Small Aneurysms with Low PHASES Scores Account for Most Subarachnoid Hemorrhage Cases

Management of small unruptured aneurysms is controversial. Small aneurysms and those with low PHASES scores are often observed. The primary aim of this study was to assess whether the PHASES score classified the patients with subarachnoid hemorrhage as high risk for rupture. We retrospectively reviewed a consecutive series of 628 aneurysmal subarachnoid hemorrhage neurosurgical cases over a 10-year period between 2008 and 2018. We collected patient and aneurysm characteristics and calculated PHASES scores. The median aneurysm size was 5.3 mm (interquartile range, 3.5–7). Of the aneurysms, 75% (473/628) were less than 7 mm in size. Nearly half of the aneurysms were less than 5 mm (48%, 302/628). The median PHASES score was 5 (interquartile range, 4–6), corresponding to a 5-year risk of rupture of only 1.3%. Most ruptured aneurysms in our series were small with low PHASES scores, suggesting a low risk of rupture. Many of these patients would have been conservatively managed. PHASES is inadequate in management of unruptured aneurysms because it fails to identify many patients at risk for subarachnoid hemorrhage. A more nuanced assessment of rupture risk should be undertaken.