Laryngeal Schwannoma and its Management: A Case Report

DISCUSSION

Schwannomas were described first as a clinical entities by Verocay. These are benign, slow-growing, encapsulated neurogenic tumors. Of all the schwannomas 25-45% appear in the head and neck region majority being located in parapharyngeal spaces. Laryngeal schwannomas are rare finding accounting to only 0.1-1.5% of clinical presentations.^1,2 The most common location in larynx is the supraglottic region like arytenoids, aryepiglottic fold, false cords, and epiglottis. Rarely vocal cords may also be involved. Subglottic location is very rare and often fatal.³ These schwannomas originate from the peripherally located Schwann cells of somatic and sympathetic nerves and extrinsically grow and encircle them. In larynx the most common nerve involved is the internal branch of the superior laryngeal nerve.⁴ Schwannomas are found in both male and female, being the more common in females, and can occur in any age group the most common being 4th and 5th decade.⁵ As the location is supraglottic the most common symptoms patient presents are due to mass effect like globus sensation, hoarseness (pseudofixation of vocal cords), dyspnea (mainly on lying down), stridor, and dysphagia, and lateral neck mass. In our case one of the chief complaints was reflux cough which indicates the aspiration of food and hence the involvement of the internal branch of the superior laryngeal nerve. Death due to asphyxia has also been reported as a rare symptom.⁵ Schwannomas are slow-growing masses that cause gradual progression of above-mentioned symptoms.⁶

Diagnosis can be made with help of clinical examination by videolaryngoscopy and radiological investigations (X-ray neck, CTscan, and MRI neck). CT and MRI reveal swelling to be smooth and encapsulated. They also entail the exact anatomical location, extension, and the normal anatomical landmark, all of which help in planning the treatment and approach. MRI findings show mass to be smooth hypo to iso-attenuated with muscle on T1w MRI and hyperintense on Tw2. MRI with gadolinium shows hyperintense enhancement of the swelling.⁷ Various differentials which can be deduced from the above findings are neurofibroma, laryngocoele, laryngeal cyst adenomas, chordomas, and malignant tumors.⁸ The definitive diagnosis can be made only by excision and histopathological examination. The histological diagnosis of schwanomma is based on Enger and Weiss criteria. Three characteristic features in the histology are presence of capsule, arrangement of Schwann cells in either Antonia A (Verocay body) or Antoni B pattern and S-100 positive staining of Schwann cells.² The most closely resembling swelling is neurofibroma and can be differentiated from schwannoma only by histology. Their differentiation is vital as neurofibromas penetrate the nerve fascicles thus making it difficult for complete surgical excision, unlike schwannoma which only encircle the nerves and can be completely excised. Neurofibroma in contrast to schwannomas has a higher chance of recurrence and malignant transformation.² The definitive treatment of Schwannoma is surgical excision. Depending upon the criticality of the location of the schwannoma, prior airway has to be secured. Various methods of securing airway include awake intubation and sometimes, there is a need for a preoperative tracheostomy. The Schwannomas small in size can be excised via microlaryngeal surgery with either cold instrument or lasers (CO₂). Transoral robotic-assisted excision has also been mentioned in the literature.⁹ The ones larger in size may require external approaches like a lateral thyrotomy, pharyngectomy, and laryngofissure approaches.⁶ Recurrence of Schwannoma is rare. A meticulous follow-up is necessary for the early recognition of recurrence and its optimum management. Ideally, follow-up is done every 6 months for 2 years followed by yearly for the next 5 years. The recurrence is rare but if encountered; the treatment could be done using laser excision, median thyrotomy, or open approach if the swelling has limited exposure intraorally. Schwannomas rarely have malignant transformation.