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 the junction points of the arteries; they are most often located on the anterior communicating artery, the posterior communicating artery and the middle cerebral artery. Size affects the risk of rupture: in small aneurysms (<7 mm) the annual rupture risk is quite low, while the risk rises as they grow. The most important modifiable risk factors are smoking and uncontrolled hypertension; in addition, advanced age, female sex and excessive alcohol consumption play a role. Genetic and congenital factors include a family history, polycystic kidney disease (ADPKD), Ehlers-Danlos type IV and Marfan syndrome. For this reason, screening (MRA) is considered in those with a family history of two or more aneurysms/bleeds and in certain genetic diseases.
Symptoms and the Emergency of Rupture (Subarachnoid Haemorrhage)
Most unruptured aneurysms are asymptomatic and are found incidentally on an MRI/CT taken for other reasons. Large aneurysms can press on neighbouring structures and cause findings such as a drooping eyelid, double vision or vision loss. When an aneurysm ruptures, a subarachnoid haemorrhage (SAH) develops, and this is a life-threatening emergency: a sudden headache beginning within seconds that the person describes as 'the worst headache of my life', neck stiffness, nausea and vomiting, light sensitivity and loss of consciousness can occur. In this situation one must go to the emergency department immediately and call the emergency number. After SAH, re-bleeding and acute hydrocephalus in the early period, and vasospasm peaking on days 7–10 in the later period, are important risks that are closely monitored in intensive care.
Observation 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. In small aneurysms located in the anterior circulation, imaging follow-up with annual MRA/CTA and control of risk factors (smoking cessation, blood-pressure management) may generally be sufficient. Treatment comes to the fore in the following situations: aneurysms above a certain size, those growing rapidly, symptomatic aneurysms causing pressure findings, smaller sizes in the presence of a family history, and young patients with a long life expectancy. For this reason, saying 'I have an aneurysm' does not by itself mean 'I need surgery'.
Endovascular Coiling (From Within the Vessel, Minimally Invasive)
Coil embolisation is based on reaching the aneurysm with a catheter introduced through the groin and placing platinum spiral wires (coils) to fill the aneurysm sac from within and isolate it from the blood flow. In wide-necked aneurysms balloon- or stent-assisted techniques are used, and in some large aneurysms flow-diverter stents. It is performed under general anaesthesia; no craniotomy is needed, recovery is relatively quick (usually a 2–3 day hospital stay) and it comes to the fore particularly in elderly patients or those at high surgical risk. Its disadvantage is the possibility of the aneurysm reopening (recanalisation) in some cases and the usual need for a period of dual antiplatelet therapy with periodic control angiography.
Microsurgical Clipping (Open Surgery)
Clipping is the placement of a small titanium clip on the neck of the aneurysm under the microscope through a craniotomy, permanently separating the aneurysm from the circulation. During the procedure the clip placement is checked with ICG angiography, micro-Doppler and neurophysiological monitoring. It offers a permanent solution and the risk of reopening is very low; it is preferred particularly in wide-necked, complex aneurysms, aneurysms located on the middle cerebral artery and aneurysms that have reopened after coiling. Its disadvantage is that it requires a craniotomy and that recovery is somewhat longer than with coiling (usually a 5–7 day hospital stay). Which method is chosen is determined by evaluating together the size of the aneurysm, the width of its neck, its location and the patient's general condition.