Diagnostic methods and their role
The primary imaging modality in acute TBI is computed tomography (CT). Its main advantages are universal availability, high speed, and the ability to perform it without intravenous contrast, which is critically important in polytrauma.
The CT examination begins with a scout radiograph (scout radiograph), which helps plan the scanning range (usually from the skull base to the vertex) and preliminarily assess the presence of cranial vault fractures or foreign bodies. For a detailed analysis of brain structures, 1–5 mm thick slices are acquired, and a specialized bone algorithm is used to evaluate the facial bones and neurocranium.
Magnetic resonance imaging (MRI) surpasses CT in sensitivity for detecting hemorrhages at any stage and parenchymal injuries (e.g., diffuse axonal injury). However, in the acute period, its use is limited due to scan duration, patient immobility requirements, and monitoring difficulties within the scanner.
Window settings for CT evaluation
For the correct interpretation of CT images, it is necessary to use various electronic windows:
- Brain window: a narrow window (e.g., WL 40, WW 80 HU) on thicker slices (~5 mm). Used to evaluate the brain parenchyma and reduce noise.
- «Blood» window: a wider window (e.g., WL 70, WW 150–200 HU). Enhances the contrast between blood and bone, helping to detect small blood collections (subdural, epidural hematomas, subarachnoid hemorrhages) that may blend with the skull bones in a standard brain window.
- Bone window: a specialized algorithm for a detailed evaluation of bone structures and the search for foreign bodies, especially in penetrating injuries.
Mechanisms of traumatic brain injury
Globally, TBI is divided into two categories:
- Open injury: the intracranial cavity communicates with the external environment through a defect in the bone and integument. High risk of pneumocephaly, cerebrospinal fluid leak, and infectious complications.
- Closed injury: without communication with the external environment.
Depending on the nature of the impact, trauma can be blunt (motor vehicle accidents, falls) and penetrating (gunshot, stab wounds). In blunt trauma, injuries are often observed at the site of impact (site of impact / coup) and on the opposite side due to inertial forces (counter-impact / contre-coup). The effect of acceleration/deceleration and rotational forces without direct impact can lead to diffuse axonal injury.
Vascular assessment: CT angiography and venography
If the trauma is associated with a high risk of vascular injury (e.g., penetrating wounds, fractures of the skull base or craniovertebral junction, or the development of focal neurological symptoms), the protocol is supplemented with CT angiography (CTA).
Using intravenous contrast and bolus tracking technique, detailed maximum intensity projections (MIP) of the arterial bed are constructed. CTA is less prone to artifacts than MR angiography, especially at the skull base. To assess venous sinuses and cortical veins, CT venography can be used, performed with a greater scan delay (about 45 seconds).
Briefly: answers to topical questions
What are the specific CT features (shape, relationship to sutures) of epidural and subdural hematomas?
The specific CT features of epidural and subdural hematomas differ in shape and relationship to anatomical structures.
| Sign | Epidural hematoma | Subdural hematoma |
|---|---|---|
| Shape | Biconvex (lentiform) | Crescentic (crescentic appearance) |
| Relationship to sutures and dural reflections | Does not cross cranial sutures (sutures), but may cross dural folds | Extends over the brain surface, limited by the falx cerebri (falx cerebri) |
In which anatomical structures of the brain are the lesions most frequently localized in diffuse axonal injury (DAI)?
Lesions in diffuse axonal injury are localized depending on the severity of the trauma.
- Subcortical and deep white matter of the cerebrum (cerebrum) — affected in grade I severity.
- Corpus callosum (corpus callosum) — involved in grade II severity.
- Brainstem (brainstem) — injured in grade III severity.
According to which clinical scale is the severity of traumatic brain injury classified at the pre-hospital and hospital stages?
To objectively assess the level of impaired consciousness and coma depth, the Glasgow Coma Scale (Glasgow Coma Scale) is used. It consists of three tests, each scored with points:
- Eye opening — evaluates spontaneous opening, response to speech, response to pain, or no response.
- Verbal response — evaluated from fully oriented to absent.
- Motor response — includes obeying commands, localizing, withdrawal, or extension responses to pain.
What types of skull bone fractures by morphology (e.g., linear, depressed) are distinguished in diagnostic imaging?
In diagnostic imaging, calvarial fractures (Calvarial fractures) are classified into several morphological types.
- Simple fractures (Simple fractures) — include linear fractures of the bone tables and diastatic fractures involving sutures.
- Comminuted fractures (Comminuted fractures) — characterized by the presence of more than two bone fragments, may be accompanied by elevation or depression.
- Depressed fractures (Depressed fractures) — can be punctate, comminuted, or terraced.
- Open fractures (Open calvarial fractures) — accompanied by skin and soft tissue damage.
Class and exam questions
Why is CT preferred over MRI in acute TBI?
CT is performed significantly faster, is more accessible, allows simultaneous evaluation of bones, and does not require prolonged immobility, which is vital for unstable polytrauma patients.
What is the purpose of the «blood» window in CT analysis?
The wide window increases the contrast between fresh blood and bone, making it possible to notice small hemorrhages near the calvarial bones that are not visible in the standard soft tissue window.
What is a coup-contrecoup injury?
This is a classic mechanism of blunt trauma, where the brain is injured at the site of direct physical impact (coup), and then inertially strikes the opposite inner wall of the skull (contre-coup).
What else to study on this topic
- CT limitations and skull base bone artifacts
- Three-dimensional (3D) bone reconstruction in fractures
- Diffuse axonal injury (DAI): mechanisms and MRI visualization
- Types of brain herniation syndromes
- MR angiography: TOF sequences and their application
- Primary and secondary injuries in TBI
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