Prevalence of ruptured small and very small aneurysms: a retrospective single-centre study

Aim of study: To retrospectively assess the occurrence and consequences of subarachnoid haemorrhages (SAH) caused by ruptured intracranial aneurysms (RIA), particularly focusing on the treatment outcomes of small aneurysms treated with either endovascular embolisation or surgical intervention.

Material and methods: We retrospectively analysed data from 408 patients (144 males and 264 females) who were hospitalised between 2013 and 2022 at the Department of Neurosurgery and Neurology in University Hospital Nr 2 in Bydgoszcz, Poland. Clinical conditions at admission, assessed using the Glasgow Coma Scale, Hunt-Hess scale (H-H), modified Rankin scale (mRS), as well as age and sex, were recorded. Additionally, aneurysm data including size, localisation, and the method and outcome of endovascular or surgical treatment were examined.

Results: Among the 408 patients hospitalised due to SAH, the most common localisation of the 375 RIAs was the anterior communicating artery (AcomA) complex (111 cases, 29.6%), followed by the medial cerebral artery (MCA) (95 cases, 25.3%), internal carotid artery (ICA) (94 cases, 25%), and the vertebrobasilar complex (consisting of the basilar artery (BA) - 25 cases, vertebral artery (VA) - 13 cases, anterior inferior cerebellar artery (AICA) - one case, and posterior inferior cerebellar artery (PICA) - four cases), which accounted for 43 SAH cases (11.46%). In 33 cases, neither RIA nor a haemorrhage source was identified, or arteriography showed no cerebral arteries contrast flow. Among the examined group of 375 RIAs, 45 (12%) were microaneurysms (≤ 3 mm), 35 (9%) were small aneurysms (3 ≤ 5 mm), 89 (24%) were medium-sized (5 ≤ 7 mm), and 151 (40%) were large aneurysms (> 7 mm), serving as the source of SAH. A better outcome was significantly associated with lower initial H-H grade (p < 0.001), higher GCS (p < 0.001), lower mRS at admission (p < 0.001), younger age (p < 0.001), smaller size (≤ 3 mm) (p < 0.001), and endovascular treatment (p < 0.001).

Conclusions: In this series, over 21% of patients suffered from SAH resulting from ruptured small aneurysms (≤ 5 mm), with 12% specifically attributed to ruptured very small aneurysms (≤ 3 mm), despite large aneurysms (> 7 mm) being the most prevalent source of bleeding in 40% of cases. A worse prognosis was primarily associated with the severity of SAH, reflected in poorer clinical status at admission and older age. Endovascular embolisation was found to be effective and associated with better outcomes compared to surgical treatment.