Type II is defined as an IC-IC bypass with an ELANA anastomosis on the proximal side and a conventional anastomosis on the distal side, as the distal MCA branch is not always large enough (>2.6 mm) to construct an ELANA anastomosis on ICe-ICc. This type was constructed in 14 patients (56 %). The proximal ELANA anastomosis was made on the ICA (n = 10) and on the proximal MCA (n = 4). Distal conventional anastomoses were made on the M2 (n = 4) and on the M3 (n = 10).

This type is defined as an extracranial-to-intracranial bypass with an ELANA anastomosis on the distal side (EC-ICe). In two patients (8 %), the intracranial ICA or MCA proximal to the aneurysm was not surgically reachable due to aneurysm size. Therefore an EC-IC bypass with a distal ELANA anastomosis on the distal MCA and a proximal anastomosis on the ECA was constructed. This type of flow replacement bypass was described previously in the treatment of internal carotid aneurysms.

All 40 ELANA attempts resulted in a patent anastomosis with a strong backflow directly after ELANA catheter retraction. In six ELANA anastomoses (15 %), the disc of the arterial wall, which is normally attached to the tip of the catheter after laser application and catheter retraction (the flap), was not found on the tip. In these patients, no adverse events occurred and bypasses were functioning well.

Mean intra-operative flow ± SD through the 23 IC-IC bypasses before any part of the MCA or aneurysm was occluded was 15 ± 10 cc/min. The mean intra-operative flow ± SD through the IC-IC bypasses after partial or full MCA occlusion, measured at the end of the operation, was 53 ± 13 ml/min. The two EC-IC bypasses had a flow before MCA occlusion of 35 and 50 ml/min, respectively. These aneurysms were treated endovascularly the next day and MR flow measurement on the first EC-IC bypass showed that bypass flow had increased from 35 cc/min (intra-operatively) to 100 cc/min postoperatively end after endovascular occlusion of the parent artery. However, nowadays we prefer to treat these aneurysms intra-operatively directly after the bypass construction by ligating the ICA.

In long-term follow-up (mean, 3.6 years; range, 0.2–7.7 years after surgery), 20 patients (80 %) had a favorable outcome, meaning that their postoperative mRS score was equal to or higher than their preoperative status. Five patients (20 %) had a long-term unfavorable outcome. In four of these patients, the unfavorable outcome was related to surgery (16 %). One patient (5 %) died 2 months after surgery from an unknown cause, although the patency of the bypass and the trapping of the aneurysm of this patient was angiographically confirmed 2 weeks before death.

Defining patients with an mRS score of 3 (moderate disability, needing help in daily life, but walking without assistance) or worse as dependent, long-term independency, amounted to 16 patients (64 %).

Although we frequently see patients with giant aneurysms of the ACA, it is rarely necessary to use the ELANA technique for bypassing these lesions. An example of this was a 61-year-old patient with an SAH and a giant aneurysm of the ACA that was not coilable, and because of multi-calcifications not easy clippable. We performed an IC-IC bypass from the A1 (ELANA) to the proximal A2 (conventional), as the STA in this case was very small. Intra-operative flow measurements on the A2 showed a flow of 30 cc/min to be replaced. After the bypass was finished, the aneurysm, including the distal A1 and anterior communicating artery, was trapped. According to intra-operative flow measurements, initial flow in the bypass with the A1 still open was 15 cc/min but went up to 30 after trapping the aneurysm, including the A1-A2 segment, demonstrating that the bypass functioned as a 100 % replacement bypass. The patient recovered very well and is back to work (follow-up at 40 months), and CTA control after 2 years showed the bypass to be fully patent.