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Year : 2021  |  Volume : 23  |  Issue : 1  |  Page : 31-35

Primary nerve sheath tumors of the parapharyngeal Space: A retrospective review

ENT Department, Combined Military Hospital, Kharian, Punjab, Pakistan

Date of Submission12-Jul-2020
Date of Decision16-Aug-2020
Date of Acceptance01-Oct-2020
Date of Web Publication08-Mar-2021

Correspondence Address:
Dr. Muhammad Noman Karim
ENT Department, Combined Military Hospital, Kharian, Punjab
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/SJOH.SJOH_32_20

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Aims: The aims of this study were to retrospectively analyze the presentation, diagnostic challenges, and optimum treatment of nerve sheath tumors (NSTs) in parapharyngeal space (PPS).
Settings and Design: This is a retrospective chart review done at a tertiary care hospital, Pakistan, from January 2009 to April 2020. Methods: All PPS tumors of nerve sheath origin were included in the study. A total of 18 patients satisfied the inclusion criteria. Their clinical presentation, diagnostic modality, surgical approach, and complications were analyzed. Statistical Analysis Used: SPSS version 20 was used for statistical analysis. Results: The male-to-female ratio was 11:7, with a median age at the time of surgery being 43 ± 10.19 years. The most common clinical symptom was neck swelling. Computed tomography scan was the mainstay of investigation (15 cases). Fine-needle aspiration cytology was diagnostic only in three cases. Transcervical approach was used in all the patients except in one patient. The sympathetic chain was involved in five, vagus in two, and hypoglossal and glossopharyngeal in one patient each. However, nerve involvement was uncertain in nine patients. Among postoperative complications, Horner's syndrome was the most common followed by first bite syndrome. Conclusions: PPS NSTs offer a great deal of diagnostic dilemma and an operative challenge. With currently available imaging techniques and meticulous surgery, it is possible to treat PPS NSTs effectively. The nerve of involvement is also important as it can indicate the potential complication that may occur.

Keywords: Neurofibroma, parapharyngeal space, schwannoma

How to cite this article:
Rashid M, Karim MN, Saleem H, Abdullah A, Akbar F, Hakim A. Primary nerve sheath tumors of the parapharyngeal Space: A retrospective review. Saudi J Otorhinolaryngol Head Neck Surg 2021;23:31-5

How to cite this URL:
Rashid M, Karim MN, Saleem H, Abdullah A, Akbar F, Hakim A. Primary nerve sheath tumors of the parapharyngeal Space: A retrospective review. Saudi J Otorhinolaryngol Head Neck Surg [serial online] 2021 [cited 2022 Dec 4];23:31-5. Available from: https://www.sjohns.org/text.asp?2021/23/1/31/310986

  Introduction Top

Parapharyngeal space (PPS) is a pyramidal space in the neck, designated as a deep neck space. It is the site for 0.5% of all head-and-neck masses.[1] The variety of these masses is diverse, ranging up to seventy different rare histopathologies.[2] Most of them (82%) are usually benign, whereas 18% are malignant. Most of them are of salivary origin followed by the tumors of neurogenic origin. Neurogenic PPS tumors include nerve sheath tumors (NSTs) and paragangliomas. The majority of the neurogenic tumors are benign, but when they are malignant, the origin is mostly the nerve sheath. The focus of this study is upon NSTs either benign or malignant. Due to their unique anatomical location, difficult surgical approach, proximity to vital vessels, and nerve of involvement, its treatment is an uphill task. NSTs include schwannomas and neurofibromas, they may arise in any part of the body, but in the area PPS, they pose special challenges in its treatment.[3] The schwannomas occur more frequently than the neurofibromas.[4] Their usual location in neck is in the poststyloid compartment of the PPS.[5] The common age at presentation is from the second to fifth decade. There is a slight female preponderance for benign and male preponderance for malignant lesions.[6] Schwannomas are solitary, slow growing, painless mass, and usually asymptomatic at their initial presentation unless it compresses the adjacent structures. In contrast, neurofibromas are nonencapsulated, soft, pedunculated tumor more often found at the peripheral parts in the body. Neurofibromas can present as a solitary swelling or generalized neurofibromatosis (von Recklinghausen's disease). Malignant peripheral NST is very rare, and only a few cases associated with von Recklinghausen's neurofibromatosis have been reported.[7],[8] Clinical presentation depends on the size and extension of the tumor in different anatomical locations of the head and neck.[9] Patients with malignant disease can present with rapidly progressive and painful lesions. Contrast-enhanced magnetic resonance imaging (MRI) is the radiological investigation of choice. It assesses the size and extent of the tumor, and MRI is even able to differentiate between malignant and benign lesion; further, contiguity to the vital structures can be evaluated for a proper preoperative workup.[10] Contrast-enhanced computed tomography (CT) scan can also be used to assess the site size and extent of the tumor, although it cannot differentiate malignant from benign lesion, and invasion of the surrounding soft tissues is less well appreciated. Fine-needle aspiration cytology (FNAC) is a valuable tool in confirming the diagnosis, with the diagnostic yield of about 80%.[11] FNAC is better avoided for the vascular tumors. Treatment of NST is primarily surgical excision. Several factors have to be taken into account before embarking on the surgery. The vicinity of the major vessels and nerves cannot be overemphasized. Due to the limited access available in PPS, its surgery is always a challenge. There are various approaches for the surgery, and primarily transcervical approach is favored and is combined with transparotid, transmandibular, maxillary swing, or intranasal endoscopic approaches in accordance with the extent of the tumor.[10] The practical challenges faced while treating these tumors include its peculiar anatomy, rarity, and paucity of clinical experience of the surgeons to name a few. The aim of this study is to share our experience of treating the NSTs using modern imaging techniques, FNAC, and meticulous surgical technique for excision as the likely factors for a successful outcome. Occurrence of complications is fairly common, so prior counseling of the patients is of paramount importance.

  Methods Top

This is a retrospective review of charts. Ethical committee's waiver was obtained for analysis of electronic and printed records of the patients presenting with a parapharyngeal mass during the period of January 2009 to April 2020 at a tertiary care hospital of Pakistan. The study comprises 18 cases of the NSTs of PPS. All patients were managed under supervision of the same surgeon. Patients meeting the diagnostic criteria on radiology and histopathology of nerve sheath origin were included in this study. Other tumors of PPS and NSTs arising outside PPS were excluded from the study. Clinical presentation, diagnostic modalities, surgical approaches, and postoperative complications were analyzed. Descriptive statistics were used to describe demographics. Data analysis was done using IBM™ SPSS version 20. Patients were followed up for a minimum of 6 months and were assessed for clinical or radiological recurrence of the disease.

  Results Top

A total of 18 patients were included in the study. The male-to-female ratio was 11:7. The median age at the time of surgery was 43 ± 10.19 years, with a range of 22–61 years. Neck swelling was the most common symptom present in all the cases (100%), followed by pulsations over the swelling (66.7%) and pharyngeal swelling (66.7%) [Figure 1].
Figure 1: Neck swellings are shown in (a) (right) and (b) (left). (c) Pharyngeal swelling is seen on the left side of the soft palate (Pictures are shown with Consent of the patients

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Among radiological investigations, contrast-enhanced CT scan was the mainstay of imaging, performed in 15 cases (83.3%) [Figure 2]. It was combined with CT angiography in eight cases (44.4%) [Figure 3]. CT scan shows a hypodense mass in PPS, whereas on contrast enhancement, CT scan lesion with rim enhancement is seen.
Figure 2: (a) The computed tomography scan axial view of a well-defined hypodense mass in the left parapharyngeal space (orange arrow) causing bulge in the nasopharynx. (b) The contrast-enhanced computed tomography coronal section depicting a mass in the left parapharyngeal space (white arrow) with marginal enhancement of the same patient

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Figure 3: (a) Digital subtraction angiography image showing lateral displacement of the left common carotid artery, left internal carotid artery, and left external carotid artery. However, there is no evidence of splaying of the left internal carotid artery and left common carotid artery. (b) Three dimensional reconstruction image of the same patient

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MRI was done in five cases (27.8%). FNAC was done in all cases; however, it was diagnostic in only three cases (16.7%). Tumor was approached by transcervical approach in all the patients, but in one patient combined, transcervical transparotid approach was used. Tumor involvement of the sympathetic chain was more common and was found in five patients (27.8%); however, nerve involvement was uncertain in nine patients (50%). Among postoperative complications, Horner's syndrome was the most common (four cases, 22.2%) followed by first bite syndrome (three cases, 16.6%). [Figure 4]a shows hypoglossal nerve paralysis after surgery, and postoperative scar is visible in [Figure 4]b. One patient was earlier operated at another hospital but presented to us with a residual tumor, which was excised through transcervical approach.
Figure 4: (a) Postoperative scar (orange arrow) visible on the right side of the neck for hypoglossal schwannoma excision. (b) Right-sided hypoglossal nerve paralysis after surgery (Pictures are shown with permission)

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[Table 1] shows a brief distribution of these variables within the cases. Histopathology of all the cases showed benign NST except for one case which was malignant in origin.
Table 1: Presentation, nerve of involvement, and complications in accordance with the number of cases

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  Discussion Top

The diagnostic and therapeutic challenges posed by unique pathophysiology of these tumors necessitate a detailed preoperative workup before undertaking any surgical endeavors. Moreover, occurrence of wide range of complications associated with surgical therapy cannot be overemphasized.

In our study, the mean age of at the time of surgery was 43.38 ± 10.19 years with a little male predominance (11/18). This is in accordance with the study by Sharma et al. which also showed no significant gender difference.[12]

According to Biswas et al., NSTs are slow-growing and painless tumors, often unnoticed by the patient unless they cause significant pressure symptoms to the adjacent neurovascular structure.[13] In our study, neck swelling was the most common presentation, followed by pulsatile neck swelling, oropharyngeal swelling, dysphagia, and ear symptoms. These results are similar to the study by Pradhan et al.[14]

In radiological evaluation, MRI is the best modality for diagnosis.[15],[16] T1-weighted images show hyper/iso-intense lesion as compared to the adjacent muscles. T2 images may show target lesion with hyperintense surrounding rim and hypointense centrally. MRI can readily point out a malignant lesion when a cystic, necrotic, or hemorrhagic degeneration is noted in the lesion.[17]

As per Kato et al., the black geode sign defined as the appearance of enhanced outer and inner rings on MRI with contrast. The enhancement of inner rings was more than the outer rings. This sign was deemed as more specific toward a schwannoma than neurofibroma.[18] In our study, MRI was done in five cases, out which only one case showed the black geode sign. The area of PPS and skull base being rich in neurovascular structures requires a neuroradiologist's keen attention to the details for accurate preoperative evaluation of a wide range of pathologies that can exist there.[19]

Although CT scan is less sensitive than MRI, due to its widespread availability, it is often the first investigation to indicate a lesion in PPS. However, due to similar densities as compared to the muscles, CT scan is not able to distinguish between the various pathologies.[20] In our clinical settings, our mainstay of investigation was CT scan due to its availability. We resorted to the MRI and CT angiography where necessary to aid in our diagnosis. In our study, CT angiography was done in eight cases. One was recurrence, and the remainder displayed significant displacement of carotid arteries and visible pulsations over the swelling.

FNAC is an excellent aid to the diagnosis which can definitely diagnose NST most of the times. Sharma et al. found FNAC to be 71.40% diagnostic for benign NSTs.[21] FNAC in our study was diagnostic in three cases out of 18. The low yield of FNAC in our cases might be due to a sampling error, difficult location, the rare occurrence of disease, lack of experience in dealing such pathologies, and nonavailability of an experienced cytopathologist. Although cytology is considered as the cornerstone for the diagnosis of most of the NSTs, it is not always conclusive.[13],[22] In our study, one patient with history of pharyngeal and neck swelling, initially nondiagnostic on FNAC later came out to be a malignant neoplasm.

The study by Pradhan et al. shows various unusual locations in a series of 13 patients, with the involvement of the spinal nerve, vallecula, superior laryngeal nerve, brachial plexus, and the trigeminal nerve.[14] However, in our cases, we found all the parapharyngeal NSTs to be located in the poststyloid space with the help of radiology.

Chijiwa et al. and López et al. in their studies found surgical excision to be the mainstay of the treatment for the NSTs. The commonly used surgical approach is transcervical. Although when the tumors are larger than 5 cm or there is suspicion of malignancy, a combined transcervical approach is used for better exposure.[23],[24] In our study, complete excision of the tumor was achieved in 17 cases with transcervical approach, and in one case, transcervical transparotid combined approach was used. We found transcervical approach very much suitable for the cervical NSTs with limited oropharyngeal extension.

A study by Kumar et al. showed the experience of two pediatric cases stressed upon the use of angle mandibulectomy and elongated incision for better exposure and complete removal.[25] In our study, there were no pediatric cases of NSTs.

In a study by Pradhan et al., the marginal mandibular nerve was commonly injured in ten patients undergoing transcervical excision, and it was attributed to the intraoperative stretching of the deep cervical fascia during the excision of the submandibular gland for the sake of better exposure.[14] In our study, there were no cases of marginal mandibular nerve compromise because we did not remove the submandibular gland in any of the cases and placement of the incision was slightly posteriorly to avoid the nerve.

In our study, the majority of the tumors involved the sympathetic chain, followed by two cases involving vagus nerve and one involving each hypoglossal and glossopharyngeal nerves. In rest of the cases, the nerve involved could not be found.

Results of the study by Sato et al. were almost similar with majority involving sympathetic chain, followed by accessory and vagus nerves.[26]

Katz and McAlpin in a series of 33 cases reported that four patients with vagus nerve involvement had permanent ipsilateral cord paralysis postsurgery despite careful dissection.[27] Our results are very similar with two cases of vagal involvement – both suffered vocal cord paralysis postoperatively.

In our study, there were no cases of injury to the facial nerve, brachial plexus, or internal jugular vein. Wound infection was not detected in any of the patients. Furthermore, approaches of the surgery were not related to the complications that occurred. The incidence of malignant transformation of the NST is not clearly demonstrated in the literature. We only found one case which was nondiagnostic on FNAC but proved to be a malignant NST on postoperative histopathology. Due to the indolent nature and the remote chance of malignant transformation, patients who deny surgical intervention can be allowed for the close follow-up. The recurrence rates after resection are not well documented in the literature. Although in our study, there was one case who presented as a residual tumor after previous surgery at some other hospitals, there were no cases of tumor recurrence in our 6 months of follow-up.

  Conclusions Top

PPS NSTs offer a great deal of diagnostic dilemma, and due to its peculiar anatomy and vicinity to the vital neurovascular structures, it is an operative challenge. The identification of the nerve of involvement is also important as it can indicate the potential complication that may occur. With currently available imaging techniques and meticulous surgery, it is possible to treat PPS NSTs effectively. Transcervical approach is generally sufficient to remove the tumor; however, a combined approach can be used for extensive tumors to achieve good results.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1]


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