Schwannoma Arising in Nasopharynx: A Case Report and Literature Review

Abstract

Schwannoma in paranasal sinus has been known as a rare tumor in this origin. This study reports on primary schwannoma arising in the nasopharynx, which is an uncommon location. A 36-year-old female presented with nasal obstruction for one month. Physical examination revealed a nasopharyngeal mass totally occluding bilateral posterior choanae and extended downward to the oropharynx. Magnetic resonance image showed heterogeneous enhancing mass at the nasopharynx extending inferiorly to the oropharynx. The tumor was excised via endoscopic combined trans-nasal/trans-oral approach under general anesthesia. The pathologic diagnosis was consistent with schwannoma. The tumor was successfully excised with en-block resection and the patient was discharged the next day after the operation, without any postoperative complications. There was no tumor recurrence at 12-months follow-up. Schwannoma primarily arising in the nasopharynx is uncommon. Minimally-invasive surgery via the endoscopic approach can be applied for tumor removal with fewer complications and reduced risk of morbidity.

Background

Schwannoma is a peripheral nerve sheath tumor that arises from neuronal axon, namely the Schwann cell. It is a benign tumor that has a very low risk of malignant transformation [1]. Most head and neck schwannoma presents with a mass in the parapharyngeal space and commonly originates from the sympathetic trunk and the vagus nerve [2]. Schwannoma rarely arises in the nasal cavity and paranasal sinuses, the incidence rate reported is at only 4% [3], which mostly occurs from the ophthalmic and maxillary branches of the trigeminal nerve [3–5]. This study reports a case of schwannoma arising in the nasopharynx, which is an uncommon location.

Case Presentation

A 36-year-old healthy female presented with symptoms of nasal obstruction for one month was referred to our hospital. Nasal endoscopy and oropharyngeal examination revealed a nasopharyngeal mass totally occluding bilateral posterior choanae and extended downward to the oropharynx, causing anterior displacement and bulging of the soft palate. The mass had a smooth surface, well-circumscribed, firm consistency without evidence of hypervascularity on general appearance. There was no neurological deficit of the cranial nerve. A tissue biopsy was performed trans-orally and histopathology reported a spindle cell tumor favoring nerve sheath tumor. Magnetic resonance image (MRI) showed a well-defined 2.4 × 2.8 × 4.5 cm mass at the nasopharynx extending inferiorly to the level of the oropharynx. The mass had heterogeneous enhancement in a T1-weighted fat suppression with gadolinium image and mixed hypo-hyper signal intensity in a T2-weighted image. (Fig. 1).

Fig. 1.

MRI showed a well-circumscribed mass at the nasopharynx extending inferiorly to the level of the oropharynx; a a coronal MRI shows heterogeneous enhancement in a T1-weighted fat suppression with gadolinium image and b an axial MRI shows mixed hypo-hyper signal intensity in a T2-weighted fat suppression image

The tumor was excised en bloc via an endoscopic combined trans-nasal / trans-oral approach under general anesthesia. Intraoperatively, the tumor was well encapsulated with 3 × 3 × 5 cm in dimension. (Fig. 2) On histopathological examination (Fig. 3), the tumor was comprised of cellular areas (Antoni A) mixed with hypocellular areas (Antoni B). The tumor cells demonstrated spindle cell shape, wavy nuclei with tapering end and fibrillary cytoplasmic border. Mitotic activities were very low and necrotic area was not identified. S100 and SOX-10 immunohistochemical studies showed diffuse strong expression in these tumor cells, but CD34 and desmin were not positive in the tumor cells. According to these findings, the pathologic diagnosis was consistent with schwannoma.

Fig. 2.

Gross specimen of nasopharyngeal mass

Fig. 3.

Demonstration of histopathology; a (HE;100×) reveals hypercellular and hypocellular areas of tumor with focal palisading of tumor nuclei (Verocay bodies). b (HE;400×) shows tumor cells which are bland-appearing and show wavy to spindled nuclei with tapered end and fibrillary cytoplasm. c (immunoperoxidase;100×) shows S100 expression in nucleus and cytoplasm of tumor cells (left), SOX10 expression in tumor nuclei (right)

The patient was discharged the next day after the operation, without any postoperative complications. She could take regular diet on the next day and had no difficulty breathing. The wound healed with adequate mucosalization within 2 weeks. There was no tumor recurrence on our most recent follow-up visit at 12 months.

Discussion

The literature review was performed. Studies in full manuscript published in English were identified from MEDLINE and Google Scholar up to March 2020. Five cases of schwannoma primarily arising at the nasopharynx were reported and summarized in Table 1 [6–10]. There were 3 male patients (60%) with median age at 24 years (range 17–59 years). The most common clinical presentation was an obstructive symptom with 8 months (range 1–12 months) median duration of symptoms before seeking treatment. Among the cases computed tomography (CT) and MRI were performed which showed varied enhancement of the tumor. Preoperative tissue diagnosis was done in two cases. One case had definite tissue pathology from biopsy after an inadequate specimen from a fine-needle aspiration cytology (FNAC). In the other case the tissue biopsy reported a benign spindle cell tumor. All cases had been successfully treated with surgical excision via different approaches, as shown in Table 1, with no reports of recurrence.

Table 1.

Reported cases of schwannoma primarily arising at the nasopharynx

Case	Author	Age	Sex	Clinical presentation	Preoperative Imaging	Preoperative tissue diagnosis	Surgical approach	Size of gross tumor	Histopathology
1	Schwartz TH et al., 2001	24	M	Nasal airway obstruction, mucopurulent rhinorrhea, and hyposmia	MRI-homogeneously enhancing mass involving the nasopharynx, sphenoid sinus, pterygopalatine fossa, and parapharyngeal space with erosion into the clivus	Biopsy-benign spindle cell tumor	Bicoronal skin incision and an extended frontal approach including bilateral orbitofrontoethmoidal osteotomies	Not described	Not described histopathologic findings
2	Gupta SC et al., 2010	17	M	Recurrent epistaxis and gradual nasal obstruction 6 months	CT-mild enhancement 5.6 × 3.5 × 3.8 cm mass in nasopharynx which extended into nasal cavity	Not done	Transpalatal approach	Piecemeal resection	Contained both hypercellular area which had elongated nuclei arranged in a palisade and hypocellular area which showed myxomatous degeneration
3	Aksoy F et al., 2016	20	F	Sleeping with an open mouth, snoring, a foreign body feeling in the throat and swallowing difficulty 1 year	MRI-vascular lesion with no high flow in nasopharynx CT-onhomogeneous lesion in nasopharynx	Not described	Transoral approach	2 × 1 cm	Showed both Antoni A, Antoni B, and Verocay corpuscles
4	Sanjaya Kumar Behera et al., 2016	59	F	Swelling in the throat and gradual bilateral nasal obstruction since 10 months	CT- moderate enhancing homogenous mass size 4 × 3 × 5 cm in nasopharynx and inferiorly extended to oropharynx	Not described	Transpalatal approach	4.5 × 4 cm	Showed majority Antony A, Antony B areas, Verocay bodies
5	Vishwakarma MB et al., 2017	24	M	Nasal obstruction 1 month	MRI-heterogenous enhancing mass size 4.3 × 3.3 cm confined in nasopharynx	FNAC- not diagnostic Biopsy-schwannoma	Combined endonasal and transoral approach	4 × 3 × 2 cm	Showed both hypercellular area (Antoni A) which had Verocay bodies and hypocellular area (Antoni B) which had degenerative changes

Abbreviations: MRI, magnetic resonance image; CT, computed tomography; FNAC, fine-needle aspiration cytology; cm, centimeter

Although schwannoma arises from the nerve sheath covering Schwann cell, it usually doesn’t causes a neurological deficit. The common clinical symptom is a noticeable or palpable mass in various organs and other symptoms, resulting in pressure effects on adjacent structures from the primary tumor. Nasal and paranasal schwannoma is uncommon and is rarely originated from the nasopharynx. Late clinical presentation of nasopharyngeal schwannoma can be observed because of the slow-growing characteristics of this tumor. Consistent with the present case, a large mass was found on nasal examination at the first visit without any neurological involvement.

The nerve origin of schwannoma might be identified by preoperative imaging or during the intraoperative tumor resection. It is easier to identify the nerve of origin on the preoperative imaging if the tumor extends up and widens the neural foramen that transmits the nerve through the skull base. However, the nerve origin is difficult to identify most of the time due to the tumor arising in the peripheral branch of the cranial nerve. Some areas, i.e. sinonasal cavity, have a rich neural innervation resulting in difficulty identifying the exact nerve origin. In the present case, the authors could not definitely identify the nerve origin of schwannoma from the preoperative imaging and even from intraoperative dissection. Consistent with all previously published studies [6–10], they also could not identify the nerve origin of the tumor. However, the most possible nerve origin in the nasopharyngeal area is the branch of the trigeminal nerve.

The preoperative imaging of choice for schwannoma is MRI, which has a better differentiation of intralesional cystic or hemorrhagic change and enables more specific findings for large schwannoma than CT imaging [11, 12]. Moreover, MRI can better demonstrates contrast enhancement due to the scantiness of venous drainage for the tumor [13]. Most sinonasal schwannoma have a highly dense cellular architecture with less loose microcystic patterns, resulting in low T2 signal intensity on MRI [4, 14]. The growth pattern of schwannoma shows the nature of a benign tumor, which is a slow, expansible and compressible pattern. Its expansion can cause pressure effect and bone resorption without destruction or the invasion of adjacent structures [15]. In the present study, MRI showed heterogeneous enhancement on both T1 and T2-weighted image, representing a cellular and internal cystic change pattern in the tumor.

A definite diagnosis of schwannoma is difficult to achieve with clinical symptoms and imaging alone. The most reliable diagnosis is based on histopathology. The histopathological characteristics of schwannoma reveal the biphasic components such as dense hypercellular areas, namely Antoni A, and myxoid hypocellular areas, namely Antoni B. Verocay bodies, which is a nuclear palisading around fibrillary process often seen in cellular regions. Diffuse strong expression of S100 and SOX10 are characteristic to confirm neural crest-derived tumors. GFAP is less expression in this tumor and variable staining [16, 17].

The mainstay treatment for schwannoma is surgery. The management of schwannoma arising in the nasopharynx is more challenging due to its deep, narrow and complicated anatomical structure. Traditional approaches to nasopharynx, i.e. transpalatal [18], mid-facial deglove [19], trans-maxillary swing [20–23], Le Fort I osteotomy [24, 25], trans-mandibular swing [26] and infra-temporal fossa approaches [27], require an external incision and osteotomy, which can result in a high risk for complications and morbidity. Endoscopic approach has been universally accepted as a standard treatment for pathologies within the sinonasal tract and skull base. It offers better visualization and magnification with lesser invasive techniques and lesser complications. The endoscopic approach to nasopharynx has been reported for the treatment of various nasopharyngeal pathologies [28]. It can be applied for the treatment of both localized benign nasopharyngeal lesions and extensive nasopharyngeal malignancy in terms of endoscopic nasopharyngectomy in which the removal of pterygoid bone and cartilaginous eustachian tube is necessary to achieve a negative tumor margin [29–33]. The endoscopic approach for nasopharyngectomy can offer rapid postoperative recovery and has minor complications, however, it carries a higher risk of major vessel i.e., internal carotid artery injury, particularly in advanced-stage diseases that involve the post-styloid parapharyngeal space. The control of major vessel via endoscopic approach is more difficult and takes more time than external approach due to the limited working space [34]. The combined endoscopic and external approach can provide adequate exposure to the management of vascular injury in the selected extensive tumors. Various approaches to the nasopharynx, specifically for tumor removal purposes, were reviewed and compared for surgical limitations and possible complications among different approaches, as shown in Table 2 [18–33].

Table 2.

Comparison of various approaches to nasopharynx for tumor removal purposes

Surgical approach	Surgical limitations	Possible complications from surgical approach
Transpalatal	-Inferior aspect by the palate -Lateral aspect and ITF on both sides by the palate	-Palatal fistula
Mid-facial deglove	-Inferior aspect by the palate	-Saddle nose -Facial numbness -Nasal crusting
Transmaxillary swing	-Ipsilateral side of ITF by the lateral wall of maxillary sinus -Contralateral side of NP and ITF by the nasal septum and they locate far from the surgical corridor	-Trismus -Facial numbness -Palatal fistula -Malunion of bone
Le Fort I osteotomy	-Extended resection of maxillary wall to gain all boundary margins	-Facial growth disruption -Malunion of bone -Palatal necrosis -Palatal numbness -Nasal septum deviation/perforation -Nasal crusting
Transmandibular swing	- Contralateral side of NP and ITF by the nasal septum and they locate far from the surgical corridor	-Trismus -Malocclusion -Malunion of bone -Palatal fistula -Glossal numbness
Infratemporal fossa	- Contralateral side of NP and ITF by the nasal septum and they locate far from the surgical corridor	-Trismus -Facial numbness -Facial palsy -Malunion of bone
Endoscopic approach via transnasal ± transoral	-Combined endoscopic transoral approach to gain inferior margin -Combined Denker’s approach to gain lateral and ITF margins -Post-styloid parapharyngeal space by the major neurovascular contents	-Nasal crusting -Facial and palatal numbness -Neck pain and occipital headache -Masticatory impairment -ICA injury

Abbreviations: ITF, infratemporal fossa; NP, nasopharynx; ICA, internal carotid artery

In the present study, the principle steps of the approach were based on preoperative tissue biopsy, which had been a benign pattern. The limitation of the space by the palate made the manipulation of the inferior margin of the tumor difficult from the trans-nasal corridor. The endoscopic trans-nasal approach combined with a trans-oral approach allowed an en bloc tumor removal endoscopically in this case. In a previous study, Vishwakarma MB et al. [10] also carried out a successful tumor removal via an endonasal and trans-oral approach with rapid wound healing reported. Other approaches for previously published nasopharyngeal schwannoma included transpalatal approach, which was done by Gupta SC et al. [7] and Sanjaya Kumar Behera et al. [9], and the trans-oral approach, which was done by Aksoy F et al. [8] for small schwannoma at the nasopharynx. Schwartz TH et al. [6] reported the extended frontal approach with bilateral orbitofrontoethmoidal osteotomies via bicoronal skin incision for extensive nasopharyngeal schwannoma involved the parapharyngeal space and sphenoid sinus.

The ideal surgical approach for tumor removal requires adequate exposure and a good surgical view for tumor dissection and vascular control. Moreover, the ideal approach should have the potential to minimize comorbidities and maintain the functional outcomes of the patients. It is difficult to judge which approach is more superior; the overall aspects regarding the histopathology, tumor extension and surgeons’ experience have to be considered when choosing the most appropriate approach.

Conclusion

Schwannoma primarily arising in the nasopharynx is uncommon. Slow progressive symptoms can result in the presentation of an extensive mass occupying the nasopharynx at the first visit. A definite diagnosis should rely on histopathology. Minimally-invasive surgery via the endoscopic approach can be applied for tumor removal with fewer complications and reduced risk of morbidity.

Author Contributions

KT was a doctor in charge of a patient, initiated study and wrote the manuscript. NT wrote and edited the manuscript. SP performed the histological examination of the tumor and wrote the manuscript. BR wrote and edited the manuscript. All authors read and approved the final manuscript.

Funding

The authors declare that there is no funding.

Compliance with Ethical Standards

Conflict of interest

The authors declare that there is no competing interests.

Ethics Approval and Consent to Participate

This study was in accordance with ethical standards of institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards (Committee on Human Rights Related to Research Involving Human Subjects, Faculty of Medicine Ramathibodi Hospital, Mahidol University, ID 1350 COA. MURA2020/370).

Consent for Publication

Written informed consent for publication of patient’s clinical details and clinical images was obtained from the patient.