Aneurysm size: a prognostic factor for rupture.

For effective management of patients with unruptured intracranial aneurysms, prognostic criteria for rupture are needed, of which aneurysm size is a key factor. However, the critical size at which an aneurysm becomes hazardous is not known. During the last 5 years, 1558 aneurysm patients have been operated on in our centre. Of these 1248 presented with a subarachnoid haemorrhage (ruptured aneurysms) and 310 without a subarachnoid haemorrhage (unruptured aneurysms). Of the ruptured aneurysms 475 (38%) were small in size with a maximum diameter < 6 mm. Most of these small ruptured aneurysms were located on the anterior communicating artery. Of the 310 patients with unruptured aneurysms 253 (81.6%) had single aneurysms; 113 (44.7%) of those were small in size. Most of these small unruptured aneurysms were located on the middle cerebral artery. The remaining 57 patients with unruptured aneurysms harboured multiple aneurysms totalling 116 aneurysms; 50% of them were small in size. Our of 160 patients with multiple aneurysms presenting with subarachnoid haemorrhage, 34 patients had small aneurysm(s) accompanied with medium or large sized aneurysm(s); in nine (26.5%) of these 34 patients the small aneurysm was the ruptured one. These data suggest that small aneurysms < 6 mm in diameter are not innocuous and hazardous, and surgical treatment should be considered for small unruptured aneurysms even if they are less than 6 mm in diameter.