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Cerebral aneurysms which cause oculomotor nerve [cranial nerve (CN) III] palsy, are frequently found with a daughter sac of the aneurysm dome. We assumed that CN III might be compressed by the daughter sac and it would be more helpful not to fill the daughter sac with coils than vice versa during endosaccular embolization for recovering from CN III palsy, because it may give a greater chance for the daughter sac to shrink by itself later. We reviewed the initial results of our experiences of such cases.
Among 9 aneurysms accompanied by CN III palsy, 7 (6 unruptured, 1 ruptured) showed a daughter sac. We tried to fill the main dome completely and spare the daughter sac from coil filling to increase the possibility of decompression. We evaluated the short-term effectiveness of this concept using medical records and angiograms.
After initial embolization, all of CN III palsy caused by unruptured aneurysms (6/6) resolved completely after various periods (3-90 days) of time. No adverse effects were noted during and after the procedures except for one case of harmless coil stretching during coil filling using double microcatheter.
During the coil embolization of the cerebral aneurysm causing CN III palsy, sparing the daughter sac from coil packing while tightly packing the main dome, can be helpful in increasing the effectiveness of decompression. However, a long-term follow-up will be required.
It is widely known that some cerebral aneurysms can cause oculomotor nerve [cranial nerve (CN) III] palsy either completely or partially by direct mechanical compression3,5,6,14). It can be induced by an increase in aneurysm volume, with or without accompanying subarachnoid hemorrhage (SAH).
Complete or partial recovery of CN III palsy after clipping has been widely reported while the recovery rate after coiling has been documented only in a small number of reports and is not as good as that of clipping1-3,6,8,16). In contrast to clipping, which can shrink or puncture the aneurysm dome at the end of the operation for more effective decompression3,15,16), coiling by its nature tends to maintain the original size of the dome by filling in detachable coils after successful embolization.
The authors found that most of the aneurysms causing CN III palsy have a daughter sac at the distal end of the long axis of the aneurysm dome which is thought to be the compressing portion of CN III. During embolization of such aneurysms, we tried to fill the main dome completely while intentionally sparing the distal daughter sac from coil packing. We thought that by sparing the daughter sac we could decompress CN III more efficiently because the daughter sac may have a greater chance of involution when there is no coil in it (Fig. 1). We report the initial clinical and radiological outcomes after embolization using such a concept.
From April 2006 to September 2009, 9 cases of aneurysm-induced unilateral CN III palsy were treated with endovascular coil embolization at our institution. All of the aneurysms were located at the distal internal carotid artery and seven of them were composed of daughter sacs presumed to compress directly on CN III. Seven aneurysms with daughter sacs are included in this study. There were 6 women and 1 man with a mean age of 67 years (range, 49-86 years) at the time of treatment. Initial complete CN III palsy was seen in 6 patients and partial in one. Most (6 of 7) patients showed CN III palsy as the only symptom except for 1 patient who presented with concomitant SAH (patient no. 5) (Table 1). Mean aneurysm size including daughter sac was 8.8 mm (range, 4.7-13.3 mm), mean aneurysmal neck size was 4.0 mm (range, 2.1-6.5 mm), and mean daughter sac size was 3.3 mm (range, 1.7-4.5 mm). All of the aneurysms showed an inferoposterior projection from the parent artery. The average duration of CN III palsy before treatment was 80 hours (range, 5 hours-7 days) (Table 1). The criteria for complete preoperative CN III palsy were as follows : 1) reports of diplopia, 2) ptosis, 3) ophthalmoplegia, and 4) pupillary dysfunction3,6). Complete recovery was defined as recovery from all of these symptoms3,6). We determined the degree of recovery by reviewing the patients' medical records.
In all cases we used current technique of endosaccular embolization using detachable platinum coils under general anesthesia10). Attempts were made not to fill the daughter sac with coils and we used the double microcatheter technique in 4 cases (patient no. 1, 4, 5, 7) and stent-assisted technique in 1 (patient no. 6). The double microcatheter technique was useful for both relatively wide aneurysmal neck and making a stable coil frame for the main dome only. The mean operation time was 2 hours 11 minutes (range, 1 hour 15 minutes-3 hours 55 minutes). Assessment criteria for postoperative radiological results were complete obliteration, residual neck, and residual aneurysm12).
In all cases, we performed coil embolization by filling the main dome while intentionally sparing the daughter sac. Postoperative radiologic results were as follows : 1) complete obliteration in 4 cases (Fig. 2), 2) residual neck in 3 cases, and 3) no case of residual aneurysm. The mean size of the coil masses (5.9 mm) is smaller than that of the pre-embolized aneurysm (8.8 mm) by 67%, by sparing the daughter sac from coil filling (Table 1). There were no serious complications associated such as thromboembolism or rupture but one case of harmless coil stretching during coil filling using double microcatheter (patient no. 1). All of the patients recovered completely from CN III palsy except for one patient who had concomitant SAH and expired from lung problems after 2 months (patient no. 5). The average time of recovery was 42 days (range, 3-90 days).
Coil packing is known to decompress CN III by reducing the pulsatile expansion of the aneurysm dome6,8,15). However, it is generally accepted that clipping is superior to coiling because there is the possibility of intraoperative decompression such as resection or shrinkage of the dome3,15,16). The average recovery rate after embolization is lower than that of clipping and even two (1 permanent) cases of new CN III palsy after embolization of aneurysms have been reported2,3). There are also reports that embolized aneurysms usually become larger than initial ones17) and can cause surrounding edema, especially when the aneurysm is located close to the brain parenchyme7). However, there has been no other report on improvement of the recovery rate after embolization except for early intervention of the partially affected patients6,8).
Our observations led us to assume that it is usually the daughter sac at the distal end of the main dome which causes the compression of the CN III and attempts were made to spare the daughter sac from coil packing. Our hypothesis is that when the daughter sac is free from coils, it can have more chance of involution to a smaller size which can help decompress the CN III (Fig. 1). There is also a possibility of aggravating the symptoms after sparing the daughter sac from coil filling because of the size increase as the thrombosis proceeds. We think that the size increase is a transient event which will, in time, eventually become a smaller size. De Gast et al.4) documented similar results from parent artery occlusion for large and giant aneurysms. They confirmed spontaneous involution of large and giant aneurysms after complete occlusion of the parent artery only. Although sizes of the daughter sacs are much smaller than those of large and giant aneurysms, we thought that even a minute involution of the daughter sac can help the decompression, especially in aneurysms with large size and long duration of symptoms. In some cases we tried to find the changes in size of the daughter sacs after sparing them from coil filling by taking thin sliced MRI. However, we could not compare the sizes of the daughter sacs precisely because they were too small.
Radiologically, we cannot confirm whether the CN III is compressed by the spared daughter sac. However, the authors think that the possibility of daughter sacs being the culprits of CN III compression is high because all of the aneurysms in this study projected inferoposteriorly from the distal internal carotid artery16). Also, all of the daughter sacs were found at the very distal end, along the long axes of the aneurysms. We think that it is more likely for an aneurysm to grow along the long axis than in any other direction, so the chances of compression are high with distal daughter sacs of aneurysms which project inferoposteriorly from a distal internal carotid artery. Although the exact influences of our concept on decompression are hard to measure, our relatively better recovery rate, compared to previous reports, supports our hypothesis of a more effective decompression than usual embolization.
Sparing the daughter sac from coil packing can decrease the need for the catheter tip to be situated deeply in the aneurysm dome, which can diminish the risk of rupture. On the other hand, technical difficulty of sparing the daughter sac can lengthen the procedure time, which can increase the possibilities of thromboembolic complications9). Our initial results indicate that there is no additional risk of such adverse effects in sparing the daughter sac. However, because we left the daughter sac unpacked, other adverse effects such as the compaction of the coil mass13), recurrence of CN III palsy2) and even bleeding should be closely monitored and follow-up of patients both clinically and radiologically for a long period of time is needed11).
During the coil embolization of the cerebral aneurysms causing CN III palsy, sparing the daughter sac from coil filling while tightly packing the main dome, can be helpful in increasing the effectiveness of decompression. Long-term follow-up is mandatory.
The authors thank to Sung-Kyung Kang for illustration.