Head Injury: Classifications, Diagnosis and Treatment

Head injury refers to trauma to the head causing alteration in mental or physical functioning (neurological functions)

Etiology

The most common causes include:

• Motor vehicle accidents (eg, collisions between vehicles, pedestrians struck by motor vehicles, bicycle accidents),
• Falls,
• Assaults,
• Sports-related injuries, and
• Penetrating trauma.

The male-to-female ratio for traumatic brain injury is nearly 2:1, and traumatic brain injury is much more common in persons younger than 35 years.

Classification of head injury

Head injuries can be classified according to;
1. The severity of the injury.
2. Anatomical classification
3. Pathological classification-penetrating or blunt injury
4. Primary and secondary brain injury.

A. The severity of the head injury

Severity is assessed by the following methods notably:

Glasgow Coma Scale.

A score below 8 is considered to represent severe head injury while 8 to 12 is assessed as a moderate head injury. 13 to 15 is a mild head injury.

B. Anatomical classification

Injury can involve one or more of the following structures.

Use the mnemonic  Scalp to remember them.

This consists of five layers; the first three layers are bound together and moved as a unit. The layers are:
S -Skin

C -Connective tissue: Dense
This is a fibro-fatty layer. The fibrous septa unite the skin to the underlying aponeurosis of the fronto-occipitalis muscle. The scalp vessels lie within this layer.

A- Aponeurosis of Galea 
This is a thin fibrous sheath attached to the bellies of the Fronto-occipitalis muscle. Deep to it is the sub aponeurotic space.

L- Loose connective(areolar) layer
Occupying the sub aponeurotic space. This layer contains emissary's veins. It is a large potential space and can contain a large amount of bleeds or pus following skull injury.

P Pericranium
Pericranium is the periosteum of the skull bone.

The scalp is very vascular and laceration can cause severe loss of blood. The vessels within the scalp do not constrict when injured because the wall is adherent to the surrounding fiber fatty tissue in the dense connective tissue layer. Bleeding can be controlled by applying pressure or suturing the scalp.

B. Skull Injuries

Skull fractures are simple or compound. Simple if there is no communication between the fracture and the atmosphere, while the fracture is compound if there is such communication. Skull fractures are classified as follows:

Simple/Closed Fractures

1. Linear or fissure fracture.

This involves the skull vault and can extend down to the base of the skull. The linear fracture indicates that there have been significant injuries to the head. Management is usually hospital admission and close observation for any complications.

2. Comminuted fracture

3. Cracked pot fracture

4. Ping-pong fracture

This is a greenstick fracture of the skull, it occurs in the first few months of life when the skull bones are still soft. It is caused after falls when the skull hits the edge of a blunt structure as the edge of a table. It shows as a deformity of the skull, it looks like a shallow trench on the surface of the skull.

If large and showing as a significant deformity it can be easily treated by elevating the depressed bone fragment

5.Depressed fracture

Skull fragment pushed below the level of the skull. Significant depression is depression twice the thickness of the diploe. This can result in dural tear and laceration of the underlying brain.
Skull fragments should be replaced to avoid the creation of skull defect and the need for cranioplasty.

The underlying dura should be repaired and any bleeding controlled. This is important in children below the age of 4 to avoid the complication of growing skull fracture.

Bone fragments should be replaced even in compound fractures and wound debrided.

Compound Fracture/open fracture e.g. Fracture Skull Base.

This starts as a vault linear fracture and extends into the skull base. It follows the weak points in the skull as the Cribriform plate, foramina, and internal ear. Nerve injury can result in involving the olfactory nerve, the facial nerve. etc

If the fracture extends into the Cribriform plate and is associated with dural tear CSF leak can result and this is called rhinorrhea. If the fracture extends into the internal ear and the middle ear we can get otorrhea, which is CSF leak from the ear.

C.Brain Injury

Injury to the brain is either localized or diffuse and can be either primary or secondary.

Primary Brain Injury

Injury directly due to the insult and occurring at the time of the injury

Brain concussion is a temporary physiological disruption of brain function.
A brain contusion is a Small petechiae and hemorrhages
Brain laceration-obvious deformity

Localized injury is a deformation of the brain at the point of impact. It is associated with dural laceration and underlying brain contusion or laceration. Usually, there is localized surrounding edema around the site of the impact.

Diffuse injury carries a greater risk of damage to the brain and the mechanisms involved in this injury are:
Acceleration/deceleration injury.

In acceleration injury, the head is put into motion from a standstill position, as a result of which the different layers of the brain travels at different velocities with shearing effects and rotation of the brain within the skull.

The shearing stresses between different layers of the brain result in petechial hemorrhages as well as diffuse axonal injury involving the white matter and brain stem. In deceleration injury, the head is brought to a standstill from a moving position as in falls. The same mechanism applies.

The extent of the diffuse injury and the axonal damage determines the outcome.
The more severe the injury is, the more brain damage occurs with more axonal injury. This would be associated with higher morbidity and mortality.

Penetrating injury

High velocity or slow velocity injury as a result of penetration with sharp objects. The base of the skull is thin bone and could easily be penetrated especially in children. This result in skull base fracture and damage to the brain overlying that area.

Compression injury 
The head is compressed between two solid objects as in motor vehicle accidents. The result is multiple linear fractures particularly in the weak areas of the skull base resulting in multiple cranial nerve injuries.

Secondary brain injury

This results as a consequence of the primary brain injury and this includes :

A. Intracranial hematomas.

These Include

1 Epidural hematoma

Epidural hematomas are located between the inner table of the skull and the dura. Usually due to laceration of the middle meningeal artery.

They are typically biconvex (lentiform) in shape because their outer border follows the inner table of the skull and their inner border is limited by locations at which the dura is firmly adherent to the skull.

Up to 10% of epidural hematomas may be venous in origin. In about 60 or 70% of cases, there is an associated skull fracture.

Usually located in the temporal area. Occasionally it is in the frontal, parietal or posterior fossa region.

As it is an arterial bleed the clot can get to a significant size within a short period of time with a rapid rise in the intracranial pressure. If untreated there is a high rate of morbidity and mortality but effective and early treatment can result in complete recovery. In these cases, there is no diffuse brain injury and the injury is localized to the area where the fracture and the hematoma is.

The aim of the management is to evacuate the clot as soon as possible and control the bleeding meningeal vessel.
In most cases this is an acute condition, however, occasionally the bleeding is a result of venous tear and the blood clot develops slowly. This is particularly the case in the frontal and occipital regions.

The clot is evacuated through a craniotomy but in acute situations where there are no facilities for the major neurosurgical procedure a burr hole should be done to release the intracranial clot and reduce the intracranial pressure.

Only 1/3 pts present with Classic "lucid interval,” normal brain function after the insult followed by focal neurologic deficits later.

2 Subdural hematoma

This is the result of a tear in one of the bridging veins between the surface of the cortex and the dural sinuses. The blood collects gradually and slowly as the bleed is of Acute subdural hematomas.

They are rare in children. Subdural hematomas are more common in alcoholics and patients > 50 yr, in whom the head injury may have been relatively trivial, even forgotten.

As the brain atrophies over time, the bridging veins become more exposed and, as a result, are more easily injured. These hematomas are usually a part of severe and diffuse brain injury. It causes significant morbidity and mortality because of associated diffuse brain injury.

Causes increased intracranial pressure with transtentoria