Schwannoma of the tongue: a case report with review of literature

Background Schwannomas (or neurilemmomas) of the tongue are benign, usually solitary, encapsulated masses derived from Schwann cells. Clinical evidence indicates that schwannoma is painless and slow growing. In general, schwannoma is treated by surgical excision. Here, we describe a case of schwannoma of the tongue, include a review of the literature from 1955 to 2016, and provide data on age, gender, location, presenting symptoms, size, and treatment methods. Case presentation A 71-year-old female patient presented with a swelling at the base of the tongue of unknown duration. Magnetic resonance images (MRI) showed a large well-circumscribed solid mass and no significant lymph node enlargement. The mass was excised without removing overlying mucosa. Conclusions The authors report a case of lingual schwannoma that was completely removed intraorally without preoperative biopsy. No sign or symptoms of recurrence were observed at 12 months postoperatively.


Background
Around 25-40% of schwannomas occur in the head and neck region, and of these, 1-12% affect the intraoral area [1], most frequently the tongue or mouth floor [2]. Because of their rarity, intraoral schwannomas are not generally part of the differential diagnosis of tongue mass which includes squamous cell carcinoma, sarcoma, granular cell tumor, salivary gland tumor, schwannoma, leiomyoma, rhabdomyoma, hemangioma, lipoma, lymphangioma, dermoid cysts, and inflammatory lesions [3].
Clinically, schwannomas are benign, usually solitary, encapsulated masses that originate from Schwann cells without pain or ulceration.
Here, we report a case of schwannoma of the tongue base and review the literature. A Google search of the terms "schwannoma (neurilemmoma) of the tongue" and "lingual Schwannoma" was performed from 1955 to 2016. Age, gender, location (anterior, posterior, base, ventral), presenting symptoms, size, and treatment methods were extracted from case reports.

Case presentation
A 71-year-old female patient presented with a firm swelling at the base of her tongue of unknown duration that had progressively increased in size. Her only symptom was distortion of the tongue. Medical history taking revealed controlled hypertension (duration X years) and thyroid grand tumor. A well-encapsulated nodular mass was evident at physical examination, but without any neurologic symptom or lymphadenopathy in the submandibular area. The mass was 3 × 2 cm sized without ulceration (Fig. 1). Magnetic resonance imaging (MRI) depicted a solid, soft, heterogeneously enhanced lesion (Figs. 2 and 3). Complete surgical excision was conducted under general anesthesia without preoperative biopsy. Blunt dissection was performed without rupturing the mass or causing dehiscence of superficial mucosa. The mass was completely excised under mucosa (Fig. 4). It had been infiltrated by a branch of the lingual nerve, and a portion of the nerve had to be removed to achieve complete resection. On gross examination, the mass was grayish-yellow and well encapsulated with exophytic lobules (Fig. 5). Microscopically, the lesion was characterized by a mixture of Antoni type A and B tissue growth patterns with hyalinized vessel walls (Fig. 6). No sign or symptoms of recurrence were detected 12 months after surgery (Fig. 7).
A review of the literature over the past 61 years that showed 84 cases, including the present case, has been reported ( Table 1). Lingual schwannoma may arise at any age between 7 and 77 and shows no sex predilection (44 males and 40 females) [4,5]. Despite the fact that it originates from nerve tissue, lingual schwannoma is usually painless.
In 51 cases, the only presenting symptom was an enlarging lump. Other symptoms were dysphagia (15 cases), pain (or discomfort, 10 cases), dysphonia (6 cases), voice change (5 cases), paresthesia (3 cases), snoring (2 cases), bleeding (2 cases), ulceration (2 cases), and abscess (1 case). Masses were located in any part of the tongue. Average size at removal was 2.4 cm (range, 0.3-8.5 cm), and all were treated by transoral excision except 3 cases. The submandibular approach was used in 2 cases and lip splint and mandibulectomy in 1 case. In all three of these cases, masses were located in posterolateral bases.

Discussion
Although the etiology of schwannoma is not clear, it is known to be derived from nerve sheath Schwann cells, which surround cranial, peripheral, and autonomic nerves [6,7]. The head and neck are rather common location of this neoplasm. Intraoral schwannomas mainly arise from the tongue, followed by the palate, mouth floor, buccal mucosa, gingiva, lip, and vestibule [8,9], though the tongue is most commonly involved [10]. The lesion is slow growing, and thus, its onset is usually long before presentation. Lingual schwannoma shows no age or gender predisposition [11]. Usually, it is presented as a painless lump in any part of the tongue of average size 2.4 cm. However, when the mass exceeds 3.0 cm, dysphagia, pain (or discomfort), dysphonia, and voice change are usually presented (Table 1).    Computed tomography (CT) usually shows welldefined homologous lesions. When a heterogeneous lesion is observed by CT, malignant change may be suspected [12]. However, MRI is superior to CT at depicting lingual schwannoma, as it is not degraded by dental artifacts that plague CT in the intraoral area. Lesion signals are isointense versus muscle on T1weighted images, but hyperintense on T2-weighted images [13]. MRI also allows mass size to be accurately measured and mass localization in relation to other structures. Characteristically, these tumors usually appear to be smooth and well demarcated and do not invade the surrounding structures.
In our case, MRI ruled out the possibility of malignancy and invasion. Enoz et al. [14] reported a malignant transformation rate for head and neck schwannoma of 8-10%. In general, schwannoma does not undergo malignant transformation [15,16]. However, several cases of malignant transformation of head and neck schwannomas have been reported, although only one involved the tongue [17]. One malignant transformation was evident in our patient.
Histologically, all schwannomas are encapsulated, and beneath capsules, two main patterns are observed, that is, Antoni type A, which is highly cellular and is composed of elongated Schwann cells, which exhibit a palisading nuclear pattern, and Antoni type B, which is also composed of elongated Schwann cells, but cells are arranged in a less dense myxoid manner and are more disorganized than Antoni type A (Fig. 6).
Schwannomas are usually treated by surgical excision with involved originating nerve [18]. In the literature, transoral excision is the most common approach used (Table 1), although some other approaches have been reported to produce success results, such as the submandibular, which is adopted to address lingual schwannoma of the posterolateral base. More recently, CO 2 laser excision has also been used to treat base of tongue Schwannomas [5,17]. On the other hand, if a mass is located at the posterolateral base, is inaccessible via the mouth, and has a size >4.0 cm, open techniques, such as the submandibular or lip split approach, are used [2,4,19]. Schwannomas are not responsive to radiotherapy [9], and incomplete surgical excision may result in recurrence, although recurrence is uncommon after complete surgical excision [20]. Because masses are encapsulated, their complete removal is straightforward. In our patient, overlying mucosa was preserved to minimize postoperative complications and promote rapid healing without inflammation, and during follow-up, she reported little inconvenience.

Conclusions
Lingual schwannoma is a relatively rare tumor of the head and neck and may occur anywhere in the tongue. At presentation, the majority of patients complain an asymptomatic mass and slight ulceration. Transoral resection preserving overlying mucosa allowed us to remove the tumor in a manner that precluded recurrence and prevented tongue dysfunction.