The authors tried to clip good grade anterior circulation aneurysms through trans-eyebrow keyhole approach. So, almost ICA and ACA aneurysm cohorts treated by supraorbital keyhole surgery. Most neurosurgeons adopt the pterional approach first for clipping of MCA aneurysms . But the authors treated MCA aneurysms when keyhole surgery was feasible according to CT simulation technique which provide a shorter straight distance from the skull. There is no significant difference between the ICA, ACA, and MCA aneurysm groups in the distribution of GCS, so it is considered sufficient data to analyze the outcome and factors analysis with ICA, ACA, and MCA aneurysm groups.
In this study, MCA aneurysm group was found to have a longer operation time than ICA and ACA aneurysm group. For the clipping of ICA or ACA aneurysms, partial sylvian dissection is needed during supraorbital approach. For the MCA aneurysm clipping, wide sylvian dissection is needed mostly, so the operation time is longer than ICA or ACA aneurysms. It was known that the longer the operation time, the more significant the complications occurred , but the results of this study did not correlate with the complication and operation time.
The rate of complications after conventional craniotomy in aneurysm surgery is various, but approximately, about 15–25% [7–9]. Complication rate of this study was 8.3%, which was a relatively low rate compared to conventional craniotomy. There was no difference depending on the location of cerebral aneurysms. And there was no case that needed re-operation due to epidural or subdural hemorrhage or infection. There were 3 cases of protrusion of bone flap, which needed reposition of bone flap for cosmetic purpose.
In ACA aneurysm group, more memory loss occurred than other locations, but no difference in the frequency of complication occurrence comparing with conventional ruptured anterior communicating artery aneurysm surgery such as hypothalamic perforator injury or hippocampal insufficiency [10, 11].
Olfactory dysfunction is also the highest incidence in ACA aneurysm group. Which is an inevitable complication because this approach needs more frontal lobe retraction and resulting a higher incidence of olfactory dysfunction than conventional approaches. To minimize this, it is useful to do olfactory nerve dissection carefully with reference of the report that the incidence of olfactory dysfunction was lowered through olfactory nerve dissection .
After surgery, patients become sensitive to the eyebrow incision and complain about sensory changes around the supraorbital nerve dermatome. Immediately after surgery, complaints were mostly dull dysesthesia and it changed to the abnormal sensation in about 3–6 months. During this period, the patients usually got more sensitive. The authors examined these scalp abnormalities in three stages: normal, slightly uncomfortable, and much uncomfortable, at 6 months after the surgery. In the case of complaining of abnormal feeling of discomfort up to 6 months after surgery, it was classified as a complication.
In transciliary keyhole surgery, the supraorbital nerve is a susceptible structure . Sensory change occurred in 26% of patients and was less pronounced in MCA aneurysm group, despite significant efforts for preservation of the supraorbital nerve during surgical treatment. (p = 0.004) In the process of making incision and bone flap, there were more unruptured aneurysm cases in the MCA aneurysm group, and craniotomy size in the unruptured aneurysm group is smaller than in the ruptured aneurysm group, and it can explain the possibility that the supraorbital nerve was actually less damaged in the MCA aneurysm group. It is estimated that less nerve injury occurred due to less skin incision size.
The operation time was shorter in ruptured cases (Fig. 5). In the analysis of operation time, one assumption as to why the operation time seemed to be shorter in ruptured aneurysm with high grade Hunt-Hess grade group is that ruptured aneurysm cases are usually treated urgent situation. So all the process focus in straight forward early clipping and frequent use of temporary clipping. Also there would have been a selection bias that relatively favorable case for keyhole clipping is selected in ruptured aneurysm cases. And in the case of unruptured aneurysm, even a relatively complex shape of aneurysm considers keyhole surgery preferentially, the surgical process can be a little more careful.
Both memory loss and olfactory dysfunction were found to be occurred more frequently in patients with ruptured aneurysm and the results are as same as conventional surgery. Scalp sensory change was dominant in patients with unruptured aneurysm, especially MCA aneurysm group. Since the surgical procedure is the same for ruptured aneurysms or unruptured aneurysms, it is not likely that there will be a difference due to surgery. The patients with unruptured aneurysm may responded more sensitively because some patients suspect a scalp sensory change as a signal of brain lesion. But when patients got explanation about clinical course of recovery after nerve injury, their complaints of sensory change were decreased. Therefore, in case of eyebrow incision for clipping unruptured aneurysm, it is necessary to detailed explain about the sensory changes before surgery.
Another interesting point is that although there was a large difference in the total number of patients, no post-operative complication occurred in elongated aneurysm group and 19 complications were occurred in saccular aneurysm group. Studies have shown that the probability of complication, such as infarction or intraoperative rupture (IOR), increases as the shape of the aneurysm becomes irregular [14, 15]. We suggest the possibility that because the pathophysiology of saccular aneurysm is thinning vessel wall to make the aneurysm [16, 17], in small sized aneurysm, the clip is often involving a part of the parent vessel for a complete clipping. In this situation, complications may have increased. In case of elongated aneurysms, mostly when neck is exposed, aneurysm clipping is done easily, relatively. In the same context, the operation time was also shorter in clipping of elongated shape aneurysm group.
IOR occurred in total 27 cases. 26 cases occurred after arachnoid dissection where proximal control was possible, and the surgical procedure did not differ from conventional surgery and did not affect complication rate. One case occurred before arachnoid dissection. In our case, manual compression of the craniotomy site about 5 minutes and bleeding was stopped, and clipping was performed after frontal lobe partial resection. The patient discharge with modified Rankin Score I.
The authors try to present the characteristics of selected cases for keyhole surgery so selection bias may occurred in the analysis of affecting factor for complications. Before the analysis, it was expected that the configuration of sylvian fissure would be an important factor in the analysis of operation time for each location, but due to the nature of transciliary keyhole surgery, there was not many cases that the configuration of sylvian fissure was clearly confirmed. There was no significant difference in our analysis, but thorough analysis of the sylvian configuration will be additionally required.
The number of patients included in the overall analysis was not small, but as a retrospective study, not all factors could be evaluated in all patients due to lack of records. There is a possibility of an error due to this point, and for this, verification through a larger scale study and a prospective study as needed is necessary.