Introduction The management of unruptured small intra-cranial arterial aneurysms or SIAs (<7 mm in size) remains non-uniform and controversial despite the results of observational studies like the ISUIA, in part because SIAs are paradoxically also responsible for the majority of aneurysmal subarachnoid hemorrhages (SAH). Recently, there has been growing interest in physical parameters other than aneurysms size such as variables obtained with computational hemodynamics for estimating rupture risk in SIAs, however, these analyzes are complicated and show confounding results. Herein, we report on the differences between stable unruptured SIAs and ruptured SIAs when the surface area to volume ratio (SAV ratio) of these lesions is measured using a simple technique.

Methods We retrospectively reviewed a prospectively maintained clinical database at our institution from 6/1/2013 to 6/1/2014 and identified patients with unruptured and ruptured SIAs. For unruptured aneurysms, we included patients with stable aneurysm size and morphology at a minimum of at least one year follow up, saccular morphology, <7mm maximum aneurysm diameter and no intervening treatment. Ruptured aneurysms were included into the analysis if they were saccular in morphology and <7mm in size at their maximum diameter. We used the source images from either MRA or CTA in both patient groups to calculate the volume and surface area by drawing a region of interest (ROI) around the SIA in every imaging slice in which it was visible and then multiplying the circumference of the ROI and the area of the ROI by the slice thickness to obtain the Surface area and Volume of the aneurysm respectively.

Results Of the 82 cases reviewed, 61 met inclusion criteria. 44 patients had unruptured stable SIAs and 17 patients had ruptured SIAs. The unruptured aneurysm group had a mean age of 52.6 years and 82% were female. The ruptured aneurysm group had a mean age of 57.2 years and 88% were female. Co-morbidities were similar in each group. In unruptured and stable SIAs, the mean SAV ratio was 1.92 with range of 1.33 to 2.98. In ruptured SIAs, the SAV ratio was 1.02 with range of 0.77 to 1.48 (p < 0.05).

Conclusion The SAV ratio was significantly lower in ruptured SIAs than in unruptured and stable SIAs with very little overlap of values. This simple measure, which is easy to calculate, could potentially be added to the other clinical decision making tools used in the identification of those patients with incidentally discovered unruptured SIAs who can be managed conservatively from those in whom endovascular or surgical treatment may be justified.

Disclosures J. Kim: None. A. Grande: None. R. Tummala: None. B. Jagadeesan: None.