Classifying the severity of a traumatic brain injury is an important part of assessment and overall treatment.
This article will explain the different head injury classifications and what they mean for recovery.
Head Injury Classification
Head injuries are typically classified according to three systems: severity, morphology, and mechanism.
Mechanism refers to how the brain was injured, morphology describes what happened to the brain tissue, and severity represents how much damage occurred.
Understanding these aspects and knowing which categories a particular head injury falls into helps healthcare professionals decide on the best treatments for their patients.
We’ll look more closely at these different categories in the sections below.
1. Mechanisms of Head Injury
Doctors will classify the mechanisms of head injury into three categories:
- Open head injuries. Also known as penetrating injuries, these occur when both the skin and the dura are pierced by either a foreign object or a skull fragment. The most common type of open head injury is a gunshot wound.
- Anoxic injuries. This occurs when the brain is completely deprived of oxygen, such as after a drowning or heart attack.
- Closed head injuries. These are injuries where the skin and skull are intact, but the brain has twisted or been slammed against the skull, causing damage.
Closed head injuries can be further classified as linear or rotational, depending on the direction the brain moved during impact.
2. Morphology of Head Injury
The morphology of head injury describes what type of damage occurred to the brain. The three main categories of morphology that doctors use are:
- Skull fractures
- Focal intracranial injury
- Diffuse intracranial injury
A focal injury refers to damage that only affects one area of the brain. Most open head injuries are also focal injuries.
A diffuse injury, in contrast, means that damage occurred across multiple areas of the brain.
Below are some examples of different focal and diffuse injuries:
Concussions are mild traumatic brain injuries that can cause diffuse or focal brain damage, depending on how severe they are.
They occur when the brain experiences trauma from a sudden impact or momentum change. During a concussion, the blood vessels in the brain might stretch or break, and the cranial nerve can become damaged.
Concussions can lead to many long-term problems if they are not taken care of.
A contusion refers to a mild form of brain-bleed, otherwise known as a bruise.
Contusions are considered focal injuries because they only affect the area of the brain that they occur. Doctors classify contusions that occur on both sides of the brain as coup-contrecoup injuries.
If a contusion does not resolve on its own, it can coalesce into a life-threatening hematoma, which must be removed through surgery.
Hematomas are large pools of blood that gather on the brain. They can lead to serious injury and even death if left untreated.
There are several different types of hematomas, including:
- Epidural hematomas. Blood clot between the skull and brain
- Subdural hematomas. Blood clot under the dura, the thin layer of protection surrounding the brain
- Intracerebral hematoma. Bleeding within the brain itself
Sometimes hematomas do not develop until several days or weeks after a head injury. If you start experiencing any of these symptoms, you should go to a hospital immediately:
- Increasing headache
- Unequal pupil size
- Slurred speech
Diffuse Axonal Injuries
Diffuse axonal injuries occur when the brain is shaken or twisted inside the skull.
As the brain twists, brain tissue slides back and forth until the long connecting fibers in the brain (called axons) are torn. Doctors refer to this as axonal shearing.
This tearing disrupts the messages that neurons send to each other, resulting in loss of function.
Because most axonal injuries are microscopic, they can be hard to detect on an MRI.
3. Severity of Head Injury
Finally, doctors will classify brain injuries according to severity. These categories help predict how well the patient will recover.
There are several scales a doctor might use to assess the severity of a TBI. By far the most widely used scale is the Glasgow Coma Scale (GCS).
The scale consists of 15 points total, with points used to measure various neurological functions such as eye-opening and verbal response.
Based on the number of points, doctors will classify patients into four groups:
- Mild TBI: GCS score = 13-15 pts
- Moderate Disability: GCS score = 9-12 pts
- Severe Disability: GCS score = 4-8 pts.
- Persistent Vegetative State: GCS score = 3 pts.
The higher the points, the higher the level of function, which means a higher likelihood of making a full recovery.
Classifying Head Injuries
Head injury classifications give doctors a good starting point to predict TBI outcome and recommend the right treatments and therapies.
They can also help patients and their families know what to expect from their injury and prepare for the side effects.
The better you understand the type of injury you have, the more efficient your recovery will be.