Traumatic Brain Injury

Traumatic Brain Injury

When an external force damages the head resulting in temporary or permanent brain dysfunction it is known as a traumatic brain injury or TBI. 

Types of Traumatic Brain Injury

As a direct result of the external force TBIS can cause extra axial and intraaxial injuries.

Extra axial injuries are within the skull but don't involve the brain parenchyma. The most high-yield ones are epidural and subdural hematomas as well as a subarachnoid haemorrhage.

Intraaxial injuries on the other hand do not involve brain parenchyma and the most high yield ones are diffuse axonal injuries.

Now sometimes trauma initiates  a series of molecular events along with a primary brain injury which can persist for hours or even days these are referred to as secondary brain injury and eventually can result in increased intracranial pressure which in turn has numerous consequences and the most important is brain herniation.

Now lets take a look at  these different types of traumatic brain injury:

Extra axial injuries 

Epidural hematomas occur when blood collects in the space between the dura mater which is the outer layer of the meninges and the inner aspect of the skull periosteum. This happens when a linear fracture occurs at the region where the frontal parietal temporal and sphenoid bones join together, this region is called the terion and it's the thinnest part of the lateral wall of the skull. A fracture at the terion can tear open the middle meningeal artery, a branch of the maxillary artery causing profuse bleeding.

The most important concept to keep in mind that individuals with epidural hematoma classically have a period of loss and consciousness and then a lucid interval during this time the individual regains consciousness and feels fine. But a lucid interval isn't always seen symptoms are due to the buildup of blood trapped between the dura mater and skull which increases intrcranial pressure.

Now what makes epidural hematoma so dangerous is that the dura mater is attached tightly to the sutures of the skull so the blood can't cross these sutures and is trapped with nowhere to go. This means the intracranial pressure can increase rapidly due to which an individual can develop headaches, nausea, vomiting and focal neurological symptoms like weakness, numbness, vision and auditory problems.

As the hematoma grows rapidly it can cause a life-threatening brain herniation resulting in the loss of consciousness coma and death.

How does it appear in a Brain CT?

A Brain CT is diagnostic and classically shows a convex lens-shaped collection of blood that does not cross the suture lines of the skull. There can also be evidence of scalp hematoma due to the head trauma in addition to the bleeding there can be surrounding cerebral edema and if the edema is significant it can cause a shift of the midline to the contralateral side. This signifies an impending brain herniation, most commonly a transtentorial herniation.

Epidural hematomas are an emergency and neurosurgical intervention is often necessary.

A subdural hematoma occurs when the blood collects between the dura mater, the outer layer of the meninges and the arachnoid mater which is the middle layer of the meninges. 

Unlike epidural hematomas the bleeding source is usually the bridging veins that connect the cerebral venous sinuses to the superficial veins of the skull. The bridging veins are very vulnerable to rapid acceleration or deceleration so they are easily damaged in car crashes.

It's also important to remember that when there is brain atrophy and shrinkage like in chronic alcohol users or the elderly the bridging veins get stretched out, so even minor head trauma like walking into a door can lead to a subdural hematoma in these individuals.

"Some individuals don't even remember the traumatic event so it's important to always consider a subdural hematoma especially in elderly individuals with neurological symptoms." 

If a subdural hematoma is detected in an infant or young child, it could be due to non-accidental trauma or child abuse. 

Infants and children have large heads with relatively small brains.                                              So vigorously shaking a young child cause a subdural hematoma as well as other signs of non-accidental trauma like retinal haemorrhages on fundoscopy.

As we know the source of the bleeding is venous the hematoma usually grows slower than epidural hematomas caused by arterial bleeding also since the blood isn't restricted by sutures. It can be distributed over larger area so pressure doesn't build up as quickly unless the haemorrhage is very large, because of these factors subdural hematomas tend to be more insidious. Now as the blood accumulates intracranial pressure increases causing symptoms like worsening headaches, unsteady, gait, nausea or vomiting, confusion, visual problems, cognitive impairment, slurred speech, seizures, dizziness and hemophoresis that can be ipsilateral or contralateral.

"A subdural hematoma is considered acute if symptoms develop within 2 days of a head trauma, subacute if they develop between 2 days and 2 weeks of a head trauma and chronic if they develop 2 weeks or more after a head trauma."

Just like with epidural hematomas if a subdural hematoma grow large enough it can lead to brain herniation and coma or death. 

How does it appear in a Brain CT?

A Brain CT is diagnostic and classically shows a concave crescent shape density that crosses the suture lines and that's extremely high yield and the density on the brain CT helps determine the age of hematoma.

Acute Subdural hematomas are hyper dense while Chronic Subdural hematomas are hypodense.                          Subacute subdural hematomas appear iso-dense meaning they blend in with the adjacent brain parenchyma making them easy to miss also a midline shift can also be seen on CT.

The morbidity and mortality of subdural hematomas are high because they can develop more insidiously and are harder to detect in the early stages.

Similar to epidural hematomas like mainstay of treatment is prompt surgical hematoma evacuation. Sometimes stable individuals with acute small hematomas can be managed non-operatively as the hematomas is reabsorbed naturally.

Subarachnoid haemorrhage is bleeding between the arachnoid mater and PIA mater the innermost layer of the meninges. In general the most common cause of subarachnoid haemorrhage is head trauma whike the most common cause of a spontaneous subarachnoid haemorrhage is the rupture of an aneurysm.

Aneurysms can burst open when there is an increase in intracranial pressure. 

The most aneurysms in the brain are saccular cerebral aneurysms also called berry aneurysms. They typically arise in the interior half of the circle of willis at bifurcations.

Bifurcations are junctions between arteries and the most common junction where sacular aneurysms take place is between the anterior communicating artery and the anterior cerebral artery. 

A brain trauma leads to temporary or permanent brain dysfunction. 

Traumatic brain injuries or TBIS can cause extra axial brain injuries such as epidural or subdural hematomas and subarachnoid haemorrhage and intraaxial brain injuries such as diffuse axonal injury.

Sometimes these brain injuries can lead to increased intracranial pressure which can have various  consequences like brain herniations which are life-threatening.

Diagnosis can be made based on clinical presentation imaging tests of the rain like CT or MRI or other techniques such as lumbar punctures.

TBIS usually require surgery...