In cases of MIA, the risk of rupture is relatively high, all aneurysms in need of treatment should be treated as soon as possible; however, as mentioned above, there are no specific guidelines for this process [7, 16, 25]. If possible, all of the aneurysms should be treated endovascularly [3, 21]. However, there is no reason to avoid one stage operation if multiple lesions can be operated simultaneously . Even in cases of lesions in multiple areas, single craniotomies may be attempted [1, 22]. In other cases, multimodality treatment  or staged operations are attempted [24, 27]. Staged operations may be performed in cases where the lesion is at a location that requires different craniotomies, such as in bilateral middle cerebral artery aneurysms. In patients with aneurysms that require multiple craniotomies, there should be a time interval between the two operations. With OSMC, we attempted an extremely shortened form of this time interval.
OSMC are an attempt to eliminate the 'time' between the surgeries by performing multiple approaches concurrently; thus, this may be considered a worthwhile method. Based on the experience of various methods of minimal invasive surgery attempts and the accumulation of knowledge accumulated by previous researchers, multiple approaches could be attempted at once. Regarding MSMC, it is difficult to keep the vital signs stable when considering the continued possibility of aneurysm rupture during the first postoperative management process [7, 19, 32]. Even if the patient recovers well without any complications in the acute postoperative phase, the second operation should be carried out within 1 to 2 months . This is because the patient needs time to physically or psychologically recover after the surgery. One study found that patients with unruptured aneurysms experienced a poor quality of life preoperatively; this concept also applies to patients who are between surgeries .
In the OSMC group, the operation and anesthesia times, and hospitalization period were short, and the economic burden (total treatment cost and co-payment amount) was lessened; however, these results may reflect the omission of the overlapping elements in each surgical procedure. Simply put, time was saved and the economic burden was lessened with the OSMC group because the induction, extubation, and recovery processes were omitted once for each patient, compared to the MSMC group. Contrastingly, there was no substantial difference in the amount of blood loss, surgical results, and complications, which may be considered variables that are only related to surgery, regardless of whether the two operations were performed separately or consecutively. In other words, we propose that two craniotomies with one type of anesthesia do not result in increased blood loss or an increased incidence of complications. Moreover, prolongation of the anesthesia time and CSF overdrainage could be factors that induce complications; however, the incidence of complications relating to these two factors did not increase.
In this study, the remnant ratio (OSMC and MSMC groups: 23.2% and 25.6%, respectively) was higher than the remnant incidence rate (13.3–18%) reported in other studies [9, 17]. DSA or brain CTA were used to determine whether there was complete obliteration after surgery and DSA can be considered a more accurate test than brain CTA . We performed a study in which the surgery results were strictly determined using DSA rather than brain CTA. In fact, in the patients for whom DSA was used to determine the presence of remnants, most of the remnants were not identified on the brain CTA that was performed at the postoperative follow-up visit, and no additional surgeries were performed due to an increase in the remnant aneurysm size.
Our study had several limitations. Since this was a retrospective study, selection bias should be considered. This study only targeted mUIAs; therefore, caution should be exercised when OSMC are applied to aneurysmal subarachnoid hemorrhage (aSAH) patients with MIAs. Although some studies have reported OSMC in patients with multiple aneurysms and aSAH who underwent emergency surgery [20, 28, 31], we propose that the use of OSMC should be considered carefully because brain relaxation is difficult. This study is the result of an analysis of the surgeries performed in a single, large-scale, neurovascular center in Korea. Therefore, we propose that the results reflect the factors that apply to OSMC performed in a well-equipped hospital with skilled neurovascular surgeons and anesthesiologists, and that OSMC is recommended under similar conditions. Finally, among the various treatment methods for multiple aneurysms, we only compared between microsurgeries, not endovascular surgery. However, most of the cases in our study could be considered significant because craniotomy is the preferred treatment method for aneurysms when compared to endovascular surgery. With the aim of studying the overall strategy for the treatment of multiple aneurysms, a follow-up study that compares and analyzes the treatment outcomes, including those for endovascular surgery, should be performed.
In conclusion, there were no significant differences in the occlusion and complication rates when OSMC was compared to MSMC. Moreover, OSMC showed favorable results in terms of the operation time, hospitalization period, blood loss, and hospital expenses. Therefore OSMC could be considered for its beneficial effect on the patient time and economic burden.