Size and location of ruptured and unruptured intracranial aneurysms measured by 3-dimensional rotational angiography

Abstract

Objective

The aim of the study was to report about accurate size and location of a consecutive series of ruptured and unruptured aneurysms taking the complex 3-dimensional (3D) anatomy and parent vessel morphology into consideration by using the newly developed 3D rotational angiography (3D-RA).

Methods

One hundred eighteen consecutive patients with 155 saccular intracranial aneurysms were included in the study and received 3D-RA reconstructions for measurement of maximal height and width of the aneurysmal sac. Statistical evaluation compared values for ruptured (n = 83) and unruptured (n = 72) aneurysms.

Results

Mean height and width of unruptured aneurysms were 5.7 and 5.7 mm; of ruptured aneurysms, 6.7 and 6.1 mm (not significant, P = .7 for height and P = .9 for width). The majority of ruptured aneurysms, 81.9% and 59%, were smaller than 10 and 7 mm; likewise, 81.9% and 68.1% of unruptured aneurysms were smaller than 10 and 7 mm. The difference in frequency of small (<10/<7 mm) aneurysms between unruptured and ruptured aneurysms was not significant (P = 1.0 and .32, respectively). The majority (69.4%) of small ruptured aneurysms (<7 mm) were located in the anterior circulation. Most ruptured aneurysms were in the size group 4 to 6 mm in height and 2 to 4 mm in width, and a critical threshold size for aneurysm rupture could not be identified.

Conclusions

An automated calibration procedure applied to all images and excellent visualization of aneurysm and parent vessel morphology using 3D-RA allow accurate size measurement of intracranial aneurysms which may be smaller than previously thought. Small aneurysm (<7 mm), also in the anterior circulation, should be carefully evaluated for treatment.

Introduction

Subarachnoid hemorrhage (SAH) from rupture of an intracranial aneurysm is a devastating event with a mortality of up to 50% [2], [5], [19]. The life-threatening and debilitating sequelae of SAH may be prevented if the aneurysm can be occluded before rupture. Recent epidemiological research [22] on patients with aneurysms and family members, as well as laboratory work on the genome [26], may open efficient ways to identify patients with a high risk of having UIAs. To offer aneurysm treatment to patients with UIAs, the periprocedural risks of surgery or endovascular coiling and the cumulative risk of rupture after treatment must be less than the cumulative risk of rupture with the associated mortality and morbidity when managed conservatively. Unfortunately, the natural history of UIAs is not exactly known. The most common estimations for the risk of rupture of a UIA were between 0.5% and 2.5% per year [9], [12], [13], [24], [31], [32]. Data from the retrospective ISUIA study [25] calculated a much lower risk of rupture (0.05%/year) of aneurysm less than 10 mm in patients with no history of SAH. Prospective data from the ISUIA found a risk of rupture of 0.52% for aneurysms 7 to 12 mm in size located at the anterior circulation and even of 2.9% per year for aneurysms of the same size located at the posterior circulation [30]. However, not a single aneurysm less than 7 mm located in the anterior circulation ruptured during an average of 4.1 years of follow-up of those patients, who did not cross over to the treatment group (31.6% were selected for treatment from the observation group during follow-up, and an additional 11.4% were removed because they died). Besides size, there are other known risk factors such as shape [21], and there are changes in the microarchitecture of an aneurysm affecting its risk of rupture [8]. These data still cause considerable confusion on how to manage a patient with a small aneurysm. Our clinical experience is that small aneurysms constitute most of ruptured aneurysms. Hence, knowing the accurate size of a series of ruptured and unruptured aneurysms may help to identify difference in the size distribution and shed light on the growth pattern of these aneurysms. However, the 3-dimensional (3D) anatomy of intracranial aneurysms is complex, and the variable magnification factor of biplanar digital subtraction angiograms make size measurements difficult. The recently introduced 3D-RA is a method to compute 3D images from projection radiograms. 3D-RA recording systems are exactly calibrated and allow for easy quantification of the size of the aneurysm. The objective of the study was to report the location and accurate size of RIAs and UIAs in a consecutive series of patients by 3D-RA taking the complex 3D anatomy and parent vessel morphology into consideration.