An intracranial aneurysm, also known as a cerebral aneurysm, is a cerebrovascular disorder characterized by a localized dilation or ballooning of a blood vessel in the brain due to a weakness in the vessel wall. These aneurysms can occur in any part of the brain but are most commonly found in the arteries of the cerebral arterial circle, also known as the Circle of Willis. The risk of rupture varies with the size and location of the aneurysm, with those in the posterior circulation being more prone to rupture. Cerebral aneurysms are classified by size into small, large, giant, and super-giant, and by shape into saccular (berry), fusiform, and microaneurysms. Saccular aneurysms are the most common type and can result from various risk factors, including genetic conditions, hypertension, smoking, and drug abuse. Symptoms of an unruptured aneurysm are often minimal, but a ruptured aneurysm can cause a subarachnoid hemorrhage which may present with severe headaches, nausea, vision impairment, and loss of consciousness. Treatment options include surgical clipping and endovascular coiling, both aimed at preventing further bleeding. Diagnosis typically involves imaging techniques such as CT or MR angiography and lumbar puncture to detect subarachnoid hemorrhage. Prognosis depends on factors like the size and location of the aneurysm and the patient’s age and health, with larger aneurysms having a higher risk of rupture and poorer outcomes. Advances in medical imaging have led to increased detection of unruptured aneurysms, prompting ongoing research into their management and the development of predictive tools for rupture risk.
Classification
Cerebral aneurysms are classified both by size and shape:
Small aneurysms have a diameter of less than 15 mm. Larger aneurysms include those classified as large (15 to 25 mm), giant (25 to 50 mm) (0.98 inches to 1.97 inches), and super-giant (over 50 mm).
Berry (saccular) aneurysms Saccular aneurysms, also known as berry aneurysms, appear as a round outpouching and are the most common form of cerebral aneurysm. Causes include connective tissue disorders, polycystic kidney disease, arteriovenous malformations, untreated hypertension, tobacco smoking, cocaine and amphetamines, intravenous drug abuse (can cause infectious mycotic aneurysms), alcoholism, heavy caffeine intake, head trauma, and infection in the arterial wall from bacteremia, i.e. mycotic aneurysms and related disorders.
Fusiform aneurysms Fusiform dolichoectatic aneurysms represent a widening of a segment of an artery around the entire blood vessel, rather than just arising from a side of an artery's wall. They have an estimated annual risk of rupture of %1.6 to %1.9.
Microaneurysms
Microaneurysms, also known as Charcot–Bouchard aneurysms, typically occur in small blood vessels (less than 300 micrometres in diameter), most often the lenticulostriate vessels of the basal ganglia, and are associated with chronic hypertension. Charcot–Bouchard aneurysms are a common cause of intracranial hemorrhage.
Signs and symptoms A small, unchanging aneurysm will produce few, if any, symptoms. Before a larger aneurysm ruptures, the individual may experience such symptoms as a sudden and unusually severe headache, nausea, vision impairment, vomiting, and loss of consciousness, or no symptoms at all.
Subarachnoid bleed
If an aneurysm ruptures, blood leaks into the space around the brain. This is called a subarachnoid hemorrhage. Onset is usually sudden without prodrome, classically presenting as a "thunderclap headache" worse than previous headaches. Symptoms of a subarachnoid hemorrhage differ depending on the site and size of the aneurysm. Symptoms of a ruptured aneurysm can include:
a sudden severe headache that can last from several hours to days nausea and vomiting drowsiness, confusion and/or loss of consciousness visual abnormalities meningism dizziness Almost all aneurysms rupture at their apex. This leads to hemorrhage in the subarachnoid space and sometimes in brain parenchyma. Minor leakage from aneurysm may precede rupture, causing warning headaches. About 60% of patients die immediately after rupture. Larger aneurysms have a greater tendency to rupture, though most ruptured aneurysms are less than 10 mm in diameter.
Microaneurysms A ruptured microaneurysm may cause an intracerebral hemorrhage, presenting as a focal neurological deficit. Rebleeding, hydrocephalus (the excessive accumulation of cerebrospinal fluid), vasospasm (spasm, or narrowing, of the blood vessels), or multiple aneurysms may also occur. The risk of rupture from a cerebral aneurysm varies according to the size of an aneurysm, with the risk rising as the aneurysm size increases.
Vasospasm
Vasospasm, referring to blood vessel constriction, can occur secondary to subarachnoid hemorrhage following a ruptured aneurysm. This is most likely to occur within 21 days and is seen radiologically within 60% of such patients. The vasospasm is thought to be secondary to the apoptosis of inflammatory cells such as macrophages and neutrophils that become trapped in the subarachnoid space. These cells initially invade the subarachnoid space from the circulation in order to phagocytose the hemorrhaged red blood cells. Following apoptosis, it is thought there is a massive degranulation of vasoconstrictors, including endothelins and free radicals, that cause the vasospasm.
Risk factors Intracranial aneurysms may result from diseases acquired during life, or from genetic conditions. Hypertension, smoking, alcoholism, and obesity are associated with the development of brain aneurysms. Cocaine use has also been associated with the development of intracranial aneurysms. Other acquired associations with intracranial aneurysms include head trauma and infections.
Genetic associations Coarctation of the aorta is also a known risk factor, as is arteriovenous malformation. Genetic conditions associated with connective tissue disease may also be associated with the development of aneurysms. This includes:
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