Ultrasound assessment of the jugular and vertebral veins in healthy individuals: selected physiological aspects and morphological parameters.

AIM: Ultrasound assessment of morphological parameters of the internal jugular veins and vertebral veins in healthy individuals as well as their dependence on the patient's position. MATERIAL: The examinations were conducted in 185 healthy individuals (101 females and 84 males) aged 18-89. Ultrasound examinations were conducted with the use of a linear probe with the frequency of 5-9 MHz in the supine (0°) and sitting position (90°).
RESULTS: In 154 cases (83.2%) on the left side and in 150 cases (81.1%) on the right side, the jugular veins were completely closed in the sitting position. In 31 cases (16.8%) on the left side and in 35 cases (18.9%) on the right side, they were merely narrowed. By contrast with the jugular veins, the cross-sectional area (CSA) of the vertebral veins was greater in the sitting position than in the supine position in a statistically significant way. The CSA values of the jugular veins in the supine position ranged from 0 cm(2) to 4.3 cm(2). There were no statistically significant differences in the CSA between men and women. The cross-sectional area of the right jugular vein in the supine position was greater in a statistically significant way than that of the left jugular vein. In this study population, the ratio of the cross-sectional areas of the jugular veins on both sides amounted to 8.5:1.
CONCLUSIONS: The width of the jugular and vertebral veins significantly varies depending on the patient's position. The range of the CSA values for the jugular veins is broad, which should be taken into account when interpreting imaging findings. The internal jugular veins can show considerable asymmetry.

Introduction

Thanks to studies on the carotid and vertebral arteries, which have been conducted for many years, the morphological parameters, physiology and pathological processes occurring within these vessels are relatively well-explored.

In the pathomechanism of head and neck diseases, disorders within the venous bed are being emphasized more and more frequently. For instance, it is known that cerebral stroke is caused by not only arterial, but also venous mechanisms. Moreover, the influence of venous abnormalities within the head and neck on transient global amnesia has been reported. It is also suggested that they play a role in the pathogenesis of multiple sclerosis(. The evaluation of physiological changes in the venous bed, associated with head positioning, is also an important element of the management of patients with intracranial hypertension.

However, the lack of knowledge about the physiology and width range of the internal jugular veins (IJVs) and vertebral veins (VVs) can lead to an erroneous diagnosis of a pseudotumor or developmental anomaly, particularly when examined by beginner examiners or those with less experience in head and neck imaging.

The aim of this paper is to evaluate morphological parameters of the internal jugular veins and vertebral veins in healthy individuals as well as their dependence on the body position using ultrasound imaging.

Material and methods

The study involved 185 healthy individuals (students, hospital employees and their relatives): 101 females and 84 males aged 18–89 (mean age 46.2 +/− 20.9). Ultrasound examinations were conducted with the use of a linear probe with the frequency of 5–9 MHz in the supine position (0°, Fig. 1) and subsequently, after 5–10 s of rest, in the sitting position (90°, Fig. 2). In both cases, attention was paid to neutral head positioning (i.e. with no flexion, extension or rotation). The jugular veins were assessed in the B-mode at the level of the thyroid cartilage in transverse plane, and the vertebral veins were scanned using the color Doppler between the C2–C6 transverse processes in the longitudinal view using the technique previously described(. The common carotid arteries were used as a reference point in internal jugular vein imaging, and the vertebral arteries in the V2 segment (between the transverse processes) helped to visualize the vertebral veins.

Fig. 1

Supine position. Internal jugular vein (IJV) is found laterally to the common carotid artery (CCA)

Fig. 2

Sitting position. In this position, the internal vein cannot be seen (it collapses)

Cross-sectional areas (CSA, Fig. 1) were measured for the jugular veins. As for the vertebral veins, the width was measured, and subsequently their cross-sectional areas were calculated assuming that they were of a round shape. If several vertebral veins were visible, the widest vessel was chosen for measurement. Jugular and vertebral vein measurements were taken in the apnea phase (following expiration). Particular attention was drawn to the scanning technique of the jugular veins in order to avoid their compression and deformation.

The results were analyzed statistically. Mean, minimum, maximum and standard deviation values were determined for the measurable parameters. When making comparisons between the groups, the Student's t-test was used for the features compatible with the normal distribution and evaluated with the Shapiro–Wilk test. When the features were not compatible with this distribution, the U Mann–Whitney test was performed. When analyzing the measurements between two sides, the paired Student's t-test or the Wilcoxon signed-rank test was performed. The Spearman's correlation coefficients were calculated as well. In the calculations, the significance level of p < 0.05 was considered statistically significant. The calculations were performed using the statistical package SPSS.

Results

The study revealed that the cross-sectional areas of the jugular and vertebral veins significantly vary depending on the patient's position. The CSA of the jugular veins was significantly greater in the supine position compared with the sitting position (Tab. 1). In 154 cases (83.2%) on the left side and in 150 cases (81.1%) on the right side, the jugular veins were completely closed in the sitting position. In 31 cases (16.8%) on the left side and in 35 cases (18.9%) on the right side, they were merely narrowed, but not completely closed, during the examination. By contrast with the jugular veins, the CSA of the vertebral veins was greater in the sitting position than in the supine position in a statistically significant way (Tab. 1).

Tab. 1

Cross-sectional area of the jugular and vertebral veins depending on the patient's position (0° – supine position, 90° – sitting position)

	Cross-sectional area [cm2]
	L IJV 0°	R IJV 0°	L IJV 90°	R IJV 90°	L VV 0°	R VV 0°	L VV 90°
Minimum	0	0.1	0	0	0.005	0.005	0.008
Maximum	2.6	4.3	0.4	0.4	0.08	0.053	0.096
Mean	0.97	1.09	0.02	0.02	0.023	0.021	0.030
Median	0.86	0.96	0	0	0.020	0.020	0.025
SD	0.537	0.721	0.060	0.054	0.015	0.012	0.017

L IJV 0° – left internal jugular vein in the supine position

R IJV 0° – right internal jugular vein in the supine position

L IJV 90° – left internal jugular vein in the sitting position

R IJV 90° – right internal jugular vein in the sitting position

L VV 0° – left vertebral vein in the supine position

R VV 0° – right vertebral vein in the supine position

L VV 90° – left vertebral vein in the sitting position

R VV 90° – right vertebral vein in the sitting position

The CSA range of the jugular veins in the supine position was broad (Tab. 1). There were no statistically significant differences in the CSA between men and women. The crosssectional area of the right jugular vein in the supine position was greater in a statistically significant way than that of the left jugular vein, and the ratio of the cross-sectional areas of the jugular veins on both sides amounted to 8.5:1.

By contrast with the jugular veins, no statistically significant differences were observed between the cross-sectional areas of the left and right vertebral veins.

There were statistically significant correlations between patients’ age and cross-sectional areas of the jugular and vertebral veins. The CSA of the jugular veins was observed to increase with age (on the right: r = 0.384; on the left: r = 0.389, Fig. 3) whereas it decreased in the vertebral veins (right: r = −0.327; left: r = −0.440; Fig. 4).

Fig. 3

Dependence of the cross-sectional area of the left internal jugular vein on patient's age

Fig. 4

Dependence of the cross-sectional area of the left vertebral vein on patient's age

Discussion

Physiologically, the internal jugular veins and vertebral veins are treated as a functional unit forming a venous outflow pathway from the region of the head. This unit is called “the cerebrospinal venous system”(. In the horizontal position, the jugular veins constitute the main blood outflow pathway from the cranium. The most important factor that decides about the width of the jugular lumen in the supine position is central venous pressure (CVP). This is the pressure in the large venous vessels within the right atrium, which ranges from 2 to 6 mm Hg. Its value depends on several factors, such as: body position, gravitational force, hydration, breathing movements (it decreases on inspiration and increases on expiration), cardiac function and the condition of the autonomic nervous system. The positive pressure in large veins within the chest is transferred to the jugular veins, which makes them continuously open in the supine position. The influence of CVP on the size of the jugular veins is confirmed in both mathematical models and clinical observations, e.g. in a Valsalva maneuver, during which an increase in pressure on the airways induces an increase in CVP(. As a result, the jugular veins widen.

The jugular veins collapse in the sitting position. This results from a decrease in CVP caused by the gravitational force, the consequence of which is negative pressure in the jugular veins. The pressure noted in the cephalic fragment of the IJVs, depending on the distance of the vein from the heart (approximately 27 cm), is about −21 mm Hg(. Because the wall of the jugular veins is rather flaccid with no mechanical support, the vessels tend to collapse. However, the lumen of the jugular veins does not close in the sitting position in each case. In 17.8% of the cases, the cross-sectional area decreased considerably during the examination (up to 10 s of assuming the upright position) but never to the value of 0 cm2. This is caused by the presence of low venous flow despite negative transmural pressure. Among the study participants in whom the IJVs remained opened in the upright position, the prevailing group consisted of middle-aged and elderly individuals. The reason for this is probably the age-related adaptation of the autonomic system to changes in the body position. Moreover, the interval between the examinations in two positions could be insufficient to ensure the complete collapsing of the jugular veins. Also, valve incompetence and, in certain cases, an anatomic variant of the venous system within the head and neck could be contributing factors. Manegati, Zaniewski and Valdueza et al. demonstrate that in the case of any obstacles in the patency of one of the venous outflow pathways, an alternative pathway compensates for such obstacles. For instance, when the azygos vein is not patent, the blood outflow from the vertebral veins is blocked and therefore the internal jugular veins always remain open irrespective of the body position(.

The vertebral veins are an alternative venous outflow pathway to the jugular veins. However, in the supine position, blood flow through the vertebral veins is hemodynamically less efficient than through the internal jugular veins. This results from the fact that small tortuous vertebral vessels create greater flow resistance than the wide internal jugular veins(. The principles underlying blood flow are those of fluid mechanics according to which flow resistance is inversely proportional to the vascular radius raised to the power of four. In a wide vessel (as IJV), the flow resistance is lower than in small vessels (as VVs). That is why the jugular veins, and not the vertebral veins, are the preferred outflow pathway in the supine position.

By contrast with the jugular veins, the vertebral veins do not collapse in the sitting position. Their low susceptibility to deformation is determined by the mechanical support of the vascular wall by the dura mater, which forms a specific support frame(. That is why the vertebral vessels do not collapse in the sitting position despite negative transmural pressure(.

The slight increase in the CSA of the vertebral veins in the sitting position is associated with blood flow hemodynamics in the jugular veins: jugular vein collapsing causes redistribution of blood that flows from the head to small but numerous vertebral veins.

By contrast with the vertebral veins, between which no statistically significant differences were observed, the right and left jugular veins can be highly asymmetrical in the supine position (even up to 850%). The right internal jugular vein is usually characterized by a greater cross-sectional area. This probably results from anatomic relations: the right internal jugular vein drains into the relatively short right brachiocephalic vein which, in turn, directly joins with the superior vena cava. The outflow pathway from the left jugular vein to the superior vena cava is longer, which causes higher blood flow resistance.

A broad range of CSA values of the jugular veins and their asymmetry should be considered an anatomic variant during neck examinations. This will help avoid an erroneous diagnosis of a pathology, e.g. a pseudotumor or venous aneurysm. The difference in CSA values between the right and left jugular veins (to the benefit of the right vein) has also found its practical application; the right IJV is more frequently selected for jugular vein cannulation. The studies conducted by Tartière et al. and Sulek et al. have demonstrated that in the R IJV cannulation, the procedure is shorter and causes fewer complications than in the L IJV(.

The age-related increase in the CSA of the jugular veins seems to be explained by the histological structure of the wall. The thickest layer is the tunica adventitia, which mainly consists of collagen fibers. The predominance of collagen fibers in the wall of the IJVs determines the morphology of these vessels to a major degree. The agerelated collagen fiber degeneration considerably affects the flexibility of the jugular vein wall, lowers their resistance to stretching and results in a CSA increase(.

Moreover, the valve system degeneration in the jugular veins seems to be associated with the value of the crosssectional area. The progressing physiological dysfunction of the valve system can render blood flow through the jugular veins more difficult and result in an increase in their cross-sectional area in elderly people.

To conclude, it should be stated that the morphology of the internal jugular veins and, to a lesser degree, the vertebral veins depends on the patient position, and the difference in the cross-sectional area between the jugular veins can highly vary. The knowledge about these facts can be useful both for the correct interpretation of imaging findings within the neck and in jugular vein cannulation.

Conclusions

The width of the jugular and vertebral veins significantly varies depending on the patient's position.

The range of the CSA values for the jugular veins is broad, which should be taken into account when interpreting imaging findings.

The right and left internal jugular veins can show considerable asymmetry.