Follow-up screening after subarachnoid haemorrhage: frequency and determinants of new aneurysms and enlargement of existing aneurysms.

Intracranial aneurysms have long been considered a once in a lifetime event. Nevertheless, patients who survive after subarachnoid haemorrhage (SAH) may be at risk for new aneurysms. In a cohort of patients with clipped aneurysms, we studied the yield of screening in the years after the SAH and we tried to identify risk factors for formation of new aneurysms as well as for enlargement of aneurysms that were already present at the time of the SAH. We screened 610 patients who had been admitted between 1985 and 2001 for SAH by means of CT-angiography. Risk factors were evaluated by Cox regression analyses. With screening we detected 129 aneurysms in 96 (16%) patients, after a mean interval of 8.9 years. Of these, 24 (19%) were located at the site of the previously ruptured and clipped aneurysm and 105 (81%) at a site remote from the clip site. Of the aneurysms at a remote site 59 could be compared with the initial (CT)-angiogram. Of these, 19 were truly de novo (32%) and 40 (68%) were already visible in retrospect. Of the 53 aneurysms that were followed over time 13 (25%) had enlarged. Risk factors for aneurysm formation and growth were presence of multiple aneurysms at time of SAH (HR 3.2, 95% CI 1.2-8.6), current smoking (HR 3.8, 95% CI 1.5-9.4) and hypertension (HR 2.3, 95% CI 1.1-4.9). These results suggest that intracranial aneurysms should not be considered as a single event in a lifetime but rather as a continuous process. Patients with a previous SAH have a substantial risk for new aneurysm formation and enlargement of untreated aneurysms. Screening these patients might be beneficial, especially in patients with multiple aneurysms, hypertension and a history of smoking. The risks and benefits of screening, however, should be carefully weighed, for example, in a decision model.