Clip rotation and blood flow reduction after giant cerebral aneurysm clipping--case report.
Introduction: Adequate blood flow monitoring in cerebral aneurysm surgery is still a challenge today. Even though pre- and postoperative care is frequently emphasized, intraoperative monitoring is often forgotten.
Case description: The authors report the clipping of a giant internal carotid artery aneurysm; however, after the frontal lobe retractor was released, the aneurysm clips rotated and flow reduction could be detected via continuous transcranial Doppler ultrasonography. Ischaemia was avoided by repositioning the clips with gelatin sponge and cellulose hemostat.
Discussion: Somatosensory evoked potential recording, intraoperative angiography and microvascular and transcranial Doppler are the most popular methods for intraoperative cerebral blood flow monitoring; however, each of methods has its own advantages and disadvantages. None of them can perfectly measure cerebral blood flow, detect insufficient aneurysm clipping and avoid stenoses; costs, the additional surgical time and potential morbidity must also be considered. Ideally, intraoperative monitoring would be prolonged to the final stages of the surgical procedure so that unusual causes of ischemia such as clip rotation may be avoided. Perhaps new monitoring methods will overcome these difficulties; today, the .perfect. monitoring method should be tailored for each patient and the vessels involved.
Aneurysm, cerebral; subarachnoid hemorrhage, aneurysmal; cerebrovascular circulation; transcranial Doppler ultrasonography.
ACA--Anterior cerebral artery
AChA--Anterior choroidal artery
cTDU--Continuous transcranial Doppler ultrasonography
ICA--Internal carotid artery
MCA--Middle cerebral artery
SSEP--Somatosensory evoked potentials
In spite of the remarkable advances in microsurgical technique which occurred during the second half of the 1900s, intraoperative monitoring of blood flow and/or ischemic damage has remained a challenge. Though its importance can never be over-stressed, most neurosurgeons normally limit themselves to visual inspection with the help of the surgical microscope and the puncture or opening of the aneurysm sac after clipping. These time-honored methods are, however, insufficient in some cases. Visual inspection of the parent vessel provides no objective clues regarding its flow; only gross obstructions are identifiable. Furthermore, visual inspection of the upper segments and branches of the internal carotid artery (ICA) is relatively easy to accomplish, but the same is not true for giant, complex anterior communicating artery and lower ICA aneurysms. Arterial vasospasm due to subarachnoid blood or surgical manipulation is not quantifiable and adequate therapeutic measures must be adopted almost empirically. On the other hand, aneurysm puncture always caries the risk of significant bleeding if the clip is not positioned adequately [2, 4, 7].
Intraoperative monitoring techniques have thus evolved. Among the most frequently employed are Doppler flow measurements, either transcranial or microvascular, intraoperative angiography and somatosensory and/or motor evoked potentials [1, 2, 8, 10]. Each of these techniques has its own advantages and disadvantages but none is currently accepted as .goldstandard.. We report a case in which the utilization of intraoperative transcranial Doppler ultrasonography allowed the identification of flow reduction in an unusual situation . not during clipping, but after the frontal lobe was released at the end of the microsurgical phase of aneurysm clipping. This case exemplifies the importance of flow monitoring during difficult aneurysm surgeries, including their final part.
A.C.S., 37 years old, female, reported intermittent headache of one year duration before seeking medical attention. Complete physical and neurological examination was unremarkable; however, during routine CT screening, a significant space-occupying lesion was found. After magnetic resonance was performed the patient refused to undergo digital angiography, therefore a three-dimensional CT angiography was made. This exam revealed one large left internal carotid artery (ICA) aneurysm in the ophthalmic segment, another left ICA aneurysm inside the cavernous sinus and a right ICA aneurysm at the emergence of the posterior communicating artery (Figure 1). After informed consent was given, the decision was made to address the giant left ICA aneurysm first and the right ICA aneurysm later.
After routine monitoring and anaesthesia, external lumbar drainage was established and the contralateral cTDU (continuous transcranial Doppler ultrasonography) apparatus installed. Proximal hemorrhage control for the ICA was obtained at the cervical level. A standard left frontotemporal craniotomy was performed followed by an extradural Dolenc approach. At this point, the lumbar drain was opened prior to the removal of the anterior clinoid process. The dura mater was then opened and the Sylvian fissure dissected to allow visualization of the aneurysm neck. After clipping with three Yasargil straight clips, the fundus was dissected and resected with no residual flow. Doppler measurements during and immediately after clipping confirmed satisfactory blood flow in the ICA, anterior cerebral artery (ACA) and middle cerebral artery (MCA). The brain retractor, which is commonly used to increase field vision by gently removing the frontal lobe out of the microscope field, was then released. As the frontal lobe slowly returned to its original position, cTDU flow rate quickly decreased. Timely inspection of the clips revealed that they had been pushed by the reaccommodating frontal lobe and had rotated toward the frontal base, thus decreasing flow in the ICA, ACA and MCA. The surgeon returned the clips to their original position with restoration of satisfactory blood flow; total ischaemia time was less than 60 seconds. Intentional rotation of the clips by the surgeon reproduced the cTDU findings; therefore, as a definite measure, Surgicel (oxidized regenerated cellulose, Ethicon Inc., Sommerville, NJ) and Gelfoam (gelatin sponge, Pharmacia & Upjohn, Kalamazoo, MI) were employed to fill the space originally occupied by the aneurysm fundus and maintain the clips correctly oriented (Figure 2). cTDU measurements remained normal for the remainder of the surgery.
The patient was discharged without any focal neurological signs five days later. Postoperative brain CT scan revealed only the area originally occupied by the aneurysm without any ischaemic regions. Thirty days later she was submitted to a right pterional craniotomy and the uneventful clipping of the right ICA aneurysm. She is currently well and conservative management was adopted for the left intracavernous aneurysm.
Flow monitoring during aneurysm surgery is of extreme importance; its maintenance while satisfactorily treating the aneurysm is the ultimate surgical objective. Even though pre- and postoperative care and monitoring is now widely recognized and performed, intraoperative monitoring is still routinely performed in a limited number of centers [2, 4].
Angiography was the first method employed to identify unexpected stenoses and residual aneurysms. Routine postoperative angiography has the inherent defect of a second surgery should inadequate clipping be detected; furthermore, symptomatic stenoses would have already resulted in permanent neurological damage by the time of the second procedure. Some authors favor intraoperative digital subtraction angiography to avoid these problems. Martin et al. and Barrow et al. report satisfactory results for the detection of insufficient clipping and stenoses, but residual aneurysms may escape detection with this method. Its complication rate must be considered . a significant risk of embolism and permanent neurological deficits must be assumed besides also being expensive, highly complex and time consuming . at least 30 to 60 minutes [3, 4, 5, 9].
Electrophysiological monitoring may also be employed intraoperatively for these purposes. It may not detect, on the other hand, inadequate aneurysm clipping. Somatosensory evoked potentials (SSEPs) allow only the indirect identification of significant cerebral ischaemia. Its results depend not only on the vessel studied but are also influenced by anaesthesia; its value is extremely limited when vessels other than the MCA are involved, especially posterior circulation branches .
Sonography has been employed intraoperatively since the 1950s and is now routinely employed in the localization of deep and/or small mass lesions in the CNS. Transcranial Doppler monitoring techniques have been employed since the mid-1980s, with great results. Even though the problem of insufficient clipping is not addressed as in other methods (angiography and microvascular Doppler) it is a reliable, fast and cheap method of assessing blood flow in large and medium arteries. Moreover, it may be employed up to the final moments of the surgical procedure. In our case, flow reduction occurred after the frontal retractor was released; had intraoperative angiography been employed, it could have been performed before and would thus not detect obstruction due to clip rotation [1, 6]. Microvascular Doppler monitoring employing an ultra-thin probe is emerging as an attractive alternative for flow monitoring. It has the inherent defect of not being able to detect insufficient clipping; it seems, however, that residual flow inside the aneurysm can be safely detected by this method. Stenoses and vasospasm were also reliably detected in the first experimental reports, even in smaller branches . Unfortunately, the probe itself is still available only in a few centers; like all techniques employing Doppler measurements, it may detect and quantify blood flow, but whether ischemia ultimately results is sometimes doubtful when borderline flow measures are obtained. In addition, microvascular Doppler probes depend on adequate vessel exposure; this would not have been possible after the retractor was released as in our case. However, it is hardly arguable that microvascular Doppler sonography offers advantages over the transcranial technique; indeed, transcranial Doppler monitoring may remain an option in centers in which the microvascular probe is not available.
Clip rotation was first described by Friedman et al. in 2001 but is routinely forgotten by neurosurgeons and anaesthesists alike. In their report, one patient developed a delayed deficit 36 hours after the end of the surgical procedure. Taken once again to the operating room, the clip was found to have rotated in situ, thus occluding the AChA. Repositioning the clip satisfactorily treats this complication, either through unclipping and repositioning or reorientation with oxidized cellulose or gelatin sponge as in our case. Even though not a common event, flow obstruction due to clip rotation is known to most neurosurgeons; the use of an intraoperative monitoring technique may prevent it from becoming an unpleasant surprise after a difficult surgery. Microvascular Doppler would not have detected ischemia since vessel contact is required; angiography, on the other hand, depicts blood flow at a single point in time, and would not have detected ischemia after frontal lobe release. Interestingly, Sakuma et al. recently also reported a case of clip rotation after frontal lobe release. These physicians could detect ischemia because motor evoked potential monitoring was being utilized and therefore could proceed to the final stages of the surgical procedure. Furthermore, the AChA was involved in their particular case. We employed the same technique as Sakuma et al. to reposition the clip with a satisfactory outcome as well .
Pre--and postoperative care have been long recognized as fundamental in the treatment of patients with subarachnoid hemorrhage due to aneurysm rupture. Given the still high mortality before and after surgical treatment, intensive care measures are as important as adequate microsurgical techniques for the treatment of these patients. Furthermore, vasospasm leads to significant morbidity in these patients; a technically wonderful surgery may be completely spoiled by perioperative ischaemia. Neurosurgeons and neuro-anaesthesists should thus always bear in mind the benefits of intraoperative monitoring techniques. Unfortunately, there is no such thing as a .gold-standard. monitoring technique; the benefits and limitations of intraoperative angiography, SSEPs, cTDU and microvascular Doppler must be considered and the adequate method chosen for each surgery and patient. New monitoring methods such as transit time flowmeters, among others, are currently being evaluated; whether a prospective, randomized trial can ever be perfomed to define which is the best intraoperative monitoring method is at best doubtful.
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Corresponding author: Ricardo B. V. Fontes, M.D.
Address: R. Jandiro J. Pereira 389
Sao Paulo. SP. Brazil
Phone # (voice): 55-11-35073726
Paulo Henrique Aguiar, M.D., Ph.D. (1, 2), Ricardo B. V. Fontes, M.D. (2) Renata Simm, M.D. (1), Julio Reno Sawada, M.D. (2), Leandro Valiengo, M.D. (2), Wagner Tavares, M.D. (2), Roberto Hirsch, M.D. (1, 2), Lauro Morabayashi, M.D. (1, 2)
(1)--Hospital Santa Paula, Sao Paulo, Brazil. Zip code: 04556-100
(2)--Neurosurgery and Neurology Department, Universidade de Sao Paulo, Sao Paulo, Brazil. Zip code: 05403-090
(Rev.Chil.Neurocirug. 27:66-69, 2006)