Page 304 - Medicine and Surgery

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300 Chapter 7: Nervous system

Aetiology If the patient is suitable for surgical intervention,
In most cases spontaneous subarachnoid haemorrhage carotidandvertebralangiographyisusedtodemonstrate
results from an underlying lesion: the site of the aneurysm or AVM.
Saccular (berry aneurysms), 85%

Arteriovenous malformations, 10% Management

No lesion found, 5% 1 Patients should be resuscitated as necessary.

Saccular or berry aneurysms arise due to defects in the 2 Oral nimodipine (a calcium-channel blocker) has
internal elastic lamina of arteries and occur in 2% of the been shown to reduce mortality. It is thought to work
population. They may be multiple, and tend to occur at by reducing vascular spasm. Severe hypertension may
junctionsofarteriesonthecircleofWillisorwithitsadja- needtobecontrolledbuthypotensionmustbeavoided
cent branches. Common sites include the anterior com- to prevent further loss of perfusion pressure, so pa-
municating artery, the posterior communicating artery tients are kept well hydrated with intravenous saline.
and the middle cerebral artery. Most are idiopathic, but 3 In suitable patients surgical or radiological interven-
theyareassociatedwithdiseasessuchasarteritis,coarcta- tion for aneurysms takes place a few days later in a
tionoftheaorta,Marfan’ssyndromeandadultpolycystic neurosurgical centre:
kidney disease. The neck of the aneurysm is clipped, and in some
Arteriovenous malformations (AVM) are develop- cases the aneurysm is wrapped in gauze to induce
mental abnormalities of blood vessels. afibrous reaction.
An alternative method is to obliterate the lumen of

Clinical features the aneurysm by intra-arterial embolisation using
Sudden onset of a very severe headache, often followed metallic coils.
byvomitingand/orlossofconsciousness.Therearesigns 4 AVMs can be treated with microembolism or focal
of meningeal irritation with neck stiffness and a positive radiotherapy.
Kernig’s sign (pain in back on flexing the hip). Neurolog-
ical signs, papilloedema and retinal haemorrhages may Prognosis
be present. 50% of patients with a subarachnoid haemorrhage die
priortoorsoonafterarrivalInhospital,andafurther10–
Macroscopy 20% die in the first few weeks from rebleeding. Without
Alayer of blood is present over the brain in the subara- interventiontheriskofrebleedingis30%inthefollowing
chnoid space and in the cerebrospinal fluid. year from a berry aneurysm, 10% for AVMs.

Complications Intracranial venous thrombosis
The blood acts as an irritant, causing vascular spasm
leading to further ischaemia, infarction and cerebral Definition
oedema. It also interferes with CSF resorption, causing Venous thrombosis of either cerebral cortical veins or
hydrocephalus which may be acute or chronic. dural venous sinuses, which may result in focal signs.

Investigations Aetiology
CT brain scanning will demonstrate the bleed in most Causesincludetrauma,dehydrationandsepsis,infection
cases, but is falsely negative in up to 15% (less >8 hours of adjacent foci in the head (e.g. middle ear or skull air
after onset), therefore a lumbar puncture to demonstrate sinuses) and it has been associated with thrombophillia,
the presence of blood in the CSF space may be required. oral contraceptives, pregnancy and puerperium.
To differentiate from a ‘bloody tap’, i.e. trauma from the
spinal tap needle, xanthochromia (yellowness of the CSF Pathophysiology
due to blood pigments) is looked for. It appears 12 hours Impairment of venous drainage due to thrombosis may
post SAH, and may persist for 1–2 weeks. lead to venous infarction as tissue congestion may