Sylvian Vein Research Articles

AB004. Transsylvian approach for radical resection of insular gliomas: emphasizing the importance of the transsylvian approach for elderly patients with Zone II and III insular gliomas.

Insular gliomas present significant challenges due to their deep-seated location and proximity to critical structures, including sylvian veins, middle cerebral arteries (MCAs), lenticulostriate arteries, long insular arteries, and functional cortices and white matter tracts. The Berger-Sanai classification categorizes them into four zones (I-IV), providing a framework for understanding insular gliomas. The key factors for successful insular glioma removal are achieving the greatest insular exposure and surgical freedom. There are two main types of approach methods, such as transsylvian approach with meticulous wider dissection of the sylvian fissure and transcorticosubcortical approach with intraoperative functional brain mapping under awake surgery to remove the functionally silent cortices and white matter tracts. Because splitting the distal sylvian fissure is more challenging, a transcortical approach through the parietorolandic operculum in awake patients has been reported to be more effective access to the posterior insular gliomas (Zone II and III) in the dominant hemisphere. The object of this study emphasize the importance of the transsylvian approach for radical resection of insular gliomas. We retrospectively analyzed our experiences with radically resected insulo-opercular gliomas. Basically, we pursue the transsylvian approach for resecting insular gliomas without removal of any normal brain. Motor pathways running beneath the parietorolandic operculum can be damaged by ischemia caused by sacrificing the medullary arteries (MAs) arising from the pial arteries of the M3 and M4 portions of the MCA. Motor deficit after resection of this area was significantly found in the elderly patients. This phenomenon might be described by the age-associated decreasing the vascular reserve capacity. Autopsy brains showed that the sclerotic rate of the MAs increased with age and hypertension. Even with the intraoperative functional brain mapping, we cannot avoid the ischemic complication caused by sacrificing the MAs during stepwise removal of the functionally silent cortices and white matter tracts. We make a suggestion not to remove the parietorolandic operculum in elderly patients with insular gliomas located at Zone II and III. Distal transsylvian approach should be applied.

Microsurgical Resection of a Left Temporal Stem Cavernous Malformation Through Transsylvian Approach: 2-Dimensional Operative Video.

Cavernous malformations (CMs) are rare, often oligosymptomatic vascular lesions. Common manifestations include seizures and focal neurological deficits. Depending on the symptoms, location, size, and risk factors of bleeding, such as the presence of a developmental venous anomaly, the injury can be highly morbid. Hence, one can consider surgical resection. Deep and eloquently located CMs, such as those located in the temporal trunk, can be quite challenging and require an exact operative technique.1-7 We present a 27-year-old patient with a history of headaches that began two years ago and significantly worsened in the last month, associated with visual blurring, scotomas, nausea, phonophobia, and photophobia as well as paresthesias in the hands and perioral region. Imaging investigation revealed a CM in the temporal stem (Zabramski classification II). Owing to the risk of rebleeding and the young age, surgical resection was performed using a transsylvian approach to preserve the temporal cortex. We describe the technique applied and demonstrate the necessary care manipulating the distal sylvian fissure and the superficial sylvian veins. We also detail the anatomy of the temporal stem and the benefit of the transsylvian approach to preserve the white matter fibers that compose the temporal stem. The patient consented to the procedure and to the publication of his/her image. This study was approved by the Ethics Committee of our institution. Performed CM resection using the transsylvian pterional craniotomy technique, and it proceeded without complications. The postoperative period was also uneventful. The postoperative imaging demonstrated total resection of the cavernoma.

Basal vein of Rosenthal classification: the key to venous outflow of the deep sylvian fissure.

Mastery of sylvian fissure dissection is essential to access lesions within the deep basal cisterns. The deep sylvian vein and its tributaries play a major role during access to and beyond the carotid cistern through the sylvian fissure and determine the complexity of microdissection. Preserving the venous outflow during sylvian fissure dissection is the best reliable strategy to prevent postoperative venous strokes or venous hypertension. The authors report the role of the basal vein of Rosenthal (BVR) in the venous outflow pattern of the deep sylvian cistern. The authors analyzed 262 consecutive surgical cases involving sylvian fissure dissection from 2015 to 2017. Inclusion criteria were complete sylvian fissure dissection for the treatment of intracranial aneurysms. Exclusion criteria were giant size (aneurysm diameter > 24 mm), meningitis, subarachnoid hemorrhage within the sylvian cistern, absence of 4D CT angiography, and previous surgery. Retrospective radiological and operative video reviews were carried out to assess the association between the superficial sylvian vein and the BVR. The authors analyzed the course of the BVR and the patterns of venous drainage of the sylvian cistern. The surgical difficulty of sylvian fissure dissection was rated by the authors to study the operative significance of the venous patterns encountered. Two clinical cases are described to illustrate the proposed BVR classification. A total of 97 patients met the selection criteria. The most frequent type of BVR was immature (diameter < 0.5 mm, 68%). When the BVR was incompletely developed or absent (immature type), the deep sylvian veins drained through a middle sylvian vein in 70% of cases, requiring advanced sylvian fissure dissection techniques. However, when the BVR was completely developed (32%), the middle sylvian vein was found in a minority of cases (6%), which allowed for an unobstructed transsylvian corridor. Interrater and test-retest reliability of the surgical difficulty was greater than 0.9. Preoperative assessment of the BVR anatomy is key to predict the deep sylvian venous pattern. The authors provide objective evidence supporting the reciprocal relationship between the type of BVR and the presence of a middle sylvian vein and the deep sylvian venous outflow. An immature BVR should alert the neurosurgeon of the high likelihood of finding a complex deep venous pattern, which may drive surgical planning.

Vascular Repair for Iatrogenic Injury during Microsurgical Procedures: Clinical Investigation and Review of 18 Cases at a Single Institution.

Intracranial vascular injury (VI) due to surgery is a critical complication that can lead to serious neurologic deficits. To our knowledge, only a few review articles on VI during an operation have been published so far. We retrospectively investigated the type, cause, and measurement of VI during surgery at our institution. Unexpected VI cases occurred in 18 of 2,228 craniotomy procedures, including 794 aneurysm clippings and 357 tumor resections. We investigated the causes and coping techniques of the VI cases, as well as their full details. There were six cases of aneurysm neck tear, one case of sylvian vein injury, and one case of superior trunk perforation during direct clipping. Regarding tumor resection procedures, nine cases of arterial injury and one case of cortical vein injury were extracted. Almost all VIs were caused by carelessness or basic manipulation mistakes. We repaired all these cases with simple placement of suture threads with or without pinch clips, flow alteration using bypass techniques, and in 16 cases no neurologic deficit or deterioration on imaging occurred; however, 3 patients were verified to have ischemic changes on postoperative imaging. Most VIs were directly caused by a simple error and carelessness of an operator or an assistant. Many of these injuries can be avoided if a basic set of rules are followed and remembered during the surgical procedure. However, the surgical procedure involves human work, and errors cannot be eradicated even upon maximum concentration levels. Neurosurgeons should be prepared for an eventual quick repair of an unexpected cerebral VI.

Sphenoparietal Sinus Transposition: Operative Technique for Optimizing Pretemporal Posterior Circulation Access While Preserving the Sylvian Venous Complex

Transsylvian approaches are a cornerstone of complex cranial operations, with wide applicability across cerebrovascular, skull base, and neuro-oncology operations. Deep lesions, especially those involving the basilar apex, midbrain, or interpeduncular fossa, require wide exposures that may be inhibited by the presence of a large complex of superficial sylvian veins (SSV) draining into the sphenoparietal sinus. This report describes technical and clinical aspects of the sphenoparietal sinus transposition (SPST) technique. Technical case report of the SPST technique, including a step-by-step neuroanatomic description, overview of common indications, clinical pearls and pitfalls, and illustrative case examples. Once the benefits of proceeding with SPST have been established, the maneuver is initiated with 2 stepwise dural incisions: an incision from lateral to medial along the lateral margin of the lesser sphenoid wing, followed by an orthogonal cut across the temporal pole down the middle fossa floor. The pretemporal dura is peeled off the lateral wall of the cavernous sinus, allowing mobilization of the SSV complex and temporal pole posteriorly without disrupting or straining the connection point at the sphenoparietal sinus. Illustrative case examples include a clip reconstruction of a basilar apex aneurysm for which earlier endovascular treatment had failed and microsurgical resection of a peduncular cavernous malformation. SPST is a simple but versatile technique with important applications in complex cranial surgery. By mobilizing the SSV complex together with its dural attachment, the transsylvian corridor can be markedly widened, allowing access to the basilar apex region and ventral midbrain.

Extravascular optical coherence tomography of cerebral vessel walls in vivo.

Evaluation of extravascular, microscope integrated OCT (iOCT) as an in vivo imaging modality of cerebral blood vessels and as an intraoperative imaging method. Microscope integrated optical coherence tomography of major cerebral arteries (n = 13) and superficial sylvian veins (n = 5) and one incidental cerebral vasospasm (n = 1) in (n = 10) patients. Post procedural analysis of OCT volume scans, microscopic images and videos during the time of scan as well as measurements of the diameter of vessel walls and its layers with an accuracy of 7.5 μm. iOCT was feasible during vascular microsurgical procedures. In all scanned arteries a clear delineation of the physiological three layered vessel wall composition could be achieved. Pathological arteriosclerotic alterations of cerebral artery walls could precisely be demonstrated. Major superficial cortical veins conversely presented a mono layered composition. First in vivo measurements of vascular mean diameters were possible. Cerebral artery walls showed a diameter of 296 μm, tunica externa 78 μm, media 134 μm and interna 84 μm. For the first time the microstructural composition of cerebral blood vessels could be illustrated in vivo. Due to an outstanding spatial resolution a clear definition of physiological and pathological characteristics was possible. Therefore, microscope integrated optical coherence tomography holds promise for basic research in the field of cerebrovascular arteriosclerotic diseases and for intraoperative guidance during microvascular surgery.

Papilledema and venous stasis in patients with cerebral venous and sinus thrombosis

BackgroundCerebral venous and sinus thrombosis (CVST) can cause increased intracranial pressure, often leading to papilledema. In this study, we investigated the association between papilledema and venous stasis on susceptibility weighted imaging (SWI) in CVST.MethodsPatients with CVST between 2008 and 2020 were reviewed. Patients without fundoscopic examination or SWI were excluded in this study. Venous stasis was evaluated and scored for each cerebral hemisphere: each hemisphere was divided into 5 regions according to the venous drainage territories (superior sagittal sinus, Sylvian veins, transverse sinus and vein of Labbé, deep cerebral veins, and medullary veins) and 1 point was added if venous prominence was confirmed in one territory on SWI. The venous stasis score on SWI between cerebral hemispheres with and without papilledema was compared.ResultsEight of 19 patients with CVST were excluded because of the absence of fundoscopic examination or SWI. Eleven patients (26.5 ± 2.1 years) were included in this study. Papilledema was identified in 6 patients: bilateral papilledema in 4 patients and unilateral papilledema in 2 patients. The venous stasis score on SWI was significantly higher (P = 0.013) in the hemispheres with papilledema (median, 4.0; 95% CI, 3.038–4.562) than in the hemispheres without papilledema (median, 2.5; 95% CI, 0.695–2.805).ConclusionsThis study shows that higher score of venous stasis on SWI is associated with papilledema. Therefore, the venous stasis on SWI may be an imaging surrogate marker of increased intracranial pressure in patients with CVST.

Cavernous Malformations: What They Have Taught Us.

Cavernous Malformations: What They Have Taught Us.

The Sphenoparietal Sinus Revisited: Anatomical and Histological Study With Application to Interventional Procedures and Skull Base Surgery.

Background The sphenoparietal sinus (SPS) is implicated in various clinical pathologies, specifically arteriovenous fistulasand venous sinus thrombosis. This study is aimed to better understand this venous structure of the skull base via histological examination. Methods Ten embalmed and latex-injected adult body donors' heads (20 sides)underwent microdissection of the SPSusing a surgical microscope. The entire dura on the underside of the lesser wing of the sphenoid bone encompassing the region known as the groove for the SPS was harvested from each body donor and submitted for histological analysis (H&E, Periodic acid-Schiff [PAS], Masson's Trichrome). Five leftand five right transverse sinuses were harvested and analyzed histologically as controls. Results A definitive SPS was identified in 14/20 (70%) of the latex-injected body donors. When present, the sinuses were classified as small, medium, or large. Tributaries included the middle meningeal veins, superficial Sylvian vein, and anterior temporal veins. All sinuses drained medially into the cavernous sinus. For the body donors analyzed histologically, 17 (85%) were consistent with a dural venous sinus and not a vein and were observed to have a rich nerve and arterial supply within their walls. The histological findings of the SPS were similar to those seen for the transverse sinus. The combined prevalence for the SPS in gross and histological body donors was 78%. Conclusions Our findings support the presence ofSPS in the majority of body donors. To our knowledge, this is the first histological study of the SPS.

Cerebral venous thrombosis in adolescence

Behçet's disease (BD) is a rare systemic vasculitis with multisystemic involvement. Neurological involvement, called neuro-Behçet's disease (NBD), mostly involves the central nervous system and cerebral venous thrombosis (CVT) is the predominant neurological manifestation in the pediatric age. A 12-year-old female with a past medical history of a CVT, without an identifiable etiology, was admitted with a five-day right fronto-orbital headache. Neuroimage showed a subacute thrombosis of a right superficial sylvian vein, with indirect signs of intracranial hypertension and no imaging signs of vasculitis. Prothrombotic screening and immunologic study were normal. She was started on acetazolamide and hypocoagulation with progressively improving. She had a history of frequent oral aphthae and an episode of a genital ulcer three months before admission. Pathergy test was negative. HLA-B51 was positive. She was diagnosed with NBD and started therapy with colchicine and infliximab. After discharge, the patient remains without symptoms, hypocoagulated, and on infliximab regimen, without complications to report. This case, only diagnosed in the second episode of CVT, is paradigmatic of the difficulty in establishing the diagnosis of BD.

Usefulness of the Multimodal Fusion Image for Visualization of Deep Sylvian Veins.

The preoperative assessment of cerebral veins is important to avoid unexpected cerebral venous infarction in the neurosurgical setting. However, information is particularly limited regarding deep Sylvian veins, which occasionally disturb surgical procedures for cerebral anterior circulation aneurysms. The predictability of detecting deep Sylvian veins and their tributaries using a modern multimodal fusion image was aimed to be evaluated. Moreover, 51 patients who underwent microsurgery for unruptured cerebral aneurysms with Sylvian fissure dissection were retrospectively reviewed. The visualization of the four components of the deep Sylvian veins in conventional computed tomography (CT) venography and multimodal fusion images was evaluated. To compare the detection accuracy among these radiological images, the sensitivity and specificity for the detection of each of the four venous structures were calculated in comparison with those of intraoperative inspections. The kappa coefficients were also measured and the inter-rater agreement for each venous structure in each radiological image was examined. In all veins, the multimodal fusion image exhibited a high detection rate without statistical difference from intraoperative inspections (P = 1.0). However, CT venography exhibited a low detection rate with a significant difference from intraoperative inspections in the common vertical trunk (P = 0.006) and attached vein (P = 0.008). The kappa coefficients of the fusion image ranged from 0.73 to 0.91 and were superior to those of CT venography for all venous structures. This is the first report to indicate the usefulness of a multimodal fusion image in evaluating deep Sylvian veins, especially for the detection of nontypical, relatively small veins with large individual variability.

Anatomical variations of dominant anastomotic veins in the superficial cortical venous system

BackgroundUnderstanding the anatomy of the anastomotic veins (AV) of the superficial cortical venous system (SCVS), viz. Superficial Sylvian vein (SSV) - also known as the superficial middle cerebral vein; vein of Labbe (VL) and vein of Trolard (VT), are imperative for neurosurgical procedures. This study aimed to investigate variant anatomical patterns of dominance of the AV, to elucidate the haemodynamically balanced SCVS, by reporting variations between the presence, diameter and dominant patterns of the AV. MethodsTwo hundred lateral angiograms were included, depicting left and right cerebral hemispheres of the same patient (n = 100 patients). Angiograms were analysed and variations recorded. Results were statistically compared against laterality, age, sex and ethnicity. ResultsPresence of the VL had the highest occurrence (96.5%), whereas the SSV and VT had an occurrence of 75.5% and 64.5%, respectively. This study reports presence of double veins of the AV: SSV (12.0%), VL (22.0%) and VT (19.5%). Furthermore, presence of a triple vein for each AV is reported. Diameters for the SSV, VL and VT were 1.99 ± 0.500 mm, 2.18 ± 0.579 mm and 2.14 ± 0.472 mm, respectively. Statistically significant relationships were established between diameters and the SSV, VL, VT and VT2 (double VT). Seven types of dominant patterns were recorded: Equilibrium; singular dominance of SSV, VL and VT; co-dominance of SSV/VL, SSV/VT and VL/VT. The Equilibrium dominant pattern of drainage had the highest occurrence (54.5%). ConclusionPatterns of dominance of these AV can aid the neurosurgeon in curbing the risk of iatrogenic injury and postoperative infarcts even after an otherwise successful surgery.

Utility of indocyanine green videoangiography with FLOW 800 analysis in brain tumour resection as a venous protection technique

BackgroundIn regard to central nervous system tumour resection, preserving vital venous structures to avoid devastating consequences such as brain oedema and haemorrhage is important. However, in clinical practice, it is difficult to obtain clear and vivid intraoperative venous visualization and blood flow analyses.MethodsWe retrospectively reviewed patients who underwent brain tumour resection with the application of indocyanine green videoangiography (ICG-VA) integrated with FLOW 800 from February 2019 to December 2020 and present our clinical cases to demonstrate the process of venous preservation. Galen, sylvian and superior cerebral veins were included in these cases.ResultsClear documentation of the veins from different venous groups was obtained via ICG-VA integrated with FLOW 800, which semiquantitatively analysed the flow dynamics. ICG-VA integrated with FLOW 800 enabled us to achieve brain tumour resection without venous injury or obstruction of venous flux.ConclusionsICG-VA integrated with FLOW 800 is an available method for venous preservation, although further comparisons between ICG-VA integrated with FLOW 800 and other techniques of intraoperative blood flow monitoring is needed.

How do I: Venous reconstruction of accidentally injured superficial sylvian vein during the clipping of an unruptured cerebral aneurysm.

The transsylvian approach is a versatile treatment method for aneurysms of the anterior circulatory system. Studies have shown that sylvian veins run in various patterns, suggesting the need for dissection between veins to obtain appropriate surgical corridor. In case of inadvertent sylvian vein injury, serious complications such as venous congestion may occur. We herein describe the "side-to-side anastomosis reconstruction technique" of the resected superficial sylvian vein. This technique can be effective for the reconstruction of other cortical veins, and indocyanine green videoangiography was effective in determining the indications for venous reconstruction.

The Superficial Anastomosing Veins of the Human Brain Cortex: A Microneurosurgical Anatomical Study.

Introduction: In this microneurosurgical and anatomical study, we characterized the superficial anastomosing veins of the human brain cortex in human specimens.Material and Methods: We used 21 brain preparations fixed in formalin (5%) that showed no pathological changes and came from the autopsy sections. The superficial veins were dissected out of the arachnoid with the aid of a surgical microscope.Results: We dissected nine female and 12 male brain specimens, with an average age of 71 ± 11 years (range 51–88 years). We classified the superficial veins in five types: (I) the vein of Trolard as the dominat vein; (II) the vein of Labbé as the dominant vein; (III) a dominant sylvian vein group, and the veins of Trolard and Labbé nonexistent or only rudimentary present without contact to the Sylvian vein group; (IV) very weak sylvian veins with the veins of Trolard and Labbé codominant; and V) direct connection of Trolard and Labbé bypassing the Sylvian vein group. The vein of Trolard was dominant (Type I) in 21.4% and the vein of Labbé (Type II) in 16.7%. A dominant sylvian vein group (Type III) was found in 42.9%. Type IV and Type V were found in 14.3 and 4.7% respectively.Conclusion: No systematic description or numerical distribution of the superior anastomotic vein (V. Trolard) and inferior anastomotic vein (V. Labbé) has been found in the existing literature. This study aimed to fill this gap in current literature and provide data to neurosurgeons for the practical planning of surgical approaches.

Acquired Pial and Dural Arteriovenous Fistulae Draining into the Sylvian Veins after Craniotomy for Hematoma Evacuation: A Case Report

Acquired Pial and Dural Arteriovenous Fistulae Draining into the Sylvian Veins after Craniotomy for Hematoma Evacuation: A Case Report

Assessment of collateral venous flow using temporary clip placement at ICG videoangiography.

As there are many collateral pathways between venous systems, intraoperative venous injury rarely induces venous infarction. In some patients, however, venous injury during microsurgical manipulation may cause acute and/or delayed serious complications. Although intraoperative evaluation using indocyanine green (ICG) videoangiography is very useful, it is difficult to assess the flow direction using this technique. A simple technique using temporary clips and ICG videoangiography was applied to assess the collateral venous pathway in 4 cases of surgical manipulation-related injury or occlusion of the main superficial Sylvian vein in patients with aneurysm. The flow direction and collateral pathway can be easily visualized after release of temporary occlusion. A collateral venous pathway can be evaluated with the present simple technique described here.

Impact of Cone-Beam Computed Tomography Angiography on Visualization of Sylvian Veins

A detailed understanding of the anatomy of Sylvian veins preoperatively is needed for venous-preserving Sylvian dissection. Better visualization of the venous architecture will facilitate surgical strategies for Sylvian dissection. This study evaluated and compared the image quality of the Sylvian veins and their tributaries using high-resolution cone-beam computed tomography angiography (CBCT-A) and three-dimensional computed tomography angiography (3D-CTA). Twenty-four patients who underwent 3D-CTA and CBCT-A as a preoperative simulation for clipping of unruptured intracranial aneurysms were retrospectively reviewed. In comparisons with intraoperative inspections, 3 raters evaluated the image quality of the Sylvian veins by 3D-CTA and CBCT-A with a 5-point scale. Visualization of the Sylvian veins and their tributaries by the 2 imaging modalities was compared using Wilcoxon signed rank test. CBCT-A showed superior image quality to 3D-CTA in evaluations of the discrimination of adjacent superficial Sylvian veins (2.8 ± 0.80 vs. 4.6 ± 0.37, P<0.0001), adjacent Sylvian veins at the sphenoid wing (3.1 ± 0.71 vs. 4.1 ± 0.56, P= 0.0001), and visualization of the tributaries of the Sylvian veins (2.5 ± 0.70 vs. 4.4 ± 0.37, P < 0.0001). CBCT-A was superior to 3D-CTA for visualizing the Sylvian veins and their tributaries. CBCT-A will provide important information on the anatomy of the Sylvian veins preoperatively.

Deep venous communication in vein of Galen malformations: incidence, Imaging, and Implications for treatment

BackgroundFailure to appreciate deep venous drainage pathways is a major cause of severe complications in the endovascular treatment of vein of Galen aneurysmal malformations (VOGMs).ObjectiveTo report deep venous drainage patterns...

Sphenoparietal sinus transposition technique: optimization of the surgical corridor with preservation of prominent bridging veins between the brain and the cranial base during aneurysm clipping via the pterional approach.

The sylvian bridging veins between the brain and the dura on the inner surface of the sphenoid wing can restrict brain retraction for widening of the lateral retrocarotid space during clipping surgery for internal carotid artery (ICA)-posterior communicating artery (PCoA) and basilar apex (BX) aneurysms. In such cases, the authors perform extradural anterior clinoidectomy with peeling of the temporal dura propria from the periosteal dura and inner cavernous membrane around the superior orbital fissure, with the incision of the dura mater stretching from the base of the temporal side to just before the distal dural ring of the ICA (termed by the authors as the sphenoparietal sinus transposition [SPST] technique). This technique displaces the bridging segment of the sylvian vein posteriorly and enables widening of the surgical space without venous injury. In this study, the authors observed the operative nuances and investigated the usefulness of this technique. The authors retrospectively reviewed the medical charts of 66 consecutive patients with ICA-PCoA and BX aneurysms between January 2016 and July 2018. This technique was performed in 8 patients (5 patients with PCoA aneurysms and 3 with BX aneurysms) in whom the bridging segments of the sylvian veins between the brain and the skull base restricted brain retraction for widening of the surgical space. The surface areas of the lateral retrocarotid space and the aneurysm were measured at the most visible working angle before and after the SPST technique was performed. With the use of the SPST technique, an adequate surgical space for aneurysm clipping was obtained with preservation of the bridging veins in all patients. The mean surface areas of the lateral retrocarotid space (p = 0.002) and aneurysm (p = 0.001) were significantly increased from 18.3 ± 18.8 and 2.8 ± 2.5 cm2 before to 64.2 ± 21.1 and 20.9 ± 20.6 cm2, respectively, after the SPST technique was performed. The SPST technique enables displacement of the bridging segments of the sylvian veins without venous injury and enables widening of the surgical space around the lateral retrocarotid area.