J Neurosurg 100:960–962, 2004 Monitoring and preventing blood flow insufficiency due to clip rotation after the treatment of internal carotid artery aneurysms Technical note JUN SAKUMA, M.D., KYOUICHI SUZUKI, M.D., TATSUYA SASAKI, M.D., MASATO MATSUMOTO, M.D., MASAHIRO OINUMA, M.D., MASAHISA KAWAKAMI, M.D., TAKESHI ITAKURA, B.S., AND NAMIO KODAMA, M.D. Department of Neurosurgery, Fukushima Medical University, Fukushima, Japan √ The authors report a case in which anterior choroidal artery (AChA) blood flow insufficiency due to aneurysm clip rotation was detected intraoperatively by motor evoked potential (MEP) monitoring and ischemia was successfully avoided. The patient had an incidentally discovered aneurysm for which occlusion of its neck was performed through a standard frontotemporal craniotomy without changing the MEP amplitude. After it was confirmed that the surrounding arteries were not stenotic, the brain retractor on the frontal lobe was released; MEP amplitude subsequently decreased. Rotation of the clip toward the frontal base by repositioning of the frontal lobe caused the AChA stenosis at the origin of its branches. On reorienting the clip toward the frontal lobe, the AChA stenosis was released and MEP amplitude recovered. To prevent repeated clip rotation, a large amount of gelatin (Spongel) was inserted between the frontal base and the clip. The authors confirmed that clip rotation did not occur after repositioning of the frontal lobe. Motor evoked potential amplitude was maintained until dural closure. Postoperatively, the patient demonstrated no neurological deficit and there was no newly developed low-density area on computerized tomography scans. KEY WORDS • clip rotation • anterior choroidal artery • motor evoked potential • intraoperative monitoring • aneurysm R ECENTLY we reported8 that intraoperative monitoring of the MEPs can detect blood flow insufficiency in the AChA during aneurysm surgery. We treated a patient in whom intraoperative MEP monitoring detected blood flow insufficiency in the AChA due to aneurysm clip rotation that was caused by repositioning of the frontal lobe after the brain retractor was released in preparation for dural closure. Ischemia was successfully avoided in this patient by keeping the position of the clips stable after release of the frontal lobe. Case Report History and Examination. This 39-year-old woman was found to have an incidental aneurysm in the right ICA at the bifurcation of the AChA. Three-dimensional computerized tomography angiography4 revealed an 8-mm ICA–AChA aneurysm protruding posterolaterally. Anesthesia administration and intraoperative MEP monitoring were performed as reported previously.8 Prior informed consent was obtained from the patient. Operation. Clip occlusion of the aneurysm neck was performed through a standard frontotemporal craniotomy. InAbbreviations used in this paper: AChA = anterior choroidal artery; ICA = internal carotid artery; MEP = motor evoked potential. 960 traoperative findings are shown in Fig. 1 and intraoperative MEP changes in Fig. 2. After exposing the ICA–AChA aneurysm (Fig. 1a), occlusion of its neck was performed using two Yasargil straight clips (Fig. 1b). Doppler ultrasonography data confirmed blood flow in the ICA and AChA, and MEP amplitude remained at the control level. No finding of AChA blood flow insufficiency was recognized. After release of the brain retractor, the frontal lobe began to reposition and contacted the clips. Oxycellulose cotton (Surgicel) was inserted between the clip heads and the surface of the brain (Fig. 1c) to avoid injury to the frontal lobe. Nevertheless, MEP amplitude subsequently fell to 50% of the control level. We noticed that the clips were pushed by the repositioning frontal lobe after release of the brain retractor and placement of the Surgicel; consequently the clips had rotated toward the frontal base. Reorienting the clips toward the frontal lobe returned the MEP amplitude to the control level within 60 seconds (Fig. 1d). Therefore, we intentionally rerotated the clips toward the frontal base (Fig. 1e) and recognized that the origin of the AChA became slightly stenotic. At 40 seconds after the repeated rotation, the MEP amplitude fell again, this time to 10% of the control level. We reoriented the clips toward the frontal lobe and the MEP amplitude recovered 60 seconds later. Therefore, to prevent clip rotation, a large amount of Surgicel and gelatin (Spongel) was inserted between the frontal base and the clips (Fig. 1f). The MEP amplitude was maintained at the control level until dural closure. J. Neurosurg. / Volume 100 / May, 2004 Prevention of blood flow insufficiency due to clip rotation FIG. 1. Intraoperative photographs showing an ICA–AChA aneurysm (AN). a: Photograph showing the untreated lesion. b: Clip occlusion of the aneurysm neck was performed using two Yasargil straight clips. c: After releasing the brain retractor, oxycellulose cotton (OC) was inserted between the frontal cortex and the clip heads to avoid injury to the frontal lobe (FL). Subsequently, the clip heads rotated toward the frontal base (FB). d: The clips were reoriented toward the frontal lobe. e: The clips were intentionally rerotated toward the frontal base. f: The insertion of oxycellulose cotton and gelatin (Ge) between the frontal base and the clips averted further rotation. Postoperative Course. This patient did not suffer hemiparesis postoperatively and a computerized tomography scan revealed no new low-density area. She was discharged with no neurological deficits. Discussion In aneurysm surgery, even though the neurosurgeon may judge that aneurysm clip placement has been performed adequately, rotation of the clip due to brain repositioning afJ. Neurosurg. / Volume 100 / May, 2004 ter release of the retractor often results in stenosis or occlusion of arterial branches and perforating arteries around the aneurysm. Friedman, et al.,3 have documented that clip rotation led to blood flow insufficiency in the AChA. In their report, one patient had a delayed deficit beginning at 36 hours and was returned to the operating room at 72 hours. In that patient the clip was found to have twisted in situ, causing occlusion of the AChA. Detection of blood flow insufficiency caused by clip rotation is, however, still difficult. In a few patients, postoperative skull x-ray films re961 J. Sakuma, et al. operative sequelae caused by blood flow insufficiency in the AChA, nor can it guarantee a sufficient blood flow. In comparison with those conventional methods, the monitoring method in which MEP8 is used facilitates the detection of blood flow insufficiency in the AChA, which perfuses the internal capsule. It can detect ischemia in the AChA in as short a time as 5 to 40 seconds. To prevent clip rotation, we used oxycellulose cotton and gelatin in this case. We have recently encountered another case in which the repositioning of the frontal lobe caused clip rotation. For that case we inserted a large, hard rectangular polyurethane sponge between the anterior skull base and the frontal lobe, because the repositioned frontal lobe was strongly pushing the clip head. When we anticipate that the force of clip rotation will be strong, a hard substance such as polyurethane sponge should be used as a prop. FIG. 2. Tracings showing intraoperative MEP changes. After clip occlusion of the aneurysm neck, the MEP amplitude did not change. After release of the brain retractor, oxycellulose cotton was placed between the clip heads and the surface of the frontal lobe to avoid injury to the brain. Subsequently, the MEP amplitude decreased to 50% of the control level. Within 60 seconds after reorienting the clips toward the frontal lobe, the MEP amplitude recovered. At 40 seconds after intentional rotation of the clips toward the frontal base, the MEP amplitude fell to 10% of the control level. Reorientation of the clips toward the frontal lobe resulted in recovery of MEP amplitude to the control level. To prevent clip rotation, oxycellulose cotton and gelatin were inserted between the frontal base and the clips, after which the MEP amplitude remained unchanged until dural closure. vealed changes in the direction of the clip. At 0.7 to 2 mm (mean 1.2 mm), the diameter of the AChA is almost half that of the posterior communicating artery and is very small6 compared with the diameter of the ICA or aneurysm neck. Just after releasing the clip applier, we often observe clip rotation due to a twisting force caused by the uneven arterial wall thickness and tension. Also, clip rotation caused by the repositioning brain results in kinking and consequent stenosis of the AChA because this artery is very small. Up until now it has been extremely difficult to detect AChA blood flow insufficiency intraoperatively in patients undergoing occlusion of an ICA aneurysm.10 The somatosensory evoked potential identifies blood flow insufficiency in the territory of cortical branches of the middle cerebral artery; however, it cannot detect this phenomenon in the AChA.5 Microvascular Doppler ultrasonography7 can detect the blood flow itself, but it cannot determine whether the blood flow is sufficient to avoid ischemia. It is possible that we detect the sound from the other artery near the targeted vessel because the frequency of sound waves determines the depth of sensitivity. Intraoperative angiography1,2,9 may depict the AChA under conditions in which temporary occlusion has already led to irreversible changes in the internal capsule and has resulted in infarction. In such cases, intraoperative angiography cannot be used to predict the post962 Conclusions We report on a case in which AChA blood flow insufficiency due to aneurysm clip rotation was detected using intraoperative MEP monitoring and in which ischemia was successfully avoided by preventing clip rotation. We emphasize that the physician should not only be careful about the clip placement itself, but should also be aware of subsequent pitfalls. References 1. Barrow DL: Intraoperative angiography, in Loftus CM, Traynelis VC (eds): Intraoperative Monitoring Techniques in Neurosurgery. New York: McGraw-Hill, 1994, pp 77–94 2. Chiang VL, Gailloud P, Murphy KJ, et al: Routine intraoperative angiography during aneurysm surgery. J Neurosurg 96:988–992, 2002 3. Friedman JA, Pichelmann MA, Piepgras DG, et al: Ischemic complications of surgery for anterior choroidal artery aneurysms. J Neurosurg 94:565–572, 2001 4. Matsumoto M, Sato M, Nakano M, et al: Three-dimensional computerized tomography angiography-guided surgery of acutely ruptured cerebral aneurysms. J Neurosurg 94:718–727, 2001 5. Mizoi K, Yoshimoto T: Permissible temporary occlusion time in aneurysm surgery as evaluated by evoked potential monitoring. Neurosurgery 33:434–440, 1993 6. Rhoton AL Jr, Fujii K, Fradd B: Microsurgical anatomy of the anterior choroidal artery. Surg Neurol 12:171–187, 1979 7. Stendel R, Pietila T, Al Hassan AA, et al: Intraoperative microvascular Doppler ultrasonography in cerebral aneurysm surgery. J Neurol Neurosurg Psychiatry 68:29–35, 2000 8. Suzuki K, Kodama N, Sasaki T, et al: Intraoperative monitoring of blood flow insufficiency in the anterior choroidal artery during aneurysm surgery. J Neurosurg 98:507–514, 2003 9. Tang G, Cawley CM, Dion JE, et al: Intraoperative angiography during aneurysm surgery: a prospective evaluation of efficacy. J Neurosurg 96:993–999, 2002 10. Yasargil MG, Yonas H, Gasser JC: Anterior choroidal artery aneurysms: their anatomy and surgical significance. Surg Neurol 9: 129–138, 1978 Manuscript received September 2, 2003. Accepted in final form January 13, 2004. Address reprint requests to: Jun Sakuma, M.D., Department of Neurosurgery, Fukushima Medical University, 1 Hikarigaoka, Fukushima 960-1295, Japan. email: jsakuma@fmu.ac.jp. J. Neurosurg. / Volume 100 / May, 2004