ANEURYSM
Definition
The word aneurysm comes from the Latin word aneurysma, which means dilatation. Aneurysm is an abnormal local dilatation in the wall of a blood vessel, usually an artery, due to a defect, disease, or injury. Aneurysms can be true or false. A false aneurysm is a cavity lined by blood clot. The 3 major types of true intracranial aneurysms are saccular, fusiform, and dissecting.
The common causes of intracranial aneurysm are haemodynamically-induced or degenerative vascular injury, atherosclerosis (typically leads to fusiform aneurysms), underlying vasculopathy (e.g., fibromuscular dysplasia), and high-flow states, as in arteriovenous malformation (AVM) and fistula. Uncommon causes include trauma, infection, drugs, and neoplasms (primary or metastatic).
Aetiology / Risk Factors
Recent studies have found scant evidence for congenital, developmental, or inherited weakness of the arterial wall. Although genetic conditions are associated with increased risk of aneurysm development (see below), most intracranial aneurysms probably result from haemodynamically-induced degenerative vascular injury. The occurrence, growth, thrombosis, and even rupture of intracranial saccular aneurysms can be explained by abnormal haemodynamic shear stresses on the walls of large cerebral arteries, particularly at bifurcation points. Less common causes of saccular aneurysms include trauma, infection, tumour, drug abuse (cocaine), and high-flow states associated with AVMs or fistulae. Conditions that have been associated with increased incidence of cerebral aneurysms are as follows:
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Anomalous vessels
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Coarctation of the aorta
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Polycystic kidney disease
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Fibromuscular dysplasia
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Connective tissue disorders (e.g., Marfan, Ehlers-Danlos)
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High-flow states (e.g., vascular malformations, fistulae)
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Spontaneous dissections
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Trauma
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Tumour
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Infection of arterial wall
Symptoms and Signs
Most aneurysms do not cause symptoms until they rupture. When they rupture, they are associated with significant morbidity and mortality. Subarachnoid haemorrhage The most common presentation of intracranial aneurysm is SAH. In North America, 80-90% of non-traumatic SAHs are caused by rupture of an intracranial aneurysm. Another 5% are associated with bleeding from an AVM, and the remaining 15% are idiopathic. On presentation, patients typically report experiencing the worst headache of their lives. The association of meningeal signs should increase suspicion of SAH.