2. Stroke


According to WHO is stroke defined as a „neurological deficit of cerebrovascular cause that
persists beyond 24 hours or is interrupted by death within 24 hours“. The symptoms stem from the
affected part of the brain.

Etiologically, stroke can be divided into hemorrhagic (15%) and ischemic (85%).

The cause of ischemic stroke is occlusion of the cerebral artery by thrombus in atherosclerotic
cerebral arteries, less common causes include embolism (eg in the left atrial thrombus) or
occlusion of the artery by thrombus in vasculitis. The cause of spontaneous intracranial hemorrhage
is rupture of the cerebral artery aneurysm, arteriovenous malformation, tumor or coagulopathy.


Diagnostic algorithm:

The initial imaging method for stroke is CT without the application of a contrast agent to rule out
intracranial hemorrhage (ie, to rule out hemorrhagic stroke).

Freshly coagulated blood is hyperdense to brain tissue (70-90HU vs 35HU) and is clearly visible on
native CT.


1. Non-traumatic intracranial hemorrhage

is most often represented by intracerebral hematoma or subarachnoid hemorrhage.

In case of intracerebral hematoma located at typical locations for spontaneous intracerebral
hemorrhage, no further imaging is required. Decision between surgical or conservative treatment is
based on the size, location and expansive behaviour of the hematoma (contralateral shift of midline
structures, edema around the hematoma, brain herniation).

Typical sites of spontaneous intracerebral hemorrhage include the area of the nucleus lentiformis,
thalamus, cerebellum, and brainstem. The most common etiology of spontaneous intracerebral
hemorrhage is hypertension. In atypical localizations of intracerebral hematoma, it is appropriate
to supplement the CT angiography of cerebral arteries to exclude vascular malformation. Tumor
masked with high density of blood may not be distinguished by CT angiography. Such tumor is often
diagnosed perioperatively, in an attempt to evacuate an intracerebral hematoma.


In the presence of non-traumatic subarachnoid hemorrhage on native CT, CT angiography of the
cerebral arteries should be performed to display aneurysm or arteriovenous malformation as a source
of bleeding. In case of a rupture of an aneurysm, in addition to subarachoid hemorrhage, an
intracerebral hematoma may form simultaneously and prolapse into the ventricular system
(hemocephalus). In case of hemocephalus, the cerebral aquaduct (Sylvii) can be blocked by
coagulating blood and hemocephalus may develop.

Subarachnoid hemorrhage (SAK) is divided into spontaneous and traumatic. The most common cause of
spontaneous SAK is a rupture of the aneurysm. It manifests clinically as a sudden, severe pain from
full health (patients report the worst pain they have experienced), it may be accompanied by
vomiting and impaired consciousness.


2. Cerebral ischemia

may have a completely normal finding on native CT in the first 12 hours. If no bleeding is present
on CT, intravenous thrombolysis can be initiated in indicated cases. To verify the vascular
occlusion before possible mechanical thrombectomy, it is again necessary to perform CT angiography
of the cerebral arteries.

In cerebral ischemia of unclear age, the so-called CT perfusion of the brain is sometimes
performed, which displays the infarct itself (already dead brain tissue) and the surrounding
penumbra (ischemized but still viable brain tissue, which can be saved by treatment).


Immediate sign of cerebral ischemia include the relatively rare " dense artery sign" (hyperdense
thrombus asymmetrically on the affected side - most often in a.cerebri media). Sometimes there are
early signs of ischemia (within 6 hours) such as blurred contours of gray and white matter and
blurred contours of cerebral gyri or nucleus lentiformis due to edema. Gradually, in the acute
phase (24 h - 1 week), the ischemic area becomes clearly hypodense due to progressive edema,
sometimes expansive manifestations are expressed (surrounding edema, contralateral shift of midline
structures, etc.). In the subacute phase, the edema gradually disappears and the density of the
affected area increases, the appearance on CT may even return to normal. In the chronic phase, the
affected area is replaced by glia, on CT it is hypodense and atrophic (reduction of brain tissue
volume, focal enlargement of subarachnoid spaces or adjacent brain chambers).


In case of clinical doubt in a normal finding on non-contrast CT, ischemia may be confirmed or
excluded by non-contrast brain MRI. The key sequence for imaging early cerebral ischemia is DWI
(diffusion weighting image) - evidence of restricted diffusion in the ischemic area can be observed
just minutes after stroke due to inactivity of ion pumps on cell membranes (these contribute to the
formation of gradients necessary for diffusion).