What is Uncal Herniation?
The uncus is a part of the brain located in the inner side of a brain area known as the parahippocampal gyrus, which is found within a larger region called the medial temporal region. This larger region is in the top part of the skull and is linked to the lower part via a structure known as the tentorium cerebelli through a space termed the tentorial notch.
The tentorial notch houses important structures like the midbrain, the third cranial nerve, rear brain arteries, and superior cerebellar arteries. The cerebellum, which is a part of your brain responsible for balance and coordination, fills the back space of the tentorial notch.
Uncal herniation is a very serious medical condition that can occur when the pressure within the skull increases. This increased pressure forces parts of the brain to move from one area of the skull to another. This is a life-threatening situation that indicates that the brain’s internal pressure regulation systems have failed.
What Causes Uncal Herniation?
Uncal herniation is a serious brain condition that can be caused by anything that significantly increases the pressure inside the skull. This often includes any situation where there is a growing mass, or lesion, inside your head. This mass puts you at risk for uncal herniation, as it can put pressure on certain parts of the brain.
Severe head trauma can also lead to uncal herniation. This can happen when the trauma causes a quickly growing pool of blood that increases the pressure inside the skull, which is known medically as a subdural or epidural hematoma.
In uncal herniation, there is typically a force from the top of the brain that is pushing down with a high amount of pressure. This pressure pushes a part of the brain called the “uncus” over a notch towards the top of the brain. This movement is what we mean when we refer to ‘uncal herniation’.
Risk Factors and Frequency for Uncal Herniation
It’s hard to determine the exact number of uncal herniation cases, which often happen as a result of traumatic brain injury. To better grasp the risk, it’s important to look at the numbers related to traumatic brain injury, often referred to as TBI. According to a report from the Centers for Disease Control and Prevention (CDC) in 2015, there are around 30 million emergency room visits, hospital stays, and deaths due to injuries every year in the U.S.
- TBI contributes to 16% of these hospital stays and a third of injury-related deaths.
- In 2010, the CDC estimated that TBI caused around 2.5 million emergency department visits, hospitalizations, and deaths, either on its own or combined with other injuries.
Signs and Symptoms of Uncal Herniation
Uncal herniation is a serious medical condition where a part of the brain starts to shift due to increased intracranial pressure. At the beginning, a person might experience symptoms like headaches, nausea, vomiting, and changes in mental state. A physical examination might reveal symptoms of increased pressure within the brain, known as Cushing’s triad, which includes high blood pressure, slow heart rate, and irregular or missed breaths.
The person could also show late signs of increased pressure within the brain like papilledema, which is a condition where the optic nerve at the back of the eye becomes swollen. This would appear as a blurring of the optic disc margin and reduced venous pulsations in an eye exam.
As the situation progresses, the person could experience an acute loss of consciousness associated with one-sided pupil dilation and paralysis on the opposite side of the body. These symptoms occur due to the compression or displacement of certain brain structures and nerves.
- One of the earliest signs could be that one pupil becomes significantly larger than the other, even without major changes in the level of consciousness or paralysis on the opposite side of the body.
- If a person comes in with isolated anisocoria (unequal size of pupils), it could indicate that uncal herniation is about to take place.
- Over time, the person might develop difficulties with eye movement which could make the eye assume a classic down-and-out appearance.
- If the midbrain gets further compressed due to uncal herniation, the person may become lethargic, fall into a coma or even die.
If left untreated, uncal herniation can advance to central herniation, which is another life-threatening condition.
Testing for Uncal Herniation
If we suspect that there’s a herniation in the brain, usually known as an uncal herniation, there are a particular set of symptoms and exam results that we would look out for and use to make our diagnosis. To confirm our suspicion, we would use brain imaging techniques.
If a patient shows all the signs of something called ‘Cushing’s triad’, we consider this an emergency situation and would immediately perform a brain scan using a technique called computed tomography, commonly referred to as a CT scan. This would allow us to check for very serious conditions, including life-threatening bleeding, herniation, or a mass lesion.
Although we can also use another type of imaging technique called magnetic resonance imaging (MRI) to confirm our diagnosis, when we’re dealing with an emergency situation, we prefer to use a CT scan. This is because it’s quicker to complete and the technology is more widely available, meaning that we can ensure we get the results as swiftly as possible to give the best care to the patient.
Treatment Options for Uncal Herniation
If you show signs of uncal herniation, a condition where the brain shifts to one side due to excessive pressure, prompt action is necessary. The goal is to quickly decrease the pressure inside your skull. This can be done by reducing the volume of one component inside the skull compartment like the brain, blood, or cerebrospinal fluid which is the fluid surrounding your brain and spinal cord.
Your doctor can manage this by:
- Raising the head of your bed at a thirty-degree angle
- Positioning your head in a straight forward direction
- Increasing your breathing rate (hyperventilation)
- Using a type of treatment known as hyperosmolar therapy, which can involve either mannitol or hypertonic saline
Hyperventilation works by lowering the levels of carbon dioxide, a gas that your body produces naturally, in your arteries. This causes the blood vessels in your brain to narrow and therefore reduce the amount of blood in your brain. This technique is mainly used in situations where the pressure inside your skull is dangerously high, such as with uncal herniation.
When pressure builds up inside your skull and goes above 20mmHg, or you show signs of brain herniation which means your brain is being squeezed, you might be given hyperosmolar therapy. This could include mannitol or hypertonic saline (a strong salt solution). These treatments work by drawing fluid out from your brain, thereby lowering the pressure.
If these methods fail to control the symptoms of uncal herniation, surgery might be considered to further reduce the pressure inside your skull. Surgical options can include:
- Inserting a drain in your brain ventricles, which are fluid-filled cavities in the brain
- Removing an excess collection of blood outside the brain area like an epidural hematoma
- Removing a lesion from within the brain
- Removing part of the brain tissue
- Performing one-sided or two-sided skull opening surgery (craniectomies)
What else can Uncal Herniation be?
Uncal herniation happens because of a considerable increase in pressure inside the skull. The signs of this can be a headache, feeling sick, throwing up, or changes in mental status. So, when doctors are trying to diagnose it, they’ll look at other conditions that might cause these symptoms:
- Diabetic ketoacidosis
- Encephalitis (brain inflammation)
- Intracranial hemorrhage (bleeding inside the skull)
- Ischemic stroke (a blockage in the brain’s blood supply)
- Meningitis (inflammation of the protective membranes of the brain and spinal cord)
- Neoplasm (a new, abnormal growth of tissue)
- Sepsis (a life-threatening response to infection)
- Subdural/epidural hematoma (bleeding outside the brain)
- Systemic lupus erythematosus (an autoimmune disease)
- TBI/concussion syndrome (head injuries)
- Toxins exposure
What to expect with Uncal Herniation
In neurosurgery, a key factor for patients with uncal herniation – a type of brain herniation where part of the brain is squeezed to a side – is to quickly detect and begin treating the condition. How well a patient recovers can also be influenced by how severe the herniation has become.
Restoring the brain to normal condition gets more challenging if a patient has multiple injuries or if new complications appear as the herniation worsens. Even so, starting treatment promptly can still make a significant difference. With quick interventions, doctors have been able to reverse uncal herniation in 50% to 75% of adult patients suffering from traumatic brain injuries or mass lesions (abnormal growths) in a specific region of the brain.
Long-term recovery after successful treatment for herniation seems to be more promising in children compared to adults.
Possible Complications When Diagnosed with Uncal Herniation
The most extreme complications of uncal herniation, a type of brain herniation, can be falling into a coma or even death if methods to reverse the herniation are unsuccessful. Depending on how much brain tissue is involved in the herniation, individuals are also at risk for developing brainstem or cortical ischemia; in simpler terms, they might experience reduced blood supply to these parts of the brain due to the closeness of major blood vessels.
Unfortunately, there are also some rare instances where children with Dandy-Walker syndrome, or other conditions involving cysts communicating with the fourth ventricle located at the base of the brain, have chronic uncal herniation due to posterior fossa shunting – the diversion of fluid away from the brain.
Potential Complications:
- Coma
- Death
- Brainstem or cortical ischemia (Reduced blood supply to the brain)
- Chronic uncal herniation in children with certain medical conditions
Preventing Uncal Herniation
The best way to prevent traumatic brain injuries is to take appropriate safety measures when driving cars or handling firearms, as these activities often cause such injuries. On the other hand, it can be difficult or even impossible to prevent medical causes that lead to space-occupying brain lesions. “Space-occupying brain lesions” are medical terms for abnormal growths in the brain, such as tumors.
