Hakyemez, Bahattin

Abstract Objective Flow diversion (FD) is a relatively new technique for treating large, wide-necked, or fusiform aneurysms. Although FD is a more preferred option than coiling or clipping techniques in neurosurgery and neuroradiology clinics, the blood flow mechanism inside the aneurysm sac is not fully understood after the treatment. Besides, effective metal surface area (EMSA), a property of an FD related to porosity, shows variation at the patient's aneurysm neck by providing more or less blood flow inside an aneurysm sac than planned, causing nonstagnant or stagnant fluid region formation in the sac, respectively. Thus, the change in FD's EMSA can significantly affect the treatment's effectiveness, making even operation unsuccessful when variation in FD's EMSA at the aneurysm neck is overlooked. Materials and Methods In this study, a large aneurysm of a 52-year-old female patient was numerically investigated by virtually placing two commercially available FDs with different EMSA values one by one into the aneurysm-carrying artery. Results While FD stents at the aneurysm site substantially reduced the blood flow into the aneurysm, an FD with a 15.6% EMSA caused blood to flow in the aneurysm sac to have six times more kinetic energy than that of FD with a 29.5% EMSA. Conclusion Although FD's EMSA value demonstrated nearly up to 20% reduction at the patient's aneurysm neck based on a product catalog value, numerical model results revealed that the stagnated region's formation inside the aneurysm sac could be determined within a 9% difference based on digital subtraction angiography reformat image.

Abstract Introduction Flow diverter (FD) stents are widely used to treat giant aneurysms by reducing blood flow into the aneurysm sac. However, choosing the optimal FD for a patient can be challenging when a nearby artery, such as the ophthalmic artery (OA), is jailed by the FD placement. This study compares the impact of two FD stents with different effective metal surface area (EMSA) values on OA occlusion. Materials and Methods A numerical model of a 59-year-old female patient with a giant aneurysm in the left internal carotid artery and a jailed OA was created based on clinical data. Two FD stents, FRED4017 and FRED4518, with different EMSA values at the aneurysm neck and OA inlet, were virtually deployed in the model. Blood flow and occlusion amount in the OA were simulated and compared between the two FD stents. Results FRED4017 had higher EMSA values than FRED4518 at the aneurysm neck (35% vs. 24.6%) and lower EMSA values at the OA inlet (15% vs. 21.2%). FRED4017 caused more occlusion in the OA than FRED4518 (40% vs. 28%), indicating a higher risk of ocular ischemic syndrome. Conclusion The EMSA value of FD stents affects the blood flow and occlusion amount in the jailed OA. Therefore, selecting an FD stent with a low EMSA value at the OA inlet may be beneficial for patients with a nearby jailed artery at the aneurysm neck.

Background Flow diverter stents (FDSs) are widely used to treat aneurysms in the clinic. However, even the same flow diverter (FD) use on different patients’ aneurysm sites can cause unexpected hemodynamics at the aneurysm region yielding low success rates for the overall treatment. Therefore, the present study aims to unfold why FDs do not work as they are supposed to for some patients and propose empirical correlation along with a contingency table analysis to estimate the flow stasis zones in the aneurysm sacs. Methods The present work numerically evaluated the use of FRED4518 FDS on six patients’ intracranial aneurysms based on patient-specific aneurysm geometries. Computational fluid dynamics (CFD) simulation results were further processed to identify the time evolution of weightless blood particles for six patients’ aneurysms. Results Stagnation zone formation, incoming and outgoing blood flow at the aneurysm neck, and statistical analysis of six patients indicated that FRED4518 showed a large flow stasis zone for an aspect ratio larger than 0.75. However, FRED4518, used for aneurysms with an aspect ratio of less than 0.65, caused small stagnant flow zones based on the number of blood particles that stayed in the aneurysm sac. Conclusion A patient-specific empirical equation is derived considering aneurysms’ morphological characteristics to determine the amount of stagnated fluid flow zones and magnitude of the mean aneurysm velocity in the aneurysm sac for FRED4518 based on weightless fluid particle results for the first time in the literature. As a result, numerical simulation results and patient data-driven equation can help perceive stagnated fluid zone amount before FRED4518 placement by shedding light on neuro-interventional surgeons and radiologists.