Former studies[14,15,16] independently reported the mean patient age of 42, 32.6 and 45 years respectively. The epidemiologic data onto the patients included in this study match previously description of gender and age distributions. Most of the literature reported the most common site of extracranial schwannomas in the head and neck is the parapharyngeal region [17], with floor of mouth localization, especially derived from HyN, being relatively rare.
Clinically, schwannomas are often misdiagnosed as other common benign lesions such as pleomorphic adenomas, fibromas, or mucous retention cysts on account of their slow growth. Patients usually present with an insidious-onset gradually progressive swelling which may or may not be accompanied by paresthesia [17]. The most common presenting symptoms of Hyn-derived schwannoma included tongue deviation [18], headaches [19], vertigo and nausea [11]. Hypoglossal nerve palsy was the most frequent presenting sign, occurring in 80% of the cases [20]. In our study, we limited the location to the mouth floor. Accordingly, the symptom of speech disturbance and tongue were noted in 66.6% and 55.5% respectively, while other symptoms were not recorded.
MRI was by far the most frequently utilized imaging modality used for the auxiliary diagnosis of schwannoma. Previous studies indicated that hypoglossal schwannomas appear T1 hypointense and T2 hyperintense, with heterogeneous enhancement in contrast-enhanced studies [21]. In case.1 of our study, the tumor displayed a heterogeneously equal signal on T1-weighted images, and showed a heterogeneously high signal on T2-weighted images. The hyperintensity of hypoglossal schwannomas on T1 images can be variable depending on the predominance of Antoni B fibers [22].
Schwannomas are highly radio-resistant; therefore, radiotherapy is not indicated for their management [13]. The surgical excision is recommended as the primary therapeutic strategy for hypoglossal schwannomas. Considering the high morbidity and mortality rates before 1970, the standard treatment for neurilemmoma is complete surgical excision [23,24,25]. The malignant transformation of schwannomas is extremely rare [26]. Outcomes after surgical excision of hypoglossal schwannomas tend to be favorable. Only two cases [27, 28] prior to 1970 ended in death were reported. In our research, no recurrence of the tumor has been observed after follow-up.
When it comes to hypoglossal schwannomas in mouth floor, intraoral approach was performed in formal studies [9, 10]. The intraoral approach remains the first choice to resect such tumor, and once removed completely, schwannomas do not recur. Identifying the nerve of origin may be difficult, as it is difficult to differentiate between tumors of the lingual, hypoglossal and glossopharyngeal nerves [29]. Some studies recommended that intraoperative neuromonitoring, particularly of the 10th and 12th cranial nerves, can be considered during surgery [30]. In our research, the mass was infiltrated by a branch of the HyN, which had to be sacrificed for complete excision of the tumor, no HyN palsy was observed immediately after surgery.
Depending on the pathological results, schwannomas is characterized as an benign tumor with encapsulated or cystic structures. Schwannoma has consisted of spindle-shaped cells, which was arranged in two different types: Antoni A and Antoni B patterns; where Antoni A type refers to a densely packed pattern of cellular arrangement, while Antoni B represents a more loosely arranged pattern. The axons of the underlying nerve are usually stretched over the tumor capsule. Moreover, immunohistochemistry of S-100 protein was selected to identify schwannoma[12]. The tumor presented in the current report showed characteristics typical of schwannomas.
