In this work, we describe the clinical case of a patient with multiple schwannomas of the left-sided marginal mandibular branch of the facial nerve, which is the first report of this entity in literature. So far, only a few groups reported on singular schwannomas of the extratemporal segment of the facial nerve mostly associated with neurofibromatosis [1,2,3,4,5]. After diagnostic work-up and an initial working diagnosis of cervical lymphoma, incisional biopsy revealed the diagnosis of multiple Schwannomas in our patient. Lesions are controlled regularly by ultrasound for more than 3 years now and show no signs of progressive growth.
Schwannomas are benign nerve sheath tumors composed of Schwann cells of myelinated peripheral or cranial nerves that are frequently located in the head and neck region but rarely affect the facial nerve [1, 2]. Multiple schwannomas of the marginal mandibular branch of the facial nerve have not been described so far [1, 2]. On ultrasound imaging, schwannomas usually present as singular homogeneous, hypoechoic, round masses, rarely with a pseudocystic appearance or an internal vascular flow . In the present case, multiple tumors were detected, which imitated cervical lymphoma at first glance. Lymphoma is a common malignant disease, and cervical or intraglandular lymph node involvement is frequently seen. The involved lymph nodes are usually located in the submandibular region, upper cervical chain, and posterior triangle regions . Ultrasound is usually able to corroborate the diagnosis. On high-resolution ultrasound, lymphomas show as round in shape, well-defined, hypoechoic tumors with infrequent hilum and/or intranodal reticulation . If there is a clinical and sonographic suspicion of lymphoma, a lymph node extirpation is usually performed to verify the diagnosis. A different surgical procedure is indicated for the suspected diagnosis of schwannoma. As intraparotid facial nerve schwannomas commonly present as slow-growing parotid mass with normal facial nerve function, cervical lymphoma or multiple adenomas of the parotid/submandibular gland could not be ruled out as differential diagnosis based on clinical and radiological examinations; therefore, a surgical biopsy was planned. In this case, we decided in favor of a representative sampling for histological examination instead of a complete removal of all nodes since this would have implied a markedly higher risk for nerve injury. Since diagnostic and therapeutic options markedly differs between parotid gland adenoma, lymphoma, and peripheral nerve schwannoma, all entities need to be considered as differential diagnoses when a patient presents with the aforementioned clinical and radiographic findings, which emphasizes the importance of a careful ultrasonography examination as initial diagnostic work-up. In our case, the patient presented with a palsy of the left lower branches of the facial nerve, which is uncommon for solitary schwannomas and impeded differential diagnosis. One potential explanation for this untypical clinical presentation is the presence of multiple tumors, which in conjunction could have compromised nerve function.
With regard to treatment, options for therapeutic management of multiple schwannomas include surgical therapy , radiation , off-label immunotherapy , or a watch-and-wait strategy  with regular clinical examinations and imaging controls depending on the localization and the patient’s individual preferences and course and function of the nerve. To our knowledge, we present so far the first case report of multiple schwannomas of the marginal mandibular branch of the facial nerve. If multiple tumors occur in the parotid gland and the angle of the jaw, this rare differential diagnosis needs to be considered. To plan the right diagnostic surgical intervention and prevent nerve damage, a thorough ultrasound examination is essential in preoperative diagnostic work-up for any suspicious lesion of the parotid gland and jaw region.