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Parapharyngeal Space Schwannomas Preoperative Imaging Determination of the Nerve of Origin

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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 sym- pathetic chain and 7 patients (58%) had schwannomas Design: A retrospective review. of the cervical vagus nerve. By imaging, the nerve of ori- gin 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 para- pharyngeal 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 (REPRINTED) ARCH OTOLARYNGOL HEAD NECK SURG/ VOL 133 (NO. 7), JULY 2007 WWW.ARCHOTO.COM 662 ©2007 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 10/04/2021 A B 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 pa- tients 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 de- termined 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 schwanno- mas, 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 ori- gin, 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- (REPRINTED) ARCH OTOLARYNGOL HEAD NECK SURG/ VOL 133 (NO. 7), JULY 2007 WWW.ARCHOTO.COM 663 ©2007 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 10/04/2021 A B 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
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