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Morphological Features of the Internal Carotid Artery

Posted Sep 30, 2013 Updated Apr 10, 2023
By Jian-Qun Xiong MM , Chen Yu BM , Yu-Wen Shi BM , Ying-Hua Li BM
8 min read

Rationale and Objectives

Previous research has determined that carotid abnormalities (CAs) are partly located >3 cm above the carotid bifurcation. However, identifying CAs occurring in this location using high-frequency linear probes is difficult. The aim of this study was to explore the efficacy of a combination of high-frequency and low-frequency probes in duplex ultrasonography for identifying morphologic features of the internal carotid artery (ICA).

Materials and Methods

A total of 1055 ICAs from 532 patients were analyzed. CAs were classified prospectively according to the criteria of Wain et al, Weibel and Fields, and Metz et al. The diagnostic rates of high-frequency ultrasonography alone and a combination of high-frequency and low-frequency ultrasonography were compared. The distances from the carotid bifurcation to the initial point of the CA and to the mandibular angle were also measured.

Results

High-frequency ultrasonography detected 23.2% of CAs, and the combination detected 32.2% of CAs ( P < .001) in the 1055 ICAs. Of these CAs, 32.4% and 16.8% began >2.5 and >3 cm above the carotid bifurcation, respectively. The distance between the carotid bifurcation and the mandibular angle was <1.5 cm in 100 arteries (9.48%). The diameter of the distal ICA was larger in patients with CAs than in those without CAs (4.33 ± 0.52 vs 4.13 ± 0.49 mm, P < .001).

Conclusions

Combining high-frequency and low-frequency probes is better than high-frequency probes alone to assess morphologic features of the ICA in duplex ultrasonography. Low-frequency convex probes should be added to traditional ultrasonography for the evaluation of morphologic features of the ICA before carotid endarterectomy, carotid artery stenting, and CA angioplasty.

Carotid endarterectomy (CEA) and carotid artery stenting have become effective means of preventing and treating ischemic stroke, and duplex ultrasonography has been used as noninvasive vascular imaging for screening carotid disease and for identifying candidates for CEA. However, because standard carotid duplex studies describe only the degree and general location of stenotic lesions in the past, only during preoperative angiography can carotid surgeons acquire the necessary anatomic information. On the other hand, carotid abnormalities (CAs) may result in submucosal masses in the posterior pharyngeal wall with clinical symptoms, and these patients can be at risk for surgical injury to the oropharynx and laryngopharynx . Although the incidence and classification of CAs have been reported in many studies using high-frequency linear probes, further improvements are required because some limitations have been reported in high-frequency linear probing, such as incomplete ultrasonography of the internal carotid artery (ICA) in subjects with short conformation of the neck or high bifurcation of the common carotid artery, resulting in exclusion of these subjects from the studies . Herein, we describe a method for improving CA diagnosis rate.

Materials and methods

Pilot Study

In a preliminary study, 64 arteries (excluding two occluded arteries and two arteries with stents) in 34 consecutive patients (22 men, 12 women; mean age, 62.27 ± 10.9 years; range, 40–87 years) were included. Hitachi HI VISION Preirus (Hitachi, Tokyo, Japan) and Toshiba SSA 660A (Toshiba, Tokyo, Japan) color Doppler instruments were used. Frequencies were in the range of 5.5 to 7.5 MHz for the linear-array probe (typically used in carotid studies) and 3.0 to 3.5 MHz for the convex-array probe (typically used in gynecologic studies). The depth of scanning was set at 5 cm for the high-frequency probe and 8 cm for the low-frequency probe. All arteries were scanned in the transverse view followed by the sagittal view. All subjects independently underwent duplex ultrasonography by two sonographers.

Duplex studies

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ICA classification

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Figure 1, Angle measurement using criteria from different authors. (a) Angle A was determined using Wain et al’s (4) classification criteria (180° − B); angle B was measured using the criteria of Weibel and Fields (5) . (b) If the angle measurement on ultrasonography was angle B = angle to A = 127°, the internal carotid artery (ICA) was defined as tortuosity or redundancy. CCA, common carotid artery. (Color version of figure is available online).

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Digital subtraction angiography (DSA)

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Consistency test

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General Study

Patients

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Ultrasound examinations

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Statistical Analysis

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Results

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Table 1

Comparison between Angiography and Duplex Scanning (Sonographer A) for the Classification of Abnormalities of the Internal Carotid Artery

Duplex Scanning Angiography Total Normal Tortuosity Kinking and Coiling Normal 40 0 0 40 Tortuosity 0 9 3 12 Kinking and coiling 0 2 10 12 Total 40 11 13 64

κ = 0.86, P < .001.

Table 2

Comparison between Sonographer A and Sonographer B for the Classification of Abnormalities of the Internal Carotid Artery

Sonographer A Sonographer B Total Normal Tortuosity Kinking and Coiling Normal 40 0 0 40 Tortuosity 0 10 2 12 Kinking and coiling 0 2 10 12 Total 40 12 12 64

κ = 0.88, P < .001.

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Figure 2, Morphologic features of the internal carotid artery (ICA). (a) Normal: ICA was linear ( blue ), and no bending in its course was found. (b) Tortuosity: there was an undulation in the course of the ICA ( blue-white ), the angle was 123°, and the diameter of the distal ICA could be measured (distance, 0.51 cm). (c) Mild kinking: there was an undulation in the course of the ICA ( blue-red-blue ), and the angle was 113°. (d) Moderate kinking: a C-shaped elongation ( red-yellow ) in the course of the ICA was shown by power Doppler. (e) Moderate kinking: an S-shaped curve ( blue-white ) was shown in the image, and the minimum angle was 35°. (f) Severe kinking: there was a V-shaped acute angulation ( blue-white ) of the ICA with an angle between the two segments forming a kink that measured <30°. (g) Coiling: an umbilical cordlike configuration ( red-yellow ) was shown in the middle part of the ICA by power Doppler. (h) Coiling (C): a circular configuration ( blue-red ) was found in the distal ICA. A, internal carotid artery; CCA, common carotid artery; ICV, internal carotid vein; LICA, left internal carotid artery; RICA, right internal carotid artery; V, internal carotid vein. (Color version of figure is available online).

Figure 3, Constituent ratios of morphologic features of the internal carotid artery.

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Figure 4, Comparison of visualization of high-frequency and low-frequency ultrasound. (a) Carotid abnormality of the bilateral internal carotid artery (ICA) was not found using the high-frequency linear probe. (b) In the same patient as in (a) , severe kinking (right ICA [RICA], by color Doppler ultrasound) and coiling (left ICA [LICA], by power Doppler) were fully evident using the low-frequency convex probe, despite occurring at 3.2 cm (RICA) and 3.8 cm (LICA) from the origin of the ICA. (c) Because there was a large acoustic shadow in the proximal ICA, the distal ICA could not be visualized using the high-frequency probe. (d) In the same patient as in (c) , N-shaped moderate kinking was displayed using the low-frequency convex probe. CCA, common carotid artery; LCCA, left common carotid artery; LECA, left external carotid artery. (Color version of figure is available online).

Table 3

Distance from the Carotid Bifurcation to the Initial Point of the Carotid Abnormality

Distance From the Bifurcation (cm) Number of Arteries Percentage 0–2.0 137 40.29 2.1–2.5 93 27.35 2.6–3.0 53 15.59 3.1–3.5 29 8.53 3.6–4.0 14 4.12 >4.0 14 4.12 Total 340 100

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Table 4

Comparison between High-frequency and Combined High-frequency and Low-frequency Ultrasonography for the Diagnosis of CAs

Combination High-frequency Ultrasound Total CA No CA CA 245 95 340 No CA 0 715 715 Total 245 810 1055

CA, carotid abnormality.

χ 2 = 95, P < .001.

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Figure 5, Diameter of the internal carotid artery (ICA). The range of variance in diameter of the proximal and distal ICA, with or without carotid abnormalities (CAs), can be described on the basis of a box plot. The thick horizontal line in each box indicates the median, the top and bottom borders of the box mark the 75th and 25th percentiles, and the two ends of the vertical lines represent the maximum and minimum values, respectively. There were significant differences between the diameters of the proximal and distal, with and without CAs of the ICA (both P < .001).

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Discussion

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Conclusions

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Acknowledgment

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Academic Radiology, Volume 20, Issue 10
Journals General Radiology
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