Acute traumatic brain injury (TBI)
Traumatic brain injury is the leading cause of death in patients under 40 years of age. In the acute period, CT is the absolute first-line diagnostic imaging method. The main advantages of the technique are its ubiquitous availability, extremely high scanning speed, and the absence of the need for contrast enhancement. This makes it possible to instantly examine patients with polytrauma, covering the brain, spine, and other areas.
The primary task of the diagnostician is to identify pathologies requiring emergency neurosurgical intervention:
- Active intracranial hemorrhage.
- Blood accumulations (extra-axial and intra-axial hematomas).
- Displacement or herniation of brain structures.
- Acute hydrocephalus.
- Depressed skull fractures.
In subsequent stages, CT is used to assess secondary complications, such as progressive edema, infarct formation, or the appearance of delayed hemorrhages.
Scanning technique and window settings
Scanning is performed in helical mode with the patient in the supine position. The scanning area covers the region from the skull base to the vertex. Prior to scanning, a topogram is acquired, which helps assess major vault fractures and foreign bodies.
For accurate diagnosis, it is essential to properly utilize density display modes (windows):
- Brain window: Uses a narrow window (level 40 HU, width 80 HU). This reduces image noise and allows for a detailed examination of brain parenchyma structures on approximately 5 mm slices.
- Hemorrhage window: Requires wider settings (level 70 HU, width 150–200 HU). Enhanced contrast between bone and blood helps avoid missing small subdural or epidural hematomas that may be obscured by standard settings.
- Multiplanar analysis: The coronal projection is indispensable for detecting blood in the projection of the falx cerebri (falx cerebri), tentorium cerebelli (tentorium cerebelli), and identifying herniation syndromes. The sagittal plane clearly demonstrates the clivus (clivus), pituitary fossa, and craniocervical junction.
The main limitation of CT is the occurrence of severe bone artifacts at the border with the brain parenchyma, especially in the posterior cranial fossa and infratemporal regions.
CT angiography and venography
To visualize blood vessels, intravenous bolus administration of an iodine-based contrast agent is used.
CT angiography (CTA) is effective for detecting dynamic contrast extravasation (a sign of an enlarging hematoma) and intracranial aneurysms. Unlike MR angiography, CTA is faster, compatible with pacemakers, safe in patients with claustrophobia, and allows the evaluation of the superior mediastinum, neck, and intracranial vessels in a single pass.
CT venography (CTV) is performed with a delayed scan time so that the contrast agent fills the venous bed. The use of dual-source scanners allows for software-based bone subtraction of the skull base. The main indications for CTV are:
- Suspected deep or superficial cerebral venous thrombosis.
- Assessment of venous sinus invasion by tumors (falx meningiomas).
- Dural venous sinus stenoses.
Blood flow assessment and perfusion
CT perfusion is the universally accepted standard of diagnosis in stroke centers. Its main goal is to search for the penumbra (penumbra), or the zone of reversible ischemia. Timely identification of this zone allows brain tissue to be salvaged via thrombolysis or thrombectomy. Perfusion is also used to detect delayed vasospasm (occurring approximately one week after subarachnoid hemorrhage) and to evaluate blood flow following the administration of vasodilators (acetazolamide).
Radioisotope methods for studying regional blood flow (PET, SPECT) are rarely used in routine practice because strokes are more frequently caused by embolism rather than primary blood flow deficiency. Color duplex ultrasonography serves as an accessible alternative for examining neck vessels, accurately detecting even minimal stenoses.
To remember CT windows: "Soft tissue is narrow, blood is wide." Brain parenchyma requires a narrow brain window to reduce noise, while fresh blood (especially near bone) is better differentiated using a wide window.
Class and exam questions
Can ongoing intracerebral hemorrhage be seen on CT angiography?
Yes, a sign of active hematoma enlargement is dynamic contrast extravasation—the leakage of contrast medium outside the vascular lumen into the brain tissue.
In what cases is the WEB intrasaccular device used for an aneurysm?
The deployment of an intrasaccular flow-diverting device is used when primary treatment fails. For example, if standard coil embolization results in compaction and the aneurysm neck refills with blood.
Why is transcranial doppler ultrasonography (ultrasound through skull bones) used less frequently than CT?
Ultrasonography is highly effective for evaluating neck vessels; however, the transcranial approach has insufficient reliability due to the dense bony barrier of the cranial vault.
What else to study on this topic
- Clinical manifestations and cerebrovascular syndromes in individual cerebral artery occlusions.
- Dependence of stroke symptom dynamics on its type (emembolic, hemodynamic, lacunar).
- Limitations of nuclear medicine (PET and SPECT) in stroke risk screening.
- CT bone algorithms and 3D reconstruction in non-displaced linear fractures.
- MR angiography for follow-up evaluation of aneurysm occlusion in the long term (at 6 months).
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