Coil Embolization of Cerebral Tiny Aneurysms

Journal of Neuroendovascular Therapy 2016; 10: 243 248 Online November 9, 2016 DOI: 10.5797/jnet.oa.2016-0035 Coil Embolization of Cerebral Tiny Aneurysms Terumasa Kuroiwa, 1 Fuminori Shimizu, 2 Taro Yamashita, 2 Ryo Hiramatsu, 3 Ryokichi Yagi, 3 Seigo Kimura, 4 Yoshitaka Yamada, 5 and Makoto Yamada 6 Purpose: We retrospectively examined the results of coil embolization for 28 cerebral tiny aneurysms (<3 mm), 73 small cerebral aneurysms (3 4 mm) and associated complications. Subjects and Methods: From a total of 418 patients who underwent coil embolization of cerebral aneurysms (n = 433) between January 2008 and August 2015, we analyzed 28 cerebral tiny aneurysms (6.5%) and 73 small aneurysms (16.9%). The type of procedure, results of embolization, and complications were compared. Results: For 23 (82.1%) of the 28 tiny aneurysms and 52 (71.2%) of the 73 small aneurysms, embolization was performed using a simple technique. Embolization resulted in complete obliteration (CO) and neck remnant (NR) in 26 (92.9%) of the 28 tiny aneurysms, and CO + NR was achieved in 62 (84.9%) of the 73 small aneurysms. Treatment was discontinued for one tiny aneurysm and one small aneurysm. Intraoperative rupture occurred in one tiny aneurysm and three small aneurysms. Thromboembolism was observed in one tiny aneurysm and one small aneurysm. Morbidity was encountered in one tiny aneurysm (thromboembolism), and mortality was associated with another tiny aneurysm (intraoperative rupture). Conclusion: The results of coil embolization for tiny aneurysms were similar to those of small aneurysms. Coil embolization-related complications and prognosis were also considered to be similar. Keywords tiny cerebral aneurysm, small cerebral aneurysm, coil embolization Introduction After coil embolization of cerebral aneurysms became covered by national health insurance in 1997, there has been increasingly rate procedures performed in Japan. With the 1 Division of Neuroendovascular Therapy, Kozenkai Yagi Neurosurgical Hospital, Osaka, Japan 2 Department of Neurosurgery, Seijinkai Shimizu Hospital, Osaka, Japan 3 Department of Neurosurgery and Neuroendovascular Therapy, Osaka Medical College, Osaka, Japan 4 Department of Neurosurgery, Kozenkai Yagi Neurosurgical Hospital, Osaka, Japan 5 Department of Neurosurgery, Nishinomiya Kyoritsu Neurosurgical Hospital, Osaka, Japan 6 Department of Neurosurgery, Takeda General Hospital, Osaka, Japan Received: March 16, 2016; Accepted: July 24, 2016 Corresponding author: Terumasa Kuroiwa. Division of Neuroendovascular Therapy, Kozenkai Yagi Neurosurgical Hospital, 2-12-13 Higashi-imazato, Higashinari-ku, Osaka 537-0011, Japan Email: terukuroiwa@mui.biglobe.ne.jp 2016 The Editorial Committee of Journal of Neuroendovascular Therapy. All rights reserved. introduction of various devices, such as coils, balloons, and stents, and advances in cerebral angiographs, coil embolization has been accepted as a standard treatment. However, tiny cerebral aneurysms measuring 3 mm (tiny aneurysm (AN)) are still difficult to treat because of a high incidence of intraoperative rupture, thromboembolism, and postoperative hemorrhage related to the extremely small size. 1 7) In this study, we retrospectively investigated comparative outcomes and complications for endovascular coil embolization of patients with tiny ANs measuring 3 mm and small aneurysms (small ANs) measuring 3 mm to 4 mm among our series of cerebral aneurysms. Subjects and Methods Of 482 patients who underwent coil embolization of cerebral aneurysms in our hospital and affiliated hospitals between January 2008 and August 2015, we retrospectively analyzed the results of 418 patients (433 aneurysms). Recurrent aneurysms and cases where measurement data were unclear were excluded. Of the 433 aneurysms, 28 were classified as tiny ANs (6.5%), and 73 as small ANs 243

Kuroiwa T, et al. Fig. 1 (a) Volume rendering image of R-VAG shows a PICA aneurysm with a maximum diameter of 2.89 mm. (b) The tip of the microcatheter is shaped to S -figure according to the volume rendering image. (c) Target 360 ultra 2.5 40 mm is deployed as a framing coil. (d) At the end of the procedure, R-VAG shows complete obliteration of the aneurysm. PICA: posterior inferior cerebellar artery; R-VAG: R-vertebral angiography (16.9%). The mean ages of tiny and small AN patients were 63.6 ± 15.7 years and 65.1 ± 13.0 years, respectively. Women accounted for 71.4% (n = 20) of the tiny AN patients and 75.3% (n = 55) of the small AN patients. Location of tiny ANs was as follows: 5 ICA aneurysms (18.5%), 14 (51.9%) ACA + Acom, 4 BA, 3 VA, and 1 MCA. The distribution for small AN was as follows: 28 aneurysms (38.9%) ICA, in 26 (36.1%) ACA + Acom, 10 BA, 4 VA, 3 MCA and 1 PCA. Rupture occurred in 19 (67.9%) of the 28 tiny ANs and in 26 (35.2%) of the 73 small ANs (p = 0.003). For patients with unruptured aneurysms, coil embolization was defined according to the following criteria, as described by Brinjikji et al. 1) : the concomitant presence of aneurysms measuring 5 mm (three tiny and eight small ANs), enlargement/neogenesis during follow-up (two tiny and seven small ANs), and irregularity (one tiny and seven small ANs). After informed consent, coil embolization was selected for 3 tiny and 23 small ANs based on patient preference due to a family history or a history of stroke. Coil embolization was performed under general anesthesia in all patients. 3D rotational angiography (RA) was applied to a work station to determine the working angle and measurement of surgical dimensions. All tiny/small ANs were embolized using a simple technique, with addition of balloon or stent as necessary. Assuming the position of microcatheter insertion as an area adjacent to the cervix (Fig. 1a), the tip of a microcatheter was manually shaped to S - or C - figure (Fig. 1b) and guided/inserted. For the coil framing, a 3D coil slightly smaller than the aneurysmal 244

Coil Embolization of Cerebral Tiny Aneurysms Table 1 Comparison of characteristics of 28 tiny aneurysms and 73 small aneurysms 28 tiny aneurysms ( 3 mm) 73 small aneurysms (3 4mm) p value Age (yr) 63.6 ± 15.7 65.1 ± 13.0 0.313 Female (%) 20 (71.4) 55 (75.3) 0.689 Location (%) 0.376 ICA 5 (18.5) 28 (38.9) ACA + Acom 14 (51.9) 26 (36.1) MCA 1 3 BA 4 10 VA 3 4 PCA 0 1 Ruptured (%) 19 (67.9) 26 (35.2%) 0.003 Procedures (%) 0.395 Simple 23 (82.1) 52 (71.2) Balloon assisted 5 18 Stent assisted 0 2 Angiographic outcome (%) 0.386 Complete obliteration 16 (57.2) 36 (49.2) Neck remnant 10 (35.7) 26 (35.6) Dome filling 1 10 (13.7) Attempt (failure) 1 1 Complication (%) 0.768 Intraprocedural rupture 1 (3.6) 3 (4.4) Thromboembolism 1 (3.6) 1 Morbidity/mortality 1/1 0/0 0.321 ACA: anterior cerebral artery; Acom: anterior communicating artery; BA: basilar artery; ICA: internal cerebral artery; MCA: middle cerebral artery; PCA: posterior cerebral artery; VA: vertebral artery diameter was selected, and inserted while adjusting the microcatheter position if necessary (Fig. 1c). Tight packing was performed as possible. For finishing, a 1.0 mm- or 1.5 mm 3D coil was selected (Fig. 1d). After sheath insertion, systemic heparinization was started. Following surgery, continuous intravenous injection of argatroban was administered for the first 48h in both ruptured and unruptured aneurysm patients. For unruptured aneurysms, an oral anti-platelet agent was administered 1 week prior to surgery. For patients with (anticipated) use of balloon/stent, two agents were administered. In one case of a tiny unruptured Acom aneurysm, it was impossible to form a stable frame and treatment was discontinued. Clipping was performed in a subsequent operation. In one small ruptured internal cerebral (IC) Pcom aneurysm, a balloon was used. However, intra-aneurysmal thrombosis occurred during framing, and the procedure was discontinued. Direct clipping was then performed. We reviewed the medical records and results of cerebral angiography. Statistical analysis was performed using the chi square and t-tests. Results (Table 1) Coil embolization of 23 tiny and 52 small ANs (82.1% and 71.2%, respectively) was performed using a simple technique. A balloon was concurrently used in 5 tiny and 18 small ANs. Of the tiny ANs, postoperative cerebral angiography confirmed complete obliteration (CO) in 16 and neck remnant (NR) in 10. In the small ANs, CO was confirmed in 36, NR in 26, and dome filling (DF) in 10. One tiny (ruptured daca AN) and 3 small (2 ruptured Acom ANs, 1 unruptured IC paraclinoid AN) ANs ruptured during surgery. In one patient with a tiny AN, coil-related perforation during framing led to CO, however the patient died from re-rupture after 5 days. Of the three small ANs, two Acom ANs ruptured (World Federation of Neurosurgical Societies (WFNS) grade 1), and treatment was performed on day 0. Rupture was related to penetration during the insertion of coil filling. One patient was discharged free of symptoms on day 21, and the other patient was discharged with an modified Rankin Scale (mrs) of 1. CO was achieved in the IC paraclinoid AN, and the patient was discharged free of symptoms. Thromboembolism was observed in one tiny (ruptured posterior inferior cerebellar artery (PICA) AN) and one small (unruptured middle cerebral artery (MCA) AN) AN patient. The former was discharged on day 30, with an mrs of 3, and the latter received intra-arterial injection of urokinase, and was discharged with no new symptoms. Concerning morbidity, the tiny AN patient with thromboembolism was discharged with an mrs of 3. As for mortality, only one tiny AN patient with succumbed death from intraoperative rupture. 245

Kuroiwa T, et al. Table 2 Comparison of our initial results of 28 tiny, 73 small, and 332 large ANs 28 tiny aneurysms ( 3 mm) 73 small aneurysms (3 4 mm) 332 large aneurysms ( 4 mm) p value Ruptured AN (%) 19 (67.9) 26 (35.6) 137 (41.3) 0.0116 Simple embolization (%) 23 (82.1) 52 (71.2) 118 (35.5) <0.0001 Adequate occlusion ( CO + NR ) (%) 26 (92.9) 62 (84.9) 270 (81.3) 0.204 Intraprocedural rupture (%) 1 (3.6) 3 (4.1) 9 (2.1) 0.8164 Intraprocedural thromboembolism (%) 1 (3.6) 1 (1.4) 8 (2.4) 0.7718 Procedure related morbidity 1 (3.6) 0 7 (2.1) 0.2016 Procedure related mortality 1 (3.6) 0 1 (0.5) 0.1954 AN: aneurysm; CO: complete obliteration; NR: neck remnant Discussion In general, advances in angiographical technology and the introduction of new devices may have contributed to improved accuracy and outcomes of cerebral endovascular treatment. However, coil embolization of small cerebral aneurysms requires intricate procedures due to their size and has remained a technical challenge. 1 7) As for small aneurysms, the proportion of wide-neck aneurysms is high, and the concurrent use of balloon assist techniques has proven useful, especially for operations with coil insertion. A recent study has indicated that balloon use was helpful for hemostasis in cases of intraoperative rupture. 8) On the other hand, the range of motion for microcatheters and coils is restricted, and coil-related penetration may occur. In addition, there is a risk of blood flow blockage-related thromboembolism. 1,7) For this reason, we typically performed embolization using a simple technique. In our series, a balloon technique was used in sidetype ANs to stabilize the microcatheter rather than for sealing the aneurysmal neck. In patients with small cerebral aneurysms, complications related to penetration when inserting microcatheters, microguidewires, or coils must be considered. 1 3) To prevent this, it is important to initially conduct shaping at the catheter end and stabilize it while restricting the motion to some degree, as the wire/coil end s motions are more flexible than the motion of the catheter end. 3 5) Tsutsumi et al. introduced a method to stabilize the catheter end through shaping at the catheter end in accordance with the torsion of the primary blood vessel (A1 and ICA). 4) However, we prepared a C -shape for side-type aneurysms and S -shape for terminal-type aneurysms via shaping using anchoring with the wall of the primary blood vessel at one or two points (Fig. 1). Thus, the utilization of friction with the primary blood vessel facilitates stable operation for catheter guiding until coil insertion. Historically, a microcatheter was inserted into an area adjacent to the aneurysmal neck, as described by Rooij and Yamaura et al. 2,3) However, in patients with terminal-type aneurysms, a microcatheter was inserted into an extraaneurysmal area, and guided to an intra-aneurysmal area while inserting a framing coil. The diameter of the first loop of a framing coil measuring 3 mm in diameter differs among manufacturers: Orbit galaxy (Codman Neurovascular, Johnson & Johnson, Miami, FL, USA), 2 mm; Axium (ev3 Covidien, Irvine, CA, USA), 2.1 mm; Target (Stryker, Kalamazzo, MI, USA), 2.3 mm; and Vtrak complex (Microvention, Termo, Tustin, CA, USA), 3 mm. Therefore, even when a catheter can be safely guided into the aneurysm, insufficient identification of the end position may lead to penetration on coil insertion. Intraoperative rupture of a tiny AN in this study corresponded to this complication. Furthermore, a frame could be safely formed by selecting a slightly small, 3D-type, slightly long coil to reduce stress against the aneurysmal wall. For a filling coil, the 1 mm or 1.5 mm piece meal technique was used, but many coils are stretch-resistant (SR), as indicated by Miyachi et al.; therefore, a straightening phenomenon may occur for filling/finishing, leading to penetration through linear coil movement. 9) However, in small aneurysms, it is difficult to evaluate coil movement on the display monitor, making assessment more difficult. In our study, intraoperative rupture in two small AN patients was associated with filling coil-related penetration. The 3D RA and work station are particularly useful for performing surgical operations on small aneurysms. 10) In our experience there were no problems regarding catheter shaping or coil size selection based on measurements using these technologies. When selecting a high-power field on fluoroscopy or angiography intraoperatively, there is the problem of increased exposure dose. However, use of a collimator, digital zoom, and high-resolution monitor were used in our series both for reduction of exposure dose and improving image clarity. 246

Coil Embolization of Cerebral Tiny Aneurysms Table 3 Studies reporting on coil embolization of consecutive tiny cerebral aneurysms Thromboembolic complication, % Intraoperative rupture, % Adequate occlusion, % Without adjunctive technique, % No. of ruptured aneursyms No. of aneurysms Nguyen et al. (1992 2007) 9) 60 60 (no information) (no information) 11.7 (no information) van Rooij et al. (1995 2008) 2) 196 149 95.9 94.9 7.7 2.1 Brinjikji et al. (2002 2008) 1) 71 24 50.7 87.3 8.5 6.3 Starke et al. (2004 2011) 8) 82 82 87.8 84.0 9.8 3.7 Meta-Analysis by Brinjikji 1) 422 171 69.2 95.3 8.3 (no information) Our series (2008 2015) 28 19 82.1 92.9 3.4 3.4 We compared the results of coil embolization of the tiny/ small ANs with those of 3324 mm or larger cerebral aneurysms treated during the same period (Table 2). In both the tiny and small AN patients, the proportions of those with rupture were markedly higher than in the large AN patients, and the higher in those treated by a simple technique. However, there were no marked differences in the results for embolization, incidence of intraoperative rupture, incidence of embolic complications, incidence of sequelae, or mortality rate. Furthermore, our results of coil embolization of the tiny ANs were similar to those of previous studies regarding coil embolization of cerebral small ANs, and the incidences of intraoperative rupture and embolic complications were lower in our study (Table 3). 1 7) As this was a retrospective study involving a limited number of patients, a definitive conclusion could not be made, however both small and tiny cerebral aneurysms can be relatively safely treated by embolization with a simple technique using work station based on 3D RA. Acknowledgment I would like to express my deepest gratitude to Dr. Toshihiko Kuroiwa of Department of Neurosurgery, Osaka Medical College, the members of related facilities, and Dr. Yukio Shimizu of Shimizu Hospital, who provided us with many opportunities of medical treatments. Disclosure Statement There is no conflict of interest to be disclosed for the first author and co-authors regarding this article. References 1) Brinjikji W, Lanzino G, Cloft HJ, et al: Endovascular treatment of very small (3 mm or smaller) intracranial aneurysms: report of a consecutive series and a meta-analysis. Stroke 2010; 41: 116 121. 2) van Rooij WJ, Keeren GJ, Peluso JP, et al: Clinical and angiographic results of coiling of 196 very small (< or = 3 mm) intracranial aneurysms. AJNR Am J Neuroradiol 2009; 30: 835 839. 3) Yamaura I, Uramoto S, Kidera M, et al: Coil embolization of small aneurysms with a maximum diameter of 3mm. JNET 2010; 4: 99 105. (in Japanese) 4) Tsutsumi M, Aikawa H, Onizuka M, et al: Endovascular treatment of tiny ruptured anterior communicating artery aneurysms. Neuroradiology 2008; 50: 509 515. 247

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