Prevalence of anatomical variants of the Willis polygon in cadavers undergoing medico-legal necropsy / Prevalencia de variantes anatómicas del Polígono de Willis en cadáveres sometidos a necropsia medicolegal

The primary function of the circle of Willis is to provide collateral blood flow between the anterior and posterior arterial systems of the brain. Its configuration can vary considering its vascular structures, this being considered an anatomical variant. Our study aims to determine the prevalence of these, discriminated by sex in corpses subjected to medicolegal autopsy at the National Institute of Legal Medicine and Forensic Sciences in 2019, in Cali-Colombia. Retrospective observational descriptive study, of photographic records, inspection records and expert reports, where variables of age, sex, anatomical variants, compromised vascular structures are differentiated. Univariate and bivariate analyzes were performed. The population consisted of 194 cases, with a median age of 33 years (interquartile range between 23-45). 24.4% corresponded to the male sex. A prevalence of 25.3% of cases with non-classic polygon was observed. The most frequent anatomical variant was hypoplasia 14.9%. The vascular structure that presented the most anatomical variants was the posterior communicating artery with 17%.

La función principal del polígono de Willis es proporcionar flujo sanguíneo colateral entre los sistemas arteriales anterior y posterior del cerebro. Su configuración puede variar teniendo en cuenta sus estructuras vasculares, considerándose esto una variante anatómica. En este estudio analizamos la prevalencia de las variaciones, discriminada por sexo en cadáveres sometidos a necropsia medicolegal en el Instituto Nacional de Medicina Legal y Ciencias Forenses en el año 2019, en Cali-Colombia. Estudio descriptivo observacional retrospectivo, de registros fotográficos, actas de inspección e informes periciales, donde se diferencia variables de edad, sexo, variantes anatómicas, estructuras vasculares comprometidas. Se realizaron análisis uni y bivariados. La población estuvo conformada por 194 casos, con una mediana de edad de 33 años (rango intercuartil entre 23-45). El 24.4% correspondieron al sexo masculino. Un 25,3% de casosse encontró un polígono no clásico. La variante anatómica más frecuente fue la hipoplasia 14.9%. La estructura vascular que más variantes anatómicas presentó fue la arteria comunicante posterior con un 17%.

Seven Microaneurysms: Description of an Experimental Rodent Model for Neurovascular Training.

AIM: To demonstrate the microsurgical procedures, and to evaluate the feasibility of living models of experimental neurovascular training by developing new complex vascular exercises mimicking the most common intracranial aneurysms. MATERIAL AND METHODS: The procedures were performed under a Zeiss (OPMI pico f170) microscope using basic microsurgery instruments, 10/0 Nylon and blue Polypropylene micro-sutures. We selected adult albino Wistar rats weighing between 258 and 471g each. Seven different aneurysm types were created using carotid, jugular, cava, aorta and femoral vessels. RESULTS: Seven types of aneurysm were designed and created in the rat with a high-medium successful rate. There are differences in terms of realism and the difficulty of performance, according to the different types: lateral wall, bifurcation, top of the basilar, fusiform, fusiform + involved branch, Anterior Communicating Artery (ACoA) and giant. The steps and technical issues to produce these exercises are described. CONCLUSION: We show the feasibility of creating several types of aneurysm using different vessels in a rodent model. Training on these models help to improve microsurgical skills, allowing safe practice for neurosurgeons in all stages of their career.

Arterial collateral anatomy predicts the risk for intra-operative changes in somatosensory evoked potentials in patients undergoing carotid endarterectomy: a prospective cohort study.

BACKGROUND: During carotid endarterectomy (CEA), significant amplitude decrement of somatosensory evoked potentials (SEPs) is associated with post-operative neurological deficits. OBJECTIVE: To investigate the association between an incomplete circle of Willis and/or contralateral ICA occlusion and subsequent changes in intra-operatively monitored SEPs. METHODS: We performed a retrospective analysis of a single center, prospective cohort of consecutive patients undergoing CEA over a 42-month period after reviewing the collateral arterial anatomy on pre-operative radiological imaging. The primary endpoint was an intra-operative decline in SEPs > 50% compared to the baseline value during arterial cross-clamping. Univariate and multivariate logistic regression analyses were performed to investigate a potential association between contralateral ICA occlusion, incomplete circle of Willis, and subsequent alteration in SEPs. RESULTS: A total of 140 consecutive patients were included, of which 116 patients (82.9%) had symptomatic carotid stenosis of at least 50% according to the classification used in the North American Carotid Surgery Trial (NASCET) (Stroke 22:711-720, 1991). Six patients (4.3%) showed contralateral ICA occlusion, 22 patients (16%) a missing/hypoplastic anterior communicating artery (Acom) or A1 segment, and 79 patients (56%) a missing ipsilateral posterior communicating artery (Pcom) or P1 segment. ICA occlusion and missing segments of the anterior circulation (missing A1 and/or missing Acom) were associated with the primary endpoint (p = 0.003 and p = 0.022, respectively). CONCLUSION: Contralateral ICA occlusion and missing anterior collaterals of the circle of Willis increase the risk of intra-operative SEP changes during CEA. Pre-operative assessment of collateral arterial anatomy might help identifying patients with an increased intra-operative risk.

Atypical Endovascular Cells in SARS-CoV-2 Pneumonia.

The autopsy findings for 3 cases of SARS-(CoV-2) pneumonia-related deaths are reported with pulmonary histology and immunohistochemistry findings. In 2 cases (cases 1 and 2), the time interval from presentation to death was approximately 1 week, whereas for case 3, the time interval from presentation to death was hours. Case 1 and case 2 presented with shortness of breath, cough, and flu-like symptoms. The decedent from case 3 died shortly after presenting to a local emergency room with high fever, chest and abdominal pain, and shortness of breath. All 3 cases had 1 or more comorbidities. The postmortem interval for cases 1 and 2 was 2 weeks as they died at sea and were stored on board within the respective cruise ships' refrigeration units, whereas case 3 was examined within 24 hours of death. The autopsies were conducted at the Miami-Dade County Medical Examiners Department under routine infectious precautions. Salient clinical history and autopsy findings are summarized. Microscopic examination revealed pneumonia with associated atypical endovascular cells.

Clinical and morphological risk factors for the recurrence of anterior communicating artery aneurysms after clipping or coiling.

BACKGROUND: The aim of this study was to evaluate clinical and morphological factors associated with recurrence in anterior communicating artery (AcomA) aneurysms after clipping or coiling. METHODS: We retrospectively reviewed the clinical and radiologic features of consecutive 214 patients with AcomA aneurysms treated between January 2012 and December 2016 in a single tertiary institute. Univariate and multivariate analyses were performed to identify the relationship between clinical and morphological variables and recurrence. RESULTS: Of 214 patients, 166 were unruptured aneurysms and 109 were treated with coiling. Overall recurrence rate was 13% (28 out of 214 aneurysms) during mean 36.9 ± 18.4-month follow-up. Multivariate logistic regression analysis showed that size greater than 10 mm (OR = 5.651; 95% CI, 1.317-24.242; p = 0.020), smoking (OR = 3.474; 95% CI, 1.342-8.996; p = 0.010), coiling (OR = 2.98; 95% CI, 1.005-8.832; p = 0.049), and anterior direction of aneurysm (OR = 3.77; 95% CI, 1.12-12.66; p = 0.032) were significantly associated with recurrence of AcomA aneurysms after treatment. CONCLUSIONS: The results of this study demonstrated that coiling, large aneurysm, anterior direction, and smoking history may be independent risk factors for the recurrence of AcomA aneurysms. Therefore, careful follow-up should be needed especially in large AcomA aneurysms with anterior direction after coiling.

Reconstruction of a dominant vertebral artery during resection of a superior sulcus tumour with an incomplete circle of Willis.

A 74-year-old man presented with a left superior sulcus tumour invading the subclavian artery. After induction chemoradiotherapy, he underwent a vertebral artery reconstruction in addition to the subclavian artery reconstruction via a transmanubrial approach and video-assisted thoracoscopic left upper lobectomy. The final pathology was ypT4N0M0 adenocarcinoma. The technical aspects and indication for a vertebral artery reconstruction are discussed in this article.

ASL perfusion features and type of circle of Willis as imaging markers for cerebral hyperperfusion after carotid revascularization: a preliminary study.

OBJECTIVES: Cerebral hyperperfusion (CH) could be a disastrous outcome causing complication after carotid revascularization if not managed properly and timely. The aim of this study was to investigate the association between preoperative arterial spin labelling (ASL) perfusion features and circle of Willis (CoW) pattern with CH. METHODS: Forty-eight consecutive carotid stenosis patients who underwent carotid endarterectomy (CEA) or carotid artery stenting (CAS) were enrolled. All patients had single post-labelling delay (PLD) ASL, territory-ASL, and 3-dimensional time-of-flight MR angiography (3D TOF MRA) within 2 weeks before surgery and within 3 days after surgery. Spatial coefficient of variation (CoV) of cerebral blood flow (CBF), whole brain, and territory perfusion volume ratio were calculated from ASL and territory-ASL. Postoperative CoW was classified into two groups based on patency of the first segment of the anterior cerebral arteries (A1) and anterior communicating artery (AcomA). ASL perfusion features, type of CoW, and clinical characteristics were analyzed between CH group and non-CH group to identify CH risk factors. RESULTS: Higher CoV (p = 0.005) of CBF, lower whole brain perfusion volume ratio (p = 0.012), missing any of A1 or AcomA in CoW (p = 0.002 for postoperative MRA and p = 0.004 for preoperative MRA), and large artery stroke history (p = 0.028) were significantly associated with higher risk of CH. Two cases with cerebral hyperperfusion syndrome (CHS) were also discussed, and their perfusion and angiographic features were shown. CONCLUSIONS: Single-PLD ASL and MRA might be useful and non-invasive imaging tools to identify patients with higher risk of CH after carotid revascularization. KEY POINTS: • Cerebral hyperperfusion is a critical complication after carotid endarterectomy or carotid artery stenting. • ASL and MRA can be used to identify patients at higher risk of cerebral hyperperfusion • Pattern of circle of Willis, ASL perfusion features, and whole brain perfusion volume ratio are potential predicting markers for hyperperfusion after carotid revascularization.

The Relationship Between the Direction of Putaminal Intracerebral Hemorrhage and Anterior Cerebral Artery Predominance.

OBJECTIVE: It is expected that anatomic variations in the circle of Willis have a direct effect on blood flow in the internal carotid artery. Rupture of the lenticulostriate artery of the middle cerebral artery 1st segment (M1) is the most common cause of putaminal intracerebral hemorrhage (ICH), and we hypothesized that this could be related to the anatomic variations of the circle of Willis and the predominance of the anterior cerebral artery 1st segment (A1). METHODS: We retrospectively reviewed the records of 544 patients who were treated for spontaneous ICH between 2013 and 2016 at Yeungnam University Hospital. Among them, 83 patients (49 men and 34 women; mean age, 60.38 years; range, 34-87 years) were admitted for the treatment of putaminal ICH. The circle of Willis was visualized on the basis of computed tomographic (CT) angiographic images with 3-dimensional (3D) reconstruction images. The number of putaminal ICH patients who showed differences in diameter between the right and left A1 segments, with a normal variation of the anterior cerebral artery (ACA), was analyzed. RESULTS: Among 83 patients with spontaneous ICH, 46 and 37 had left and right putaminal hemorrhages, respectively. Sixty-seven patients were treated conservatively, and 16 patients underwent surgery. The number of patients with a dominant A1 segment on either side was 58 (67.4%). Forty patients had a dominant A1 segment and putaminal ICH located in the same direction (P = 0.007). CONCLUSION: It was concluded that putaminal ICHs occur more frequently on the side of the dominant A1 segment. This information can help an understanding of the mechanism of putaminal spontaneous ICH development and may even assist in the treatment of ICH.

Posterior communicating artery aneurysms causing facial pain: A comprehensive review.

Posterior communicating aneurysms are commonly associated with oculomotor nerve palsy. However, trigeminal nerve involvement among these aneurysms is a rare event with no previous analysis. In order to describe the main features of posterior communicating aneurysms causing trigeminal neuralgia (TGN-PComAAs) eight cases (six from the literature plus two more illustrative cases) were included in the present series. All cases were thoroughly studied in order to collect their epidemiological, radiological, clinical, therapeutic, pathogenic, and outcome data. The mean age at diagnosis was 57 years. Gender distribution showed a female predominance (M-to-F ratio 3:5), while side distribution showed a slight left dominance (62%). The aneurysms mean size was 24.7mm (range: 7-40mm). In 7 cases (87.5%) the PComAA was reported to project posteriorly, associated with cavernous sinus extension/compression in two of them and posterior fossa extension in three. No case presented with hemorrhage. Facial pain was the clinical onset in all eight cases, which was reported as an atypical TGN (continuous with exacerbating fits) in 87.5%. Trigger points were absent in all cases but one (87.5%). The most frequent anatomical distribution of the pain was V2 alone (n=3), followed by V1-2 (n=2) and V1-2-3 (n=2). Three different mechanisms for trigeminal neuralgia were observed, namely, cavernous sinus compression (n=4), direct trigeminal root compression (n=3), and oculomotor nerve compression (n=1). Three different treatment options were performed: surgery (n=6), trigeminal thermo-rhizotomy (n=1) and medical management (n=1). According to the Barrow Neurological Institute (BNI) score the pain control after main treatment was I (no pain with no medication) in 7 cases (87.5%). The average modified Rankin scale (mRS) score was 1. In sum, TGN-PComAAs are infrequent lesions characterized by large size and posterior-medial-inferior projection. They mainly cause atypical TGN, most commonly involving the first and second trigeminal distributions (V1-V2). Surgical aneurysmal clipping has been the most frequent treatment option for these aneurysms, providing good neurological results in a vast majority and complete trigeminal pain relief in all cases.

Comparison of 3D magnetic resonance imaging and digital subtraction angiography for intracranial artery stenosis.

OBJECTIVES: To compare three-dimensional high-resolution magnetic resonance imaging (3D HR-MRI) and digital subtraction angiography (DSA) for diagnosing and evaluating stenosis in the entire circle of Willis. METHODS: The study included 516 intracranial arteries from 43 patients with intracranial artery stenosis (ICAS) who underwent both 3D HR-MRI and DSA within 1 month. Two readers independently diagnosed atherosclerosis, dissection, moyamoya disease and vasculitis, rated their diagnostic confidence for each vessel and measured the luminal diameters. Reference standard was made from clinico-radiologic diagnosis. Diagnostic accuracy, diagnostic confidence, the degree of stenosis and luminal diameter were assessed and compared between both modalities. RESULTS: For atherosclerosis, 3D HR-MRI showed better diagnostic accuracy (P = .03-.003), sensitivity (P = .006-.01) and positive predictive value (P ≤ .001-.006) compared to DSA. Overall, the readers were more confident of their diagnosis of ICAS when using 3D HR-MRI (reader 1, P ≤ .001-.007; reader 2, P ≤ .001-.015). 3D HR-MRI showed similar degree of stenosis (P > .05) and higher luminal diameter (P < .05) compared to DSA. CONCLUSIONS: 3D HR-MRI might be useful to evaluate atherosclerosis, with better diagnostic confidence and comparable stenosis measurement compared to DSA in the entire circle of Willis. KEY POINTS: • 3D HR-MRI showed better diagnostic accuracy for atherosclerosiscompared to DSA • 3D HR-MRI showed better overall diagnostic confidence for stenosiscompared to DSA • 3D HR-MRI and DSA showed similar degree of stenosis.

Vasoespasmo cerebral y déficit isquémico tardío en la hemorragia subaracnoídea aneurismática: guías para su manejo clínico / Cerebral vasospasm and delayed ischemic deficit in the aneurysmal subarachnoid hemorrhage: guidelines to its clinical management

La presente revisión del tema Vasoespasmo y Déficit Isquémico Cerebral tardío (DIT) en la Hemorragia subaracnoidea aneurismática tiene como objetivo actualizar su manejo, basado en las hipótesis mas aceptadas que se han logrado para explicar su patogénesis. Se efectúa una introducción con conceptos generales, se revisan las bases patogénicas del Vasoespasmo y se plantea su manejo, tomando en cuenta su diagnóstico, monitorización, profilaxis y manejo avanzado de acuerdo a las últimas Guías de Manejo Clínico y según medicina basada en las evidencias.

The objective of the present review on cerebral vasospasm and cerebral delayed isquemic deficit due to subarachnoid haemorrhage secondary to ruptured cerebral aneurysm, is to update their management, based on the most accepted pathophysiological hypotesis explaining their pathogenetic mechanisms. An introduction is performed presenting general concepts, review of the most recent research works explaining their pathogenesis, and the management is stated touching diagnosis, monitoring, prophylaxis, and advanced management according with the last clinical guidelines for his management using medicine based on evidences.

Temporal profile of magnetic resonance angiography and decreased ratio of regulatory T cells after immunological adjuvant administration to mice lacking RNF213, a susceptibility gene for moyamoya disease.

Moyamoya disease (MMD) is a chronic, occlusive cerebrovascular disease with an unknown etiology and is characterized by an abnormal vascular network at the base of the brain. Recent studies identified the RNF213 gene (RNF213) as an important susceptibility gene for MMD; however, the mechanisms underlying the RNF213 abnormality related to MMD have not yet been elucidated. We previously reported that Rnf213-deficient mice and Rnf213 p. R4828K knock-in mice did not spontaneously develop MMD, indicating the importance of secondary insults in addition to genetic factors in the pathogenesis of MMD. The most influential secondary insult is considered to be an immunological reaction because RNF213 is predominantly expressed in immunological tissues. Therefore, we herein attempted to evaluate the role of an immunological stimulation as a supplementary insult to the target disruption of RNF213 in the pathophysiology of MMD. Rnf213-deficient mice were treated with strong immunological adjuvants including muramyl dipeptide (MDP)-Lys (L18), and then underwent time-sequential magnetic resonance angiography (MRA) up to 40 weeks of age. The results obtained did not reveal any characteristic finding of MMD, and no significant difference was observed in MRA findings or the anatomy of the circle of Willis between Rnf213-deficient mice and wild-type mice after the administration of MDP-Lys (L18). The ratio of regulatory T cells after the administration of MDP-Lys (L18) was significantly decreased in Rnf213-deficient mice (p<0.01), suggesting the potential role of the RNF213 abnormality in the differentiation of regulatory T cells. Although the mechanisms underlying the development of MMD currently remain unclear, the RNF213 abnormality may compromise immunological self-tolerance, thereby contributing to the development of MMD.

WILIS IRLE ARITINS, IMPORTANT FOR CEREBRAL PROTECTION IN AORTIC SURGERY - PRIMARY CT ANGIO DATA.

Unilateral selective cerebral perfusion (SCP) is a method for cerebral protection in aortic arch surgery. However variations of the circle of Willis (CoW) could vitiate its protective effect. The aim of our present work was to make a retrospective analysis of 30 patients, in whom CT angio was performed between January and March 2008. Variations of Willis circle, which could compromise the perfusion during unilateral SCP were found in 21 patients (70%). We also found that many patients have significant stenosis of cerebral arteries. Our present study shows the need of extensive preoperative examination and meticulous intraoperative monitoring.

Hypertension and Estrogen Deficiency Augment Aneurysmal Remodeling in the Rabbit Circle of Willis in Response to Carotid Ligation.

Increased cerebral blood flow has been shown to induce pathological structural changes in the Circle of Willis (CoW) in experimental models. Previously, we reported flow-induced aneurysm-like remodeling in the CoW secondary to flow redistribution after bilateral common carotid artery (CCA) ligation in rabbits. In the current study, we tested the hypothesis that loading rabbits with biological risk factors for vascular disease would increase flow-induced aneurysmal remodeling in the CoW. In the same series as the previously-reported bilateral CCA-ligation-alone (n = 6) and sham surgery (n = 3) groups, eight additional female rabbits (the experimental group in this study) were subjected to two risk factors for intracranial aneurysm (hypertension and estrogen deficiency) and then bilateral CCA ligation. Upon euthanasia at 6 months, vascular corrosion casts of the CoW were created and analyzed by scanning electron microscopy for morphological changes and aneurysmal damage. In rabbits with hypertension and estrogen deficiency, arterial caliber increased throughout the CoW, similar to rabbits with CCA ligation alone. However, aneurysmal remodeling (i.e., local bulging) in the CoW was significantly greater than in CCA-ligation-only rabbits and was more widespread, presenting in regions that did not show aneurysmal changes after CCA ligation alone. Furthermore, hypertension and estrogen deficiency caused greater increases in vessel length and tortuosity. These results suggest that hypertension and estrogen deficiency make the CoW more vulnerable to flow-induced aneurysmal remodeling and tortuosity. We propose they do so by lowering the tolerance of vascular tissue to hemodynamic forces caused by CCA ligation, thus lowering the threshold necessary to incite vascular damage.

Early clinical signs, lesion localization, and prognostic factors in unilateral symptomatic internal carotid artery occlusion.

BACKGROUND: The aim of this study was to assess infarct localization, clinical signs, and prognostic factors in cases with unilateral symptomatic total internal carotid occlusion. METHODS: In total, 101 patients who had a diagnosis of symptomatic unilateral carotid occlusion in the Department of Neurology, Trakya University Faculty of Medicine, between January 2008 and May 2012, were included in this study. The relationship between infarct localizations and prognosis of patients was evaluated by cranial magnetic resonance imaging (MRI) and diffusion-weighted MRI. The condition of ipsilateral middle cerebral artery (MCA) and posterior communicating arteries (PCoAs) was assessed by cranial and cervical magnetic resonance angiography besides opposite carotid. Patients were evaluated by modified Rankin Scale in terms of prognosis at discharge and after 3 months. Furthermore, they were evaluated in terms of risk factors, such as cigarette and alcohol use, presence of temporary ischemic attack and stroke history, hypertension, diabetes mellitus, coronary artery disease, previous myocardial infarction, hyperlipidemia, and peripheral vascular disease. RESULTS: Territorial infarct was commonly seen as acute ischemic stroke pattern especially in cases with a poor MCA circulation and insufficient collateral circulation. Development of territorial stroke, occlusion of MCA, and nonvisualization of PCoA were found to be associated with poor prognosis. CONCLUSIONS: In unilateral symptomatic intracranial carotid artery occlusion, poor prognosis and high mortality-associated territorial stroke pattern is frequently observed. Besides, presence of severe stenosis or occlusion and absence of collateral circulation in MCA are associated with poor prognosis.

Circle of Willis abnormalities in children with neurofibromatosis type 1.

BACKGROUND AND PURPOSE: The aim of the study was to assess anatomical variants and abnormalities in cerebral arteries on magnetic resonance angiography in 67 children with neurofibromatosis type 1 (NF1). MATERIALS AND METHODS: The study included 67 children aged 9 months to 18 years (mean 6.6 years). Control group comprised 90 children aged 2-18 years (mean: 11.8 years). All patients were examined at 1.5T scanner. RESULTS: We found cerebral arteriopathy (moyamoya disease) in one child (1.5%) in the study group. No aneurysms were found. Twenty-nine NF1 children (43.3%) had arterial anatomical variants. In 13 of them, more than one variant was diagnosed (44.8% of group with variants, 19.4% of study group). In control group, 19 children (21.1%) had variants, including four children with more than one variant (21% of group with variants, 4.4% of control group). Arterial variants were more common in NF1 patients compared with control group (p=0.026, binomial test for two proportions). Percentage of multiple variants was higher in study group than in control group, but this difference was not significant. Variants were more frequent on left side than on the right one (significant difference in control group; p=0.022, McNemara test). In study group, the number of left-sided anomalies (25) was similar to that of right-sided ones (22). There was no correlation between gender and variants, unidentified bright objects and variants or between optic gliomas and variants. CONCLUSIONS: Occurrence of arterial variants in NF1 patients was twofold higher than in control group. Multiple variants were more frequent in the study group although the difference did not reach statistical significance. Features of cerebral arteriopathy were found in one child with NF1.

Anterior communicating artery aneurysm surgery: which is the most appropriate head position?

Head positioning and the degree of rotation for anterior communicating artery aneurysm surgery is controversial. With this anatomic study, we aimed to give a broad description of head positioning for various aneurysm dome projections. In addition, with the use of a corrosion-cast technique, a three-dimensional arterial tree was demonstrated, an anterior communicating artery region aneurysm model was prepared, and pictures were taken at various angles. According to our observations, 30-degree head rotation was found to be the most suitable position for the anterior and superior projected aneurysms. For posterior projection, aneurysm neck was best viewed with 15-degree head rotation. Aneurysms projecting inferiorly necessitated the greatest rotation at 45 degrees. Each aneurysm dome projection of the anterior communicating artery aneurysm should be individually considered, and the head position should be adjusted accordingly. The use of appropriate head positions during surgery will prevent the development of postoperative ischemic complications and will increase the success of surgery by preventing unnecessary tissue manipulation.

Towards understanding ocular motility: III, IV and VI.

The study of the ocular-motor nerves must be exhaustive from their source (nuclei in the brainstem) down to the effector muscles (orbit). Visual disturbances have to be analysed by differentiating between a decrease in visual acuity and ocular-motor disorders. Imaging tests are dominated by MRI, including fine slices and gadolinium injection. A study of the Circle of Willis vessels is often useful, and essential in the case of type III impairment. A further CT scan is essential for analysis of the foramina, base of the skull and orbital walls. Impairment of CN VI requires a CT scan of the apex of petrous. The study of the cavernous sinuses must be in-depth (T2 and T1 after gadolinium and elimination of fats) and always comparative. Impairment of CN III is often complex, difficult to identify precisely (complete or partial, with or without a pupil impairment, associated with other neurological signs) and requires a reasoned study based on anatomical, semiological and pathological knowledge. Other than tumour diseases, it is necessary to consider less well known malformative, ischemic and inflammatory aetiology.

Incompleteness of the circle of Willis is related to EEG-based shunting during carotid endarterectomy.

OBJECTIVES: The occurrence of cerebral ischemia during carotid endarterectomy (CEA) can be prevented by (selective) placement of an intraluminal shunt during cross-clamping. We set out to develop a rule to predict the likelihood for shunting during CEA based on preoperative assessment of collateral cerebral circulation and patient characteristics. METHODS: Patients who underwent CEA between 2004 and 2010 were included. Patients without preoperative magnetic resonance (MRA) or computed tomography angiography (CTA) were excluded. The primary endpoint was intraluminal shunt placement based on electroencephalography changes. Age, sex, cardiovascular risk factors peripheral artery disease, symptomatic status, degree of ipsilateral and contralateral carotid, status of the vertebral arteries, and morphology of the CoW were studied as potential predictors for shunt use. A prediction model was derived from a multivariable regression model using discrimination, calibration, and bootstrapping approaches and transformed into a clinical prediction model. RESULTS: A total of 431 patients were included, of which 65 patients (15%) received an intraluminal shunt. In the MRA group (n = 285) factors related to shunt use in multivariate analysis were ipsilateral carotid stenosis 90-99% (odds ratio [OR] 0.15, 95% CI 0.04-0.53), contralateral carotid occlusion (OR 4.29, 95% CI 1.68-10.95) and any not-visible anterior (OR 4.96, 95% CI 1.95-12.58) or ipsilateral posterior segment of the CoW (OR 5.08, 95% CI 2.10-12.32). In the CT group none of the factors were independently related to shunt use; therefore, only predictors describing morphology of CoW derived from MRA findings were included in our model. The c-statistic of this model was 0.79 (95% CI 0.72-0.86). Among patients with an estimated chance of needing a shunt of under 10% (49% of the population), the likelihood of shunting was 5%. In those in whom this chance was estimated higher than 30% (13% of the population) the likelihood was 51%. CONCLUSIONS: Among patients scheduled for CEA, assessment of cerebral arteries and of the configuration of the CoW based on MRA-derived images can help to identify patients with low and high likelihood of the need of shunt use during surgery.