speak, and move their body. These thre ...

s of three to five. One or both pupils may be dilated and fail to constrict in response to light. Vomiting can also occur due to compression of the

vomiting center The area postrema, a paired structure in the medulla oblongata of the brainstem, is a circumventricular organ having permeable capillaries and sensory neurons that enable its dual role to detect circulating chemical messengers in the blood and t ...

in the

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (invol ...

. Severe

headaches Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a resu ...

and

seizures An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with lo ...

as a result of increased intracranial pressure are not uncommon. Cardiovascular and pulmonary symptoms may also be present as the brain loses function, but might also be associated with bleeding. They can include:

hypertension Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high b ...

respiratory depression Hypoventilation (also known as respiratory depression) occurs when ventilation is inadequate (''hypo'' meaning "below") to perform needed respiratory gas exchange. By definition it causes an increased concentration of carbon dioxide (hypercapni ...

, arrhythmia and in severe cases

cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possi ...

Causes

Causes of brain herniation include: * Brain edema *

Hematoma A hematoma, also spelled haematoma, or blood suffusion is a localized bleeding outside of blood vessels, due to either disease or trauma including injury or surgery and may involve blood continuing to seep from broken capillaries. A hematoma is ...

Stroke A stroke is a disease, medical condition in which poor cerebral circulation, blood flow to the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemorr ...

Tumour A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

Infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...

Classification

The tentorium is an extension of the dura mater that separates the

cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebe ...

from the

cerebrum The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. ...

. There are two major classes of herniation: supratentorial and infratentorial. Supratentorial refers to herniation of structures normally found above the

tentorial notch The tentorial notch (also known as the tentorial incisure or incisura tentorii) refers to the anterior opening between the free edge of the cerebellar tentorium and the clivus for the passage of the brainstem. The midbrain continues with the t ...

, and infratentorial refers to structures normally found below it.Orlando Regional Healthcare, Education and Development. 2004
"Overview of Adult Traumatic Brain Injuries."
Retrieved on January 16, 2008. * Supratentorial herniation 1) Uncal (transtentorial) 2) Central 3) Cingulate (subfalcine/transfalcine) 4) Transcalvarial 5) Tectal (posterior) * Infratentorial herniation 6) Upward (upward cerebellar or upward transtentorial) 7) Tonsillar (downward cerebellar)

Uncal herniation

In uncal herniation, a common subtype of transtentorial herniation, the innermost part of the

temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved i ...

, the

uncus The uncus is an anterior extremity of the parahippocampal gyrus. It is separated from the apex of the temporal lobe by a slight fissure called the incisura temporalis (also called rhinal sulcus). Although superficially continuous with the hippo ...

, can be squeezed so much that it moves towards the tentorium and puts pressure on the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is ...

, most notably the midbrain. The tentorium is a structure within the

formed by the dura mater of the meninges. Tissue may be stripped from the

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...

in a process called decortication. The uncus can squeeze the

oculomotor nerve The oculomotor nerve, also known as the third cranial nerve, cranial nerve III, or simply CN III, is a cranial nerve that enters the orbit through the superior orbital fissure and innervates extraocular muscles that enable most movements of ...

(a.k.a. CN III), which may affect the

parasympathetic The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of ...

input to the eye on the side of the affected nerve, causing the pupil of the affected eye to dilate and fail to constrict in response to light as it should. Pupillary dilation often precedes the somatic motor effects of CN III compression called oculomotor nerve palsy or third nerve palsy. This palsy presents as deviation of the eye to a "down and out" position due to loss of innervation to all ocular motility muscles except for the

lateral rectus Lateral is a geometric term of location which may refer to: Healthcare * Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle * Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics * Lateral ...

(innervated by

abducens nerve The abducens nerve or abducent nerve, also known as the sixth cranial nerve, cranial nerve VI, or simply CN VI, is a cranial nerve in humans and various other animals that controls the movement of the lateral rectus muscle, one of the extraocu ...

(a.k.a. CN VI) and the superior oblique (innervated by trochlear nerve a.k.a. CN IV). The symptoms occur in this order because the parasympathetic fibers surround the motor fibers of CN III and are hence compressed first. Compression of the ipsilateral posterior cerebral artery will result in ischemia of the ipsilateral primary visual cortex and contralateral visual field deficits in both eyes (contralateral homonymous hemianopsia). Another important finding is a ''false localizing sign'', the so-called Kernohan's notch, which results from compression of the contralateral cerebral crus containing descending corticospinal and some corticobulbar tract fibers. This leads to Ipsilateral

hemiparesis Hemiparesis, or unilateral paresis, is weakness of one entire side of the body ('' hemi-'' means "half"). Hemiplegia is, in its most severe form, complete paralysis of half of the body. Hemiparesis and hemiplegia can be caused by different med ...

in reference to the herniation and contralateral hemiparesis with reference to the cerebral crus. With increasing pressure and progression of the hernia there will be distortion of the brainstem leading to Duret hemorrhages (tearing of small vessels in the parenchyma) in the median and paramedian zones of the mesencephalon and pons. The rupture of these vessels leads to linear or flamed shaped hemorrhages. The disrupted brainstem can lead to decorticate posture, respiratory center depression and death. Other possibilities resulting from brain stem distortion include

lethargy Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overwo ...

, slow heart rate, and

pupil dilation Pupillary response is a physiological response that varies the size of the pupil, via the optic and oculomotor cranial nerve. A constriction response (miosis), is the narrowing of the pupil, which may be caused by scleral buckles or drugs such ...

. Uncal herniation may advance to central herniation. The sliding uncus syndrome represents uncal herniation without alteration in the level of consciousness and other sequelae mentioned above.

Central herniation

In ''central herniation'', the

diencephalon The diencephalon (or interbrain) is a division of the forebrain (embryonic ''prosencephalon''). It is situated between the telencephalon and the midbrain (embryonic ''mesencephalon''). The diencephalon has also been known as the 'tweenbrain in o ...

and parts of the

temporal lobes The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved in pro ...

of both of the

cerebral hemisphere The vertebrate cerebrum ( brain) is formed by two cerebral hemispheres that are separated by a groove, the longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemisphere ...

s are squeezed through a notch in the

. Transtentorial herniation can occur when the brain moves either up or down across the tentorium, called ascending and descending transtentorial herniation respectively; however descending herniation is much more common. Downward herniation can stretch branches of the

basilar artery The basilar artery () is one of the arteries that supplies the brain with oxygen-rich blood. The two vertebral arteries and the basilar artery are known as the vertebral basilar system, which supplies blood to the posterior part of the circle of ...

(pontine arteries), causing them to tear and bleed, known as a Duret hemorrhage. The result is usually fatal. Other symptoms of this type of herniation include small, fixed pupils withToronto Notes paralysis of upward eye movement giving the characteristic appearance of "sunset eyes". Also found in these patients, often as a terminal complication is the development of

diabetes insipidus Diabetes insipidus (DI), recently renamed to Arginine Vasopressin Deficiency (AVP-D) and Arginine Vasopressin Resistance (AVP-R), is a condition characterized by large amounts of dilute urine and increased thirst. The amount of urine produced ...

due to the compression of the pituitary stalk. Radiographically, downward herniation is characterized by obliteration of the

suprasellar cistern The sella turcica ( Latin for 'Turkish saddle') is a saddle-shaped depression in the body of the sphenoid bone of the human skull and of the skulls of other hominids including chimpanzees, gorillas and orangutans. It serves as a cephalometr ...

from temporal lobe herniation into the tentorial hiatus with associated compression on the cerebral peduncles. Upwards herniation, on the other hand, can be radiographically characterized by obliteration of the quadrigeminal cistern. Intracranial hypotension syndrome has been known to mimic downwards transtentorial herniation.

Cingulate herniation

In ''cingulate'' or ''subfalcine herniation'', the most common type, the innermost part of the frontal lobe is scraped under part of the falx cerebri, the dura mater at the top of the head between the two hemispheres of the brain.Dawodu ST. 2007
Traumatic brain injury: Definition, epidemiology, pathophysiology.
Emedicine.com. Retrieved on January 28, 2007. Cingulate herniation can be caused when one hemisphere swells and pushes the cingulate gyrus by the falx cerebri. This does not put as much pressure on the brainstem as the other types of herniation, but it may interfere with

blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide awa ...

s in the frontal lobes that are close to the site of injury (anterior cerebral artery), or it may progress to central herniation. Interference with the blood supply can cause dangerous increases in ICP that can lead to more dangerous forms of herniation. Symptoms for cingulate herniation are not well defined. Usually occurring in addition to uncal herniation, cingulate herniation may present with abnormal posturing and

coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...

. Cingulate herniation is frequently believed to be a precursor to other types of herniation.

Transcalvarial herniation

In ''transcalvarial herniation'', the brain squeezes through a fracture or a surgical site in the skull. Also called "external herniation", this type of herniation may occur during

craniectomy Decompressive craniectomy ('' crani-'' + '' -ectomy'') is a neurosurgical procedure in which part of the skull is removed to allow a swelling brain room to expand without being squeezed. It is performed on victims of traumatic brain injury, ...

, surgery in which a flap of skull is removed, the protruding brain region preventing the piece of skull from being replaced during the operation.

Upward herniation

Increased pressure in the posterior fossa can cause the

to move up through the tentorial opening in ''upward'', or ''cerebellar herniation''. The

midbrain The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal ( alertness), and temperature regulation. The name comes from the Greek ''mesos'', ...

is pushed through the tentorial notch upward. This is also known as ascending transtentorial herniation since it occurs across the tentorium cerebelli.

Tonsillar herniation

In ''tonsillar herniation'', also called ''downward cerebellar herniation'', transforaminal herniation, or "coning", the cerebellar tonsils move downward through the foramen magnum possibly causing compression of the lower brainstem and upper cervical spinal cord as they pass through the foramen magnum. Increased pressure on the brainstem can result in dysfunction of the centers in the brain responsible for controlling respiratory and cardiac function. The most common signs are intractable headache, head tilt, and neck stiffness due to tonsillar impaction. The level of consciousness may decrease and also give rise to flaccid paralysis. Blood pressure instability is also evident in these patients. Congenital tonsillar herniation of the

is also known as a

Chiari malformation Chiari malformation (CM) is a structural defect in the cerebellum, characterized by a downward displacement of one or both cerebellar tonsils through the foramen magnum (the opening at the base of the skull). CMs can cause headaches, difficulty ...

(CM), or previously an Arnold-Chiari malformation (ACM). There are four types of Chiari malformation, and they represent very different disease processes with different symptoms and prognosis. These conditions can be found in asymptomatic patients as an incidental finding, or can be so severe as to be life-threatening. This condition is now being diagnosed more frequently by radiologists, as more patients undergo MRI scans of their heads, especially upright MRI, which is more than twice as sensitive for detecting this condition. Cerebellar tonsillar ectopia (CTE) is a term used by radiologists to describe cerebellar tonsils that are "low lying" but that do not meet the radiographic criteria for definition as a Chiari malformation. The currently accepted radiographic definition for a Chiari malformation is that cerebellar tonsils lie at least 5mm below the level of the foramen magnum. Some clinicians have reported that some patients appear to experience symptoms consistent with a Chiari malformation without radiographic evidence of tonsillar herniation. Sometimes these patients are described as having a 'Chiari

ype Peace River Airport is a municipally owned airport located west of the Town of Peace River, Alberta, Canada. The airport has one runway, which is , and a terminal building, which is . Northern Air is based at the airport and provides scheduled ...

0'. There are many suspected causes of tonsillar herniation including: decreased or malformed posterior fossa (the lower, back part of the skull) not providing enough room for the cerebellum; hydrocephalus or abnormal CSF volume pushing the tonsils out; or dural tension pulling the brain caudally. Connective tissue disorders, such as

Ehlers Danlos syndrome Ehlers may refer to: * Ehlers–Danlos syndrome * Ehlers (surname) {{disambig