AJR 2001; 176:745-749
© American Roentgen Ray Society
Sonography of the Cervical Vagus Nerve
Normal Appearance and Abnormal Findings
Francesco Giovagnorio1 and
Carlo Martinoli2
1
Cattedra di Radiologia, Università "La
Sapienza," Viale Regina Elena 324, 00161 Rome, Italy.
2
Cattedra di Radiologia "R," DICMI,
Università di Genova, Largo Rosanna Benzi 8,
16132 Genova, Italy.
Received August 7, 2000;
accepted after revision September 15, 2000.
Address correspondence to F. Giovagnorio.
Abstract
OBJECTIVE. The purpose of this study was to assess the appearance of
the cervical vagus nerve in healthy individuals and to investigate the
potential role of sonography in revealing neck masses that cause vagal
dysfunction.
SUBJECTS AND METHODS. We examined 150 consecutive patients. In 144
patients the presence of thyroid, salivary gland, or lymph node disease was
suspected. In three patients a cervical mass was palpable, and three patients
had symptoms of dysfunction of the inferior laryngeal or vagal nerves. The
pathologic diagnoses of the masses were obtained at biopsy.
RESULTS. In 144 individuals the normal vagus nerve was recognized on
each side of the neck as a thin band that occupied the posterior angle formed
by the common carotid artery and the internal jugular vein. Three patients had
tumors arising from the vagus nerve: one neurofibroma, one neurinoma, and one
chemodectoma. These tumors were located in the neurovascular bundle and
posterior to the vessels; their origin from the vagus nerve was clearly
visible in all patients because of the contiguity of the mass with the nerve
bundle. In the other three patients, sonography revealed an extrinsic mass
that compressed and displaced the vagus nerve out of its longitudinal axis;
two cases were hyperplastic nodules of the thyroid, and in one case the nodule
was a branchial cyst.
CONCLUSION. Sonography can reveal the vagus nerve in healthy
conditions and correctly reveal the vagal origin of some tumors in the
parapharyngeal spaces.
Introduction
High-resolution small-parts transducers with frequencies higher than 10 MHz
and sophisticated focusing in the near field have improved the diagnostic
outcome of most sonographic examinations of superficial organs and structures.
In the neck, for example, high spatial resolution is required to differentiate
among many small anatomic structures in close contact with each other. The
visibility of subtle anatomic details has been reported in many studies, some
of which investigated the sonographic appearance of peripheral nerves such as
the recurrent laryngeal nerve
[1]. The possibility of
revealing the vagus nerve as an anatomic landmark in the neck was proposed in
a recent article [2].
The purpose of this study was to assess the appearance of the vagus nerve
in healthy individuals and to investigate the potential value of sonography in
revealing the causes of vagal dysfunction in masses arising in the neck.
The cervical course of the vagus nerve starts from the foramen jugulare
behind the glossopharyngeal nerve and the sinus petrosus inferior. From behind
the stylohyoid ligament to the thoracic inlet, the nerve descends along the
angle formed posteriorly by the internal and common carotid arteries, which
are located anteromedially, and the internal jugular vein, which is located
anterolaterally. The nerve, artery, and vein form the major neurovascular
bundle of the neck, anatomically delimited by a common connective sheath
(Fig. 1). At the lower neck,
the neurovascular bundle is partially covered anteriorly by the lateral lobes
of the thyroid. At the thoracic inlet, the right vagus nerve is located behind
the confluence of the internal jugular vein with the subclavian vein, whereas
the left vagus nerve lies posterior to the venous brachiocephalic trunk. The
recurrent laryngeal nerves originate at this level and ascend into the neck in
the tracheoesophageal groove, passing posteromedially to the lateral lobes of
the thyroid to penetrate the larynx.
Variations of the cervical course of the vagus nerve are possible but rare.
The anterior location of the nerve, which passes in front of the common
carotid artery, has been described
[3].
Subjects and Methods
We examined 150 consecutive patients (87 females, 63 males; age range,
15-83 years) undergoing sonographic examination of the neck for a variety of
reasons. In 144 patients the presence of thyroid, salivary gland, or lymph
node disease was suspected; in three patients a cervical mass was palpable;
and three patients had symptoms of dysfunction of the inferior laryngeal or
vagal nerves, including dysphonia and dysphagia.
Sonographic studies were performed on two scanners (HDI-3000, Advanced
Technology Laboratories, Bothell, WA; Au5-Idea, EsaOte Biomedica, Genoa,
Italy) equipped with broadband (12-15, 7.5-10, 10-13 MHz) linear array
transducers.
Examinations were performed with the patients supine and the neck
hyperextended. The region of interest (lateral margins of the anterior
cervical region beneath the sternocleidomastoidei muscles) was scanned in the
transverse plane. A thin (<2 mm in cross-sectional diameter) cordlike
structure, centrally hypoechoic, which occupied the angle formed posteriorly
by the common carotid artery and the internal jugular vein, inside the major
neurovascular bundle, was visualized and, according to a previously published
experience [2], identified as
the vagus nerve. The scanning plane was then oriented longitudinally to
elongate and optimally display the nerve. Nerves were imaged along their
transverse and longitudinal axes. Images were obtained by one of the authors
and were later examined by the other. Both authors agreed on all the
interpretations proposed.
In one patient with chemodectoma, CT was performed to better evaluate the
anatomic relationship of the mass to the surrounding organs and the presence
of calcifications.
The pathologic diagnosis of the masses was made at biopsy performed with
fine-needle aspiration under sonographic guidance.
Results
Normal Findings
In the 144 patients who underwent sonography, the vagus nerve was visible
bilaterally and was clearly recognizable throughout its cervical course
(approximately 10-15 cm in craniocaudal direction) (Fig.
2A,2B,2C,2D).
The sonographic appearance of the vagus nerve varied depending on the
equipment used. With 12-15-MHz frequency probes, the nerve exhibited a
striated arrangement of its internal structure, which was made of hypoechoic
parallel fascicles separated by a hyperechoic envelope. On transverse scans,
the nerve assumed a honeycomb appearance with two to four hypoechoic rounded
fascicles surrounded by hyperechoic epineurium. On lower sonographic
frequencies, the image of the fascicles was poorly defined as a result of
decrease in image resolution. However, recognition of the vagus nerve was
still possible at frequencies as low as 7.5 MHz. In addition, difficulty
recognizing the nerve structure was encountered in patients with large, short
necks or with coincident postsurgical scarring in the cervical area. Whatever
the frequency used, the outer boundaries of the nerve appeared undefined
because a similar hyperechoic appearance of the superficial epineurium and the
surrounding connective tissue of cervical spaces.
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Fig. 2A. —37-year-old man with no signs of vagal disease. Axial
sonogram (10 MHz) of left neurovascular bundle shows internal jugular vein
(IJV), common carotid artery (CCA), and vagus nerve (arrow). TR =
trachea.
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Fig. 2C. —37-year-old man with no signs of vagal disease. Axial
sonogram (15 MHz) of right neurovascular bundle shows vagus nerve
(arrow) with honeycomb appearance and two to four hypoechoic rounded
fascicles surrounded by hyperechoic epineurium.
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Fig. 2D. —37-year-old man with no signs of vagal disease. Sagittal
sonogram (15 MHz) clearly shows internal structure made of some hypoechoic
parallel fascicles separated by hyperechoic envelope
(arrowheads).
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An abnormal course was observed in two (0.7%) of 288 nerves examined: the
nerve was in the normal position in the cranial half of its cervical course,
then the nerve crossed the space between the vessels at the level of the
thyroid to run in the anterior angle formed by the common carotid artery and
the internal jugular vein before entering the thoracic inlet (Fig.
3A,3B,3C).
This alteration was not associated with any significant disease.
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Fig. 3A. —28-year-old woman with no signs of vagal disease. Axial
sonogram (7.5 MHz) of left neurovascular bundle at level of superior third of
thyroid shows vagus nerve in its normal position (arrow).
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Fig. 3B. —28-year-old woman with no signs of vagal disease. Axial
sonogram (7.5 MHz) at level of middle third of thyroid shows vagus nerve
crossing space between internal jugular vein and common carotid artery
(arrow).
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Abnormal Conditions
Three patients with occasional symptoms of laryngeal dysfunction (cough,
dysphonia) had tumors arising from the left (two patients) and right (one
patient) vagus nerves: one plexiform neurofibroma (multiple nodules 1-2 cm in
diameter) in a 15-year-old boy with a type I neurofibromatosis (Fig.
4A,4B),
one neurinoma (1.5 cm in diameter) in a 45-year-old man
(Fig. 5), and one chemodectoma
(1.2 cm in diameter) in a 43-year-old man (Fig.
6A,6B,6C).
Two masses (neurinoma and neurofibroma) were hypoechoic and oval, with regular
and well-defined margins; one mass (chemodectoma) was poorly defined on
sonography because of the presence of coarse calcifications that was confirmed
on CT.
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Fig. 4A. —15-year-old boy with type I neurofibromatosis and no signs of
vagal disease. Axial sonogram (10 MHz) of right neurovascular bundle at level
of superior third of thyroid shows multiple hypoechoic nodules
(asterisks and arrows) in neurovascular bundle displacing
internal jugular vein (IJV) externally and common carotid artery (CCA)
medially.
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Fig. 4B. —15-year-old boy with type I neurofibromatosis and no signs of
vagal disease. Longitudinal sonogram (10 MHz) clearly shows vagal origin of
two nodules (asterisks). Normal vagus nerve cranial to tumors is
indicated by arrowheads.
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Fig. 6A. —43-year-old man with cough, dysphonia, and biopsy-proven
chemodectoma. Axial sonogram (10 MHz) of right neurovascular bundle at level
of superior third of thyroid shows poorly defined tumor (T) (arrows)
inside neurovascular bundle that is displacing internal jugular vein (IJV) and
common carotid artery (CCA) anteriorly.
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Fig. 6B. —43-year-old man with cough, dysphonia, and biopsy-proven
chemodectoma. Longitudinal sonogram (10 MHz) clearly shows vagal origin of
tumor (T) (arrows). Normal vagus nerve cranial to tumor is indicated
by arrowheads. IJV = internal jugular vein.
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Fig. 6C. —43-year-old man with cough, dysphonia, and biopsy-proven
chemodectoma. CT scan at lower anatomic plane than A and B shows
calcified tumor (arrow) in anatomic location of vagus nerve, with
evident separation of common carotid artery from internal jugular vein.
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In these three patients, the tumors were located inside the neurovascular
bundle, posterior to the vessels, which were stretched apart by the masses
(the common carotid artery was displaced anteromedially and the internal
jugular vein anterolaterally). The origin from the vagus nerve was clearly
shown in all patients. A presumptive diagnosis of the intrinsic neurogenic
nature of the tumor was made on sonography by showing the direct connection of
the mass with the nerve bundle at its proximal and distal poles, which
required careful scanning. Outside the tumor, the entering and exiting nerve
may be thickened and have loss of fascicular structure, thus producing a
tapering appearance of the oval mass.
In three patients, sonography showed a prominent extrinsic mass that
invaded the anatomic location of the vagus nerve, which was compressed and
displaced externally. In two patients (two women, who were 56 and 65 years
old, with persistent coughs), the masses originated from the posterolateral
aspect of the left lobe of the thyroid, had diameters of 2.5 and 3.5 cm, and
were diagnosed at biopsy as hyperplastic nodules. In a 25-year-old woman with
mild dysphagia, an oval 1.5-cm hypoechoic nodule in the right parapharyngeal
space was diagnosed as a branchial cyst at biopsy
(Fig. 7).
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Fig. 7. —25-year-old woman with mild dysphagia. Longitudinal sonogram
(7.5 MHz) of right vagus nerve shows hypoechoic nodule (C) compressing vagus
nerve (arrowheads). Surgical excision revealed branchial cyst.
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Discussion
The cervical portion of the vagus nerve is cranial to the origin of the
recurrent laryngeal nerve, hence tumors arising from the vagus nerve or
cervical masses that compress or infiltrate the nerve may cause symptoms as a
result of dysfunction of the inferior recurrent laryngeal nerve (cough,
dysphonia) or dysfunction of the vagus nerve itself (arrhythmia, dysphagia,
dyspnea, nausea, hiccups). These symptoms are not specific and are not
commonly attributed to a malfunctioning vagus nerve; therefore, significant
diagnostic delays may occur and patients may undergo unnecessary
examinations.
Visibility of the cervical vagus nerve on sonography has been reported by
Knappertz et al. [2], who
describe a centrally hypoechoic and peripherally hyperechoic structure between
the common carotid artery and the jugular vein and inside the carotid sheath
on transverse B-mode images of the neck. This structure was also identified in
a nonpreserved cadaver and was marked with a hypodermic needle by means of a
transdermal approach. Neck dissection was performed, which showed the vagus
nerve as the target of the needle. In our experience, the sonographic
appearance of the vagus nerve varies depending on the equipment used: with
lower frequencies (7.5-10 MHz) the nerve is visible as a cordlike structure,
centrally hypoechoic, whereas higher frequencies (13-15 MHz) show an internal
structure composed of hypoechoic parallel fascicles separated by a hyperechoic
envelope.
Tumors arising from the vagus nerve are rare and generally benign.
Schwannoma, neurinoma and neurofibroma are histologically similar and may
arise from the vagus nerve or other peripheral nerves (neurofibromas are
generally found in patients affected by von Recklinghausen's disease).
Paraganglioma, also referred to as chemodectoma, is less common, arises from
either the vagus nerve or the carotid body, and is rarely malignant
[4,5,6,7,8].
Paragangliomas derive from stem cells of the neural crest and can be found
in any part of the body in which there are sympathetic ganglia, including
chemoreceptors, adrenal medulla, retroperitoneal ganglia, and the vagus nerve.
A familial tendency has been reported, and in these patients bilateral tumors
are often present [7]. Multiple
tumors arising from different sites are common. When the tumor arises from the
vagus nerve, it presents as a painless neck mass behind the carotid artery
that compresses the internal jugular vein with normal cranial nerve function
[7]. Vocal cord paralysis has
been described as an associated finding in 47% of cases. The literature
contains few reports of imaging of paragangliomas of the vagus nerve
[9,
10]. Sonographically, this
tumor has been described as a solid hypoechoic and heterogeneous lesion
containing small vascular structures. In our patient, the mass presented with
a medium-level echogenicity similar to that of the thyroid, a hypervascular
pattern with low-velocity arterial flows on color Doppler sonography, and
coarse calcifications. Further experience is needed to establish whether this
tumor has differential features on sonography compared with those of other
neurogenic tumors arising from a nerve, such as schwannomas and
neurofibromas.
Intrinsic tumors of the vagus nerve do not have a specific appearance on
sonography because they present as fusiform hypoechoic masses with
well-defined margins; therefore, it is impossible to differentiate masses
arising from the vagus nerve from other common neck masses such as lymph node
enlargements on the basis of sonographic appearance alone. Absence of an
echogenic hilum has been proposed as a criterion to differentiate a lymph node
from a peripheral nerve tumor
[11], but this sign can
generally be found with most other malignant nodes
[12]. The direct visualization
of a contiguity between the nerve and the tumor on longitudinal scan, is
therefore the only pathognomonic sign of the vagal nerve origin of the mass.
When an abnormally large mass displaces the nerve so that the proximal and
distal poles are not clearly visible, sonography can provide important
indirect clues previously seen only on CT
[13,
14], such as increased
distance between the internal jugular vein (displaced anterolaterally) and the
carotid artery (displaced anteromedially) when the tumor arises from the vagus
nerve, as opposed to lateral or medial displacement of the entire
neurovascular bundle when the tumor arises from the thyroid, the carotid body,
the cervical sympathetic chain, or other organs located in the parapharyngeal
space.
The sonographic visualization of the normal and abnormal vagus nerve may be
compromised by increased thickness of the local subcutaneous fat in patients
with thick, short necks and by the presence of scars in patients having
undergone neck surgery. These conditions do not compromise the direct
visualization of the nerve but may increase the difficulty of differentiating
the displacement of the nerve by an extrinsic mass from its encasement by a
mass originating from the nerve. Possible misdiagnosis can be avoided by
recognizing that only tumors arising from the nerve can increase the distance
between the carotid artery and the internal jugular vein, with the possible
exception of masses arising from other anatomic elements in the neurovascular
bundle (fat tissue, connective tissue of the external sheath, muscular or
connective layers of the vessels). In this case, sonographic differentiation
of tumors arising from the vagus nerve from other tumors originating in the
neurovascular bundle may be impossible.
In conclusion, the presented data suggest that sonography can noninvasively
reveal the cervical portion of the vagus nerve and answer most of the
diagnostic questions related to the nerve when a nodule of uncertain origin is
encountered near the neurovascular bundle of the neck. Sonographic findings
can show the origin of the nodule from the vagus nerve. Future applications of
the method could also include sonographic localization of the nerve to improve
the outcome of stimulation that has been proposed for seizure therapy
[15].
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Abstract
Introduction
