Schwannoma is a benign nerve sheath tumor that mainly occurs in youth. However, all ages can be affected [1]. Male and female are approximately affected similarly [2]. The etiology of schwannomas is unknown. One quarter to half of all schwannomas cases occur in cervico-facial region. Vestibulo-cochlear nerve is the commonly most affected in head and neck region especially in neurofibromatosis [17]. In the oral cavity, schwannoma is rare (1 to 12%) [18]. Intraoral schwannomas mainly arise from the tongue, followed by the palate, mouth floor, gingiva, lip, and vestibule [18]. Usually, it presents as a painless mass in any part of the tongue of less than 2 cm. However, when the mass grows over 3 cm, compression symptoms may occur such as dysphagia, odynophagia, or swallowing discomfort, altered voice. Dyspnea is a warning manifestation that make surgical management urgent [3].
The differential diagnosis for lingual schwannoma may include neurofibroma, lingual thyroid lipoma, lymphangioma, leiomyoma, and benign salivary gland tumors [19]. However, malignant tumors such as liposarcomas, lymphoma, or carcinoma should be kept in mind. Nevertheless, malignant tumors are unlikely to present a slow growth course as typically schwannoma does. Malignant transformation of schwannoma is exceptional and mainly happens in “ancient” schwannoma according to Ackerman and Taylor [20] or in case of neurofibromatosis [2].
Imaging techniques include ultrasound scanning, CT scan, and MRI. Most schwannomas are shown at no contrast CT scan as a well-circumscribed homogeneous soft-tissue masses. MRI is the imaging modality of choice for showing the exact extent of the tumor. Therefore, it should be performed at the first place before tongue base schwannoma. MRI shows the tumor as a well circumscribed mass isointense to muscle on T1-weighted images and homogeneously hyperintense on T2-weighted images [19]. However, tumor necrosis due to the mass volume or its transformation may alter those radiologic characteristics, as in our case, the mass exhibited a hypointense T1 area of necrosis.
The exact diagnosis are suggested by fine needle aspiration biopsy, which is not always practicable, and confirmed by pathology examination [4].
Histologically, schwannomas are composed of two prototypes of cell organization called Antoni A and Antoni B. The Antoni A region is a hypercellular zone with fusiform cells that have nuclei arranged in palisade forming parallel rows and producing the Verocay bodies. The Antoni B region is a hypocellular with a loose myxoid stroma that might exhibit degenerative features, such as cysts, calcifications, hemorrhages, hyalinization, and inflammatory infiltrate. It is not common for these degenerative aspects to evolve into malignant sarcomas with invasive behaviors and metastatic potential [21]. Immunohistochemistry shows that schwannoma cells tongue exhibits strong and diffuse nuclear and cytoplasmic S-100 protein expression and extensive nuclear SOX10. Other cellular markers associated with neuronal tumors are might be present such as E.N.E., vimentin, glycoprotein, SMA, desmin, and dimentin [21].
Complete surgical excision is the main treatment modality. The transoral approach remains the most used. Other approaches were reported such as submandibular, suprahyoid pharyngotomy, trans-hyoid, and lip split approach [2]. Besides surgical approach, tongue base schwannoma presents another challenge regarding securing airways before surgery. Intubation might require the use of fibroscope or videolaryngoscope, but most importantly the hands of an experienced anesthesiologist. However, in some cases, transient tracheotomy might be performed.
