Traumatic brain injury

Trauamtic brain injury is what it sounds like, you hit your head and damage your brain. The stuff you must know comes from type of damage that can be caused, how to recognise it, what to do for treatment, and what it means going forward.

General types of TBIs

TBI can cause a number of issues, depending on factors like age how injury occured and energy of injury.

Types:

• Skull fracture
• Parenchymal tissue injury (general brain tissue)
  • concussion
  • contusion
  • Laceration
  • Diffuse axonal injury
• Haemorrhage
  • epidural haemorrhage
  • subdural haemorrhage
  • subarachnoid haemorrhage
  • intraparenchymal (or intraventricular) haemorrhage

Concussion

A concussion is mainly defined by its observed symptoms, where you see an either an immediate but transient loss of consciousness and brief amnesia or daze and confusion. Macroscopic or histological changes in the brain arent generally seen. Concussion is caused by sudden deceleration or acceleration causing the brain to hit the cranial walls. This can be a direct blow, or indirect blow (whiplash).

Concussion can be followed by brain compression by a developing hematoma (see later); so, patients must be put under observation.

Contusion

This is a “brain bruise” and is from a blow to the head causing the brain to impact the skull, causing bleeding and visible damage. This can be thought of as a more serious concussion as it related to the mechanism of injury.

The bleeding and tissue damage is most of then found where the cortical gyri impact rough and irregular sections of the cranium. The location can the site of impact, or the other site as the brain bounces between the 2. These are called coup and contracoup injuries, respectively.

Note from path tut

A fall backward is most likely to produce contrecoup injuries to the inferior frontal lobes; whereas a blow to a stationary head is more likely to produce a coup injury directly at to the site of the blow.

Morphology

Early morphology is: Haemorrhage on the site of injury, as well as possible deformation of parenchymal tissue. Inflammation and oedema can be found there can be lots of tissue lost

older lesions will be yellow brown as macrophages break down RBC and haemoglobin. The older lesions will also show gliosis and a possible cavity surrounded by gliosis

Laceration

Laceration is caused by foreign bodies ripping through brain tissue, and can be caused by bullets, bone fragments and are a severe form of contusion

Diffuse axonal injury

This is a serious brain injury often caused by severe inertial injuries. It results in axonal connections in deep white matter structures being severed and disrupted. It is seen in immediate and prolonged coma following a a head injury. This is a

morphology

This presents with brain oedema and small petechiae in the white matter which are ruptured capillaries and vessels. Axonal damage cannot be seen macroscopically.

microscopically you see axon swellings, termed retraction balls that are accumulations of cell organelles at the proximal stump of the axon. The distal end degenerates.

Epidural haemorrhage

This is a bleed in between the inner surface of the skull and the dura. It stops at suture lines and usually results from tearing of the middle meningeal arteries following a fractures of the temporal bone or just temporal trauma. This is an acute arterial bleed and will present in hours.

Morphology

On CT the haemorrhage looks like a white biconvex disc. you will see midline shift and ventricular compression as the blood displaces the brain. Over time the bleed will lose its opaque look, as globin is broken down.

Subdural haemorrhage

This is caused by bridging veins rupturing in between the arachnoid and dura. Bridging veins cross from the cortical surface to the dural sinuses and are vulnerable to tearing, as the dural sinuses are fixed in the skull and the brain is not.

Elderly patients are more at risk, as brain atrophy puts greater traction on bridging veins. Additionally the bleeding may accumulate more slowly, over days, as bleeding is venous.

Presentation is depends on extent of damage for example in smaller venous bleeds it can be more vague symptoms like headache and confusion whereas larger vascular injury can lead to larger mass expanding lesions.

Morphology

this bleed surrounds the entire brain. as it is not restricted by suture lines in the skull. it thus looks like a crecent shape on CT

Overtime the bleed to develop into granulation tissue and adhere to the dura as a fibrous tissue if the patient survives

Subarachnoid haemorrhage

these are covered in the stroke path tut

Intraparenchymal haemorrhage

these are covered in the stroke path tut

Brain herniation and raised ICP

A large risk from brain bleeds Intracranial space occupying lesions and Stroke is that of raised intracranial pressure.

This happens as the space in the cranium is limited, and so raise in pressure in the intracranial space will lead to herniation. additionally if the brain is swelling (oedema), it will press against the skull causing damage.

Brain herniation is when, due to increased pressure, structures will press on other structures, leading to fail in function, as everything tries to expand through the foramen magnum.

Additionally brain herniation and raised ICP, can both lead to decreased perfusion into the brain, especially in shock (BP drop)

There are a few main types of brain herniation:

Subfalcine

This is when there is a pressure differential when one hemisphere can a different pressure compared to the other. The cingulate gyrus will push through under the falx cerebri. It does not cause clinicially specific signs but can depress one of both of the anterior cerebral arteries leading to ischaemia

Transtentorial

This is the most common herniation phenomenon

This is where the uncus pushes around the tentorial notch and pushed on the rostral midbrain and often the oculomotor nerve, one or both cerebral peduncles can be compressed, leading to a blown pupil, or hemispherical weakness.

Duret haemorrhages can also result in the midbrain or upper pons.

It has 3 classic signs

1. blown pupil. This will be ipsilateral to the side effected
2. pressure on the cerebral peduncles can lead to contralateral hemiparesis
3. pressure in the midbrain reticular formation and or duret haemorrhages in the midbrain leads to decresed level of consciousness or come

additionally sometimes something called kernohans phenomenon can occur where the midbrain is pushed to the other side which compresses the other cerebral peduncle causing ipsilateral hemiparesis.

Cerebellar

This is where the the tonsils of the cerebellum push through the foramen magnum compressing the cardiac and respiratory centres in the medulla, leading to cardiac and or respiratory arrest and death.

Symptoms of ICP

the symptoms of raised ICP are

• headache

• confusion

• nausea

• vomiting

• and papilloedema

• as well as characteristic signs of brain herniation.

Consequences of TBI

some other long term effects can be post traumatic epilepsy, post traumatic hydrocephalus, chronic traumatic encephalopathy (CTE, dementia followed by repeated head trauma. ) and other psychiatric disorders