Quantitative Prediction of the Location of Carotid Bifurcation and Neurovascular Structures in the Carotid Region: A Cross-Sectional Cadaveric Study.

INTRODUCTION: The carotid region is encountered in vascular and neurological surgery and carries a potential for vascular and cranial nerve trauma. The carotid bifurcation is an especially important landmark and difficult to predict based on currently established landmarks. This study is a detailed analysis of the carotid region and proposes a novel methodology to predict the height of the bifurcation. MATERIALS AND METHODS: Superficial and deep dissections were performed on the anterior triangle of the neck to expose the carotid region in twenty-one formalin-fixed donor cadavers. Musculoskeletal and neurovascular structures were assessed in relation to the carotid bifurcation and the medial border of the clavicle (MBC). RESULTS: The carotid bifurcation occurred, on average, 11.4 mm higher on the left (p < 0.001; 95% CI: 9.28, 13.54). The superior thyroid artery (p < 0.001), facial vein (p < 0.001), and cranial nerve XII (p < 0.001) were all more distal on the left side when measured from the MBC while the angle of the mandible and stylohyoid muscle remained symmetric. Left- and right-sided vascular structures were symmetric when measured from the carotid bifurcation. CONCLUSIONS: Neurovascular structures within the carotid region are likely to be anatomically superior on the left side while vessels are likely to remain symmetric in relation to the carotid bifurcation. When measured from the MBC, the bifurcation height can be predicted by multiplying the distance between the MBC and mastoid process by 0.65 (right side) or 0.74 (left side). This novel methodological estimation may be easily learned and directly implemented in clinical practice.

Feasibility of kilohertz frequency alternating current neuromodulation of carotid sinus nerve activity in the pig.

Recent research supports that over-activation of the carotid body plays a key role in metabolic diseases like type 2 diabetes. Supressing carotid body signalling through carotid sinus nerve (CSN) modulation may offer a therapeutic approach for treating such diseases. Here we anatomically and histologically characterised the CSN in the farm pig as a recommended path to translational medicine. We developed an acute in vivo porcine model to assess the application of kilohertz frequency alternating current (KHFAC) to the CSN of evoked chemo-afferent CSN responses. Our results demonstrate the feasibility of this approach in an acute setting, as KHFAC modulation was able to successfully, yet variably, block evoked chemo-afferent responses. The observed variability in blocking response is believed to reflect the complex and diverse anatomy of the porcine CSN, which closely resembles human anatomy, as well as the need for optimisation of electrodes and parameters for a human-sized nerve. Overall, these results demonstrate the feasibility of neuromodulation of the CSN in an anesthetised large animal model, and represent the first steps in driving KHFAC modulation towards clinical translation. Chronic recovery disease models will be required to assess safety and efficacy of this potential therapeutic modality for application in diabetes treatment.

Carotid Sinus Nerve: A Comprehensive Review of Its Anatomy, Variations, Pathology, and Clinical Applications.

The carotid sinus nerve branches off the glossopharyngeal nerve just after its appearance from the jugular foramen, descends along the internal carotid artery, and enters the carotid sinus. There have been many studies of the pathway and the course of the carotid sinus nerve and its communications with surrounding nerves. The intercommunication is exceedingly complicated. Acknowledgment of its anatomic diversity can be important in specific operations dealing with this area. Herein we review the anatomy, variations, pathology, and clinical applications of the carotid sinus nerve.

Variations in carotid sinus anatomy and their relevance to carotid interventions.

BACKGROUND: The carotid sinus (CS) is a dilatation in the carotid bifurcation usually at the origin of proximal internal carotid artery (ICA). It contains baroreceptors which influence blood pressure. Variations in the location of the CS are of importance as atheromatous plaque commonly forms in this area and procedures such as carotid endarterectomy are performed to reduce the risk of stroke. Inadvertent stimulation of the CS baroreceptors during interventions can have profound effects on the patient's haemodynamic status both intra- and postoperatively, causing serious complications. The aim of this study is to determine the inter- and intra-individual variations in the location of the CS. MATERIALS AND METHODS: Eighty-two carotid arteries were dissected bilaterally from 41 cadavers. The locations of the CS were noted and divided into four potential sites. RESULTS: The commonest site is the origin of the ICA (74.3%), but the CS can also be found in the distal part of the common carotid artery (CCA) inferior to the bifurcation (17.1%); at the bifurcation involving the distal CCA and origins of both the external carotid artery (ECA) and ICA (7.32%); and at the origin of the ECA (1.22%). In individual cadavers, the CS was located at the origin of the ICA in 97.6% on at least one side. The sites of the CS were asymmetrical in 34.1%. CONCLUSIONS: Clinicians performing carotid interventions should be aware of these anatomical variations to avoid inadvertent stimulation of the CS which can cause profound bradycardia and hypotension.

The accuracy of anatomical landmarks for locating the carotid sinus.

BACKGROUND: carotid sinus massage (CSM) is a valuable clinical test for carotid sinus syndrome (CSS) and relies on accurately locating the carotid sinus (CS). OBJECTIVE: in this study, we sought to examine the accuracy of using anatomical landmarks for locating the CS. METHODS: consecutive patients (n = 20) were recruited prospectively. Two clinicians, trained in CSM, were asked to locate the CS using anatomical landmarks. A point on the skin overlying the CS was then marked by a vascular technician using ultrasound. Accuracy of techniques was compared using intra-class correlation coefficients and Bland-Altman statistics. RESULTS: anatomical landmarks underestimated the CS location by 1.5 ± 1.3 cm. Error extremes ranged from 4 cm below to 2 cm above CS using anatomical landmarks. A moderate correlation between ultrasound and anatomical landmarks was found, r = 0.371 (P = 0.031). CONCLUSION: this is the first study to characterise the accuracy of standard anatomical landmarks used in CSM. Results suggest that the point of maximal pulsation has the lowest associated error. Future work should examine CSM yield across this and a range of other methodological factors.

Ansa cervicalis - variable course of the superior root

In the past few years, techniques have been developed using ansa cervicalis to innervate muscles of the larynx paralyzed due to surgical procedures performed in the area of the chest and neck. In the present report, during routine dissection in a middle-aged male cadaver, we observed an unusual course of the superior root of the ansa cervicalis on right side. The superior root of the ansa cervicalis fused with the vagus, and ran within the carotid sheath before joining the inferior root forming the ansa cervicalis in the anterior wall of the carotid sheath. The present case should add to our existing knowledge of ansa cervicalis, and should help surgeons in avoiding injury to the nerve during various surgical procedures

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Study of the formation and distribution of the ansa cervicalis and its clinical significance

The ansa cervicalis is a neural loop in the neck. It is formed by the union of two main nerve roots -i.e., superior and inferior- derived from the ventral rami of the cervical nerves. The aim of this study was to explore the anatomical variations of the ansa cervicalis with a view to preventing accidental injury during surgical procedures. Fifty formalin-fixed cadavers were dissected bilaterally for the ansa cervicalis, in which abnormalities were observed in three cadavers. In one cadaver, the ansa cervicalis was absent and the strap muscles of the neck received their innervations from the vagus nerve. Two cadavers displayed an ansa cervicalis formed by the superior root, which branched out from the vagus nerve instead of the hypoglossal nerve. In recent years, there has been an abundance of techniques utilizing the ansa cervicalis to reinnervate the paralyzed larynx. Because of its proximity to major nerves and vessels of the neck, a good understanding of the topography and morphology of this loop is essential. Any variation in the course, contributing roots or branching pattern of the ansa cervicalis, potentially modifies and complicates the course of procedures relating to this nerve (AU)

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Sex differences in carotid bifurcation anatomy and the distribution of atherosclerotic plaque.

BACKGROUND AND PURPOSE: Plaque formation at arterial bifurcations depends on vessel anatomy, particularly the relative sizes of the branches, and the ratio of the outflow to inflow area. The facts that carotid plaque is more common in men and that carotid bruits in the absence of stenosis are more frequent in women raise the possibility that there are sex differences in carotid bifurcation anatomy. We studied 5395 angiograms from the European Carotid Surgery Trial. METHODS: To minimize secondary changes we excluded angiograms with >/=50% stenosis and also studied vessels with no disease. We measured arterial diameters at disease-free points and calculated the following ratios: internal/common (ICA/CCA); external/common (ECA/CCA); internal/external (ICA/ECA) carotid arteries; carotid bulb/CCA; and outflow/inflow area. We related these to sex and also studied the distribution of plaque in the whole trial population. RESULTS: Among 2930 angiograms with <50% stenosis, the mean ICA/CCA ratio, ICA/ECA ratio, and outflow/inflow area ratio were larger in women than in men (all P<0.0001). The findings were similar in 622 bifurcations without atheroma. There were also differences in the distribution of plaque, with men more likely to have the maximum stenosis distal to the carotid bulb (odds ratio, 2.29; 95% CI, 1.33 to 4.01; P=0.001) and women more likely to have stenosis of the ECA (odds ratio, 1.54; 95% CI, 1.30 to 1.85; P<0.0001). CONCLUSIONS: Sex differences in carotid bifurcation anatomy are not limited to absolute vessel size. In addition, the outflow to inflow area ratio is bigger in women, and relative to the CCA and ECA, women have larger ICAs than men. Irrespective of whether these differences are congenital or acquired, they may partly explain the sex differences that we found in the distribution of plaque and the sex differences in the prevalence of carotid atheroma in the general population.

Anatomical and functional characteristics of carotid sinus stimulation in humans.

Transmission characteristics of pneumatic pressure to the carotid sinus were evaluated in 19 subjects at rest and during exercise. Either a percutaneous fluid-filled (n = 12) or balloon-tipped catheter (n = 7) was placed at the carotid bifurcation to record internal transmission of external neck pressure/neck suction (NP/NS). Sustained, 5-s pulses, and rapid ramping pulse protocols (+40 to -80 Torr) were recorded. Transmission of pressure stimuli was less with the fluid-filled catheter compared with that of the balloon-tipped catheter (65% vs. 82% negative pressure, 83% vs. 89% positive pressure; P < 0.05). Anatomical location of the carotid sinus averaged 3.2 cm (left) and 3.6 cm (right) from the gonion of the mandible with a range of 0-7.5 cm. Transmission was not altered by exercise or Valsalva maneuver, but did vary depending on the position of the carotid sinus locus beneath the sealed chamber. These data indicate that transmission of external NP/NS was higher than previously recorded in humans, and anatomical variation of carotid sinus location and equipment design can affect transmission results.

Anatomía microquirúrgica y microvascular: el tríangulo optocarotídeo: consideraciones en cirugía vascular / Microsurgical and microvascular anatomy: the opto-carotid triangle: considerations in vascular surgery

La descripción del triángulo opto - carotídeo (TOC) es muy escasa en la literatura neuroquirúrgica, a pesar de ser un área importante en el manejo de patología vascular variada y frecuente. Con la introducción de nuevas tecnologías imagenológicas y la evolución en las técnicas microquirúrgicas y en cirugía de base de cráneo, es sumamente importante el conocimiento y definición de las áreas anatómicas relevantes en cirugía microvascular, incluyendo su descripción morfométrica. El TOC es un área anatómica que debe de ser abordada durante un importante número de procedimientos neurovasculares, así como para patologías no vasculares y que involucran la región.

Mapping of carotid baroreceptor subtype projections to the nucleus tractus solitarius using c-fos immunohistochemistry.

This study has combined physiological pressure stimulation of carotid baroreceptors via a vascularly isolated carotid sinus and anodal block of baroreceptor afferent fibers in the carotid sinus nerve to examine the medullary projections of type I vs. type II (large A- vs. small A- and C-fiber afferent) baroreceptors. The control distribution of cells in the nucleus tractus solitarius expressing c-fos in response to physiological activation of carotid baroreceptors in the isolated sinus was compared to that during anodal block of large A-fibers in the carotid sinus nerve. Carotid baroreceptor stimulation primarily activated neurons in the ipsilateral commissural and medial subnuclei of the caudal nucleus tractus solitarius and the dorsolateral, dorsomedial and medial subnuclei in the intermediate and rostral levels of the nucleus tractus solitarius. Elimination of large A-fiber carotid baroreceptor afferents, during similar carotid baroreceptor stimulation resulted in a decrease in the number of cells expressing c-fos in the dorsomedial subnucleus of the rostral nucleus tractus solitarius. These data indicate that projections of larger A-fiber (type I) carotid baroreceptors are localized primarily to the rostral dorsomedial subnucleus, while those of smaller A- and C-fiber baroreceptors are more widely distributed to the commissural, medial and dorsal subnuclei of the nucleus tractus solitarius.

Circumsinus branch: a convenient source of baro- and chemoreceptor activity in dogs.

We found a branch of the carotid sinus nerve in 44 of 48 dogs. We propose that this branch be referred to as the "circumsinus" branch of the carotid sinus nerve. Both chemoreceptor and baroreceptor activity were detected in this branch during electrophysiological recording efforts utilizing classic nerve recording techniques. Its convenient location permits whole nerve or single unit recording without having to transect, dissect, or even expose the carotid sinus nerve. Carotid baroreceptor and chemoreceptor activity can be monitored with most of the carotid bifurcation's neural pathways intact.

Shear stress at a compliant model of the human carotid bifurcation.

To investigate the role of a compliant wall to the near wall hemodynamic flowfield, two models of the carotid bifurcation were constructed. Both were of identical internal geometries, however, one was made of compliant material which produced approximately the same degree of wall motion as that occurring in vivo while the other one was rigid. The inner geometries were formed from the same mold so that the configurations are directly comparable. Each model was placed in a pulsatile flow system that produced a physiologic flow waveform. Velocity was measured with a single component Laser system and wall shear rate was estimated from near wall data. Wall motion in the compliant model was measured by a wall motion transducer and the maximum diameter change varied between 4-7 percent in the model with the greatest change at the axis intersection. The mean shear stress in the compliant model was observed to be smaller by about 30 percent at most locations. The variation in peak shear stress was greater and occasionally reached as much as 100 percent with the compliant model consistently having smaller positive and negative peaks. The separation point was seen to move further upstream in the compliant cast. The modified flowfield in the presence of a compliant wall can then be important in the hemodynamic theory of atherogenesis.

Indomethacin reduces acute baroreceptor resetting in the dog.

1. The influence of local perfusion of the carotid sinus with the cyclo-oxygenase blocker indomethacin on acute baroreceptor resetting was investigated in anaesthetized dogs. 2. The carotid sinus was isolated and perfused with oxygenated Krebs-Henseleit solution. Single units from the carotid sinus nerve were recorded. The carotid sinus was conditioned with static pressures of 50, 100 and 150 mmHg for 15 min. Following the conditioning period a carotid sinus pressure (CSP)-discharge curve was constructed using static stepwise increases in CSP. 3. Perfusion of the carotid sinus with indomethacin (20 microM) caused an elevation in the threshold at every conditioning pressure (96.8 +/- 4.8 vs. 83.8 +/- 4.1 mmHg for 100 mmHg, P < 0.01; 91.9 +/- 4.7 vs. 70.3 +/- 4.4 mmHg for 50 mmHg, P < 0.01; and 103.5 +/- 4.4 vs. 96.4 +/- 4.1 mmHg for 150 mmHg, P = 0.06, respectively) and a significant reduction in the peak discharge rate at each conditioning pressure (32.0 +/- 4.4 vs. 48.2 +/- 5.5 spikes/s for 100 mmHg, P < 0.01; 32.2 +/- 5.8 vs. 45.8 +/- 5.1 spikes/s for 50 mmHg, P < 0.01; 32.0 +/- 3.7 vs. 51.1 +/- 8.1 spikes/s for 150 mmHg, P < 0.01). The resetting ratio (change in threshold/change in conditioning CSP) for both downward resetting (conditioning CSP from 100 to 50 mmHg) and upward resetting (conditioning CSP from 100 to 150 mmHg) was significantly decreased after indomethacin (0.10 +/- 0.02 vs. 0.27 +/- 0.02 for downward resetting, P < 0.01 and 0.14 +/- 0.03 vs. 0.25 +/- 0.01 for upward resetting, P < 0.01, respectively). 4. Conversely, perfusion of the carotid sinus with arachidonic acid (20 microM) significantly decreased the threshold at each conditioning CSP and increased the peak discharge rate at each conditioning CSP. The resetting ratio was significantly increased after arachidonic acid. 5. There was no change in resting carotid diameter or in the carotid sinus pressure-carotid diameter relationship after indomethacin or arachidonic acid. 6. Removal of the endothelial cells in the carotid area with saponin did not prevent the effects of indomethacin on baroreceptor resetting. 7. These results suggest that prostaglandins have a tonic effect on the activity of the carotid sinus baroreceptor and may play a role in acute baroreceptor resetting.

Mechanism of baroreceptor adaptation in dogs: attenuation of adaptation by the K+ channel blocker 4-aminopyridine.

1. Increased arterial pressure increases baroreceptor activity but activity declines (i.e. baroreceptors adapt) as the pressure is maintained at the higher level. The purpose of this study was to investigate the role of a 4-aminopyridine (4-AP)-sensitive K+ current in causing baroreceptor adaptation. 2. Multi- and single fibre recordings of baroreceptor activity were obtained from the vascularly isolated carotid sinus in anaesthetized dogs during step increases in carotid sinus pressure sustained for periods up to 5 min. 3. Baroreceptor activity increased with the rise in pressure, declined markedly over the first minute, and continued to decline at a slower rate during the remainder of the 5 min period of elevated pressure. Exposure of the isolated carotid sinus to 4-AP (10(-5) and 10(-4) M) attenuated adaptation in a dose-dependent and reversible manner (P < 0.05). 4-AP attenuated the gradual decline in single fibre activity and also prevented derecruitment or dropout of fibres that occurred over time. 4-AP did not alter peak nerve activity measured within the first 2 s of the pressure step. 4. Ouabain (5 x 10(-7)-10(-6) M), an inhibitor of Na+,K(+)-ATPase, increased baroreceptor activity but did not attenuate baroreceptor adaptation. 5. Neither 4-AP nor ouabain altered the distensibility of the carotid sinus as measured with sonomicrometer crystals suggesting that the agents act directly on the nerve endings. 6. The results suggest that activation of a 4-AP-sensitive K+ current contributes significantly to baroreceptor adaptation with little or no contribution of Na+,K(+)-ATPase.

New technique to completely isolate carotid sinus baroreceptor regions in rats.

We developed a method by which we can completely isolate the carotid sinus baroreceptor regions in the rat. The carotid sinus baroreceptor region is exposed and, with the use of extra-fine forceps, a human hair is placed around and tied at the root of the bifurcation. This procedure occludes the external carotid artery and blood flow to the carotid body. An injector is then attached to a catheter in the common carotid artery. We introduce a cylindrical rubber plug into either the palentine or internal carotid artery. A second plug is introduced to occlude the other artery. In six of the eight rats studied, these procedures completely isolated the carotid sinus region. In those cases where a small leak persisted at a carotid sinus pressure of 180 mmHg, we introduced a small particle of the animal's own previously clotted blood. Carotid sinus pressure was either randomly changed between 40 and 180 mmHg in 20-mmHg increments or in sequential 20-mmHg steps from 40 to 180 mmHg while measuring the animal's pulsatile and mean blood pressures. Arterial pressure-carotid sinus pressure relationship indicates that there is a highly sigmoidal relationship between the two pressures. The peak gain of the carotid sinus reflex system had a range from 1.5 to 4.0 and a mean value of 2.07 +/- 0.08. Our data indicate that the rat exhibits a significant carotid sinus baroreceptor reflex response. This technique combined with other techniques will allow for the study of neural control of cardiovascular function in the rat.

Structure of the carotid sinus of the dromedary camel (Camelus dromedarius).

The morphology of the terminal segment of the common carotid artery of the camel was studied. It was found that this artery terminated by giving off a patent internal carotid artery and continuing as the external carotid artery. A presumptive carotid sinus was present at the region of origin of the internal carotid. Similar to that of other mammals, the carotid sinus of the camel was characterized by a comparatively thin vascular wall rich in elastic fibres. With the electron microscope, free (non-encapsulated) afferent endings, efferent endings, encapsulated axons and bundles of unmyelinated and myelinated nerve fibres were found in the wall of the presumptive carotid sinus. The free afferent endings closely resembled baroreceptor endings of the carotid sinus of other mammalian species in their mitochondrial content and the presence of abnormal organelles such as lamellar bodies, vesicular mitochondria and dense bodies. They were regarded as slowly adapting baroreceptors. The presumptive efferent endings were considered adrenergic whereas the encapsulated axons were thought to be the proximal parts of encapsulated sensory nerve endings.

The carotid sinus connections: a WGA-HRP study in the cat.

The neural connections of the carotid sinus were studied by administration of horseradish peroxidase or a lectin conjugate to the adventitia of the carotid sinus of cats. The carotid sinus afferents project exclusively to the nucleus of the tractus solitarius (NTS). Rostral to the obex the projection is mainly ipsilateral with a strong contralateral component caudal to the obex. The carotid sinus projects to several NTS territories that do not receive afferents from the carotid body chemoreceptors; they are: the dorsolateral, the lateral extension of the commissural, the caudal intermediate, the ventrolateral and the gelatinosus subnuclei. In addition the carotid sinus central representation includes territories occupied also by carotid body terminals: dorsal, interstitial, rostral intermediate, medial and the medial part of commissural subnuclei (see previous paper). Labeled cell bodies were found in the petrosal (216 +/- 37, mean +/- S.E.M.) nodose (825 +/- 434) and superior cervical ganglia (3583 +/- 1227) demonstrating the sympathetic efferent innervation of the carotid sinus and a dual sensory innervation via both the glossopharyngeal and vagus nerves.