Subarachnoid Haemorrhage

Angiography (contd)

Four-vessel angiography is usually performed in all patients. Antero-posterior, lateral and oblique views are required for each vessel.

Look for aneurysms at vessel bifurcations around the circle of Willis, on the middle cerebral and pericallosal vessels, and on the vertebral artery at the posterior inferior cerebellar artery origin. (Mycotic aneurysms lie more peripherally.)

Note 'spasm' of an arterial segment, usually near a ruptured aneurysm, although it may be distant or diffuse.

Carotid angiogram - lateral view

Carotid angiogram - lateral view

Look for arteriovenous malformations - an abnormal leash of blood vessels demonstrated in the arterial phase. N.B. Small AVMs are difficult to detect and only early filling of a vein may draw attention to their presence.

Beware mistaking a vessel loop seen end-on for an aneurysm - an aneurysm will be evident on more than one view, e.g. lateral and oblique.

MAGNETIC RESONANCE ANGIOGRAPHY (MRA) is a useful noninvasive technique for demonstrating intracranial aneurysms (see page 41), but the resolution is still insufficient to ensure that small aneurysms are not missed.

Negative angiography

Angiography fails to reveal a source of the subarachnoid haemorrhage in approximately 20% of patients. In the presence of arterial spasm, reduction in flow may prevent the demonstration of an aneurysm and repeat angiography may be required at a later date.

Prognosis: In patients with a 'perimesencephalic' pattern of haemorrhage on CT scan and with negative angiography, the outlook is excellent; those patients with an 'aneurysmal' pattern with blood lying in the interhemispheric or Sylvian fissure still run a risk of rebleeding.

n.b. Rupture of a spinal angioma also results in SAH - if the patient's pain begins in the back before spreading to the head, or if any features of cord compression are apparent, then myelography should be the preliminary investigation (see page 409).

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