CT Angiography Head and Neck
CT angiography (CTA) of the head and neck images the arteries from the aortic arch to the vertex of the skull after a fast intravenous bolus of iodinated contrast.
The bolus is 50 to 70 mL of non-ionic medium at 4 to 5 mL each second, followed by a 40 mL saline flush. Timing uses bolus tracking in the aortic arch or a fixed delay of 20 to 25 seconds.
Thin slices (0.5 to 0.625 mm) are reconstructed in axial planes, with multiplanar, curved planar, maximum intensity projection and volume rendered images, and bone subtraction for the skull base. A venous phase or a delayed phase can be added for venous sinus thrombosis.
The scan takes under 20 seconds and the whole examination 10 to 15 minutes. Effective dose is about 2 to 5 mSv.
Stroke affects about 12 million people each year, and large vessel occlusion accounts for about 25 to 40% of ischaemic strokes and a larger share of disabling ones.
CTA has a sensitivity of over 95% for large vessel occlusion and for intracranial aneurysms over 3 to 4 mm (about 85 to 90% for those under 3 mm). Sensitivity and specificity for carotid stenosis over 70% are about 90 to 95%.
Subarachnoid haemorrhage from aneurysm rupture affects about 6 to 10 in 100 000 people yearly. CTA is often done together with non-contrast CT head and CT perfusion in one visit.
Indications. Acute ischaemic stroke or transient ischaemic attack (large vessel occlusion, selection for thrombectomy, carotid and vertebral disease). Subarachnoid haemorrhage (aneurysm detection and treatment planning). Intracranial haemorrhage of uncertain cause (arteriovenous malformation, aneurysm, venous thrombosis).
Suspected arterial dissection after neck trauma, neck pain with Horner syndrome, or blunt cerebrovascular injury. Penetrating neck injury. Carotid and vertebral stenosis, occlusion and plaque.
Screening for intracranial aneurysm in selected high risk patients. Vascular tumours (paraganglioma, carotid body tumour, juvenile angiofibroma). Pulsatile tinnitus and vascular malformations.
Vasculitis and moyamoya disease (as first look, MR often preferred). Pre-operative planning of skull base and neck surgery. Post-operative assessment of stents, clips and coils (with metal artefact limits).
Brain death confirmation support in selected settings. Not for routine screening of the general population.
Contraindications and precautions. Previous severe reaction to iodinated contrast (premedication or MR angiography instead). Renal impairment (estimated glomerular filtration rate under 30 mL each minute each 1.73 square metres: weigh benefit against risk; in acute stroke and haemorrhage do not delay the scan for creatinine). Metformin (follow local advice).
Thyroid disease and recent iodine treatment. Pregnancy: low foetal dose from a head and neck scan, so acceptable for urgent indications. Children: low dose, weight based contrast.
A 18 to 20 G cannula in the right antecubital vein is used, and extravasation is watched.
Preparation and technique. No fasting is needed in emergencies. The patient lies supine with the head in a holder, chin slightly tucked, and is told not to swallow or move during the scan. The scan runs from the aortic arch to the vertex, after a non-contrast head scan if one is needed.
Contrast is given by pump through the right arm (to reduce dense artefact from the left brachiocephalic vein). Arterial phase is triggered by bolus tracking at the arch. A late arterial or venous acquisition shows collaterals and dural sinuses.
Tube voltage of 80 to 100 kV reduces contrast and dose in slim patients. Reconstructions include curved planar views along each carotid and vertebral artery, with measurement of stenosis by comparing the narrowest lumen diameter with the normal distal internal carotid artery diameter.
