Unruptured intracranial aneurysms: initial and follow-up screening

Abstract

Unruptured intracranial aneurysms may rupture, causing subarachnoid haemorrhage (SAH). SAH is a devastating subtype of stroke, resulting in death or severe disability in half the patients. This thesis has a focus on initial and follow-up screening for unruptured intracranial aneurysms, and consists of two parts. The first part aims to find risk factors for growth and/or rupture of unruptured aneurysms. In this thesis it is shown that local arterial geometry of the circle of Willis, analysed as arterial diameter and bifurcation angles, is related to aneurysm development. For small unruptured aneurysms, the risk of rupture is small, and follow-up screening is often performed rather than immediate preventive aneurysm treatment. During a median follow-up of 2 years, around 10% of these aneurysms show growth. Risk factors for growth during follow-up are aneurysm size, aneurysm shape and smoking. Patient related risk factors such as age, gender and alcohol use may influence the actual location of the aneurysm that ruptures.

The second part of this thesis has a focus on familial SAH. Persons with two or more first degree relatives with SAH have an increased risk of SAH themselves. In this thesis, the incidence of SAH is compared between persons without a relative with SAH, with one relative with SAH and with two or more relatives with SAH. Persons with one first degree relative with SAH have a slightly increased risk of SAH, whereas persons with two or more first degree relatives with SAH have a markedly increased risk of SAH. This markedly increased risk of SAH is equal to a substantial life time risk of SAH, and thus makes preventive screening for unruptured aneurysms in these persons an attractive alternative. As aneurysms develop during life, screening would have to be repeated. The cost-effectives of screening and the optimal screening interval for persons with familial SAH is calculated using a Markov model. With the data available at this point, any form of screening is cost effective in persons with familial SAH, with repeated screening every 3-7 years, from age 20-80 as the most cost effective strategy. The University Medical Center Utrecht has been offering repeated screening for persons with familial SAH for the last 20 years. In total 458 persons decided to have at least one screening angiography. Per screening cycle (median screening interval 5 years) around 5% of the angiographies show a newly diagnosed intracranial aneurysm. Risk factors for an aneurysm at the initial screening are smoking and three or more first degree relatives with SAH (as opposed to exactly two first degree relatives with SAH). Persons with a previous aneurysm have an increased risk of a new aneurysm at the initial screening as well as at follow-up screening. Not all SAH can be prevented by screening, as two persons developed SAH despite adherence to the screening program.