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).

Fig. 1
figure 1

Preoperative intraoral photograph. The mass, which is located in the left tongue base, is covered by normal oral mucosa

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Fig. 2
figure 2

T1-weighted magnetic resonance image showing a well-defined heterogeneous lesion (white arrow). a Axial view. b Coronal view

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Fig. 3
figure 3

T2-weighted magnetic resonance image showing a well-defined heterogeneous lesion (white arrow). a Axial view. b Coronal view

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Fig. 4
figure 4

Perioperative clinical photographs. a The mass (white arrow). b The well-encapsulated mass is removed without adhesion (white arrow). c Photograph of the lesion through an overlying mucosal flap (white arrow). d Sutured state

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Fig. 5
figure 5

Gross anatomy. a Macroscopically, the excised specimen is nodular, soft, and grayish and had dimensions of 2.8 × 2.0 × 3.5 cm. The mass was attached to the lingual nerve (white arrow). b The cut surface of the mass has a pearly white appearance

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Fig. 6
figure 6

Microscopic examination. The mass is composed of Antoni A (black arrow) and Antoni B (black empty arrow) regions. a Antoni type A consists of closely packed Schwann cells arranged in rows with palisading and elongated nuclei (white arrow). b Antoni type B of hyalinized vessels in a myxoid background (white arrow) (H&E, ×100)

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Fig. 7
figure 7

Intraoral photograph obtained at 12 months postoperatively showing no sign of recurrence

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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.

Table 1 Patients and tumor characteristics of tongue schwannomas
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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 well-defined 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 T1-weighted 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, CO2 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.