Schwannoma base of Tongue - Case Report with a Novel Reconstruction Technique

Abstract

Introduction: Schwannomas are benign, slow-growing well-encapsulated neoplasms arising from Schwann cells of nerve sheaths. Oral cavity schwannomas are very rare with an incidence less than 1%. The posterior third of the tongue is not frequently involved. Case report: We report a rare case of a large tongue base schwannoma in a 44 year old female managed surgically by lateral pharyngotomy approach. A novel reconstruction method involving the use of submental flap is described for the functional reconstruction of the defect. Conclusion: Being a rare tumor, schwannoma should not be missed in the differential diagnosis of tongue base tumors. Complete surgical resection is the treatment of choice with recurrence being very rare.

Introduction

Schwannomas, also known as neurilemmomas, are benign nerve sheath neoplasms that typically arise from Schwann cells enveloping peripheral, cranial, or autonomic nerves [1]. Previous studies have reported that approximately 25–40% of extracranial schwannomas are located in the head and neck region, with intraoral schwannomas being rare, accounting for 1–12% of cases, most commonly found on the tongue [2]. It has been noted that in more than 50% of tongue schwannomas, distinguishing between the nerves of origin - lingual, hypoglossal, or glossopharyngeal - can be challenging [3].

The most common clinical features of tongue schwannoma include change in voice, difficulty in swallowing and breathing difficulty. Surgical resection is the mainstay of treatment. Malignant transformation and recurrence following complete surgical excision are rare [4].

Case Report

A 44-year-old lady presented to our outpatient department with complaints of swelling in the posterior part of the tongue and change of voice for 7 years.

On examination, a 7 × 6 cm submucosal swelling was noted over the base of tongue filling oropharyngeal isthmus. The swelling was more on the left side with around 1 cm uninvolved tongue base mucosa on the right. Fullness was also noted at the submental and the left submandibular area. There were no significant neck nodes.

Her MRI showed a 5.3 × 5.2 cm lesion base of tongue left lateral aspect causing narrowing of the oropharynx, closely abutting submandibular gland and parapharyngeal muscles. The fat planes with adjacent structures were well preserved. The lesion is hypointense on T1, hyperintense on T2 and STIR image which were consistent with schwannoma (Fig. 1).

Fig. 1.

MRI images of the patient - A, B, C, D representing the Sagittal, Axial, Coronal, and Post Contrast Coronal images showing tumour mass

USG Guided trucut biopsy from the lesion confirmed the diagnosis. Immunohistochemistry showed S100 positivity.

She was counseled and taken for surgical resection. Awake nasotracheal intubation was done under fibro optic bronchoscopic guidance. Examination under anesthesia was done. A 7 × 6 cm submucosal tumor, involving the base of tongue, more towards the left side, extending up to the vallecula and pushing the epiglottis posteriorly.

With a plan for submental flap [5] reconstruction, neck incision was done accordingly (Fig. 2). A 5 × 4 cm sized submental flap was harvested. After elevating the flap, the submandibular gland was resected preserving lingual and hypoglossal nerves. The tumor was approached via lateral pharyngotomy. Lip split and mandibulectomy was avoided in this case. The tumor was resected en bloc with a minimal cuff of the base of tongue mucosa and the defect was reconstructed with submental flap (Fig. 2). At the one-month follow-up naso-pharyngo-laryngoscopy, the healing was excellent, and the flap uptake was highly satisfactory (Fig. 3).

Fig. 2.

Intra-op pictures - A: Submental Flap Design, B: Intraoral view with thick black arrow pointing to the tumour, C: Tumor delivery, D: Excised tumor specimen

Fig. 3.

Post op picture showing well uptake of the flap in the base of tongue (the thick black arrow points to the flap)

In view of anticipated airway compromise and tongue base bleeding, postoperatively, the endotracheal tube was retained and she was observed in the intensive care unit for 24 h. She was started on oral sips the next day and a semisolid diet within 2 days. She was gradually started on a normal diet by 10 days.

Her histopathology reports were consistent with schwannoma (Fig. 4). On gross examination, the tumor was well encapsulated, grey white soft tissue measuring 6.5 × 5 × 3 cm. Cut surface was grey yellow with areas of necrosis. Microscopic examination revealed a well encapsulated neoplasm composed of classical Antoni A and Antoni B type growth patterns. Antoni A was hypercellular with presence of verocay bodies while Antoni B were fewer and had loosely arranged cells. Immunohistochemistry showed S-100 positivity. These features led to the conclusive diagnosis of Schwannoma.

Fig. 4.

Histopathology of the specimen, A: Hypercellular areas (Antoni A areas) with Verocay Bodies; B: Hypocellular areas (Antoni B areas)

Excision was complete on histopathology. On follow up, there was no speech and swallowing deficits.

Discussion

Schwannomas are slow-growing, benign neoplasms arising from Schwann cells in the nerve sheath. Schwannomas could affect all ages and show no sex predilection. Exact etiology of schwannoma is unknown, probable causative factors hypothesized are external injury, chronic irritation, or exposure to radiation[6]. Multiple schwannomas in a single patient suggest a possible association with neurofibromatosis 2[7].

A mong extracranial schwannomas, 25–40% are found in the head and neck area, with over 90% of those being schwannomas of the vestibulocochlear nerve. Intraoral schwannomas are rare, with the tongue being the most common site, followed by the palate, floor of the mouth, buccal mucosa, and mandible [2]. Tongue schwannomas can occur at any age but have a slightly higher incidence in the second to fourth decades of life, showing no gender predilection.

Initially, tongue base schwannomas present as solitary slow-growing painless swellings. In later stages, patients may experience throat discomfort, odynophagia, voice changes, breathing difficulties, snoring, and sleep apnea [2]. Typical diagnostic differentials for tongue base schwannomas include lingual thyroid, lipoma, neurofibroma, hemangioma, lymphangioma, leiomyoma, and minor salivary gland tumors [8].

Histopathological analysis reveals characteristic patterns, including Antoni type A or B. Antoni type A demonstrates tightly packed Schwann cells with elongated nuclei arranged in a palisading fashion, interspersed with Verocay bodies. Antoni type B consists of loose, hypocellular material lacking a specific arrangement. Immunohistochemical markers like S-100 and Leu 7 can support the Schwann cell nature of these tumors [2].

Magnetic Resonance Imaging (MRI) is the preferred imaging modality for evaluating tongue schwannomas. On MRI, tongue schwannomas typically appear as well-defined, smooth tumors without infiltration into adjacent structures. They exhibit iso-intensity to muscle on T1-weighted images and homogeneously hyper-intensity on T2-weighted images.

Complete surgical excision is considered the gold standard for treating tongue base schwannomas, leading to low recurrence rates. However, this procedure presents challenges due to difficulties in accessing the tongue base, limited operative exposure, functional deficits associated with resection, and reconstruction options. Tongue base tumors can pose difficulties in airway management during anesthesia induction, and emergency tracheostomy may be required [2]. To mitigate potential airway problems, awake fiber optic guided intubation can be considered, with the assistance of a skilled anesthetist.

Multiple surgical approaches are available to access the tongue base, including trans-oral, mandibulotomy with lip splitting, mandibulectomy with lip splitting, submandibular (visor flap), suprahyoid pharyngotomy, and transhyoid pharyngotomy. The choice of approach depends on the tumor’s size and location. Transoral laser and robotic surgeries has emerged as an alternative to traditional surgical approaches, offering benefits such as high preservation of organ and nerve function, minimal postoperative care and complications, and avoidance of excessive bleeding and obstruction at the lesion site [9].

For smaller lesions, primary closure of the defect is possible, while larger defects require reconstruction. The primary goal of tongue base reconstruction is achieving good functional outcomes, including intelligible speech, swallowing, and quality of life. Various reconstruction options can be considered, such as skin grafts, local tongue flaps, myocutaneous pedicle flaps, and microvascular free tissue transfer [10]. Notably, our case represents the first reported instance in the literature where a submental flap was used to reconstruct a tongue base defect following schwannoma excision.

The submental flap technique for oral cavity reconstruction has been previously described by the senior author [5]. The submental flap is an axial pattern skin flap based on the submental artery, a well-defined branch of the facial artery in the neck. Venous drainage occurs through the submental vein, which drains into the common facial vein or external jugular vein.

Recurrence after complete surgical resection is extremely rare, with a low incidence of malignant transformation (8–10%), mostly associated with schwannomas in individuals with neurofibromatosis [2, 11].

Conclusion

Schwannomas are uncommon, benign neoplasms that develop from nerve sheaths. They have a slow growth rate and typically manifest with symptoms such as dysphagia, voice changes, sleep apnea, and breathing difficulties. Magnetic resonance imaging is the preferred diagnostic tool, and confirmation of diagnosis is achieved through characteristic histological patterns and immunohistochemistry. Despite the challenges posed by their location, complete surgical resection remains the optimal treatment approach. When planning for reconstruction, the primary focus should be on preserving functional outcomes. The occurrence of recurrence following complete resection and the likelihood of malignant transformation in schwannomas are rare.