Parapharyngeal Space Schwannomas Preoperative Imaging Determination of the Nerve of Origin

ORIGINAL ARTICLE Parapharyngeal Space Schwannomas Preoperative Imaging Determination of the Nerve of Origin

David M. Saito, MD; Christine M. Glastonbury, MD; Ivan H. El-Sayed, MD; David W. Eisele, MD

Objectives: To determine if preoperative radiographic Main Outcome Measure: Identification of the nerves cross-sectional images can predict the nerve of origin of of origin using the displacement of vessels as a marker. a parapharyngeal schwannoma and, specifically, whether it originates from the vagus nerve or the cervical sym- Results: At the time of operation, it was determined that pathetic chain. 5 patients (42%) had schwannomas from the cervical sympathetic chain and 7 patients (58%) had schwannomas Design: A retrospective review. of the cervical vagus nerve. By imaging, the nerve of origin was successfully determined in 4 of 5 cases of sym- Setting: Academic medical center. pathetic chain schwannoma (80%) and in 7 of 7 cases of vagal nerve schwannoma (100%). Schwannomas of the Patients: The study population comprised 12 patients cervical sympathetic chain were found to displace both who underwent surgical resection of schwannomas of the the carotid and jugular vessels without separating them. Vagal nerve schwannomas were found to separate the ca- parapharyngeal space. The nerve of origin was identi- rotid arteries from the internal jugular vein. A vagal nerve fied based on operative findings and postoperative physi- schwannoma may also displace the sheath vessels pos- cal examinations. Of the 12 patients, 11 underwent pre- teriorly, without splaying them. operative magnetic resonance imaging and 1 underwent preoperative contrast-enhanced computed tomogra- Conclusions: Carotid and jugular vessel displacement, phy. A CAQ (Certificate of Added Qualification)– as determined by cross-sectional imaging, can predict certified neuroradiologist reviewed the imaging studies, the likely nerve of origin of a parapharyngeal space blinded to the surgically determined nerve of origin. For schwannoma. This determination allows for effective pre- each case, it was predicted whether the tumor arose from operative counseling regarding the expected sequelae of the vagus nerve or sympathetic chain based on the loca- surgical resection. tion of the schwannoma with reference to the carotid sheath vessels. Arch Otolaryngol Head Neck Surg. 2007;133(7):662-667

CHWANNOMAS ARE UNCOM- operative diagnosis of the nerve of origin mon neurogenic tumors that would allow directed preoperative coun- are typically benign, slow seling as to the risks of surgery and there- growing, and asymptomatic. fore permit the patient to make an in- Up to 45% of all schwanno- formed decision on whether to undergo mas originate in the head and neck re- surgery or adopt a course of observation. S1,2 gion. They are reported to occur in the face, scalp, intracranial cavity, orbit, na- CME course available at sal and oral cavities, parapharyngeal space, middle ear, mastoid, larynx, and medial www.archoto.com and lateral regions of the neck. In the parapharyngeal space, schwannomas most With a series of 9 patients in 1996, commonly arise from the vagus nerve and Furukawa et al3 reported that preopera- Author Affiliations: cervical sympathetic chain. tive imaging studies revealed differences Departments of in vessel displacement patterns caused by Otolaryngology–Head & Neck The accepted treatment of schwanno- Surgery (Drs Saito, El-Sayed, mas is surgical resection. However, sur- vagal and sympathetic chain schwanno- and Eisele) and Radiology gery is not always recommended because mas. The vagal nerve schwannomas al- (Dr Glastonbury), University of the indolent nature of the tumor and the ways resulted in a separation between the of California, San Francisco. risk of postoperative neural deficits. A pre- internal carotid artery (ICA) or common

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T1 T1 + Gd

Figure 1. T1-weighted (A) and T1-weighted plus gadolinium (Gd) (B) magnetic resonance images of vagus nerve schwannoma below the skull base splaying the internal jugular vein (black arrow) and internal carotid artery (white arrow) (case 8).

carotid artery (CCA) and the internal jugular vein (IJV). RESULTS In contrast, sympathetic chain schwannomas did not pro- duce an observable separation. With our series of 12 patients who have received surgical treatment for schwanno- Our series consists of 12 patients with parapharyngeal space mas of the parapharyngeal space, we tested the efficacy schwannomas. The schwannoma arose from the cervical of this observation and investigated other imaging char- sympathetic chain in 5 patients, and the vagus was the nerve acteristics that may refine our ability to preoperatively of origin in 7 patients. The imaging findings, the neurora- diagnose the nerve of origin. diologist’s predicted nerve of origin, and the operatively determined nerve of origin are listed in the Table. Of the 5 METHODS cases of sympathetic chain schwannomas, 4 (80%) were correctly predicted. Of the 7 cases of vagal nerve schwannomas, the neuroradiologist correctly identified 6 (86%). Between 1997 and 2005, at the University of California, San We encountered 2 cases that necessitated refinement of Francisco, 14 patients with schwannomas of the parapharyn- 3 geal space underwent surgical excision. All resected tumors were the criteria of Furukawa et al. In cases 2 and 9, the ICA and confirmed pathologically as schwannomas. In 11 of 14 cases, CCA were not significantly splayed apart from the IJV but the nerve of origin was determined by direct visualization dur- were displaced posteriorly. By the criteria of Furukawa et ing the operation. In 2 cases, the nerve of origin could not be al,3 this predicts the nerve of origin to be the sympathetic identified during surgery, and the patients’ postoperative re- chain. The neuroradiologist’s concern was that the cervical covery revealed no neurologic deficits. These 2 cases were ex- sympathetic chain runs posterior to the carotid sheath in the cluded from our study group. In one other case, the nerve could parapharyngeal space and should not be expected to displace not be determined in surgery, but the patient developed a sig- the carotid sheath vessels posteriorly. The schwannoma in nificant Horner syndrome postoperatively. Therefore, we de- case 2 was an exceptionally large tumor (4ϫ4ϫ5 cm), and termined that this schwannoma was of sympathetic chain origin, and the patient was included in the study. we proposed that it could still arise from the sympathetic Eleven patients underwent preoperative magnetic reso- chain and distort the surrounding anatomy enough to dis- nance imaging (MRI), and 1 patient underwent contrast- place the vessels together posteriorly and slightly laterally enhanced computed tomography (CT). The imaging studies into the posterior cervical space (Figure 3). We therefore were retrospectively reviewed by a CAQ (Certificate of Added agreed with the criteria of Furukawa et al3 and diagnosed Qualification)–certified neuroradiologist (C.M.G.), who was thisschwannomaasasympatheticchaintumor,whichproved blinded to the operative findings but informed that all pa- tobethecorrectdetermination.Incontrast,case9wasamore tients were diagnosed as having parapharyngeal space schwanno- modestly sized tumor (3ϫ3ϫ4 cm) that would not be ex- mas of either the vagus nerve or the sympathetic chain. The pected to significantly distort the surrounding tissue neuroradiologist was also provided with the article by Furukawa (Figure 4). Also, although the ICA and IJV are not splayed et al3 and asked to consider the proposed criteria in making the radiographic predictions. The article by Furukawa et al3 pro- apart by this tumor, there is still demonstrable separation poses that vagal nerve schwannomas will splay the CCA and of the vessels on imaging. Thus, because of these additional ICA away from the IJV, whereas sympathetic chain schwanno- considerations, it was proposed that this was a vagus nerve mas will not result in separation of the vein and arteries schwannoma with minimal vessel separation. This corre- (Figure 1 and Figure 2). sponded with operative identification of the nerve. As a re-

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T1 T2

Figure 2. T1-weighted (A) and T2-weighted (B) magnetic resonance images of sympathetic chain schwannoma displacing the internal jugular vein (black arrow) and internal carotid artery (white arrow) together in a lateral direction (case 3).

Table. Imaging Findings With Estimated Nerves of Origin vs Actual Nerves of Origin

Probable Nerve Origin Patient No./ Imaging Probable Nerve Origin as per Saito et al Sex/Age, y Type Imaging Findings as per Furukawa et al3 (Present Study) Diagnosis 1/F/34 MRI 5ϫ2ϫ2-cm Tumor medial to the IJV and ICA, Sympathetic chain Sympathetic chain Sympathetic chain posterior to the CCA 2/F/17 MRI 4ϫ4ϫ5-cm Tumor displaces the CCA and ICA Sympathetic chain Sympathetic chain Sympathetic chain and the IJV posteriorly 3/F/45 MRI 3ϫ3ϫ4-cm Tumor displaces the CCA and ICA Sympathetic chain Sympathetic chain Sympathetic chain and the IJV laterally 4/M/17 MRI 3ϫ3ϫ6-cm Tumor displaces the ICA and IJV Sympathetic chain Sympathetic chain Sympathetic chain laterally 5/F/59 MRI 2ϫ3ϫ2-cm Tumor separates the ICA and IJV Vagus nerve Vagus nerve Sympathetic chain 6/M/44 MRI 5ϫ2ϫ3-cm Tumor separates the CCA and IJV Vagus nerve Vagus nerve Vagus nerve 7/F/25 MRI 3ϫ3ϫ4-cm Tumor separates the ICA and IJV Vagus nerve Vagus nerve Vagus nerve 8/F/51 MRI 3ϫ3ϫ3-cm Tumor separates the ICA and IJV Vagus nerve Vagus nerve Vagus nerve 9/F/33 MRI 3ϫ3ϫ4-cm Tumor displaces the ICA and IJV Sympathetic chain Vagus nerve Vagus nerve posteriorly 10/F/35 MRI 4ϫ4ϫ6-cm Tumor separates the ICA and IJV Vagus nerve Vagus nerve Vagus nerve 11/F/17 MRI 3ϫ2ϫ2-cm Tumor separates the ICA and IJV, Vagus nerve Vagus nerve Vagus nerve enters skull base 12/M/35 CT 3ϫ2ϫ2-cm Tumor separates the ICA and IJV Vagus nerve Vagus nerve Vagus nerve

Abbreviations: CCA, common carotid artery; CT, computed tomography; ICA, internal carotid artery; IJV, internal jugular vein; MRI, magnetic resonance imaging.

sult, our approach correctly identified 100% (7/7) of the va- ential diagnosis for a mass found in the parapharyngeal gal nerve schwannomas, improving on the accuracy rate of space is wide and can include tumors of the deep lobe of 86% (6/7) in the article by Furukawa et al.3 In the 1 misdi- the parotid gland, tumors of minor salivary gland ori- agnosed case (case 5), the intraoperative findings definitely gin, metastatic cervical nodes, paragangliomas, bran- implicated the sympathetic chain as giving rise to the chial cysts, lymphomas, neurofibromas, and aneurysms schwannoma, but the imaging studies showed splaying of of the ICA.1,2 Most tumors in the parapharyngeal space the IJV and ICA, which predicted vagal nerve origin. are benign (70%-80%). In a series of 51 patients with parapharyngeal space tumors, schwannomas made up 18% COMMENT of the series, with 6 (12%) arising from the vagus nerve and 3 (6%) from the sympathetic trunk.5 The parapharyngeal space surrounds the pharynx and har- Schwannomas of the parapharyngeal space are usu- bors 0.5% of all head and neck neoplasms.4,5 The differ- ally reported to occur in patients between the ages of 30

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T1 + Gd T2

Figure 3. T1-weighted plus gadolinium (Gd) (A) and T2-weighted (B) magnetic resonance images of a large sympathetic chain schwannoma displacing the common carotid artery (white arrow) and the internal jugular vein (IJV) (black arrow) together in a posterior and slightly lateral direction (case 2). Despite originating from a structure posterior to the carotid sheath, an especially large lesion such as this one can distort the surrounding fascial planes and push the vessels in an unpredictable posterior direction. Note that the vessels remain immediately adjacent to one another.

A B

T2 T1 + Gd

Figure 4. T2-weighted (A) and T1-weighted plus gadolinium (Gd) (B) magnetic resonance images of a vagus nerve schwannoma that is displacing the common carotid artery (white arrow) and internal jugular vein (black arrow) posteriorly without splaying them apart (case 9). With average-sized lesions, direct posterior displacement of vessels should suggest a vagus nerve origin given its anterior position in the carotid sheath. This diagnosis is further supported by the small separation observed between the vessels.

and 70 years.2 Most of these uncommon tumors affect choice.2,7 Their slow growth, low recurrence rate, and the cervical vagus nerve and the cervical sympathetic noninvasive nature, however, often allow for an observa- chain.1 While the male-female ratio for cervical sympa- tional approach. Prior to 1931, most parapharyngeal thetic chain schwannomas has been reported as either schwannomas were resected by the transoral route, with equal or at a 3:1 ratio,1,6 there does not seem to be a sex- complications such as incomplete removal, serious hem- related predisposition for vagal nerve schwannomas.2,7 orrhage, infection, and cranial nerve damage.2 The trans- Although schwannomas are typically benign, they cervical surgical approach to the parapharyngeal space may affect adjacent tissues by expansion with pressure is the current preferred operation. If the schwannoma effect. The neoplasms are relatively radioresistant, so is completely removed, recurrence rates are extremely complete surgical resection remains the treatment of low.1

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©2007 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 10/04/2021 Because schwannomas arise outside the involved fas- ICA, CCA, IJV, and vagus nerve. The cervical sympa- cicle, they tend to compress the nerve fascicles to the pe- thetic chain runs posterior and slightly medial to the ca- riphery as they enlarge and can usually be dissected free rotid sheath. Therefore, as schwannomas from this struc- of all structures except the parent fascicle.6,7 Sometimes, ture grow and expand, they will tend to displace its the involved nerve does not course through the tumor but contents anteriorly and laterally.6 Although there is col- can pass over in the tumor capsule.2 The literature re- lective displacement of these vessels, there is not any sepa- ports rare cases of schwannoma resection with preserva- ration between the IJV and the ICA or CCA. The vagus tion of postoperative neurologic dysfunction.2 In most cases, nerve, in contrast, runs within the carotid sheath be- however, patients should be prepared for dysfunction of tween the ICA and the IJV on the cranial side of the bi- the involved nerve after schwannoma resection. furcation and between the CCA and IJV on the caudal It is difficult to determine the nerve giving rise to a para- side. As a schwannoma enlarges from the vagus nerve, it pharyngeal space schwannoma on the basis of the pa- tends to displace the IJV laterally and the ICA and CCA tient’s symptoms. These tumors typically present as an medially. Thus, imaging will reveal a separation of these asymptomatic neck mass, often accompanied by vague vessels as the schwannoma expands. symptoms such as an awareness of mass in the throat, sore In a series reported in 1996 of 9 patients with para- throat, or dysphagia. Patients with malignant tumors are pharyngeal schwannomas, Furukawa et al3 reported that more likely to present with a rapidly growing neck mass, the tumor’s relationship with the carotid sheath vessels pain, trismus, otalgia, or cranial nerve deficits.2,5 provided useful preoperative estimation of the nerve of The presence of Horner syndrome before excision has origin. All of their patients underwent preoperative CT only been recorded in 6 previously reported cases of para- and MRI. The series’ 5 patients with vagal nerve pharyngeal schwannomas.8 Because the cervical sympa- schwannoma all displayed separation of the IJV and the thetic chain runs in a relatively loose fascial compartment, ICA or CCA. In the 4 patients with sympathetic chain compression injury of the nerve by a schwannoma is rare.6 schwannoma, the tumor was found posterior to the ca- Preoperative Horner syndrome has been reported to be re- rotid sheath, and imaging failed to show any separation lated to parapharyngeal space tumors other than sympa- between the IJV and the ICA or CCA. thetic chain schwannomas and does not necessarily indi- In our series of 12 patients, the criteria of Furukawa et cate that the sympathetic chain is the nerve of origin.8 al3 yielded good results. We correctly diagnosed 10 of 12 With the lack of symptoms and physical examina- nerves of origin (83%) using the displacement of vessels tion findings, imaging plays the central role in diagnos- as a marker. In addition, we observed that a schwannoma ing and distinguishing parapharyngeal space neo- of the vagus nerve may displace the IJV and the CCA or plasms. Over the past 15 years, CT and, more recently, ICA in a posterior direction without splaying them apart MRI have become the routine imaging studies that are (as in case 9). A large schwannoma of the sympathetic chain used. Angiography is used selectively to assess enhanc- can result in a similar picture (as in case 2) with posterior ing lesions of the parapharyngeal space for evaluation of and slight lateral displacement. Hence, we propose a cor- a vascular tumor and consideration for preoperative em- ollary to the paradigm of Furukawa et al.3 When the ca- bolization. On noncontrast CT, schwannomas are hy- rotid sheath vessels are displaced posteriorly but not splayed podense as compared with muscle. Contrast administra- apart by the lesion, one should also consider (1) the vol- tion results in some degree of enhancement, which may ume of the lesion and (2) if any distance between the ves- be homogeneously solid or heterogeneous and patchy.6,8,9 sels exists. Posterior vessel displacement would be ex- It can be difficult to differentiate the rare hypervascular pected from enlargement of the more anteriorly situated schwannoma from a paraganglioma. Magnetic reso- vagus nerve rather than a lesion from the posteriorly based nance imaging allows for superior soft tissue contrast reso- cervical sympathetic chain. An especially large lesion from lution and does not expose the patient to ionizing radia- the sympathetic chain, however, can distort the surround- tion. For these reasons, MRI is now considered the ing anatomy and displace the vessels posteriorly. In this imaging study of choice to evaluate parapharyngeal space case, the vessels would be expected to stay immediately tumors.5,9 A recent series showed that MRI carries a 95% adjacent to each other in the carotid sheath (as in case 2), accuracy in delineating a parapharyngeal space mass in and slight lateral displacement may also be observed. Any relation to the prestyloid vs poststyloid compartments, observable separation of the artery and vein (as in case 9) its relationship to the deep lobe of the parotid, and its suggests a lesion within the carotid sheath and implicates inherent soft-tissue characteristics (vascular vs solid neo- the vagus nerve. plasm).5 On MRI, schwannomas are well-circumscribed A review of the literature yields another useful con- homogenous masses that exhibit high-signal intensity on sideration. A schwannoma of the cervical sympathetic T2-weighted images and a relatively homogeneous low- chain has been reported to splay the internal and exter- signal intensity on T1-weighted images.5,6 In contrast with nal carotid arteries on preoperative imaging,10,11 a phe- paragangliomas, there are no vascular flow voids seen in nomenon that was not present in any of our cases. The schwannomas.6,9 CCA bifurcates into the internal and external arteries near The parapharyngeal space is an inverted pyramid that the level of the superior cornu of the thyroid cartilage. extends from the skull base to the hyoid bone. The space The ICA is initially posterolateral and then ascends pos- is divided into an anterior and a posterior compartment teromedially into the carotid canal of the skull base. The by the styloid process. The poststyloid compartment con- external carotid artery (ECA) lies anteromedial near the tains the carotid sheath, sympathetic chain, and cranial bifurcation and is slightly anterolateral to the ICA near nerves IX through XII. The carotid sheath contains the the level of the skull base. Splaying of the carotid bifur-

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©2007 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 10/04/2021 cation (the “lyre” sign) classically suggests a carotid body Submitted for Publication: September 10, 2006; final re- tumor. The cervical sympathetic trunk, however, at the vision received January 15, 2007; accepted February 21, level of the carotid bifurcation, lies just posteromedial 2007. to the ICA and the carotid sheath on the prevertebral Correspondence: David M. Saito, MD, Department of Oto- fascia.12 Because of limitation by the cervical vertebral laryngology–Head & Neck Surgery, University of Cali- column medially and the longus capitis muscle posteri- fornia, San Francisco, 400 Parnassus Ave, Seventh Floor, orly, a cervical sympathetic chain schwannoma occa- Box 0342, San Francisco, CA 94143 ([email protected] sionally grows anteriorly into the space between the .edu). ICA and the ECA. Wang et al11 described this finding in Author Contributions: Dr Saito had full access to all the a case report from 2004 and noted that 8 cervical sym- data in the study and takes responsibility for the integ- pathetic chain schwannomas with splaying of the ca- rity of the data and the accuracy of the data analysis. Study rotid bifurcation have been mentioned in the English concept and design: Saito, El-Sayed, and Eisele. Acquisi- language literature. tion of data: Saito, El-Sayed, and Eisele. Analysis and in- Schwannomas from the vagus nerve, on the other hand, terpretation of data: Saito, Glastonbury, and Eisele. Draft- will not splay apart the ICA and ECA. Green et al13 note ing of the manuscript: Saito and Glastonbury. Critical that 9 of their 11 patients with vagal nerve schwanno- revision of the manuscript for important intellectual con- mas, the schwannoma occurred at the nodose ganglion, tent: Glastonbury, El-Sayed, and Eisele. Statistical analy- which is above the level of the carotid bifurcation. The va- sis: Saito and Eisele. Administrative, technical, and mate- gus nerve fibers in the carotid sheath course lateral to the rial support: Saito and Eisele. Study supervision: ICA above the bifurcation. Therefore, a vagus nerve Glastonbury, El-Sayed, and Eisele. schwannoma can splay the IJV posterolaterally and the ICA Financial Disclosure: None reported. anteromedially but cannot separate the ICA and ECA.11 Previous Presentation: This study was presented as a As the carotid arteries were not splayed in any our se- poster presentation at the Annual Meeting of the Ameri- ries’ images, we cannot comment on the validity of this can Head & Neck Society; August 17-20, 2006; Chi- observation in the prediction of a sympathetic chain cago, Illinois. schwannoma. It may, however, prove to be another useful corollary to the criteria of vessel displacement dis- cussed in the present report and by Furukawa et al.3 REFERENCES CONCLUSIONS 1. Mikaelian DO, Holmes WF, Simonian SK. Parapharyngeal schwannomas. Oto- The surgical resection of parapharyngeal schwannoma laryngol Head Neck Surg. 1981;89(1):77-81. 2. Chang SC, Schi YM. Neurilemmoma of the vagus nerve: a case report and brief often results in postoperative neurologic deficits. With literature review. Laryngoscope. 1984;94(7):946-949. careful examination of vessel displacement and separa- 3. Furukawa M, Furukawa MK, Katoh K, Tsukuda M. Differentiation between schwannoma tion on MRI or CT, it is possible to predict with consid- of the vagus nerve and schwannoma of the cervical sympathetic chain by imaging erable precision the nerve giving rise to a parapharyn- diagnosis. Laryngoscope. 1996;106(12, pt 1):1548-1552. 4. Khafif A, Segev Y, Kaplan DM, Gil Z, Fliss DM. Surgical management of para- geal schwannoma. This information allows the surgeon pharyngeal space tumors: a 10-year review. Otolaryngol Head Neck Surg. 2005; to counsel the patient on specific anticipated postopera- 132(3):401-406. tive neurologic deficits. In addition, patients with sus- 5. Miller FR, Wanamaker JR, Lavertu P, Wood BG. Magnetic resonance imaging pected vagal nerve schwannomas, for instance, may be and the management of parapharyngeal space tumors. Head Neck. 1996;18 referred to a laryngologist and speech or swallow thera- (1):67-77. 6. Wax MK, Shiley SG, Robinson JL, Weissman JL. Cervical sympathetic chain pist preoperatively to discuss rehabilitation options af- schwannoma. Laryngoscope. 2004;114(12):2210-2213. ter surgery. 7. Gilmer-Hill HS, Kline DG. Neurogenic tumors of the cervical vagus nerve: report Our experience confirms the criteria for the determi- of four cases and review of the literature. Neurosurgery. 2000;46(6):1498- nation of nerve origin proposed by Furukawa et al3 and 1503. 8. Hood RJ, Reibel JF, Jensen ME, et al. Schwannoma of the cervical sympathetic proposes an additional consideration. Vagal nerve chain. Ann Otol Rhinol Laryngol. 2000;109(1):48-51. schwannomas will splay the carotid artery and jugular 9. Som PM, Sacher M, Stollman AL, Biller HF, Lawson W. Common tumors of the vein apart on imaging studies, while sympathetic chain parapharyngeal space: refined imaging diagnosis. Radiology. 1988;169(1): schwannomas displace these vessels together. Addi- 81-85. tional criteria must be considered when a schwannoma 10. Myssiorek DJ, Silver CE, Valdes ME. Schwannoma of the cervical sympathetic chain. J Laryngol Otol. 1988;102(10):962-965. displaces the carotid sheath posteriorly. As the vagus nerve 11. Wang CP, Hsiao JK, Ko JY. Splaying of the carotid bifurcation caused by a cer- courses through the anterior aspect of the carotid sheath, vical sympathetic chain schwannoma. Ann Otol Rhinol Laryngol. 2004;113 this finding typically predicts vagal origin, but only subtle (9):696-699. splaying of the vein and artery may be observed. In the 12. Lyons AJ, Mills CC. Anatomical variants of the cervical sympathetic chain to be considered during neck dissection. Br J Oral Maxillofac Surg. 1998;36(3): case of a very large schwannoma, posterior vessel dis- 180-182. placement with slight lateral displacement predicts sym- 13. Green JD Jr, Olsen KD, DeSanto LW, Scheithauer BW. Neoplasms of the vagus pathetic nerve origin. nerve. Laryngoscope. 1988;98(6, pt 1):648-654.

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