New Days for Old Ways in Treating Giant Aneurysms—From Hunterian Ligation to Hunterian Closure?

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6 New Days for Old Ways in Treating Giant Aneurysms—From Hunterian Ligation to Hunterian Closure?

Miikka Korja, Mika Niemelä, Leena Kivipelto, Martin Lehecka, Rossana Romani, Jouke van Popta, Hanna Lehto, Hideki Oka, Juha Hernesniemi

Hunterian ligation

Hunterian ligation (i.e., proximal artery ligation) was the first surgical method for treating intracranial aneurysms. At the end of 18th century, a Scottish surgeon and scientist, John Hunter, established the procedure more or less in its current fashion by ligating certain peripheral arteries.^2,^8,¹² However, the first planned ICA ligation for the treatment of a preoperatively diagnosed nontraumatic saccular aneurysm was apparently performed in 1928,¹⁶ and in subsequent decades several papers reported inconsistent mortality rates of the procedure. In 1966, a highly detailed and one-of-a-kind analysis of nearly 800 cases of Hunterian ligation for aneurysm patients reported an ischemic complication rate of 30% and a mortality rate of 24%.¹¹ However, 89% of the occlusions were CCA occlusions, and they were mainly performed in the acute phase of subarachnoid hemorrhage (SAH). Following Hunterian ligation, only 16 (12%) and three (2%) out of 129 patients with unruptured aneurysms experienced ischemic deficits or died, respectively. Hunterian ligation of the ICA had almost a double risk of ischemic complications in comparison to CCA occlusion, even though severely ill and high-risk patients were more frequently selected for CCA rather than ICA occlusion.

The series of Drake and Peerless, which the senior author (JH) has scrutinized, represents the largest and most experienced data of the procedure for giant aneurysms to date; it consists of 732 giant aneurysms, 396 of which were treated with Hunterian ligation before December 1992. Due to their special referral policy, posterior circulation aneurysms outnumbered anterior circulation aneurysms in the series.²¹ Excluding infraclinoid aneurysms (five petrous and 77 intracavernous carotid aneurysms), more than two thirds (69%) of the 253 giant anterior circulation aneurysms were treated with direct clipping, whereas only one third (32%) of the 397 giant posterior circulation aneurysms were directly clipped. For the remainder, Hunterian ligation was used in the treatment of 48% and 60% of the anterior and posterior circulation aneurysms, respectively.

In general, Hunterian ligation has been used on every major intracranial artery, mostly as the only reasonable treatment option for impractical giant aneurysms, but occasionally as the safest and most simple alternative of all possible options. In our own literature survey of more than 2000 giant aneurysms, which were treated between 1970 and 1994 (i.e., microsurgery era) at various institutions all over the world, Hunterian ligation was used as the only treatment method in one third of the cases. However, the method does not seem to be very widespread; many of the reported cases come from London, Ontario, Canada. In our own database, which contains all intracranial aneurysms treated between 1977 and 2000 in eastern Finland, 128 (5.5%) of the 2330 treated aneurysms were giant. The same incidence rate has also been seen in southern Finland in the last 13 years (during which Professor Hernesniemi has been working in Helsinki), where roughly 15 giant aneurysms are treated every year. Of these 15 giant aneurysms, Hunterian ligation without other treatment modalities was involved in only one or two desperate cases.

Today, even though most saccular aneurysms at any site can technically be considered as clippable, especially fusiform, dissecting highly atherosclerotic and giant aneurysms remains cumbersome. Since giant aneurysms often have a very slow or stagnant intra-aneurysmal blood flow, resulting in asymptomatic or symptomatic distal perfusion changes, Hunterian ligation can provide better than expected surgical results in these otherwise inoperable and unfavorable cases. For the aforementioned reasons, Hunterian ligation has remained a useful adjunct to tackle giant aneurysms, often combined with a bypass procedure. Therefore, the number of Hunterian ligation procedures performed at our institution has continued to be more or less the same throughout the years. Disappointing results in using Hunterian ligation for patients with ruptured giant aneurysms have made us cautious in attempting Hunterian ligation in the week following SAH.^11,¹³

After the early years of Hunterian ligation, the field of neurovascular treatments was revolutionized by endovascular approaches. Proximal closure of any intracranial vessel, in principle, can be achieved by endovascular means as well. Thus, instead of Hunterian ligation, it would perhaps make more sense to use the term Hunterian closure, which is not tied to any particular occlusion technique, when any kind of proximal occlusion of an intracranial artery is performed. The following surgical views represent our simplified perspective of using Hunterian closure in the treatment of giant aneurysms at different locations.

Anterior circulation

Giant ICA Aneurysms

Permanent occlusion of the ICA with or without a prior test occlusion leads to a high cumulative stroke rate and mortality of 26% and 12%, respectively.⁹ Therefore, a preoperative evaluation of collateral potential of the circle of Willis is necessary. After a diagnostic angiography, we typically perform a test occlusion for a minimum of 30 minutes using an inflated endovascular balloon in the high cervical ICA (at the C1-2 level of the ICA) of a conscious patient. If the patient tolerates the test occlusion without neurological symptoms, and the angiographic architecture of the venous phase does not show substantial asymmetry, Hunterian closure of the ICA can be considered as a treatment option. The venous phase is symmetrical if the venous phase of both cerebral hemispheres is synchronous (venous filling delay is less than 0.5 seconds) after collateral filling via the anterior communicating artery, or if the venous phase of the posterior circulation on vertebral angiography is simultaneous (venous filling delay is less than 0.5 seconds) after collateral filling via the posterior communicating artery.¹⁸ We do not routinely use blood flow or perfusion analyses (e.g., MRI-NOVA, perfusion CT, perfusion MRI) during or after the balloon test occlusion. At present, we do not perform Hunterian closure of the CCA, because we have seen retrograde recanalization of the ICA, which increases the risk of aneurysm rupture.¹¹ In addition, we have not found test occlusions of the CCA reliable, and permanent occlusion of the CCA evidently affects EC-IC collateral flow. Whatever the clinical preoperative evaluation of the collateral flow potential of the ICA territory, unexpected ischemic events are always possible after Hunterian closure of the ICA. Even though today it is also possible to measure the blood flow intraoperatively, current flow probes and intraoperative monitoring modalities cannot be used to reliably estimate the circulatory changes after Hunterian closure.

If any doubts or objective signs of insufficient collateral flow of the ICA territory exist, it is advisable to do a bypass instead of sole Hunterian closure or a direct attack to the aneurysm. Depending on the degree of the patient’s collateral circulation, either a low-flow or a high-flow replacement or protective bypass is constructed, prior to occlusion of the ICA or direct aneurysm clipping. When a high-flow bypass is needed, we usually construct a nonocclusive, high-flow, laser-assisted Excimer Laser-Assisted Nonocclusive Anastomosis (ELANA) bypass.¹⁷

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