Unveiling the unseen: anterior nasal septal schwannoma

INTRODUCTION

Peripheral nerve tumours are classified based on their specific cellular differentiation. The commonest benign peripheral nerve tumours are schwannomas and neurofibromas. They may occur sporadically or may be part of genetic syndromes such as neurofibromatosis type 1 or neurofibromatosis type 2.¹ Neurofibromas are benign peripheral nerve sheath tumours that can include components from several elements of peripheral nerves, including axons, Schwann cells, endoneuria fibroblasts, and perineurial cells. Schwannomas on the other hand originate from Schwann cells of the myelin sheath.² They can develop at multiple anatomical sites but most commonly affect the vestibular branch of cranial nerve VIII where it is known as an acoustic neuroma or vestibular schwannoma. Less common sites for schwannomas are scalp, face, oral cavity, and the respiratory tract.^3,4 The head and neck accounts for about 45% of schwannomas but only 4% arises from nasal and paranasal sinuses.⁴ Of the benign peripheral nerve sheath tumours involving the sinonasal tract, only 32 reported cases of nasal septal schwannomas have been documented in the literature.⁵

CASE REPORT

A 50-year-old Malay lady with underlying hypertension presented with left sided nasal congestion, intermittent left epistaxis, and clear mucinous nasal discharge for 6 months prior to initial presentation. The bleeding was painless, spontaneous and mild in severity. There was no history of cacosmia, purulent nasal discharge, facial pain, hyposmia or facial distortion. She denied any constitutional symptoms or neck swelling. Rigid endoscopy of the nose revealed a large mass occupying the entire left nasal cavity. It had a smooth surface with prominent blood vessels and minimal bleeding upon manipulation (Figure 1). The origin of the tumour could not be identified with probing due to patient discomfort. The right nasal cavity was normal. A biopsy of the mass was undertaken under local anaesthesia, which was initially suggestive of a neurofibroma. Examination of the rest of the head, neck ear, nose and throat were unremarkable and there were no palpable neck nodes.

Computerized tomography (CT) scan of the paranasal sinuses showed a well circumscribed soft tissue mass occupying the anterior part of the left nasal cavity measuring approximately 2.2×3.3×3.4 cm with significant obliteration of the left nasal cavity, causing nasal deviation to the right with no adjacent bone erosion (Figure 2 and 3).

The patient underwent a left endoscopic excision of the mass under general anaesthesia. Intraoperatively, there was a smooth surfaced mass occupying the whole wall of the left nasal cavity taking origin from the left anterior aspect of nasal septum.

Postoperative histopathological examination found features of a benign peripheral nerve sheath tumour favoring a schwannoma. The tumour composed of neoplastic spindle cells with wavy nuclei and pale eosinophilic cytoplasmic processes arranged in intermediate fascicles with areas showing vague nuclear palisading (Figure 4). Immunohistochemical staining of the tumour cells showed they were diffusely positive for S100 (Figure 5) with CD34 highlighting interspersed fibroblasts only at the edges of tumour which is indicative of schwannoma. The tumour cells were negative for CKAE1/AE3, EMA, SMA and Desmin.

One month postoperatively, the patient was well and reported marked improvement in nasal congestion. There were no signs of recurrence seen after 3 months. Endoscopic examination of left nasal cavity appeared to be clear. The patient was later discharged well and remains asymptomatic.

DISCUSSION

Schwannomas are benign peripheral nerve sheath tumours that arise from the Schwann cells of the myelin sheath. These tumours are slow-growing, and rarely undergo malignant transformation.^6,7 The presentation varies and depends on the anatomical location and specific nerve involved.¹ There is no racial or gender predilection and these tumours can occur at any age, but they most commonly occur in the 30s to 60s.⁶ Only 32 reported cases of nasal septal schwannomas have been documented in the literature.⁵ This tumour most frequently involves the posterior third of the septum which comprises 60% of nasal septal schwannomas, followed by the middle and anterior parts.⁸

The most common symptoms at presentation are nasal obstruction (92.4%), epistaxis (30.3%), and rhinorrhea (18.1%) 9. Other symptoms include headache, deformity of the nasal pyramid, loss of smell, hyposmia, facial swelling and pain.^4,10 Of the sinonasal masses arising in the nasal septum, 87.5% are benign neoplasms while another 12.5% are malignant. The differential diagnosis for lesions arising from the nasal septum include pyogenic granuloma, inverted papilloma, schwannoma, and mucosal melanoma.¹¹ Other causes that may mimic the tumour include nasal polyps, neuroblastomas, angiofibromas, neurofibromas, and meningiomas.¹

The diagnosis of schwannoma is confirmed by histopathological examination due to the lack of specific radiological features. Computerized tomography (CT) scans are fundamental to determine the origin and extent of the tumour, but it cannot differentiate tumour from infections and retained secretions.^10,12 Magnetic resonance imaging (MRI) scans on the other hand provide better soft tissue resolution than computerized tomography allowing for the differentiation of tumours from inflammatory disorders and normal tissue. MRIs also provide better visualization of any intracranial extension of the tumour.¹³

On MRI, sinonasal schwannomas appear to have intermediate intensity on T1 weighted images and intermediate to high intensity on T2 weighted images contingent on the characteristic of the tumour whereas in the computerized tomography (CT) scan of the sinonasal schwannoma typically shows homogeneous heterogeneous enhancement with contrast, homogenous soft tissue density, or bony erosion.^13,14

The gold standard for the diagnosis of schwannomas is by histopathological examination.⁵ Macroscopically, Schwannomas are usually encapsulated tumour with various shapes including oval, round and fusiform. They appear fleshy, and can be glistening grey to yellow in color.

Microscopically, they typically have two distinct morphologic areas, namely Antoni A and Antoni B. Antoni A refers to more cellular areas with spindle cells forming fascicles and often palisades around eosinophilic cytoplasmic processes known as Verocay bodies, while Antoni B are hypocellular myxomatous areas.^12,15 The tumour cells have spindled to ovoid nuclei which appear wavy with tapered ends and intranuclear inclusions may be observed. Immunohistochemical studies of Schwannomas typically diffusely express S100 compared to Neurofibromas which show more heterogenous expression.^16,17 The tumour described in this case showed almost exclusively cellular Antoni A areas with typical nuclear features but absence of well-formed Verocay bodies. Diffuse expression of S100 further supported the diagnosis.

Treatment of this tumour depends on the location, size and the invasion of the surrounding structures. The gold standard treatment for sinonasal schwannoma is complete surgical excision which can be achieved via endoscopic or open approach.^9,10 Open surgical approaches include lateral rhinotomy, Denker’s operation, trans palatal incision, gingivobuccal incision, or midfacial degloving are used for more extensive tumours.⁹ In current era of endoscope, excision of the tumours is generally undertaken endoscopically, and is more preferred than open surgery.¹⁰ It is safe, effective and confers the advantage of providing a shorter duration of hospital stay and it is also a minimally invasive procedure without any external incision needed . This treatment provides a good prognosis with complete resection of the tumour and postoperative recurrence is highly unlikely.^10,17

CONCLUSION

In conclusion, sinonasal schwannomas are rare benign peripheral sheath tumours which can manifest as unilateral nasal congestion, epistaxis or nasal discharge. Despite being rare, this tumour should be considered as a differential diagnosis in patients presenting with a unilateral nasal mass. Diagnosis is established by histopathological examination of the tumour morphology and supported by immunohistochemistry. The treatment is achieved by complete resection of the tumour with excellent prognosis and low rate of recurrence is reported following excision.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: Not required

REFERENCES

1. 1. Mrugala MM, Batchelor TT, Plotkin SR. Peripheral and cranial nerve sheath tumors. Curr Opin Neurol. 2005;18(5):604-10.
2. 2. Jeon YJ, Kim YR, Lee SY, Lim SJ. Single Stage Nasal Reconstruction for Solitary Neurofibroma Isolated in the Columella. Ear Nose Throat J. 2023;1:1177.
3. 3. Belakhoua SM, Rodriguez FJ. Diagnostic Pathology of Tumors of Peripheral Nerve. Neurosurg. 2021;88(3):443-56.
4. 4. Dhawle MS, Rathod SG, Bhatkule MA, Bindu RS. Sinonasal Schwannoma: a case report. J Clin Diagn Res. 2017;11(5):22-3.
5. 5. Freeman E, Hecht L, Crum J, Lutz M. Anterior Nasal Schwannoma: A Rare Sinonasal Neoplasm. Cureus. 2023;10;423.
6. 6. Zhou HY, Jiang S, Ma FX, Lu H. Peripheral nerve tumors of the hand: Clinical features, diagnosis, and treatment. World J Clin Cases. 2020;8(21):5086.
7. 7. Kuppusamy T, Devi S, Prasad A, Kalyanasundaram B. Schwannoma in the nasal cavity: A benign nerve sheath tumor at an odd location. Ind J Case Reports. 2023;9(4):106-8.
8. 8. Min HJ, Hong SC, Kim KS. Nasal Septal Schwannoma: Advances in Diagnosis and Treatment. J Craniofac Surg. 2017;28(1):97-101.
9. 9. Liao JY, Lee HS, Kang BH. Nasal Cavity schwannoma-a case report and review of the literature. Ear Nose Throat J. 2024;103(1):19-24.
10. 10. Alrasheed W, Almomen A, Alkhatib A. A rare case of nasal septal schwannoma: Case report and literature review. Int J Surg Case Rep. 2019;55:149-51.
11. 11. Tchounwou B, Kaatsch P, Chénais B. Tumours of Nasal Septum: A Retrospective Study of 32 Patients. J Environ Res Public Health. 2022;19:1713.
12. 12. Suh JD, Ramakrishnan VR, Zhang PJ. Diagnosis and endoscopic management of sinonasal schwannomas. ORL J Otorhinolaryngol Relat Spec. 2011;73(6):308-12.
13. 13. Pauna HF, de Carvalho GM, Guimarães AC, Maunsell RCK, Sakano E. Schwannoma of the nasal septum: evaluation of unilateral nasal mass. Braz J Otorhinolaryngol. 2013;79(3):403.
14. 14. Venkatasamy R, Singh A, Singh M, Arasu K, Husain S, Mianxin C. Nasal Septal Ancient Schwannoma: Ancient and Rare. Cureus. 2023;2:94.
15. 15. Kim YS, Kim HJ, Kim CH, Kim J. CT and MR imaging findings of sinonasal schwannoma: a review of 12 cases. Am J Neuroradiol. 2013;34(3):628-33.
16. 16. Schwannoma FU. In: WHO Classification of Tumours Editorial Board. WHO classification of tumours: head and neck tumours. IARC. 2024;9(5):513-5.
17. 17. Kumar S, Sayoo C. Sinonasal Schwannoma: A Rare Sinonasal Neoplasm. Indian J Otolaryngol Head Neck Surg. 2017;69(3):425-7.