Acute Haemorrhagic Stroke

Introduction

Haemorrhagic stroke is less common than occlusive ischaemic stroke. About 15% of stroke is due to primary haemorrhage which can be SAH, subdural, parenchymal, intraventricular, or any combination. Vascular imaging is essential in SAH and in many cases of parenchymal haemorrhage where a structural cause is likely on imaging criteria or if urgent surgical evacuation is planned.

MDCTA is now accepted (almost univerally) as the primary investigation of acute SAH if it is available. It has been proved to be accurate and acceptable to patients and DSA is only occasionally required as a diagnostic tool if MDCT is not available, or normal and a vascular cause remains likely. Cerebral aneurysms are the commonest cause of SAH, but MDCTA must be good enough to include the accurate diagnosis of the other causes including arteriovenous malformation (AVM), dural fistula, vascular dissection, and other rarer causes. MDCTA is almost as good as rotational DSA in the display of vascular and aneurysm anatomy necessary for treatment planning. Such DSA requires selective carotid/vertebral artery catheterization, which limits it to dedicated neuroradiological sites.

The technique is also useful in the immediate postoperative phase or in delayed referral when secondary vasospasm requires vascular imaging in addition to transcranial Doppler ultrasound assessment. It can also be used to assess aneurysms clipped with titanium clips, or aneurysms at other locations in patients treated with other types of clips or coils.

MDCTA is also used extensively as a first examination in the investigation of spontaneous parenchymal haemorrhage and, because of its ease of use, it is applied even if an underlying vascular cause is not very likely.

It must always be remembered that venous thrombosis can also present as an acute haemorrhagic stroke (see figure 1.6 and Chapter 11).

Technique

CT angiography of the Circle of Willis

The field of view selected routinely covers only the Circle of Willis from C1 to above the ventricles. Other centres will routinely include the whole head. In any case, if there is an intracerebral haematoma, the field of view must cover it completely. Table 9.1 presents optimal patient preparation, Table 9.2 presents the parameters for CTA of the Circle of Willis, and 9.1 shows surviews for a bolus tracking Circle of Willis study.

As the patient is likely to go for interventional treatment of many of the vascular abnormalities found, in all patients aged 60 or over the scan should begin at C6 to include the carotid bifurcation and so aid DSA planning. The trigger for bolus tracking is set to 150 Hounsfield units (HU). A sufficient post-threshold delay should be anticipated to allow for the distance between tracker and clinical scan starting position (usually 4 seconds for a 4-slice scanner).

The initial routine CT should be reviewed prior to setting up the MDCTA to ensure that any parenchymal haematoma will be completely included in the scan. If there is a large clot, marked hydrocephalus, or the patient is in a very poor clinical grade, it is better to forego bolus tracking in favour of a scan delay of 22 seconds from the start of the injection. If there is increased intracranial pressure there will be a delay to the intracranial vessel filling, which is not allowed for with cardiac dependent bolus tracking.

Reconstruction and reformation

Base image review should be followed by a VR3D review of all likely aneurysm sites. This usually gives the best appreciation of the shape and vascular relationships of any aneurysm. Measurements must be made on base images or MIP/MPR reformations. Surface VR3D often aids in the understanding of a superficial AVM.

Table 9.1 Patient preparation for CTA

Patients must be completely still throughout this scan as even slight movement during the sequence renders the volume data useless for postprocessing
The agitated patient should be supported in the scanner if possible to avoid the need to repeat examinations
A venflon (18 or 20 gauge) should be placed in the antecubital fossa in preparation for the high-pressure pump injection
A careful explanation of the effects of the high-pressure injection should be explained to conscious patients to avoid movement during the scan due to discomfort

Pathology and illustrations

Aneurysm

AVM/fistula

Intracerebral vessel dissection

Fragile collaterals:

atheroma
moya-moya

Mycotic aneurysm

Tumour

Bleeding/coagulation disorder

Venous thrombosis (see Chapter 11)

Many of the above causes will be demonstrated with the emphasis on aneurysm assessment.

Table 9.2 Protocol parameters for CTA of the Circle of Willis

Patient position	Supine
Surview	Dual – AP/LAT
First Slice	Spinous process C1
Last slice	To cover Circle of Willis
Field of view	˜180 mm
Slice width	0.67 mm
Slice increment	0.33 mm
Pitch	0.685 mm
Collimation	64 × 0.625 mm
Rotation time	0.5 sec
kV/mAs	120 kV/300 mAs
Resolution	Standard
Filter	Soft tissue with bone/brain correction if available
Reconstructive zoom	To include Circle of Willis, anterior cerebral arteries, pericallosal arteries, and basilar artery with associated vessels (see figure 9.1)
Windowing	WC 60
	WW 360
Contrast	60 ml contrast
	High-pressure pump
	injection at 5 ml/sec
	Bolus tracking – trigger
	150 HU on ascending aorta