What Is a Brain Aneurysm and Who Is at Risk?
Aneurysms usually form around the circle of Willis at the base of the brain, at arterial junction (bifurcation) points; the most common locations are the anterior communicating artery, the posterior communicating artery and the middle cerebral artery. The most common type is the sac-shaped saccular (berry) aneurysm; in the rarer fusiform type the entire vessel wall is dilated. Size affects the risk of rupture: in small aneurysms (<7 mm) the annual rupture risk is quite low and increases as they grow. The most important modifiable risk factors are smoking and uncontrolled hypertension; older age, female sex and excessive alcohol also play a role. Genetic and congenital factors include a family history, polycystic kidney disease (ADPKD), Ehlers-Danlos type IV and Marfan syndrome. Screening with MRA is therefore considered in those with two or more aneurysms/haemorrhages in the family and in certain genetic conditions.
Symptoms and the Rupture (Subarachnoid Haemorrhage) Emergency
Most unruptured aneurysms are asymptomatic and are found incidentally on MRI/CT done for other reasons. Large aneurysms can press on neighbouring structures and cause drooping eyelid, double vision or visual loss; a posterior communicating artery aneurysm in particular produces a typical picture through third-nerve compression. When an aneurysm ruptures, subarachnoid haemorrhage (SAH) develops and this is a life-threatening emergency: a sudden headache starting within seconds that the person describes as 'the worst headache of my life' (thunderclap), neck stiffness, nausea-vomiting, light sensitivity and loss of consciousness. In this picture one must go to the emergency department immediately and call the emergency number. Early after SAH, rebleeding and acute hydrocephalus, and in the later phase vasospasm peaking on days 7–10, are important risks; the patient is closely monitored in intensive care and nimodipine is given routinely.
Surveillance or Treatment? How Is the Decision Made?
An unruptured aneurysm does not always require surgery; the decision is patient-specific and risk is estimated with tools such as the PHASES score (population, hypertension, age, size, prior haemorrhage and location are weighed). In small, anterior-circulation aneurysms, annual imaging follow-up with MRA/CTA and control of risk factors (smoking cessation, blood-pressure management) may be sufficient. Treatment comes to the fore in: aneurysms above a certain size, those growing rapidly, symptomatic aneurysms causing compression, smaller sizes in the presence of a family history, posterior-circulation location and young patients with a long expected life span. Having an aneurysm therefore does not by itself mean 'I must be operated on'; avoiding unnecessary surgery is a decision at least as important as treatment.
Endovascular Coiling (From Within the Vessel, Closed Method)
Coil embolisation is based on reaching the aneurysm via a catheter introduced from the groin (femoral artery) and placing platinum spiral wires (coils) to fill the aneurysm sac from the inside and isolate it from blood flow. In wide-necked aneurysms balloon- or stent-assisted techniques are used, and in some large, wide-necked aneurysms flow-diverter stents. It is performed under general anaesthesia; no craniotomy is required, recovery is relatively quick (usually 2–3 days in hospital, return to work in 1–2 weeks) and it comes to the fore especially in older or high-surgical-risk patients. The ISAT study showed that in suitable patients coiling can be applied with less morbidity. Its drawback is the possibility of the aneurysm reopening (recanalisation) in some cases and generally the need for a period of dual antiplatelet therapy with periodic control angiography.
Microsurgical Clipping (Open Surgery)
Clipping is performing a craniotomy and, under the microscope, placing a small titanium clip across the neck of the aneurysm to permanently separate it from the circulation. During the procedure clip placement is checked with ICG (indocyanine green) angiography, micro-Doppler and neurophysiological monitoring; in complex cases temporary clipping may be used. It offers a permanent solution and the risk of reopening is very low; it is preferred especially in wide-necked and complex aneurysms, in middle-cerebral-artery aneurysms and in aneurysms that have reopened after coiling. Its drawback is that it requires a craniotomy and recovery is slightly longer than with coiling (usually 5–7 days in hospital, return to work in 4–6 weeks). Which method is chosen is decided jointly according to the size of the aneurysm, neck width, location and the patient's general condition; in experienced centres both methods are successful.