Limitations of Clipping Large or Giant Carotid-Ophthalmic Aneurysms by Using Conventional Microsurgery
The size and shape of the aneurysms were the key issues for such operations. Previous studies reported that the rates of fatality and morbidity were still as high as 20–30% in neurosurgical centers which had well-developed technologies, despite that patients could take safer and relatively simpler operations such as aneurysm exclusion and EC-IC bypass. The critical difficulties of performing these operations are the proximal control of the ICA; the field of vision influenced by the aneurysm, width of the aneurysm necks, complex branches and perforating blood vessels, formation of endoluminal thrombosis, and as well as atherosclerosis and dysplasia. For the clipping of giant carotid-ophthalmic aneurysm, control of the proximal end of the parent artery was the most crucial step. In treating some patients with giant carotid-ophthalmic aneurysms, the removal of ACP would provide sufficient space between the aneurysm neck and the DDR of cavernous sinus for the placement of temporary blocking clips, including control of the proximal end of the ICA.
The vast majority of patients with giant carotid-ophthalmic aneurysms required an incision of neck to be performed first to do proximal ICA control. However, both ACP removal and neck incision would increase operational trauma and lengthen surgical time, especially for elderly patients over the age of 65. Elderly patients were less tolerant for trauma. The research by ISAT subgroup presents that the patients over the age of 65 have higher rates of epilepsy, lung infection, cerebral vasospasm, infarction and neurological complications. Therefore, intraoperative neck incision and proximal part blocking should be prevented in treating carotid-ophthalmic aneurysm patients. This should minimize surgical trauma and shorten the operation time.
Due to the size of the carotid-ophthalmic aneurysms, the aneurysm necks located in ICA leading to the skull, around the ACP, and the optic nerve blocked the field of vision. As a result, finding the aneurysm neck and its branches through craniotomy would be difficult due to blind spots. Especially large and complex intracranial aneurysms, the aneurysm neck might be obstructed which could lead to it rupturing before clipping. As reported in the literature, after conventional aneurysm clipping with intraoperative indocyanine green (ICG) video angiography check, post-operation DSA showed the rate of incompletion of aneurysm clippings was at 6.3% while parent vessel stenosis was 5.7%. For giant aneurysms, the rates of incompletion of clippings and occurrence of stenosis were as high as 15% even more. So, compared to intraoperative DSA, intraoperative ICG could not demonstrate clearly and accurately images of parent vessel stenosis and aneurysm neck residues due to blocked vision and other reasons. Besides, intraoperative ICG was not able to directly observe the situation of the distal blood vessels.
Limitations of Intra-Arterial Embolization for Treating Giant Carotid-Ophthalmic Aneurysms
Recently, interventional treatments for intracranial aneurysms have been in rapid development, which could reveal its advantages in treating intracranial aneurysms. Currently, usable interventional technologies in treating complex wide-necked aneurysms are balloon-assisted coiling embolization, stent-assisted embolization and dual micro-catheter coiling embolization. However, a wide-necked aneurysm with complex conformation was difficult to be totally removed by endovascular treatments. Although new interventional devices, tools, and technologies are evolving, a variety of interventional techniques are techniques challenging for treating giant carotid-ophthalmic aneurysm. For the method of stent-assisted coiling embolization, it is possible that the stent guidewire could not overcome the technical difficulties of placing the stent through an aneurysm. The stent is used in stent-assisted coiling embolization to reconstruct the parent vessel and set as a block on the aneurysm neck and to prevent coil dislocation. However, within a few months of surgery, dual antiplatelet therapy (DAPT) must be strictly performed to the patients until the internal membrane of the parent vessel has completely regenerated before the aneurysm neck. Therefore, in most cases, stent-assisted coiling embolization technology could not be safely used to treat ruptured aneurysms.
Carotid-ophthalmic aneurysms often show mild symptoms or none until they grow to a larger size due to their unique anatomic features. It was reported 30–50% of patients who have had carotid-ophthalmic aneurysms grown to giant size (diameter > 25 mm) on their first visit to the hospital. The main symptoms are often loss of vision and visual field defects. And intervention embolization was used to treat these patients; however, the aftermath of the aneurysm could not be eliminated, and the symptoms were not only not alleviated after the operation, but also keep growing progressively which requires craniotomy to remove emboli in order to save the patient's’ vision and visual field[10, 11]. Moreover, carotid-ophthalmic aneurysms often contain important vessels or artery branches which originates from the aneurysm dome or fundus parts such as the ophthalmic artery, PComA, and even anterior choroidal artery (AChA).
Under these circumstances, the ideal treatments were to reconstruct the parent vessel based on retaining important perforator vessels and its branches. In this case, using the common interventional embolization technologies and flow-directed devices to solve the aforementioned problem was pretty difficult. Furthermore, another difficulty in treating giant complex carotid-ophthalmic aneurysms was the high risk of relapse after surgery. As reported, the incidences of relapse after carotid-ophthalmic aneurysm operations ranged 27.4 to 31.6%,[12–14] however, the rates of relapse after interventional embolization had reached 50% in treating giant aneurysm. Therefore, It was extremely difficult to use the interventional embolization method to treat patients with wide-necked, giant and/or branch vessel accumulated carotid-ophthalmic aneurysms.
In recent years, the flow diverters (e.g. SILK embolization device, Pipeline embolization device) have been widespread used to treat complex anterior circulation aneurysms, especially the giant types of the carotid-ophthalmic segment and clinoid segment. But publications reported that flow diverters used for dealing with giant anterior circulation aneurysms, dissecting aneurysms and microaneurysms were relatively rare. However, due to the rigidity and low compliance characterized by the hardness of the dense diverter, the excessive friction when the diverter went through tortuous vessel parts, for instance, the ICA siphon, might cause stent translocation, insufficient expansion, stent fracture (SF), in-stent restenosis (ISR) or occlusion, and covered branch or perforator vessel stenosis or occlusion. Besides, after placing the flow-diverter stent, the follow-up treatment would be extremely difficult if there were recurrent or residual aneurysms.
The Advantages of Hybrid-OR in Dealing with Large or Giant Carotid-Ophthalmic Aneurysms
Current surgical limitations have been overcome due to this technological breakthrough, while expanding the potential of surgery. The DSA system in the Hybrid-OR provided neurosurgeons with a brand new, intraoperative, image-guided environment, which eliminated the limitation of traditional operating rooms and DSA systems when they functioned individually.
Firstly, using balloon occlusion with the Hybrid-OR could quickly block the proximal end of the ICA. The control of the proximal end of the ICA had the following advantages: (I)preventing neck incisions, shorten operation time, and reduce surgical trauma; (II)preventing operation of two surgical sites, which reduces the possibility of complications of intracranial infection; (III) reducing operations on the ICA, which could reduce the rate of complications of intraoperative vasospasm and cerebral infarction; and (IV) dealing with ACP using the IAC technique rather than EAC technique, and no need to totally remove ACP, but removed a part of ACP in accordance with operational needs. IAC technique was safer and more timesaving than EAC.
Secondly, compared to direct observe under the microscope or interoperation ICG technique, it’s more clearly and accurately to evaluate the effect of aneurysm-clipping using the intraoperative DSA. It was extremely difficult under the microscope in 360 degrees to detect and observe the relationship between the aneurysm and their surrounding branch vessels, giant carotid-ophthalmic aneurysms were in big size, deep location, shade of ACP and optic nerve and wide necks. And it was impossible using ICG technology to observe aneurysms residual, ICA stenosis, preservation of important perforator vessels, and the status of the distal blood supply. These were the reasons why the rates of incompletion of clippings and occurrence of stenosis were as high as 15% and more in conventional aneurysm clipping method with intraoperative ICG verification. Nevertheless, Hybrid-OR is applied to observe and evaluate aneurysm-clipping in 360 degrees by intraoperative DSA. As shown in our cohort, 3 incomplete clipping events (1, 2 and 7) and 2 vessel stenosis events (1 and 2) were found intraoperative DSA in Hybrid-OR.
Furthermore, balloons could be directly deployed across aneurysms neck and block the blood for wide-necked carotid-ophthalmic aneurysms. This kind of neck across deployment was effective to decrease escape of blood clots in the aneurysm sac, proper placement of the aneurysm clip and good reconstruction of ICA. In our study, the balloon was deployed across the aneurysm neck in 5 cases with wide-neck (≥ 8 mm). Four cases (80%) got good reconstruction of the parent ICA, however, good reconstruction of the parent ICA could not be obtained in one case (Case 2) because of severe atherosclerosis in the aneurysm neck. no balloon-deployment related vasospasms occurred in the group of 12 patients.