ABSTRACT
Tumors occurring in the submandibular space are infrequent among pediatric patients, and benign peripheral nerve tumors in this region are exceptionally rare. This study describes the uncommon occurrence of a schwannoma in the submandibular space in a child and describes its management. A 7-year-old child presented with a gradually enlarging swelling over a 7-month period in the submandibular region, clinically resembling a salivary gland tumor. There were no associated marginal mandibular, lingual, or hypoglossal nerve palsy. The mass was excised completely, and histopathological examination revealed it to be a schwannoma. It is appropriate to consider benign peripheral nerve tumors, such as schwannoma, in the differential diagnosis of submandibular space tumors in children.
INTRODUCTION
Salivary masses in children comprise 10% of all tumors affecting the head and neck in the pediatric population. While uncommon, it is about five times more likely to be malignant than in an adult, with rates of 50% and 10%, respectively. The parotid gland (66%) emerged as the most frequently affected site, followed by the submandibular gland (34%). Benign lesions accounted for 94% of submandibular gland tumors. Pleomorphic adenoma was the predominant benign tumor (92%), whereas acinic cell carcinoma stood out as the leading malignancy (64%)1. Other benign tumors of the submandibular space include Warthin’s tumor, embryoma, monomorphic adenoma, lipoma, and teratoma, listed in decreasing order of occurrence2.
CASE REPORT
A 7-year-old girl of Bajau descent, with no medical comorbidities, presented to us with a history of painless, slow-growing right submandibular swelling for 7 months. There were no associated skin changes or pus discharge. There were no history of preceding trauma or insect bite. On examination, there was a right submandibular swelling measuring 4x3 cm, which was firm in consistency and non-tender (Figure 1). No punctum or skin changes were noted. There were no remarkable findings in the oral cavity and no associated marginal mandibular, lingual, or hypoglossal nerve palsy. There was no medialization of the lateral pharyngeal wall on flexible nasopharyngolaryngoscopy, with normal supraglottic and glottic structures observed. On the basis of our initial clinical assessment, a provisional diagnosis of a submandibular gland pleomorphic adenoma was made.
Tru-cut needle biopsy of the right submandibular swelling, however; revealed a low-grade spindle cell lesion, with features favoring a benign peripheral nerve sheath tumor.
Computed tomography (CT) scan of the neck (Figure 2) showed a large, well-defined, heterogeneously enhancing hypodense mass (45 Hounsfield unit) at the right submandibular space measuring approximately 4.7x3.2x3.5 cm (AP x W x CC). The mass displaces the right submandibular gland posteriorly and extends from the level of the right medial pterygoid muscle superiorly to the level of the hyoid bone inferiorly. No significant cervical lymphadenopathy was observed.
The patient underwent excision of the right submandibular mass under general anesthesia. A skin incision was made 2 cm below the angle of the mandible, and the subplatysmal flap was raised. The marginal mandibular nerve was protected using the Hayes-Martin maneuver. Upon entering the submandibular space, there was a solid whitish mass with a smooth surface measuring 3x5 cm (Figure 3). The lingual nerve and submandibular gland were identified and preserved. The originating nerve of the tumor was not determined in this case. Nonetheless, a meticulous intracapsular dissection was performed to completely excise the mass.
Histopathological examination of the specimen confirmed that it was a benign peripheral nerve sheath tumor, which was consistent with Schwannoma; as sections show a thinly encapsulated lesion composed of proliferation of spindle cells arranged in hypercellular (Antoni A) and hypocellular areas (Antoni B) (Figure 4). Verocay bodies were observed in the hypercellular areas (Figure 5). This tumor was further classified as a conventional schwannoma because it does not exhibit features specific to other special subtypes; for example, the ancient, cellular, plexiform, or microcystic subtypes. The child recovered well postoperatively with no recurrence or nerve deficit within 6 months of follow-up. The patients parents provided written informed consent for the publication of this article.
DISCUSSION
Schwannoma, initially described by Verocay in 1908, typically manifests in individuals aged between 30 and 50 years. They are benign tumors that are solitary and well differentiated and originate from Schwann cells. Approximately 25-45% of extracranial schwannomas are found in the head and neck region; with the temporal bone, lateral neck, and paranasal sinuses being the most frequently affected areas. Schwannomas typically occur as solitary lesions; however, in some cases, they may manifest as multiple lesions as part of neurofibromatosis type 2. The nerve of origin is unidentifiable in approximately 10-40% of schwannomas3.
Extracranial schwannomas situated in the salivary glands are infrequent, with the majority arising in the parotid gland from a peripheral branch of the facial nerve. Schwannomas originating in the submandibular space are exceedingly rare, and only a limited number of cases have been reported. Patients present with a painless and mobile mass in the submandibular region. These benign tumors tend to displace rather than infiltrate the associated nerve, which accounts for the absence of nerve palsy4.
Ultrasonography reveals a well-defined solid hypoechoic mass, not unlike pleomorphic adenomas. CT characteristics of schwannomas include well-defined tumors with low or soft tissue attenuation and either homogeneous or heterogeneous enhancement. Magnetic resonance imaging (MRI) is recognized as the most effective imaging technique for diagnosing schwannomas. On MRI, schwannomas display low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. In T2-weighted images, a distinctive target signal pattern is evident, featuring heightened peripheral signal intensity and reduced central signal intensity5.
Schwannoma exhibits a distinctive histological profile characterized by an encapsulated lesion originating from a nerve. It is composed of a close intermingling of spindle cells that form highly cellular areas known as Antoni type A, along with less cellular and myxoid Antoni type B areas. Within the palisades of Antoni type A cells, there are regions without nuclei referred to as Verocay bodies6.
Schwannomas found in various regions of the human body have demonstrated immunoreactivity to proteins S-100 and vimentin. Furthermore, varying immunoreactivity to EMA and GFAP was identified in areas corresponding to the perineurium. Although uncommon, positivity for additional markers like CD56 and CD57 has been noted in both benign and malignant schwannomas7.
The preferred approach for treating schwannoma typically involves removing the tumor while preserving the associated nerve8. The usual challenge lies in the inability to identify the nerve of origin, and even with nerve-preserving intracapsular enucleation, preserved nerve function post-surgery is not guaranteed. In some cases, postoperative neurological deficits may help establish the tumor’s origin9.
After a thorough surgical excision, there is no need for long-term follow-up; as recurrence is rare after surgery. However, in cases of incomplete excision, it is advisable to undergo annual ultrasonography and review10.
In conclusion, submandibular space schwannoma is a rare entity; and this, to the best of our knowledge; is the first reported case in the pediatric age group. Diagnosis of the lesion is typically achieved through a contrast-enhanced CT scan of the neck coupled with fine needle aspiration cytology. Complete surgical resection is generally considered curative.
Acknowledgments: We would like to thank the Director General of Ministry of Health Malaysia for his permission to publish this article as a case report.