Temporary Clip Application Research Articles

The use of near-infrared spectroscopy (NIRS) in surgical clipping of giant cerebral aneurysm

EDITOR: A 49-yr-old male patient was scheduled for clipping of a giant right middle cerebral artery (MCA) aneurysm. He presented with Grade IV subarachnoid haemorrhage (SAH) and large intracerebral haemorrhage. Upon admission, the patient's Glasgow Coma Scale score was 8 (E2V2M4) with left-sided hemiplegia. The patient was transferred to the operating room, sedated and intubated. Two 18-G peripheral intravenous lines and a left radial arterial line were placed. In addition to the routine standard monitors, electroencephalograph (EEG) electrodes were placed over the midline and left cerebral hemisphere. Two near-infrared spectroscopy (NIRS) sensors (model INVOS-4100; Somanetics Corporation, Troy, MI, USA) were applied, one on either side of the forehead. The sensors were covered with adhesive cover to shield them from ambient light. Baseline rSO2 recordings from both sides were 71-73%. Baseline systemic temperature was 37.0°C. General anaesthesia was maintained with sevoflurane (0.5% MAC (minimum alveolar concentration)), oxygen/air (40-60%) and remifentanil (0.15 μg kg−1 min−1). Mechanical ventilation was adjusted to maintain a PCO2 in the 30-35 mmHg range. Following right fronto-temporal craniotomy, right femoral artery to right carotid artery (FA-CA) extracorporeal hypothermic bypass was instituted. After 40 min of cooling and right brain surface temperature of 23°C, a temporary clip was placed on the right MCA. Systemic temperature was 37.3°C. Shortly after temporary clip application, the right rSO2 recordings were in the range of 55-60%. After 26 min of temporary clip application, right rSO2 readings dropped below 50% on two separate occasions 5 min apart each episode lasted for 3 min. Left-sided rSO2 recordings remained unchanged and EEG recording from midline and left hemisphere did not show any changes suggestive of ischaemia. In response to the episodes of cerebral desaturation, the neurosurgeon was informed and the temporary clip position was adjusted. Propofol infusion (3-5 mg kg−1 h−1) was started to reduce cerebral metabolic rate and titrated until EEG burst suppression was achieved. Right cerebral oxygen saturation readings returned to baseline values after 5 min of temporary clip adjustment (Fig. 1). Total temporary clipping time was 67 min and 54 s and the total duration of surgery was 12 h and 15 min.Figure 1: Time course of changes in cerebral oxygen saturation. Point A: correspond to temporary clip application, areas B&C: represent periods of desaturation, Point D: correspond to temporary clip adjustment.Postoperatively, the patient was transferred to the ICU on mechanical ventilation. The patient was extubated 3 days following surgery and discharged from ICU on day 4. He was awake, obeying commands. His preoperative left-sided hemiplegia did not change. There was no new neurological deficit and postoperative cerebral angiography did not reveal any evidence of new infarction or haemorrhage. Discussion Intraoperative cerebral ischaemic complications may be due to improper temporary or permanent clip application, prolonged temporary clipping time, retraction injury and cerebral vasospasm. With respect to intraoperative neuromonitoring, in addition to EEG, NIRS was used to monitor cerebral oxygen saturation during periods of potentially compromised cerebral blood flow (in this case, prolonged temporary parent artery occlusion of 67 min). Several investigators have reported the use of NIRS during carotid endarterectomy and found rSO2 recordings less than 50% is indicative of cerebral ischaemia [1,2]. However, the efficacy and clinical outcome associated with the use of NIRS during cerebral aneurysm surgery has not yet been established. In this case report, the patient developed two episodes of right rSO2 desaturation (<50%) which were not detected clinically or by EEG. This could have resulted in significant cerebral ischaemia. NIRS can provide a useful feedback to the anaesthesiologist and neurosurgeon that could allow early detection of cerebral ischaemia and thus early intervention. In this case report, in response to the episodes of cerebral desaturation and after discussion with the surgeon, the potential cerebral protection of propofol was considered [3,4]. The findings of this report are consistent with earlier studies showing the clinical utility of multimodal neuromonitoring in the prevention of uncommon but possibly catastrophic cerebral ischaemia [5]. This modality is relatively new in neurosurgery and appears to be a promising technology that could support clinical decisions regarding detection of cerebral ischaemia. Since limited data are available, more research is needed to establish its clinical efficacy and justify its routine use in neurosurgery.

CONTROVERSIES IN THE SURGICAL TREATMENT OF RUPTURED INTRACRANIAL ANEURYSMS

The management of aneurysmal subarachnoid hemorrhage has evolved over time, including the use of the microscope for aneurysm clip application, improved imaging modalities, endovascular methods for aneurysm treatment, dedicated neurointensive care units, and more aggressive therapy for cerebral vasospasm. Although these advancements have reduced the morbidity and mortality associated with aneurysmal subarachnoid hemorrhage, outcomes for this patient population continue to leave much room for improvement. This work highlights controversial adjuvant techniques, maneuvers, and therapies surrounding the surgical treatment of ruptured cerebral aneurysms that currently lack a consensus opinion. These treatments include centralized care in high-volume centers, as well as the use of antifibrinolytic therapy, routine cerebrospinal fluid diversion, intraoperative hypothermia, temporary clip application, neuroprotective drugs, intraoperative angiography, and decompressive hemicraniectomy. Although definitive answers will only be possible through future multicenter collaboration, we review the controversy surrounding these adjuncts and report the consensus opinion from a highly experienced audience.

SURGERY OF CEREBRAL ARTERIOVENOUS MALFORMATIONS

Despite remarkable progress, the microsurgical extirpation of cerebral arteriovenous malformations (AVMs) even by experienced neurosurgeons is not always easy or safe. This article focuses on how to render AVM surgery safer, and offers strategies and tactics for avoiding perilous bleeding and preserving postoperative neurological function. Our treatment strategies and surgical techniques are offered from the operating surgeon's perspective. An understanding of pathophysiology of cerebral AVMs is important for their appropriate surgical treatment. Sophisticated neuroimaging techniques and scrupulous neurophysiological examinations alert to possible complications, and improved surgical approaches help to minimize the sequelae of unanticipated complications. At the early stage of cerebral AVM surgery, extensive dissection of the sulci, fissures, and subarachnoid cistern should be performed to expose feeders, nidus, and drainers. Problems with the surgery of large and/or deep-seated lesions are exacerbated when arterial bleeding from the nidus continues even after all major feeders are thought to have been occluded. We routinely place catheters for angiography at the surgery of complex AVMs to find missing feeding arteries or to identify the real-time hemodynamic status of the lesion. Temporary clip application on feeders and less coagulation of the nidus is necessary to control intranidal pressure and to avoid uncontrollable bleeding from the nidus and adjacent brain. Intraoperative navigation images superimposed on tractography images can provide us with valuable information to minimize neurological deficits. Deeper insight into AVM nature and into events that occur during AVM surgery as well as the inclusion of molecular biological approaches will open new horizons for the safe and effective treatment of AVMs.

Arterial suturing followed by clip reinforcement with circumferential wrapping for blister-like aneurysms of the internal carotid artery

Objective Blister-like aneurysms of the internal carotid artery (ICA) are very fragile, thin-walled aneurysms. These lesions are susceptible to premature rupture intraoperatively. We describe two cases of successful arterial suturing of these blister-like aneurysms of the ICA, followed by a clip reinforcement technique and circumferential wrapping with a silastic sheet. Methods Two young men presented with a diffuse and dense subarachnoid hemorrhage (SAH) in the basal cistern. The initial angiogram obtained soon after the SAH showed a broad-based, small bulging appearance of the dorsal wall of the ICA. Intraoperatively, a very thin-walled aneurysm was identified on the C2 and C1 segment of the ICA. The aneurysms ruptured abruptly during surgical manipulation. After application of temporary clips, an aneurysmal tear of the ICA was repaired with 8-0 nylon. To prevent the regrowth of the aneurysm, clip reinforcement, by circumferential wrapping with a transparent silicone sheet, was added. Results The postoperative clinical course was uneventful, although one patient showed transient right hemiparesis due to cerebral vasospasm. Angiographic studies performed postoperatively showed complete obliteration of the aneurysm as well as a patent ICA lumen in one case and total occlusion of the ICA in the other case. Both patients were discharged with no neurological deficits. Conclusion This technique can be a useful treatment option for these fragile aneurysms in cases where other options, such as direct clips or encircling clips, may be impossible.

Effects ofTemporary Clips on Somatosensory Evoked Potentials in Aneurysm Surgery

Changes in somatosensory evoked potentials (SEPs) were used to identify cerebral ischemia and to predict neurological outcome during the application of temporary clips in aneurysm surgery. SEPs were recorded intra-operatively in 76 patients with 79 aneurysms (8 in the posterior fossa). Twenty aneurysms ruptured during surgery, and 37 temporary clips were applied over an average of 8.1 minutes (range: 2-25 minutes). Of 17 cases with complete loss of potential, 14 were associated with temporary clips. Two losses were persistent with postoperative neurological deficit after 10 minutes of clipping. Six showed incomplete recovery after a mean loss of 19.2 minutes following clipping of 9.3 minutes, resulting in a new deficit in four patients. Despite complete recovery of potential in six patients after a 1 loss over 18.8 minutes following clipping of 10.7 minutes, four patients developed neurological deficits. The sensitivity of SEPs in determining permanent neurological deficits was 57%, and the was specificity 88%. The duration of temporary clipping was significantly shorter in patients without resulting new neurological deficit (Mann-Whitney Test; p < 0.01). The risk of a new deficit was 30.7% in cases where less than 8 minutes of clipping was performed, and the risk was 80.9% when clipping exceeded 8 minutes. The extent of recovery of potentials and the duration of SEP changes was strongly associated with the postoperative deficits (Kolmogorov-Smirnov Test, p = 0.009; p = 0.001, Mann-Whitney Test). Pathological p(ti)O2 measurements were obtained in 6 of 12 patients. In four patients, temporary occlusion was followed by a parallel alteration of SEPs and p(ti)O2 below 10 mmHg. There is no genuinely safe permissible occlusion time. Despite complete recovery of SEPs after a loss of potential, the patient may develop new deficits.

Use of elective temporary clips in preventing intraoperative cerebral aneurysm rupture

Objective: To review the result of microsurgical treatment for cerebral aneurysms at Princess Margaret Hospital, Hong Kong, SAR, with the focus on the use of elective temporary clipping (ETC) in reducing intraoperative aneurysm rupture (IOR).Methods: All clinical notes and operation records of patients who had undergone aneurysm‐clipping microsurgery from July 1996 to November 2002 were reviewed.Results: In the past 6 years, 148 patients with 150 aneurysms had undergone microsurgical clipping operations. The overall usage rate of ETC was only 25% (38 out of 150) in the present surgical series. Elective temporary clipping was most frequently applied (40%) in treating anterior communicating artery aneurysm. The overall IOR rate was 26% without ETC, versus 8% with ETC, with 18% absolute risk reduction (95% confident interval: 3.2%−28.2%) and 70% relative risk reduction, respectively. The numbers needed for treatment was 5.55. The benefit of ETC was most prominently observed in treating anterior communicating artery aneurysm in which the IOR rate was reduced from 42 to 12%, with 30% absolute risk reduction. Among cases of IOR that occurred without prior elective temporary clip application, the mortality rate was 20.7%. For IOR patients with prior elective temporary clip application, there was no mortality.Conclusion: The present study demonstrates that ETC had led to a significant overall reduction in IOR rate and ETC was associated with better clinical outcome. We encourage and recommend the use of ETC in preventing IOR during aneurysm microsurgery. A prospective study will be conducted on the same topic in our hospitals.

Temporary occlusion of the middle cerebral artery in intracranial aneurysm surgery: time limitation and advantage of brain protection

The risk of focal infarction secondary to the induced reversible arrest of local arterial flow during microsurgical dissection of middle cerebral artery (MCA) aneurysms was evaluated further to define the optimal approach to temporary arterial occlusion. To compare the effectiveness of potential brain-protection anesthetics, a group of patients treated with the intravenous agents propofol, etomidate, and pentobarbital, administered individually or in combination, was compared to a group treated with the inhalational agent isoflurane. Forty-nine consecutive MCA aneurysm surgeries involving the temporary clipping of the parent vessel were retrospectively reviewed. Thirty-eight patients received intravenous brain-protection (IVBP) anesthesia. Groups of patients with and without infarctions, and receiving and not receiving IVBP anesthesia, were compared based on the duration and nature of temporary arterial occlusion. Postoperative radiographic evidence of new infarction was used as the threshold for failure of occlusion tolerance. The overall infarction rate was 22.4% (11 of 49 patients), including 15.8% (six of 38 patients) in the IVBP group versus 45.5% (five of 11 patients) in the group that did not receive brain protection (NBP). In the NBP group, the mean duration of temporary occlusion was 3.9 +/- 2.2 minutes for patients without infarction versus 12.2 +/- 4.3 minutes for patients with focal infarction (p < 0.01). In contrast, the mean duration was 13.6 +/- 10.6 minutes for patients without infarction and 18.5 +/- 9.9 minutes for patients with infarction in the IVBP group. All patients (four of four) in the NBP group who underwent occlusion lasting 10 minutes or longer suffered an infarction versus five of 23 patients in the IVBP group (p < 0.0001). Patients with multiple aneurysms were found to be at increased risk of developing focal infarction, whereas those treated with intermittent temporary clip application were at decreased risk. It is concluded that patients in whom focal iatrogenic ischemia is induced during MCA aneurysm clip ligation have a significant advantage compared with those receiving isoflurane when they are given pentobarbital as the primary neuroprotective agent or when they receive propofol or etomidate titrated to achieve electroencephalographic burst suppression, particularly if more than 10 minutes of occlusion time is required. It is also concluded that 10 minutes is a general guideline for safe, temporary occlusion of the MCA. The use of intermittent temporary arterial occlusion and its use in patients with multiple aneurysms need further evaluation before specific recommendations can be made.

Temporary occlusion of the middle cerebral artery in intracranial aneurysm surgery: time limitation and advantage of brain protection

The risk of focal infarction secondary to the induced reversible arrest of local arterial flow during microsurgical dissection of middle cerebral artery (MCA) aneurysms was evaluated further to define the optimal approach to temporary arterial occlusion. To compare the effectiveness of brain-protection anesthetics, a group of patients treated with the intravenous agents, propofol, etomidate, and pentobarbital, administered individually or in combination, was compared to a group treated with the inhalational agent isoflurane. Forty-nine consecutive MCA aneurysm surgeries involving the temporary clipping of the parent vessel were retrospectively reviewed. Thirty-eight patients received intravenous brain-protection (IVBP) anesthesia. Groups of patients with and without infarctions, and receiving and not receiving IVBP, were compared based on the duration and nature of temporary arterial occlusion. Postoperative radiographic evidence of new infarction was used as the threshold for failure of occlusion tolerance. The overall infarction rate was 22.4% (11 of 49 patients), including 15.8% (six of 38 patients) in the IVBP group versus 45.5% (five of 11 patients) in the isoflurane (ISO) group. In the ISO group, the mean duration of temporary occlusion was 3.9 ± 2.2 minutes for patients without infarction versus 12.2 ± 4.3 minutes for patients with focal infarction (p &lt; 0.01). In contrast, the mean duration was 13.6 ± 10.6 minutes for patients without infarction and 18.5 ± 9.9 minutes for patients with infarction in the IVBP group. All patients in the ISO group who underwent occlusion lasting 10 minutes or longer suffered an infarction versus five of 23 patients in the IVBP group. Patients with multiple aneurysms were found to be at increased risk of developing focal infarction, whereas those treated with intermittent temporary clip application were at a decreased risk. It is concluded that patients in whom focal iatrogenic ischemia is induced during MCA aneurysm clip ligation have a significant advantage compared with those receiving ISO when they are given pentobarbital as the primary neuroprotective agent or when they receive propofol or etomidate titrated to achieve electroencephalographic burst suppression, particularly if more than 10 minutes of occlusion time is required. It is also concluded that 10 minutes is a general guideline for safe, temporary occlusion of the MCA. The use of intermittent temporary arterial occlusion and patients with multiple aneurysms need further evaluation before specific recommendations can be made.

Temporary vessel occlusion during intracranial aneurysm repair.

Any method that decreases the risk of intraoperative rupture should improve outcome if complications associated with its use do not negate positive effect. If application time is limited and a form of cerebral protection and appropriate monitoring of cerebral function are used, temporary clip application may meet these requirements. The efficacy of temporary occlusion as an adjunct to aneurysm clipping may be limited by technical considerations with respect to regional anatomy, aneurysm size, and aneurysm consistency. In areas of limited access, positioning proximal clips may not be feasible. The use of endovascular techniques of balloon occlusion may provide proximal control in these situations (9, 106). The decision to use total circulatory arrest and profound hypothermia, as opposed to temporary clip application, remains largely a matter of the surgeon's judgment. The role of proximal parent vessel ligation must also be considered in the decision-making process regarding the treatment of giant or technically difficult aneurysms (114). Further refinements in cerebral monitoring that can accurately reflect intracellular processes in all territories affected by the application of temporary clips or balloon occlusion and development of more effective forms of cerebral protection may permit safer use of this technique. An adequately controlled clinical trial of temporary occlusion with or without putative "cerebral protection" is needed to confirm the efficacy of this technique.

Temporary vessel occlusion for aneurysm surgery: risk factors for stroke in patients protected by induced hypothermia and hypertension and intravenous mannitol administration

Temporary vessel occlusion is an effective technique used by microvascular surgeons to facilitate dissection and permanent clipping of cerebral aneurysms; however, several questions remain regarding the overall safety of this technique. To identify technical and patient-specific risk factors for perioperative stroke, the authors examined a series of patients in whom induced hypertension and mild hypothermia and intravenous mannitol administration were used as protection during temporary vessel occlusion for aneurysm clipping. The study comprises a nonconcurrent prospective analysis of 132 consecutive aneurysm clippings performed with the aid of temporary vascular occlusion and a specific antiischemic anesthetic protocol at the Massachusetts General Hospital from 1991 to 1993. Factors studied included duration of the temporary clip application, number of occlusive episodes, patient age and neurological status, presence of preoperative subarachnoid hemorrhage (SAH), and intraoperative aneurysm rupture ("forced" temporary clipping), as well as whether proximal vessel occlusion or complete aneurysm trapping was used. In a univariate analysis, patient age, intraoperative aneurysm rupture, temporary clipping lasting more than 20 minutes, clipping between the 4th and 10th day after SAH, and multiple clipping episodes were all significantly associated with stroke outcome. Multivariate logistic regression revealed that intraoperative aneurysm rupture (relative risk 5.6, p = 0.02) and a duration of temporary clip application that lasted more than 20 minutes (relative risk 9.4, p = 0.04) were independently associated with stroke outcome. Overall, 5.2% of the patients had postoperative clinical strokes. Based on their findings the authors conclude that temporary clipping is a safe adjunct to aneurysm surgery, particularly when the duration of clipping is short.

Intraoperative endovascular surgery for cerebral aneurysms

The application of a number of procedures that can be considered intraoperative endovascular neurosurgery has enhanced our ability to treat cerebral aneurysms from the abluminal surface. This study identifies a role for these techniques in the management of difficult aneurysms. A review of the last 1202 aneurysms undergoing direct clipping by the authors disclosed that these methods were used in 62 cases. Of these aneurysms, 36 arose from the internal carotid artery, 12 from the middle cerebral artery, eight from the vertebrobasilar distribution, and six from the anterior cerebral artery. The indications for applying these methods were large size (12-60 mm), intraluminal thrombus, broad neck, plaque at the neck, the potential compromise of branches at the base of the aneurysm, or a combination of these problems. The most frequently chosen intraoperative technique was suction decompression with direct removal of plaque and thrombus using suction, dissection, and/or ultrasonic aspiration. The application of temporary clips was required in all cases in which the aneurysm was opened before definitive clipping. No special pharmacological cerebral protective regimen was used. In one case in which a greater occlusion time was anticipated, cardiopulmonary bypass with profound hypothermia was performed. A favorable outcome was achieved in 73% of these difficult cases. An increased neurological deficit after surgery was seen in 11%, and the mortality rate was 8%. These methods should be considered and can be anticipated before surgery for unusual aneurysms. Many cases now being considered for embolization may be more suitable for definitive surgical obliteration.

脳動脈瘤術中血流一時遮断時のSEPモニタリングの有用性

Changes in the somatosensory evoked potentials (SEPs) were monitored during the application of temporary clips in 97 aneurysm procedures. SEPs in response to median nerve stimulation were used as an index of cortical function. Aneurysm locations were as follows: middle cerebral artery (MCA): 46 cases, internal carotid artery (ICA): 51 cases.The period of temporary occlusion ranged from 2 minutes to 70 minutes, and the mean occlusion time was 20.3 minutes at the M1 segment of MCA and 15.8 minutes at the cervical ICA.In 8 patients with MCA aneurysms and 33 patients with ICA aneurysms, no changes in SEPs during temporary occlusion were seen. Among these 41 patients, however, there were 3 patients with postoperative motor deficits (false negative), 2 of which improved markedly within a few days.In 14 patients (8 MCA aneurysms, 6 ICA aneurysms), temporary occlusion caused a significant prolongation in central conduction time (CCT). None of these 14 patients showed any postoperative deficits.In 42 patients (30 MCA aneurysms, 12 ICA aneurysms), the SEP cortical component (N20) became flat during temporary vascular occlusion. In thirty nine of these 42 patients, the N20 peak reappeared immediately following recirculation and returned to the baseline recordings. None of these 39 patients showed postoperative neurological deficits. The length of disappearance of the N20 ranged from 2 to 38 minutes (mean of 12.3 minutes). Therefore, it is likely that the postoperative outcome can be expected to be favorable if the temporary clip is released within about 10 minutes after attenuation of the N20. The remaining three patients with ICA aneurysms whose SEP did not recover following recirculation showed postoperative morbidity. In these three patients, vascular occlusions were done at multiple sites (ie, ICA. MCA and ACA), and SEPs disappeared rapidly after temporary occlusion. Judging from this result, rapid disappearance of SEPs following temporary occlusion can be considered a danger signal.In conclusion, intraoperative SEP monitoring during temporary occlusion was useful in detecting the severity of ischemia if the vascular territory of the occluded vessel includes the sensory pathways.

Temporary clippingを極力使用しない立場での脳動脈瘤手術

We operated on 267 (87.8%) out of 304 patients with ruptured aneurysms and all of the 33 patients with unruptured aneurysms between April 1983 and December 1989. In this period patients with ruptured aneurysms were managed under lower blood pressure preoperatively, with no antifibrinolytics, and we used infrequent temporary occlusion of the parent vessels to avoid the risk of cerebral ischemia. Two hundred and seventeen patients (81.2%) were operated on in the early stage to prevent preoperative rerupture.Intraoperative rupture occurred in 32(12.0%) of 267 ruptured aneurysms and in 1 (1.2%) of 83 unruptured aneurysms. To complete permanent neck clipping after intraoperative rupture, temporary clipping of the parent vessels was required in 13 cases (39.4%), point suction “bursting” bleeding in 8, and tentative dome or neck clipping in 6. Bleeding from the rent of the neck ceased spontaneously in 4 and Oxycel cotton was effective on 1 case. Temporary clipping was also used in 4 patients with large and giant aneurysms, 3 with fragile and blister aneurysms, and 1 with a complex fenestrated Acom aneurysms without occurrence of intraoperative rupture. Occlusion times ranged from 3.5 to 24.0 minutes. Of the 21 cases (7.0%) where temporary clipping was used, only one patient had new neurological deficits in the immediate postoperative period, but made a good recover.To minimize the risk of cerebral ischemia, it is important to use temporary clipping in only selected cases and to avoid early placement of temporary clips. In particular, reduction of intraoperative rupture results in low frequency of temporary clip application. The tight clot and adhesion surrounding an aneurysm make dissection of an aneurysm-artery complex more difficult and lead to intraoperative rupture. In our experience of management of patients with ruptured aneurysms without antifibrinolytics, removal of the clot was easier in most cases because the clot was gelatinous and soft.

Pharmacologic response of endothelium to microvascular temporary clip application

To assess the effects of microvascular temporary clip application on vessel relaxing capability and endothelial substance release, the carotid rings of rats clipped for various durations were studied via bioassay. Noradrenaline and phenylephrine produced an immediate contraction and subsequent relaxation that failed to be suppressed by lysine acetylsalicylate or nicotine in the controls and in the arteries clipped for 0.5, 1, and 5 minutes; however, this relaxation was greatly reduced when the duration was 10 minutes. The results suggest the possible role of inadequate endothelium-derived relaxing factor release following prolonged application of the clips.

Large high flow AVMにおけるpressure breakthrough syndromeの検討

The treatment of large high flow AVM's is one of the most difficult operations not only because of the operative technique but also due to the postoperative NPPB. Pre and postoperative cerebral blood circulatory changes in 10 cases of large high flow AVM were evaluated by SPECT study, angiography and CT studies. Preoperative SPECT showed a misery perfusion area (decreased CBF, increased CBV) around the nidus in 4 cases.In these cases a postoperative 1st day dynamic scan showed remarkable hyperperfusion areas around the former nidus. But these hyperperfusion areas normalized 7 days after the operation.Nidal volume of these 4 cases was over 70 cu cm. Local CBF during operation increased suddenly after application of temporary clips on the main feeders. An angiogram taken one or two weeks after the operation showed remarkable stagnating artery, fragile vessels and prolonged circulation time.In conclusion, these cases were expected to develop postoperative NPPB. Pre and postoperative SPECT study, especially a postoperative dynamic SPECT study done after the 1st day, was the most useful examination for ascertaining the postoperative NPPB.

Effects of temporary arterial occlusion on somatosensory evoked responses in aneurysm surgery

Changes in the central conduction time (CCT) during the application of temporary clips were studied in 40 patients who had undergone operations for intracranial aneurysms in relation to postoperative neurological outcome. Ten of these 40 patients (25%) showed postoperative morbidity, although promptly recoverable in 5. None of the patients whose CCTs did not change following temporary occlusion of major vessels showed any postoperative morbidity, except in one case of anterior cerebral artery aneurysm. In 6 patients, temporary vascular occlusion caused a considerable transient prolongation in CCT of up to 10 msec. Two of these 6 patients were associated with postoperative neurological deficit (which was recoverable in 1). The cortical response became flat in 15 patients. Seven of these 15 patients showed hemispheric deficits postoperatively, although recoverable in 4. There was a correlation between the change in the somatosensory evoked response and postoperative outcome. Disappearance of the N 20 potential following occlusion is regarded as a danger signal, but postoperative, irrecoverable neurological deficit seems to be unlikely if its disappearance takes more than 3–4 minutes. Even if the cortical response disappears, the clinical outcome is expected to be good if the N 20 potential recovers within 20 minutes after recirculation.

The dissecting microscope for intracranial vascular surgery.

In the past year we have used 1-3 a Zeiss dissecting microscope (Fig. l) during surgery in 17 cases: 13 intracranial aneurysms, 3 arteriovenous malformations and for studies of vasospasm during one hemispherectomy. We believe it is helphd in the following ways. 1. An aneurysmal neck and its junction with the parent vessel can be seen more clearly than with the naked eye (Fig. ~). The surgeon can therefore apply an aneurysm clip more accurately and with less chance of traumatizing or compromising the lumen of the parent vessel (Fig. 8). The microscope has proved especially useful for aneurysms of the anterior communicating and middle cerebral artery. ~. The small but vital perforating vessels that arise from major arteries of the circle of Willis can be clearly identified with the aid of the microscope. Injury to these vessels can therefore be avoided during dissection or during the application of temporary clips. For example, branches from the proximal or A-1 portion of the anterior cerebral artery, which are distributed to the anterior hypothalamus, septal region, and adjacent structures of the brain can be visualized so well that injury to them can be avoided during the surgical treatment of anterior communicating artery aneurysms (Fig. 4). 8. Changes in the circulation of small partly transparent vessels can be observed during some procedures. We have occasionally noted, for example, circulatory slowing with clumping of red cells within some of tile small semi-transparent arteries of the optic chiasm while they were being exposed. 4. The laminar flow in arterialized veins of intracranial arteriovenous malformations can also be plainly seen and studied. Changes in these vessels can therefore be effectively appraised after feeding vessels are tested by temporary occlusion. 5. Vasospasm induced by mechanical stimuli of cortical as well as larger cerebral arteries can be studied and the results of topical application of 8% Papaverine documented. 6. The bright, well-focussed light from the microscope lamp affords superb illumination of the surgical field.