Neurilemmoma of Maxillary Alveolus: A Rare Case Report and Review of Literature.

Schwannomas or neurilemmomas are benign, slow growing, usually solitary and encapsulated tumor, originating from Schwann cells of the nerve sheath. Intraoral schwannomas account for 1% of head and neck region and are commonly seen at the base of the tongue. Most of the literature, reports of schwannomas in the tongue region are common. In this article we report a rare occurrence of schwannoma in the maxillary alveolus region and its management. A 45 year old female patient reported to the department of oral and maxillofacial surgery with a complaint of swelling in the left maxillary alveolus in relation to molar teeth that had been present for more than 3 months. Apparently the swelling was small one initially, which gradually increased in size. Such a rare cas e of intraoral schwannoma should be followed up periodically to look for any malignant transformation and recurrences. An important conclusion that has evolved from the reviewed articles, is that the differential diagnosis of painless nodules in head and neck must include schwannomas.

INTRODUCTION

Neurilemmoma was first described by Verocay in 1910. He called it “Neurinoma” then. In 1935, the term “Neurilemmoma” was coined by Stout.[1] Neurilemmoma also known as schwannoma, neurinoma, or perineural fibroblastoma is a rare benign connective tissue tumor arising from the neural sheath Schwann cells of the peripheral cranial nerves or autonomic nerves. Its origin most commonly associated with nerve trunk.[2] The etiology is unknown, but it is postulated that the lesion arises by proliferation of Schwann cells at one point of the perineurium. This neoplasm has predilection for the head and neck region where one-third of the cases are reported. However, intraoral lesions are rare.[3] The tongue being the most common intraoral site.[4]

CASE REPORT

A 45-year-old female patient reported to our oral surgery department with a complaint of swelling in the left maxillary alveolus in relation to molar teeth that had been present for more than 3 months [Figure 1]. Apparently, the swelling was small one initially, which gradually increased in size. Her dental history revealed that she underwent extraction of the left maxillary second molar tooth 3 months before the appearance of the swelling because of loosening a tooth. On intraoral examination, the swelling was solitary, nodular, firm in consistency, fixed to the underlying alveolus of maxilla located in the left maxillary alveolus of first molar region extending from premolar to tuberosity region and measuring approximately 2 cm × 2 cm in size [Figure 2]. The skin over the swelling skin appeared normal. There was no cervical lymphadenopathy.

Figure 1

Frontal view of the patient

Figure 2

Clinical intraoral picture of the lesion

The radiologic examination (intraoral periapical radiograph) showed radiolucency in the molar region with healing of extraction socket [Figures 3 and 4]. After examining clinically and radiologically, the provisional diagnosis given was that the swelling was either of inflammatory origin epulis, granuloma, or neoplastic outgrowth from the maxillary sinus.

Figure 3

Intraoral periapical radiograph of the lesion

Figure 4

Occlusal view of the maxilla

Due to the small size of lesion, the treatment plan was to excise the lesion completely under local anesthesia. On complete excision of the lesion, no erosion of bone and extension of the lesion into the alveolar bone were evident in the surgical field [Figure 5]. The specimen was sent for histopathological examination. The histopathologic report revealed that there were mesenchymal epithelial densely arranged irregular cells and elongated spindle cells covered by thin fibrous connective tissue. The tumor cells had no cytoplasmic limits, organized forming arrangement of Antoni type B cells with numerous blood vessels, and verocay bodies were seen [Figure 6]. These features are characteristic of schwannoma. Hence, the final diagnosis of schwannoma.

Figure 5

Complete excision of the lesion

Figure 6

Histopathological picture showing Antoni A and B type cells

DISCUSSION

The schwannoma is a rare benign neural tumor, arising from the neural sheath Schwann cells of the peripheral, cranial, or autonomic nerves. It does not arise from cranial nerves I and II (optic and olfactory nerves) because they lack Schwann cells. Two types are distinguished: central or peripheral schwannoma, located in bone or in soft tissues, respectively.[1] They are usually solitary tumor, though in a minority of cases, it may be multiple and associated with Von Recklinghausen's disease.[5] According to Willis, it is slightly more common in women, and there is no significant variation with age.[6] If it invades submucosal areas, it leads to pain and discomfort.[789] Approximately 25%–40% of all schwannomas are seen in the head and neck region.[1246789101112] Of this, intraoral schwannoma accounts for 1% of the head and neck region[5] and commonly seen intraoral site in the base of tongue. Reviewing the literature, it was seen that only 9 cases of ancient schwannoma were reported[8] [Table 1] as per Subashraj K. Wright and Jackson[2] reported 146 cases of schwannoma in oral cavity 52% in tongue and 8.9% affecting the soft palate and 19.6% in the buccal and vestibular mucosa, and 19.24% affecting the lip and gingiva.[2] The tumor is reported to develop in patients of all ages, without an obvious preference for either sex.[12] Worth described neural sheath tumors that arise subperiosteally causing saucerization of the bone.[13] These tumors are radiolucent and may or may not have a cortical outline. Mortada and Sciubba and Sachs reported cases of schwannomas with secondary penetration into the bone, but they could not determine if the lesion arose centrally or from the periosteum.[14111214] We have added 4 cases of schwannomas that was reported till now.[151617]

Table 1

Neurilemmoma cases reported till now

Radiographically, schwannomas of either jaw are well-demarcated, unilocular radiolucencies with a thin sclerotic border. As diagnostic tools, ultrasonography, computed tomography, and magnetic resonance imaging may be helpful for the estimation of tumor margins as well as infiltration of surrounding structures in case of large lesions.

The schwannoma of maxilla is a rare occurrence. In this case, the lesion developed from the extraction socket of the maxillary teeth and formed the encapsulated mass in the maxillary buccal vestibule and alveolar region without causing significant discomfort to the patient. Manoela Domingues Martins reported a case of maxillary schwannoma[2] in 2011 which was allocated in the maxillary vestibule, and lesion was completely excised. SK Shim in 2016 reported schwanomma arising from the floor of the mouth.[17]

Histopathologically, the tumor tissue consists of so-called Antoni A and B type cells. Type A tissue shows densely packed, elongated spindle cells, while Type B tissue has a more myxoid consistency; Antoni A zone has parallel formed thin reticular fibers, fusiform-shaped cells, and curled nucleus. In general, the zone includes a variety of different cells without apparent borders, among their cytosols. Among the sheats, there are acellular eosinophilic bodies called as verocay bodies, formed by thin cytoplasmic fibers.[18] The treatment for benign schwannomas is complete removal of the lesion. Malignant transformation is mentioned in 8%–10% of the cases.[6] Recurrences were very rarely reported.

CONCLUSION

An important conclusion that has evolved from the reviewed articles is that the differential diagnosis of painless nodules in the head and neck must include schwannomas. It is likely that nerve sheath neoplasms are more common than previously reported. Such a rare case of intraoral schwannoma should be followed up periodically to look for any malignant transformation and recurrences.

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Conflicts of interest

There are no conflicts of interest.