Recurrent schwannoma of the tongue in a pediatric patient—report of a rare case with an updated review of literature

Head and neck is a relatively common site of occurrence for the peripheral nerve sheath tumors, and majority of these tumors are seen involving neck, involving vagus nerve, and cervical sympathetic chain. Schwannomas involving mobile tongue are rarely encountered, especially in the pediatric population We present a case of recurrent tongue schwannoma in a 13-year-old female successfully managed with transoral excision. At a follow-up of 3 years, no recurrence is observed. Surgical excision is the recommended modality of treatment for lingual schwannomas, and when excised adequately, recurrences are not expected. A clear margin of surrounding normal tissue should be aimed for to avoid possible recurrence.


Background
Schwannomas are benign tumors arising from the nerve sheath cells (Schwann cells), cranial nerves/autonomic nerves, and peripheral motor-sensory nerves. Head and neck involvement is common, constituting~25-45% of all the cases and the commonest site of involvement in head and neck is cerebello-pontine angle/8th nerve complex [1]. Of the extracranial/non-vestibular cases, the commonest location is parapharyngeal space (vagus nerve and cervical sympathetic trunk). Oral cavity schwannomas constitute only~1% of head and neck schwannomas and as such are quite low down in the list of differential diagnosis of oral tumors. The age group usually affected with pathology is 3rd to 6th decade [2]. We discuss a pediatric patient with recurrent schwannoma of tongue managed with surgical excision and review pertinent literature regarding the schwannomas of tongue in the pediatric population.

Case presentation
A 13-year-old female patient presented to us with a 6month history of gradually enlarging mass lesion involving tongue. The patient did not report pain, bleeding, chewing difficulty, dysphagia, breathing difficulty, snoring, neck swelling, or any systemic symptoms. The patient had a history of excisional biopsy under general anesthesia for swelling at the same site 3 years back at another center and the post-operative histopathology was suggestive of benign nerve sheath tumor (schwannoma). On examination, the lesion was ovoid, smooth surfaced, mucosa covered, yellowish-pink,~2−1.5 cm in size, non-tender, firm with a broad base located at the junction of anterior two-third and posterior one-third of the left side of the tongue (Fig. 1a). Tongue mobility was normal. The rest of the systemic examination did not reveal any abnormality. With a possibility of a recurrent lesion, a contrast-enhanced MRI was obtained, which showed a 1.6 mm × 1.4 mm × 1.4 mm wellcircumscribed lesion, hypointense on T1, homogenously hyperintense on T2, and with avid homogenous enhancement on contrast administration (Fig. 2). A wedge biopsy taken under local anesthesia from the lesion showed features suggestive of benign nerve sheath tumor. The patient and the relatives were explained about the need for surgical intervention and opted for the excision of the tumor under sedation (ketamine 1 mg/kg along with intravenous ondansetron 4 mg stat dose). With a good mouth opening and mobile tongue, the tumor could be adequately exposed transorally and wide excision with a cuff of surrounding soft tissue (0 .5-1 cm) was carried out (Fig. 1b, d). The nerve of origin was not discernible intraoperatively. The defect was primarily closed (Fig. 1c) and the post-operative period was uneventful. Post-op histopathology confirmed the diagnosis of schwannoma ( Fig. 3) with clear margins. The post-operative period was uneventful. During a follow-up of 3 years, the surgical site is well healed without any evidence of recurrence.

Discussion
Intraoral schwannomas tend to involve the tongue followed by the floor of mouth, palate, buccal mucosa, gingiva, lip, and vestibule [3]. Involvement of tongue in the pediatric age group is a rare occurrence. A PubMed English language literature review of lingual schwannomas in pediatric patients, dated 28th February 2021, including the case reports and series with clearly defined individual patient characteristics revealed a total of 34 cases of patients in age group ≤ 18 years (Table 1) [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. The first documented case of pediatric lingual schwannoma was by Craig [4] in 1964 in an 8-year-old female patient. The youngest patients (7 years old) were reported by Cinar [9] in 2004 and Enoz [10] in 2006 and recently by Thompson et al. [16]. There were 16 male and 18 female patients. The most common symptom, present in nearly three-fourth of the patients, was a painless lump. Other symptoms at the time of presentation included paresthesia, ulceration, bleed, and mechanical obstructive symptoms in the form of snoring, difficulty in mastication, swallowing, breathing, and phonation in varying combinations. The average size at the time of presentation was 19.6 mm (standard deviation: 10.5; range 5 to 50 mm) and the tumor was present in anterior/ anterolateral part of the tongue in 58.8% of the cases. An uneventful and complete excision of the tumor could be carried out in all the patients transorally without resorting to more invasive and It is interesting to note that despite having nerve sheath origin, these tumors are seldom painful. In tongue, these tumors may arise from hypoglossal, lingual, or glossopharyngeal nerve but the nerve of involvement may be difficult to discern. It is easy to misinterpret these tumors with other soft tissue tumors like granular cell tumors, neurofibromas, mucoceles, salivary gland tumors, and leiomyomas on the basis of clinical appearance.
The gold standard of diagnosis remains histopathology. The light microscopic findings are distinctive enough to confer a diagnosis of schwannoma. If needed, the diagnosis can be reinforced with immunohistochemical staining with S-100 protein, which is seen to be present diffusely and uniformly in the tumor tissue [12].
Surgical excision remains the treatment of choice given the radioresistant nature of these tumors and relatively straightforward transoral access in cases of tumors involving the mobile tongue. In the current review, all the tongue tumors could be accessed transorally. However, in cases with large tumors especially involving the posterior tongue/base of tongue or in cases with restricted mouth opening, an external approach (submandibular, lip split, mandibulotomy, or anterior midline glossotomy approach) may need to be resorted to for adequate surgical exposure. A complete surgical excision leaves no room for recurrence.

Conclusion
Schwannomas involving tongue are rare neurogenic tumors, especially in the pediatric age group. A complete excision with sufficient margin leaves no room for recurrence. However, enucleation of the lesion or excisional biopsy in the tongue can result in recurrence of the lesion predisposing the patient to the morbidity of repeat surgical procedure.