Background: The purpose of this retrospective population-based study was to investigate the incidence of subarachnoid haemorrhage from small (5 mm and below) cerebral aneurysms and their localisation in consecutive patients surgically treated in the State of Vorarlberg/Austria.
Methods: Altogether, during the last 4 years, 82 patients after spontaneous subarachnoid haemorrhage (mean age 53.7 years, range 21-84 years, 47 females and 35 males) were referred to the Neurosurgical Department of the Academic Teaching Hospital Feldkirch, serving for all 360,000 inhabitants of the State (corresponding to a subarachnoid haemorrhage incidence of 5.7/100,000/year). In 70 patients (85.4%), a cerebral aneurysm was detected by computed tomography angiography and/or digital cerebral angiography. Out of these, 47 patients (66.2%, mean age 52.1 years, range 24-77 years) were treated with aneurysm clipping and included in the study. Preoperatively, computed tomography, computed tomography angiography and/or digital cerebral angiography were assessed for amount of blood, aneurysm size and localisation, respectively. Clinical status was graded according to the Hunt and Hess classification at admission and according to the Glasgow Outcome Scale at discharge.
Findings: According to Koivisto categories, 18 aneurysms were localised at the anterior cerebral artery, 17 aneurysms at the middle cerebral artery, 11 at the internal carotid artery, and 1 at the vertebrobasilar artery. The mean aneurysm diameter was 7.7 mm (range 3-30 mm). In 34% of the aneurysms the diameter was 5 mm or smaller (n = 16), in 51% between 6 and 10 mm (n = 24) and in 15% between 11 and 30 mm (n = 7). Only 1/17 ruptured middle cerebral artery aneurysms (5.9%), 4/11 internal carotid artery aneurysms (36.4%) and the vertebrobasilar artery aneurysm were small. However, in 10/18 anterior cerebral artery aneurysms (55.6%) the diameter was 5 mm or below.
Conclusions: In conclusion, in our consecutive patient series with clipped cerebral aneurysms after subarachnoid haemorrhage, one third had small ruptured aneurysms, with the anterior cerebral artery complex as the main predilection site. Therefore, despite the previously reported low rupture risk, incidental small aneurysms should also be considered for therapy, depending on localisation and individual risk factors.