Intracranial–Intracranial Bypass for Aneurysms: Quantitative Intraoperative Assessment of Flow Preservation

Intraoperative flow measurement has proven utility in extracranial-intracranial bypass, particularly in assessing the adequacy of donors by measurement of cut flow. The nature of intracranial-intracranial (IC-IC) bypass precludes cut flow measurement, but quantitative intraoperative flow measurements may evaluate augment assessment of the bypass.To retrospectively evaluate flow measurements performed in IC-IC bypass to determine the adequacy of the constructs in preserving flow.With institutional review board approval, we performed a retrospective review of our bypass database from 2001 to 2021 for aneurysms treated with IC-IC bypass and with intraoperative flow measurements. Patients' preoperative characteristics, bypass indications, prebypass and postbypass intraoperative flow measurements, and patient outcomes were recorded.Of 346 bypasses, 21 cases using 22 IC-IC bypasses were included. The median age was 55 years; 13 of 21 cases were ruptured aneurysms. Aneurysms involved posterior inferior cerebellar artery (n = 7), middle cerebral artery (n = 6), distal anterior cerebral artery (n = 5), and anterior communicating artery (n = 3). Six bypasses were end-to-side (ETS), 10 were side-to-side (STS), and 6 were excisional with reanastomosis (end-to-end, ETE). Intraoperatively, 21 of the bypasses were patent; the postbypass/prebypass flow index averaged 1.15 (±0.32): ETE (n = 6) 1.22 ± 0.34 and ETS/STS bypasses (n = 15) 1.11 ± 0.32. All intraoperatively patent bypasses were patent on postoperative angiography. One occluded on delayed angiography without clinical sequelae.Despite advances in endovascular therapy, IC-IC bypass remains essential to the treatment of large and fusiform aneurysms. We demonstrate quantitatively that IC-IC donors provide adequate direct (ETE) and redistributed (STS ETS) flow to the recipient territory. Flow measurement provides valuable information regarding the patency and adequacy of IC-IC bypass for flow preservation.