Hypoglossal Schwannoma Masquerading as a Submandibular Gland Tumor: a Case Report

Background: Hypoglossal nerve schwannoma in the submandibular space is rare. This case report presents the treatment of a young patient affected by an unusual hypoglossal nerve schwannoma at the right side of the submandibular region. Case representation: A 31-year-old female presented to our department with complaints of a right-sided submandibular region mass. None calculi was observed by CBCT. An MRI of the neck demonstrating a 18×12mm mass located at the submandibular region. Based on clinical presentation and imaging, a diagnosis of a submandibular gland tumor was conferred and the patient scheduled for excision. Intraoperatively, the mass was noted to arise from the hypoglossal nerve, remaining independent of the submandibular gland. On histopathologic analysis, the mass was determined to be consistent with hypoglossal schwannoma. Conclusion: Though rare, the hypoglossal schwannoma should remain a consideration in the evaluation of a submandibular space mass. During operation, it might be better to explore the mass before managing the submandibular gland.


Background
Schwannomas are histologically benign, slowly growing tumors of the myelin-producing Schwann cells in the peripheral nervous system 1 . The schwannomas most commonly reported in the vestibular nerve 2 , while the motor nerve schwannomas are rare. Hypoglossal nerve schwannomas account for less than 5% of all head and neck schwannomas 3 .The tumor could arise from any portion of the nerve throughout its course 4 . Kaye et al. classi ed schwannomas into three subtypes based on the location: type Aintracranial, type B -intracranial/extracranial, and type C-extracranial 4 . Type B is the commonest type and often described as dumb-bell shaped schwannoma. The common presenting symptom of patients with hypoglossal schwannomas is a neck mass, as well as hypoglossal nerve paralysis on clinical examination 5 . Hypoglossal nerve schwannoma in the submandibular space is rare. Here, we presented a hypoglossal nerve schwannoma in a young female in the right side of the submandibular region.

Case Report
The study was approved by the institutional review board of the Second Xiangya Hospital and informed consent was obtained from the patient. A 31-year-old female was referred to the second Xiangya Hospital with a progressively enlarging right-sided neck mass. The feeling of slight pain in the right submandibular region had lasted for 6 months. She had no history of dysphagia or hypoglossal nerve paralysis related symptoms. The clinical examination showed a mobile and soft mass with an approximate size of 1.5cm × 2cm. The right Wharton's duct and Neurological examination were normal. No submandibular salivary gland calculus was found by cone -beam computed tomographic (CBCT). Magnetic resonance imaging (MRI) scan revealed that a 1.8cm ×1.2cm sized mass with a clear border located at the right submandibular space. The mass was partly coated by the submandibular gland (Fig. 1a). Moreover, the lesion was isointense on T1 and hyperintense on fat-suppressed T2 images (Fig. 1b-c). After injecting contrast medium, the bulk homogeneously enhanced (Fig. 1d).
According to the radiographic characteristics and clinical palpation of the lesion, a preliminary diagnosis of the lesion was a submandibular gland benign tumor. The surgical treatment plan was treated with submandibular gland and tumor excision. Surgical treatment was performed using a standard submandibular approach. When the submandibular gland was separated from the deep tissue, we found the mass arose from the hypoglossal nerve and well capsulated ( Fig. 2a-b). Then, the operator excised the tumor in hypoglossal nerve subcapsular dissection with preservation of the hypoglossal nerve and submandibular salivary gland ( Fig. 3a-b).
The histopathological examination after operation showed a mixture of Antoni type A and Antoni type B The patient had the complication that the apex of tongue was slightly deviated to the right side after the operation (Fig. 5a). The complication was relieved with the follow-up period of three months (Fig. 5b).

Discussion
Schwannomas are benign neoplasms of the myelin-producing Schwann's cells which are always slow growing and affect sensory nerves 7 . Extracranial hypoglossal nerve schwannomas are exceedingly rare and have a greater preponderance among women [8][9][10] . The case in this study have similar characteristics with the previous studies.
Extracranial hypoglossal nerve schwannomas often present as a solitary, painless neck mass in the neck 11 . Most of the patients commonly have tongue deviation and speech disturbance, but small portion of the patients presented without any neurological symptoms 10 . In this study, the patient didn't have the history of the tongue deviation.
According to history the pain of patient, we speculated that the patient was submandibular lymphandenitis in priority. However, negative ndings on CBCT reduced the possibility of submandibular lymphandenitis.
MRI played an key role in preoperative diagnosis of the tumor and was the most frequently used imaging modality 10 . Hypoglossal nerve schwannomas exhibit hypointense or isointense on T1, hyperintense on T2, with heterogeneous enhancement on contrast-enhanced studies 4,12,13 . That was consistent with the ndings presented in our study. The location of the lesion was deep and tightly close to the igastric intermediate tendon. Pleomorphic adenomas, which frequently present in the submandibular gland, have similar MRI image with Hypoglossal nerve schwannomas 14 . This suggested that the MRI ndings of hypoglossal nerve schwannomas were not speci c 15 . The patient was diagnosed preoperatively as a submandibular gland tumor base on the symptom and MRI ndings.
Surgical treatment is universally accepted for submandibular gland tumor and the hypoglossal schwannoma. During the operation, we found that the mass separated from submandibular gland and located in hypoglossal nerve. Then, the tumor was excised with preservation of hypoglossal nerve and submandibular gland. Due to the limit reports, the outcomes in nerve preservation versus sacri ce during surgical resection were uncertain but the overall outcomes in both are favorable 10 . If the hypoglossal schwannoma was identi ed preoperatively, the smaller surgical incision could be performed for only dissecting hypoglossal nerve and tumor. The diagnosis was con rmed as a hypoglossal schwannoma histopathologically by the presence of Antoni A bers, which are narrow elongated bipolar cells, and Antoni B bers, which are less organized and distributed cells 2,6 . Microscopically, in this case, it contained a mixture of Antoni A bers and Antoni B cells.

Conclusion
Hypoglossal schwannomas are rare tumors and limit reports have been described in the literature. If images showed that the tumor coated by submandibular gland, it would be better to explore the lesion initially rather than resect the submandibular gland. The goal of surgery should be total resection of the tumor with preservation of nerve function. Progress after surgery tends to be favorable.   (a) Tumor mass exposed yellow arrow). (b) the mass arosed from the hypoglossal nerve and well capsulated yellow arrow).  (a) the apex of tongue was slightly deviated to the right side after the operation. (b) no tongue deviation after three-month follow-up