Letter to the Editor: test occlusion under monitoring of motor-evoked potentials for giant distal

Transcription

1 Letter to the Editor: test occlusion under monitoring of motor-evoked potentials for giant distal anterior cerebral artery aneurysm Acta Neurochirurgica Kampei Shimizu, Shoichi Tani, Hirotoshi Imamura, and Nobuyuki Sakai Department of Neurosurgery, Kobe City Medical Center General Hospital, Kobe, Japan Correspondence to: Kampei Shimizu, MD Department of Neurosurgery, Kobe City Medical Center General Hospital, Minatojima-Minamimachi, Chuo-ku, Kobe , Japan Tel: Fax:

2 Dear Editor The article by Guo et al. contributed to estimate the correlation between intraoperative motor-evoked potential (MEP) events and postoperative neurological deficits [2]. In that study, permanent intraoperative MEP events were strongly associated with postoperative motor deficits, with a positive predictive value of 1.0 (13/13), while approximately 30% of transient MEP events (16/53) were also related to postoperative motor impairment. These findings demonstrate that a rapid response to intraoperative MEP event is necessary for preventing postoperative neurological defect. However, immediate response is not always possible depending on the intraoperative situation [7]. In this letter, we present a rare case of giant distal anterior cerebral artery (DACA) aneurysm that was successfully treated by aneurysm trapping with A3-A3 side-to-side bypass under MEP monitoring. Intraoperatively, we could effectively predict ischemic tolerance to the parent artery occlusion using a 15-min test occlusion. Case Report A 48-year-old woman was incidentally diagnosed with a giant thrombosed cerebral aneurysm (26.0 mm in diameter) located on the A3 segment of the right anterior cerebral artery (ACA) (Fig. 1a, b). Conventional neck clipping with aneurysm resection and thrombectomy was planned if the 15-min test occlusion at just proximal to the aneurysm would not cause any MEP event. Otherwise, aneurysm 2

3 trapping with prior revascularization by A3-A3 side-to-side anastomosis was planned. Intraoperatively, an Endeavor CR intraoperative monitor (Nicolet VIASYS Healthcare, USA) was used for transcranial electrical stimulation and recordings. Corkscrew-like stimulation electrodes were placed subcutaneously at the C3-anode/C4-cathode (or C3-cathode/C4-anode) with the anode serving as the active electrode to elicit MEP of the lower extremity muscles (the abductor hallucis muscles) on each side. We defined a significant event in MEP as a reduction of amplitude by 50% or an increase of peak latency by more than 10% [4]. During proximal test occlusion, the amplitude of MEP derived from the left lower extremity decreased below 50% at 6 min (arrows of Fig. 2a). We finished the test occlusion, and MEP was restored to baseline state by 5 min. By contrast, a 15-min distal test occlusion of the bilateral ACA (arrow of Fig. 1b) did not cause any event in MEP and the pair of arteries were chosen for the site of anastomosis. After the patency of anastomosis was confirmed with indocyanine green angiography, the 15-min test occlusion by aneurysm trapping did not cause any event in MEP (Fig. 2b). The aneurysm was trapped with two clips. Thereafter, no MEP event was recorded up to the end of surgery. Stable blood pressure of /40 50 mmhg was sustained during all the procedures. Magnetic resonance imaging one day after the surgery revealed asymptomatic focal contusion along the interhemispheric fissure (Fig. 1c). The postoperative circulation was assessed by digital subtraction angiography (DSA) (Fig. 1d). The patient was discharged two weeks after the surgery with no neurological sequelae. The patient has been free from 3

4 ischemic event for six months. Discussion Giant DACA aneurysms are extremely rare. There have been 37 cases of giant DACA aneurysms reported so far [3, 5, 6, 8]. To our knowledge, there are six cases, including our one, where the result of test occlusion was available. We reviewed the results of the six cases and one additional case where test occlusion was not performed but a MEP event was recorded during temporary occlusion for aneurysmal resection (Table 1) [1, 3, 5, 6, 8]. Events during temporary occlusion (positive finding) were recorded in two cases (29%), which occurred at 5 and 6 min after occlusion. Our case was the first case where a positive finding led to an immediate change in the surgical strategy. The time required for recovery of MEP among the two cases was much shorter in our case (5 min) than that in the other case presented by Yoneda et al. (78 min) [8], suggesting that a rapid response to MEP event by performing test occlusion is effective for preventing postoperative neurological defect. The findings are consistent with previously presented data by Wiedemayer et al. [7] that the intraoperative interventions following IONM events contributed to prevent a neurological deterioration. The results of test occlusion may be false-negative, where an event is not recorded during test occlusion while an IONM event or new deficits were found subsequently. A false-negative finding was reported in one case (14%) of pericallosal-callosomarginal artery aneurysm [3]. In this case, test 4

5 occlusion was conducted by proximal occlusion for 20 min. During the test occlusion, DSA demonstrated that flow in the callosomarginal artery was anterograde, which was supplied by good retrograde flow in the distal pericallosal artery. The condition of the occlusion was changed by aneurysm trapping during thrombectomy and subsequent unpredicted occlusion of the parent artery caused by severe calcification of the aneurysm neck, both of which made the flow in the callosomarginal artery retrograde. In test occlusion, it is especially important that occlusion condition during test occlusion is identical with that during subsequent surgical procedure. We present the first case where a positive finding of test occlusion under MEP monitoring led to an immediate change of the surgical strategy for treatment of giant DACA aneurysm. Our data provide further support for the importance of test occlusion for treating complex DACA aneurysms. Conflict of Interest The authors declare that they have no conflict of interest. Patient Consent The patient has consented to submission of the case report. 5

6 References 1. Biondi A, Jean B, Vivas E, Le Jean L, Boch AL, Chiras J, Van Effenterre R (2006) Giant and large peripheral cerebral aneurysms: Etiopathologic considerations, endovascular treatment and long-term follow-up. Am J Neuroradiol 27: Guo L, Gelb AW (2011) The use of motor evoked potential monitoring during cerebral aneurysm surgery to predict pure motor deficits due to subcortical ischemia. Clin Neurophysiol 122: Matsushima K, Kawashima M, Suzuyama K, Takase Y, Takao T, Matsushima T (2011) Thrombosed giant aneurysm of the distal anterior cerebral artery treated with aneurysm resection and proximal pericallosal artery-callosomarginal artery end-to-end anastomosis: Case report and review of the literature. Surg Neurol Int 2: Neuloh G, Schramm J (2004) Monitoring of motor evoked potentials compared with somatosensory evoked potentials and microvascular Doppler ultrasonography in cerebral aneurysm surgery. J Neurosurg 100: Van Rooij WJ, Sluzewski M, Beute GN (2008) Endovascular treatment of giant serpentine aneurysms. Am J Neuroradiol 29: Senbokuya N, Kanemaru K, Kinouchi H, Horikoshi T (2012) Giant serpentine aneurysm of the distal anterior cerebral artery. J Stroke Cerebrovasc Dis 21:910.e Wiedemayer H, Fauser B, Sandalcioglu IE, Schäfer H, Stolke D (2002) The impact of neurophysiological intraoperative monitoring on surgical decisions: a critical analysis of 423 cases. J Neurosurg 96: Yoneda H, Suzuki M, Ishihara H, Koizumi H, Nomura S, Fujii M (2014) A case of thrombosed giant aneurysm of the azygos anterior cerebral artery: clipping under monitoring of motor evoked potentials of the lower extremities. Neurol Med Chir (Tokyo) 54:

7 Figures Fig. 1 Fig. 1 a Preoperative sagittal contrast-enhanced T1-weighted MRI shows partially thrombosed aneurysm. b Preoperative 3D-digital subtraction angiography (lateral view) shows the site of aneurysm and distal test occlusion (arrow). c Postoperative fluid-attenuated inversion recovery MRI shows focal brain contusion along interhemispheric fissure. d Postoperative 3D-digital subtraction angiography (lateral view) shows patency of the bypass and postoperative circulation. 7

8 Fig. 2 Fig. 2 a Motor-evoked potentials (MEP) of the abductor hallucis muscles during proximal test occlusion. The amplitude of MEP decreased below 50% at 6 min (arrow) after starting proximal test occlusion (arrowhead) and took 5 min for recovery. b No MEP event was recorded by 15-min proximal test occlusion after the A3-A3 bypass. The scales between neighboring baselines of waves on downward vertical arrows are 1 mv. The MEP waves elicited every 1 (a) or 3 min (b) are shown from the top to the bottom. 8