Preoperative ultrasound detection of arteria lusoria and non-recurrent laryngeal nerve anatomical variation: a retrospective study

Abstract

Purpose

Arteria lusoria (AL), a rare vascular variant (prevalence of 0.5–3.2%), is linked to a right non-recurrent laryngeal nerve (RNRLN), thereby increasing nerve injury risk during thyroid and parathyroid surgery. This study evaluates ultrasonography (US) for preoperative AL detection.

Materials and Methods

Retrospective analysis of 1406 hyperparathyroidism patients undergoing 18F-fluorocholine PET/CT with subgroup analysis in 270 patients with “expert US” performed on-site. An experienced senior radiologist assessed the US Y-image (brachiocephalic artery division), with low-dose CT as the standard of truth for AL confirmation.

Results

18F-fluorocholine PET/CT analysis found 22 cases of AL (prevalence: 1.57%). US identified 259 Y-images, excluding AL, confirmed by CT. Five absent Y-images indicated AL, all were confirmed by CT. Six non-assessable Y-images were AL-negative on CT. US performance: sensitivity 100% (95% CI: 0.463–1), specificity 98% (95% CI: 0.95–0.99), negative predictive value (NPV) 100%, accuracy 98%.

Conclusion

US Y-image assessment reliably excludes AL with an NPV of 100%, offering a non-invasive tool to reduce RNRLN injury risk in thyroid and parathyroid surgery.

Zusammenfassung

Ziel

Die Arteria lusoria (AL), eine seltene Gefäßvariante (Prävalenz 0,5–3,2%), ist mit einem nicht rezidivierenden rechten Nervus laryngeus (RNRLN) assoziiert und erhöht somit das Risiko einer Nervenverletzung während einer Schilddrüsen- und Nebenschilddrüsen-Chirurgie. Diese Studie untersucht den Stellenwert der Ultraschalluntersuchung (US) zur präoperativen Detektion der AL.

Material und Methode

Retrospektive Analyse von 1406 Patienten mit Hyperparathyreoidismus, die sich einer 18F-Fluorcholin-PET/CT unterzogen. Subgruppen-Analyse bei 270 Patienten mit vor Ort durchgeführtem „Experten-US“. Ein erfahrener Oberarzt für Radiologie beurteilte das US-Y-Bild (Teilung des Truncus brachiocephalicus), wobei eine Niedrigdosis-CT als Referenzstandard zur Bestätigung der AL diente.

Ergebnisse

Die 18F-Fluorcholin-PET/CT-Analyse identifizierte 22 AL (Prävalenz: 1,57%). Im Ultraschall wurden 259 Y-Bilder ohne Nachweis einer AL gefunden, bestätigt durch CT. Fünf fehlende Y-Bilder wiesen auf eine AL hin, die alle durch CT bestätigt wurden. Sechs nicht beurteilbare Y-Bilder waren in der CT AL-negativ. Die US-Leistung: Sensitivität 100% (95%-KI: 0,463–1), Spezifität 98% (95%-KI: 0,95–0,99), negativer prädiktiver Wert (NPV) 100%, Genauigkeit 98%.

Schlussfolgerung

Die Beurteilung des US-Y-Bildes schließt das Vorliegen einer AL zuverlässig mit einem NPV von 100% aus – und stellt somit ein nicht invasives Verfahren dar, um das Risiko einer RNRLN-Verletzung während einer Schilddrüsen- und Nebenschilddrüsen-Chirurgie zu reduzieren.

Keywords

right non-recurrent laryngeal nerve - cervical ultrasonography - cervical surgery - laryngeal paralysis - arteria lusoria

1. Introduction

Vocal fold paralysis due to recurrent laryngeal nerve (RLN) injury remains the main complication of thyroid and parathyroid surgery [1]. The RLN is a mixed nerve that arises from the vagus nerve. On the right side the vagus nerve becomes the right RLN (RRLN) after looping under the right subclavian artery (RSCA). The RRLN ascends on the right side of the trachea up to the first tracheal ring ([Fig. 1]a), before innervating the vocal cord muscles, allowing phonation. On the right side, the embryological development of the RLN is intertwined with the brachiocephalic artery (BCA), which commonly originates from the aortic arch before splitting into the RSCA and the right common carotid artery (RCCA). The Y-shaped common division of the BCA is described in medical imaging as a Y-image or “Y-sign” [2].

Fig. 1 Anatomy. a) Normal BCA’s division with vagus nerve becoming the RRLN with a vertical ascending trajectory by trachea’s right side. b) AL arising directly from the aortic arch and the RNRLN with a horizontal trajectory. AL: arteria lusoria; BCA: brachiocephalic artery; RCCA: right common carotid artery; RRLN: right recurrent laryngeal nerve; RSCA: right subclavian artery.

AL is a rare anatomical variant (prevalence of 0.5% to 3.2%) [3] [4] [5], resulting from an anomaly during development of the pharyngeal arches [6], leading to an aberrant RSCA, originating directly from the aortic arch. The AL then posteriorly crosses the esophagus before reaching the right axillary region ([Fig. 1]b). Almost all AL cases [7] are associated with a right non-recurrent laryngeal nerve (RNRLN) [5] [8]. The RNRLN originates from the vagus nerve, at a higher position than the normal RRLN, with a horizontal trajectory towards the larynx.

If the surgeon is unaware of an RNRLN, risks of intraoperative nerve damage and subsequent vocal fold paralysis increase (12% vs 1.8%) [9] [10], highlighting the importance of preoperative anatomical assessment [11] [12]. Preoperative AL detection would predict an existing RNRLN, allowing surgeons to adapt their surgical protocol, thereby reducing nerve damage risks and surgery duration [13].

One prospective study explored the use of preoperative US for the specific detection of AL to predict RNRLN and found an accuracy of 100% compared to CT scan [4]. Three retrospective studies explored the preoperative US prediction of RNRLN with surgery as the standard of truth and found an accuracy between 98% and 100% and a reduction in operating time [13] [14] [15].

This study focuses on the exclusion of AL using the simple identification of the Y-image on day-to-day routine systematic cervical ultrasonography to avoid any unnecessary CT scans and to help reduce surgical complications.

2. Materials and methods

2.1 Study design and PET/CT procedure

We retrospectively analyzed the preoperative imaging workup of 1406 patients with primary or secondary renal hyperparathyroidism who underwent an ¹⁸F-fluorocholine (FCH) PET/CT scan performed with the same PET/CT machine according to the same protocol at our center between May 2016 and 2022 ([Fig. 2]). 270 of them had their cervical US examination performed by a single radiologist who was an expert in otorhinolaryngology imaging.

Fig. 2 Flow chart.

Retrospective studies derived from this database without any further interaction with patients were approved by the ethics committee of our institution.

All patients benefited from an FCH-PET/CT scan using the same time of flight PET/CT machine in 3D acquisition mode (Biograph mCT 20/4R). Image acquisition was started on average 20 min after injection of 3 MBq/kg of body mass of FCH. The low-dose CT scan component with native contrast of the PET/CT examination had the following technical characteristics: 20 slices, 140kVp acquisition, use of the CARE Dose4D algorithm for adaptation of the current.

2.2 US procedure

All 270 “expert” cervical US examinations were performed in order to identify parathyroid glands (PT) by systematically assessing the thyroid gland. The presence or absence of the Y-image (defined as the division of the right subclavian and right common carotid arteries from the brachiocephalic artery) was mentioned in standardized on-site reports. Different sonograms from various manufacturers were used: Aloka (ProSound α10), Toshiba (APPLIO 500), GE (Voluson E8, E10, GE Logiq E10,) Canon (Aplio i800, Aplio MX).

A large multi-frequency superficial linear array (8–18 MHz) was used for superficial analysis of the thyroid and retrothyroid areas. A systematic complementary analysis was performed using either a micro-convex (6–11 MHz) or an endo-cavitary probe (7–11 MHz). The probe was positioned transversally on the cervical notch. After identification of the RCCA, high- or low-frequency arrays were angled caudally to search for the division of the BCA, i.e. the Y-image.

A standardized US report was written for each patient mentioning the presence or absence of the Y-image, based on the following criteria:

• Y-image present: identification of the RSCA and RCCA division from the BCA ([Fig. 3]a).

• Y-image absent: no identification of the RSCA and RCCA division from the BCA, suggesting AL ([Fig. 3]b).

Fig. 3 US exploration of BCA’s division. a) Presence of Y-image reflecting BCA’s modal division. The probe is positioned transversally on the cervical notch. After identification of the RCCA, high or low frequency is angled caudally, searching for the division of the BCA. b) Absence of Y-image with an RCCA arising directly from the aortic arch, and an RSCA with postero-anterior blood flow.

The surgeon was aware of the US report, so particular attention was given in cases of an absent Y-image.

2.3 CT scan as standard of truth

To determine US performance with respect to AL detection, another radiologist retrospectively analyzed all low-dose CT scan components of PET/CT examinations, without knowledge of the US results.

The standard of truth for AL was its direct visualization on the CT scan with native contrast ([Fig. 4]).

Fig. 4 CT scan exploration of BCA’s division. a) Coronal CT reconstruction with normal BCA’s division (CT Y-image). b) AL = RSCA, originating directly from the aortic arch, posteriorly crossing the esophagus and trachea.

PET/CT reports did not mention the presence of AL, so the surgeon was not alerted in relevant cases.

2.4 Statistical analysis

Continuous variables were reported as medians and interquartile range (IQR), and categorical variables were expressed as numbers (percentages).

Performance analysis for US prediction of AL (sensitivity, specificity, positive predictive value [PPV] and negative predictive value [NPV]) with 95% confidence interval was performed.

3. Results

The analysis of the CT scans of the FCH PET/CT examinations in the whole series of 1406 patients revealed a total of 22 cases of AL (17 without the expert US mentioning the AL), yielding a 1.57% (95% CI: 0.91; 2.2) prevalence for AL.

The subgroup with the “expert” US cohort included 270 patients (74% female with a median age of 60 [IQR: 48–70]). There was a female-to-male ratio of 2:1, mostly due to a recognized gender bias in the case of primary hyperparathyroidism.

Retrospective analysis of hybrid FCH-PET/CT low-dose CT scan components confirmed 5 cases of AL out of 270 CT scans, yielding a 1.85% (95% CI: 0.24; 3.46) prevalence for AL in this subgroup ([Table 1]). The prevalence of AL was similar in this subgroup and in the rest of the cohort (chi-square-test p>0.6).

Table 1 Principal diagnostic test’s parameters.

	Absent US Y-image	US Y-image
TP: true-positive; FP: false-positive; TN: true-negative; FN: false-negative; PPV: positive predictive value; NPV: negative predictive value; CI: confidence interval; US: ultrasonography; BCA: brachiocephalic artery
Arteria lusoria on CT	5 TPs	0 FNs	Sensitivity (95% CI): 1 (0.463; 1)
Normal BCA division on CT	6 FPs	259 TNs	Specificity (95% CI): 0.98 (0.95; 0.99)
	PPV (95% CI): 0.45 (0.18; 0.75)	NPV (95% CI): 1 (0.98; 1)	Prevalence: 1.85%

A US Y-image was not seen in 11 patients in total, with 5 patients having AL confirmed by CT scan (true positives) ([Table 1]).

For the 6 remaining patients without a US Y-image who had no AL on CT (false-positives): 2 were overweight, 2 had a voluminous thyroid goiter, 1 had both, and the last one presented with a lower than usual division of the BCA in the mediastinum, behind the sternum. The trajectory of the RSCA was most likely not able to be assessed on US.

No patients with a Y-image on US had an AL on CT (false-negatives).

This resulted in the following diagnostic performance for the US prediction of AL: a sensitivity of 1 (95% CI: 0.463; 1), a specificity of 0.98 (95% CI: 0.95; 0.99), a PPV of 0.45 (95% CI: 0.18; 0.75), and an NPV of 1 (95% CI: 0.98; 1) ([Table 1]).

Overall, the accuracy was 98%.

All 5 patients with AL detected on “expert” US underwent surgery. After review of their postoperative reports, none of the 5 patients suffered from intraoperative nerve damage or subsequent vocal fold paralysis:

• Three of them had a right abnormal PT resected (1 adenoma, 2 hyperplastic PTs) and presented higher nerve damage risks. RRLN was surgically unidentified (surgeons were aware of the very high suspicion of RNRLN) and none of the postoperative reports confirmed the existence of RNRLN through direct visualization.

• The remaining 2 cases of AL underwent surgical intervention for left PTs and were not at risk of RNRLN damage.

Of the 17 patients without expert US mentioning AL, 9 were treated surgically (right-side exploration in 8 cases), without any intraoperative nerve damage or subsequent vocal fold paralysis (RRLN was not mentioned in 5 cases and explicitly not found in 3 cases).

4. Discussion

Our retrospective cohort presented a female-to-male ratio of 2:1 – due to a known female predominance in primary hyperparathyroidism.

Five of the 270 patients in the expert US subgroup had an AL, yielding a prevalence of AL similar to that of the whole cohort of 1406 patients, i.e., 1.57% (95% CI: 0.91; 2.2).

All AL cases identified on CT in this subgroup were detected on US based on the absence of the Y-image, giving a sensitivity of 1 (95% CI: 0.463; 1). The corresponding PPV for an AL was 0.45 (95% CI: 0.18; 0.75). In the presence of a Y-image, US excluded the possibility of an AL with an NPV of 1 (95% CI: 0.98; 1).

None of the 5 patients with AL experienced nerve damage following surgery. The local surgeons were aware of the very high suspicion of AL after a US examination was unable to find a Y-image.

Our 1.57% prevalence for AL falls within the range of previous studies (0.5% to 3.2%) [3] [4] [5] [16] [17].

Previous RNRLN surgical incidence findings ranging between 0.3% and 0.8% [10] [14] are in contrast with higher AL prevalences of up to 3.16% observed in other studies [3]. RNRLNs are probably underestimated by surgeons unaware of AL: Some surgically unfound RRLNs are most likely RNRLNs missed by surgeons, due to their aberrant trajectory. In cases of failure to surgically identify the RRLN in its expected location, or when doing a PT surgery with PT glands so superficial that RRLN/RNRLN dissection is not required, surgeons should consider an existing RNRLN, sometimes found in different dissection planes. Two different RNRLN positions have been described [14] [18] [19]:

• One where the nerve arises from the cervical vagus and runs together with the superior thyroid pedicle at the upper pole of the thyroid gland.

• Another where the nerve arises at a lower level, sometimes by the thyroid isthmus [20] and runs transversely under the trunk or between the branches of the inferior thyroid artery [14] [17].

The wide 95% CI for sensitivity (0.463; 1) reflects the low number of cases of AL in the “expert US” subgroup of our cohort due to its low prevalence.

Our Y-image US detection excluded the possibility of an AL with an NPV of 1 (95% CI: 0.98; 1), which is concordant with the literature [4] [8]. Our 6 false-positives, accounting for a low PPV of 0.45 (95% CI: 0.18; 0.75), were due to patients being overweight or obese, to voluminous thyroid goiters, or to a low localized division of the BCA behind the sternum, suggesting a need for complementary imaging in such cases. The literature is very divergent on this subject, with a PPV ranging from 4% [21] to 46% [15] and even 100% [4]. The probes that were used and population morphotype variations are a possible explanation to this extreme range.

Another cause for false-positives has been described in cases with an overly tortuous BCA [14]. A possible cause of false-negatives, which was not observed in our study but reported in anatomical descriptions [22], corresponds to the right vertebral artery originating from the RCCA (false Y-image), observed in cases of AL. It has a smaller diameter than the RSCA and a higher origin, by the thyroid gland, with a vertical trajectory towards transverse processes of the vertebrae. Similarly, 30% of cases of AL have been associated with a common trunk for left and right common carotids [7] [22] originating from the aortic arch, easily distinguishable from the Y-image by following the cervical trajectories of both carotids. Other extremely rare and unusual vascular variants without a right Y-image include [6]:

• Situs-inversus, where the RCCA and RSCA have separate aortic origins, and patients have a left BCA with a Y-shaped division.

• Right aortic arches where all supra-aortic arteries have separate distinct origins [23].

In our 5 AL postoperative reports, no RNRLN was surgically confirmed, even though the surgeon was aware of the US results. No vocal fold paralysis was reported. All of our patients benefited from a minimally invasive inferior parathyroidectomy. In cases of upper positioned RNRLNs (first type described above), the RNRLN might stay out of the surgeon’s trajectory. Surgeons would have to dissect the vagus nerve and identify the RNRLN from its origin to confirm its existence.

In the study by Iacobone in 2015 [15], patients without a preoperative US examination had a significantly higher rate of surgically unidentified RRLN/RNRLN of 2.67% compared to 1.14% when a preoperative US examination was performed. Nonetheless, they had a higher prevalence of RNRLN of 1.94% for patients with a preoperative US examination compared to the prevalence of 0.67% in the control group without a preoperative US examination. The retrospective analysis of 163 preoperative CT scans conducted by Hermans et al. [3] showed an AL prevalence of 3.16% (5 cases), although AL was never mentioned in the initial reports. Only one RNRLN was surgically confirmed and one of these patients suffered from immediate and permanent unilateral vocal fold paralysis.

Preoperative imaging assessment is different before PT vs. thyroid surgery:

• Our patients suffering from HPT benefited from a recommended combination of US and a functional imaging modality [24], allowing comparison between US and CT scans for detecting AL. None of the on-site reports mentioned the existence of AL.

• Before a right thyroid lobectomy, patients usually do not benefit from a functional imaging modality combined with a CT scan. Since an RNRLN is more susceptible to damage, efforts should focus on the preoperative identification of AL [7]. US is the main preoperative imaging modality for assessing thyroid pathologies. It is also the cheapest and doesn’t require radiation exposure.

US is a simple, non-invasive, and effective method to easily detect the common Y-shaped division of the BCA. A systematic preoperative neck and chest CT scan [13] before thyroid surgeries [17] or thyroid cancer surgeries [25] can accurately identify AL but entails high healthcare costs and radiation exposure in order to identify a rare anatomical variant. An existing AL is rarely described in CT scan reports [3] [17] [25] and is considered inconsequential since its association with RNRLN is poorly known [26]. Considering our results, CT scan or MRI examination should only be used in specifically difficult US cases.

A previous review [11] listed 4 factors to avoid iatrogenic nerve injury, the first one being knowledge of potential anatomical variations, the other 3 being visual identification of at-risk nerves, intraoperative nerve monitoring, and the surgeon’s expertise. An RNRLN indeed increases intraoperative nerve damage risks [5] and subsequent vocal fold paralysis (12% vs. 1.8%) [10]. AL and its association with an RNRLN are poorly known [26] and should be taught to surgical residents [12].

Visual RNRLN identification during surgery remains the reference standard for confirmation [27]. Surgical recommendations encourage systematic dissection of the RLN during thyroid and parathyroid surgeries [5]. Direct visualization of the RRLN/RNRLN is key to its preservation and has significantly reduced the global rate of RRLN palsy [28]. Failing to do so constitutes a major risk [27].

Following standardized specific guidelines [9], intraoperative neurophysiological monitoring (IONM) is recommended [16] [29], although not fully effective [12], allowing a functional assessment of the RLN. It has been associated with a reduced risk of laryngeal paralysis with an RNRLN incidence of 2.7% to 6% [29]. Surgical direct visualization and IONM complement each other [5] [7] [8]. In cases where the nerve is not directly visualized and is not detected by IONM, being aware of the presence of an AL and its strong association with RNRLN is even more crucial [12] [15] and is the surgeon’s “best defense” [5]. Some studies have leaned towards combining preoperative CT scan AL detection with IONM [16] [17] [25]. Our study establishes US as an accessible and effective method for complementary AL detection before surgery.

Detecting AL via imaging is easily done but is rarely mentioned by healthcare professionals [3]. AL and the RNRLN are distinct but strongly associated entities [16] [17]. Only one isolated case of AL with a normal RRLN has ever been described [30]. Conversely, the presence of a Y-image does not exclude an RNRLN. Rare cases of RNRLNs can exist without AL [5] [7] [8]. Our study emphasizes how Y-image US detection suffices to exclude AL [14]. It is the first study to use the CT scan component of a PET/CT examination as the standard of truth for AL diagnosis. Previous studies [4] [14] [15] considered the absence of the Y-image on US to be positive for RNRLN when it should only suggest an existing AL [7]. Surgical false-positives for RNRLNs are possible [15], corresponding to RRLN and cervical sympathetic trunk anastomoses. A left non-recurrent laryngeal nerve is an extremely rare variant [7] associated with conditions like a right aortic arch, dextrocardia, or situs inversus [5] [23].

Our study had several limitations. Firstly, it is a retrospective monocentric cohort. Our recruitment bias was due to an expected higher primary HPT prevalence in women, whereas renal HPT prevalence was the same for women and men. Secondly, all included patients underwent their low-dose CT scan on the same PET/CT machine, whereas the ultrasound examinations were performed by the same radiologist using various ultrasound equipment. This choice of a homogeneous dataset does not reflect day-to-day practice and does not account for inter-individual variations linked to ultrasound operators. We deliberately chose to limit our cohort to patients with US performed by the same expert radiologist who prospectively reported the presence or absence of the Y-image. Nevertheless, the assessment of the BCA division is simple and easy to check, even for juniors in our department. Our standardized US reports did not specify which probe was used (linear superficial or micro-convex/endo-cavitary probe) for the Y-image assessment. Huang et al. [14] reported a higher number of absent Y-images with a 10 MHz superficial probe (with 2 false-positives) compared to a 3.5 MHz probe. Thirdly, we also did not specify whether the direct origin of the RCCA from the aortic arch could be assessed. Combined with an RSCA postero-anterior trajectory (added value of US Doppler mode to characterize the artery flow), visualization of the direct origin of the RCCA from the aortic arch accounted for a PPV of 100%, and an overall accuracy of 98.9% in the 2015 study by Iacobone et al. [15].

5. Conclusion

The detection of arteria lusoria (AL), which is strongly associated with a right non-recurrent laryngeal nerve (RNRLN), aims to reduce intraoperative nerve damage risks and subsequent vocal cord paralysis. Patients scheduled for thyroid/parathyroid surgery should undergo a systematic ultrasound examination of the neck and upper mediastinum to assess the presence or absence of the Y-image, reliably excluding AL with an NPV of 100%. Only when the Y-image is absent should low-dose CT be considered to confirm the supra-aortic anatomy and resolve false-positives.

Contributorsʼ Statement

Jean-baptiste Safa: Data curation, Writing – original draft. Marc Tassart: Methodology, Supervision, Validation, Writing – review & editing. Jean-Noel Talbot: Writing – review & editing. Pierre-Yves Marcy: Writing – review & editing. Sophie Périé: Writing – review & editing. Isabelle Thomassin-Naggara: Writing – review & editing. Alexandre Faure: Data curation, Formal analysis, Methodology, Supervision, Visualization, Writing – review & editing.

Conflict of Interest

The authors declare that they have no conflict of interest.

Acknowledgement

This publication was performed on behalf of the AFTHY (Association Française de Thyroïdologie)

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Publication History

Received: 28 June 2025

Accepted after revision: 24 October 2025

Accepted Manuscript online:
24 October 2025

Article published online:
16 January 2026