Morphological Differences between Single and Multiple Unruptured Aneurysms

Review Article

Austin Neurosurg Open Access. 2014;1(5): 1021.

Morphological Differences between Single and Multiple Unruptured Aneurysms

Sudheer Ambekar, Mayur Sharma and Hugo Cuellar*

Department of Neurosurgery, Louisiana State University Health Sciences Center, USA

*Corresponding author: Hugo Cuellar, Department of Neurosurgery, Louisiana State University Health Sciences Center, Shreveport, 1501 Kings Highway, Shreveport, Louisiana 71130-3932, USA

Received: March 17, 2014; Accepted: July 14, 2014; Published: July 18, 2014

Abstract

The natural history and risk of rupture in multiple unruptured aneurysms is not clearly known. Various Morphometric indices have been proposed to correlate with risk of rupture of intracranial aneurysms. The present study aims to characterize and compare the morphology of patients with unruptured single and multiple aneurysms and correlate the results with rupture risk reported in previous studies. All patients with unruptured single and multiple aneurysms who presented to the hospital from 2009 to 2012 and who had complete 3D digital subtraction angiographic studies were included in the study. Their angiograms were analyzed for aneurysm height, width, and neck width and parent artery diameter. Aspect ratio, bottleneck ratio, height to width ratio and size ratio (SR) of single and multiple aneurysms were compared. 30 patients with single aneurysms and 18 patients with multiple (38) aneurysms were included in the study. Multiple aneurysms had a significantly smaller height and size ratios when compared to single aneurysms. There was no difference in age, gender, history of smoking and hypertension, aneurysm width, neck width, parent artery diameter, aspect ratio, bottle neck ratio and height to width ratio in both the groups. Multiple aneurysms have a lower size ratio than single aneurysms which may translate to a lower rupture risk per aneurysm. However, when patients with multiple aneurysms are considered, the cumulative risk of rupture should be taken into consideration.

Keywords: Unruptured aneurysm; Size ratio; Aspect ratio; Bottleneck ratio

Introduction

ntracranial aneurysms are reported in 0.2 to 9.9 percent of autopsy studies in general population [1,2]. Patients with unruptured intracranial aneurysms (UIA) constitute a unique cohort when compared to those with previous aneurismal subarachnoid hemorrhage (SAH). The prevalence of unruptured aneurysms in general population varies with studies reporting a prevalence of up to 6.5% [3]. The decision whether to actively treat unruptured aneurysms remains a matter of debate due to the small risk of rupture in these aneurysms and the risk of morbidity and mortality due to treatment. On the other hand, treatment of UIAs with high risk of rupture can potentially reduce the morbidity and mortality associated with aneurismal SAH. With rapid advances in intracranial imaging and greater availability of advanced imaging modalities, more and more patients are being diagnosed with UIAs. Multiple intracranial aneurysms are reported in 15-33.5% of patients with intracranial aneurysms [4]. The risk of SAH in patients with multiple intracranial aneurysms remains a matter of debate with some studies reporting an increased risk whereas others reporting similar risk of rupture as in single aneurysms [5,6]. Hence, it is unclear whether multiple unruptured aneurysms behave differently than single unruptured aneurysms.

The major ethical issue in evaluating the natural history of unruptured aneurysms is that, patients with high risk aneurysms cannot be left untreated. Recently, literature has focused on anatomical and morphological characteristics of these lesions with an aim of identifying characteristics associated with high risk of rupture [7-9]. Apart from aneurysm location and size, various parameters have been proposed to identify risk of rupture. Of these, aspect ratio, bottleneck factor and size ratio have been widely studied between ruptured and unruptured aneurysms. However, to date, no study has evaluated the difference in aneurysm morphology between single and multiple unruptured aneurysms. The present study is an attempt to fulfill this lacuna.

Patients and Methods

This is a retrospective study conducted at our institution. Patients who presented to the hospital between 2009 and 2012 were included in the study. Fifty-six patients with unruptured aneurysms presented to the hospital during the study period. Of these, thirty five patients had single unruptured aneurysm and twenty one patients had multiple unruptured aneurysms. Due to incomplete 3D study or unavailable images, eight patients were excluded from the study, leaving thirty patients with single unruptured aneurysms and eighteen patients with multiple unruptured aneurysms. Patients with multiple aneurysms with a history of SAH were excluded from the study. Demographic details, smoking and hypertension were recorded from the case records and aneurysm characteristics recorded from the 3D angiograms of these patients. Aneurysm height, maximum width, neck width and parent artery diameter at the site of aneurysm were measured. In cases where the aneurysm originated at branching point, the mean of all the vessels in relation to the aneurysm was calculated.

Aspect ratio was calculated by dividing height by neck width, bottleneck factor was calculated by dividing maximum width by neck width, height-width ratio was calculated by dividing maximum height by width and size ratio was calculated by dividing maximum height by parent artery diameter.

Statistical Analysis

Age, gender, smoking and hypertension were compared between the two groups using Fisher's extract test and Chi square test. Aspect ratio, bottleneck ratio, height-width ratio and size ratio were compared between the two groups using Mann-Whitney U test. Statistical analysis was performed using SPSS 20 (SPSS Inc.). A statistical difference of P<0.05 was considered significant.

Results

Forty eight patients were included in the study. Thirty patients had single unruptured aneurysms and eighteen patients had thirty-eight unruptured aneurysms. Two patients had three unruptured aneurysms and the rest had two unruptured aneurysms. Majority of the aneurysms in both the groups were located on the internal carotid artery followed by anterior communicating artery, middle cerebral artery and basilar artery in that order. There was one aneurysm on the anterior cerebral artery in the single aneurysm group. Figure 1 depicts the distribution of aneurysms on arteries in both the groups. There were 23 (61%0) aneurysms on ICA in the multiple aneurysms group as against 10 (33.3%) in the single aneurysm group.