Vagal Schwannoma Mimicking a Parotid Tumor: A Case Report

Abstract

Vagal schwannoma is a rare benign tumor of the head and neck, originating from Schwann cells of peripheral nerves. These tumors are typically slow-growing and often present with nonspecific clinical features. The most common manifestation is a gradually enlarging neck mass; therefore, preoperative diagnosis is quite challenging, and such lesions are frequently misdiagnosed as parotid tumors, paragangliomas, or metastatic lymph nodes. We report the case of a 55-year-old male who presented with a right infra-auricular mass. The initial clinical evaluation suggested a parotid tumor; however, preoperative computed tomography revealed that the tumor was located posterior to the carotid space. After thorough discussion with the patient regarding surgical risks, including the possibility of postoperative vocal cord paralysis, the patient elected to proceed with surgical treatment. Intraoperatively, the tumor was identified as originating from the vagus nerve, and the diagnosis of schwannoma was confirmed by postoperative histopathological examination. The patient developed right vocal cord paralysis after surgery, and the symptoms gradually improved after voice rehabilitation therapy. This case demonstrates that for neck masses located in the infra-auricular or parotid region, vagal schwannoma should be included in the differential diagnosis. In addition, detailed preoperative counseling regarding potential complications, such as vocal cord paralysis, is essential for informed decision-making and optimal treatment planning.

Introduction

Schwannoma is a benign tumor originating from Schwann cells and can occur along any peripheral nerve pathway in the body. Approximately 25-45% occur in the head and neck region. However, schwannomas originating from the vagus nerve are relatively uncommon, accounting for only about 5-8% of head and neck schwannomas.^1,2

Vagal schwannomas most commonly occur in the parapharyngeal space. A typical imaging feature is the separation of the internal carotid artery and the internal jugular vein by the tumor. Clinically, these lesions are often asymptomatic or present with nonspecific findings, most commonly as a slowly enlarging, painless neck mass.^3,4 Some patients may develop hoarseness, dysphagia, or even paroxysmal cough upon palpation due to nerve compression. Although these clinical features are not pathognomonic, they may provide clues for diagnosis. ²

Due to the lack of characteristic clinical symptoms, vagal schwannomas are often difficult to diagnose preoperatively and are easily confused with parotid tumors, paragangliomas, or metastatic lymph nodes. While computed tomography (CT) and magnetic resonance imaging (MRI) are valuable for lesion localization and surgical planning, they are often insufficient for definitive differentiation from other neck masses. ⁴

Definitive diagnosis relies on pathological examination. Typical histopathological features include the alternating distribution of Antoni A and Antoni B areas, as well as the formation of Verocay bodies. Immunohistochemical staining usually shows positive expression of S100 protein ¹ .

In terms of treatment, complete surgical excision is the first-line strategy. However, because the tumor originates from the vagus nerve, the incidence of postoperative vocal cord paralysis is relatively high. ⁵ Therefore, thorough preoperative communication with the patient regarding surgical risks and planning for postoperative voice and swallowing rehabilitation are essential.

In this report, we present a case of right vagal schwannoma that clinically mimicked a parotid tumor in preoperative clinical features. The diagnosis was confirmed after surgical excision and pathological examination. The patient developed postoperative vocal cord paralysis and subsequently underwent voice rehabilitation, highlighting the clinical importance of accurate diagnosis and comprehensive perioperative management.

Case Report

The patient was a 55-year-old male who presented with a right preauricular mass for 1-2 months (Figure 1A), accompanied by ipsilateral facial numbness. No tenderness over the lesion site was noted. He also denied any history of systemic diseases and had no history of trauma or surgery. The patient had a 30-year smoking history (one pack per day) and denied alcohol consumption. The patient did not have fever, trismus, or facial nerve palsy.

Figure 1.

Right preauricular mass of the patient. (A). Clinical photograph of the right preauricular mass. A prominent swelling is observed extending from the infra-auricular to the preauricular region, located near the parotid gland. Based on the clinical appearance, a parotid tumor was initially suspected. (B). Ultrasonography revealed a cystic lesion in the right parotid region with relatively well-defined margins and heterogeneous internal echogenicity, showing imaging features similar to a parotid tumor. The arrow indicates the position of the needle during fine-needle aspiration. (C). CT imaging demonstrated a large, well-defined oval mass located posterior to the right carotid space with mild heterogeneous enhancement. Based on its location and imaging characteristics, a vagal schwannoma could not be excluded. Red arrow: tumor; blue arrow: internal jugular vein (IJV); green arrow: common carotid artery (CCA)

On physical examination, a mass of approximately 3 cm was palpated below the right ear. The mass was elastic in consistency, smooth in surface, and mildly tender. Oral cavity and nasopharyngeal endoscopic examinations revealed no obvious lesions, and bilateral vocal cord movement was normal.

Neck ultrasonography demonstrated a cystic lesion in the right parotid region (Figure 1B). Fine-needle aspiration cytology revealed only red blood cells with a small number of inflammatory cells and no epithelial components. Based on the clinical and ultrasonographic findings, a parotid tumor was initially diagnosed, and the patient was admitted for surgical management.

During hospitalization, CT was performed. The results showed a large oval tumor located posterior to the right carotid space, with well-defined margins and mild heterogeneous enhancement. Given its location and imaging characteristics, a vagal schwannoma could not be excluded (Figure 1C).

Prior to surgery, the patient was thoroughly counseled regarding potential risks, including postoperative vocal cord paralysis despite the use of intraoperative nerve monitoring. After informed consent was obtained, surgical excision was performed.

During surgery, the tumor was identified deep to the internal jugular vein and was found to arise from the vagus nerve (Figure 2A). Intraoperative nerve monitoring was applied throughout the procedure. For vagus nerve monitoring, needle electrodes were inserted into the ipsilateral cricothyroid muscle, while facial nerve monitoring was performed using electrodes placed in the orbicularis oculi and orbicularis oris muscles. An intracapsular excision was initially attempted to preserve neural function; however, a decrease in vagal nerve signals compared with baseline was noted during dissection. Therefore, the surgical strategy was converted to extracapsular excision. The tumor was completely removed with the use of energy devices. Facial nerve monitoring showed preserved function throughout the procedure, whereas vagal nerve signals were reduced significantly compared with baseline levels.

Figure 2.

Intra-operative findings and pathologic results. (A). The tumor was identified deep to the internal jugular vein and was connected to the vagus nerve, with a well-defined capsule. (B). Microscopic examination revealed the characteristic alternating Antoni A and Antoni B areas of schwannoma, along with focal degenerative changes (ancient change). Immunohistochemical staining demonstrated diffuse positivity for S100 protein, supporting the diagnosis of schwannoma (original magnification ×100). (C). A visual timeline summarizing the patient’s clinical course

Pathological examination showed that the tumor measured 4.0 × 3.3 × 1.6 cm, with a pale yellow, translucent, and elastic appearance. Microscopically, typical Antoni A and Antoni B areas were observed, along with partial ancient changes. Immunohistochemical staining showed diffuse positivity for S100 protein, focal positivity for CD34 (limited to vascular components), and negativity for desmin. The final diagnosis was benign vagal schwannoma (Figure 2B).

Postoperatively, the patient developed hoarseness and subjectively reported a weak, breathy voice with increased vocal effort during speech, with an initial self-rated voice VAS score of 7/10. Nasopharyngolaryngoscopy confirmed right vocal cord paralysis. The patient subsequently underwent structured voice rehabilitation, including semi-occluded vocal tract exercises and vocal function exercises.

During approximately 11 months of follow-up, objective voice assessments demonstrated progressive improvement. The patient’s self-rated voice satisfaction score increased from 7/10 to 9/10. Acoustic analysis revealed improvements in jitter (0.519% to 0.152%), shimmer (0.307 dB to 0.185 dB), and noise-to-harmonics ratio (0.0576 to 0.0040). Maximum phonation time improved from 8 seconds to 13 seconds at the latest follow-up. Although flexible laryngoscopy continued to show persistent right vocal cord paralysis, no obvious glottic gap was observed, and the airway remained patent. The patient reported satisfactory voice function and effective communication in daily life. A visual timeline summarizing the patient’s clinical course from initial presentation to diagnosis, surgical treatment, postoperative voice rehabilitation, and follow-up outcome is shown in Figure 2C.

Discussion

Vagal schwannoma is a rare tumor in the head and neck, most commonly found in the parapharyngeal space or carotid space. It usually grows slowly and lacks specific clinical symptoms, making preoperative diagnosis challenging.^1,2

Most patients present with a painless unilateral neck mass, but some cases may be associated with neurological symptoms, including hoarseness, dysphagia, or paroxysmal cough upon palpation.^2,6 In this case, the patient presented with a right infra-auricular mass accompanied by facial numbness, and was initially misdiagnosed as having a parotid tumor based on clinical and ultrasonographic findings, consistent with previously reported diagnostic challenges.^3,7,8

Among head and neck schwannomas, the most common origin is the vestibular nerve (approximately 40%), followed by the cervical sympathetic chain (approximately 30%). Vagal schwannomas account for only about 5-10%, making them relatively uncommon. Other origins, such as the hypoglossal nerve, glossopharyngeal nerve, and other peripheral nerves, account for about 20%. This distribution is consistent with previous reports^1,3,7 and explains why vagal schwannomas are difficult to diagnose preoperatively and are often misidentified as other tumors.

Imaging studies play an important role in preoperative diagnosis. CT usually shows a well-defined low-density tumor, and some cases may exhibit cystic changes or mild to moderate heterogeneous enhancement.^3,7 MRI typically reveals low to intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images, with heterogeneous enhancement after contrast administration. ⁴ Some cases may show the “target sign” or “fascicular sign,” which helps differentiate them from other tumors. ⁶

In addition, a typical feature of vagal schwannoma is the separation of the internal carotid artery and the internal jugular vein, which provides an important clue for determining the tumor origin^4,9.

Histologically, schwannomas are composed of Schwann cells and are characterized by Antoni A areas (densely arranged spindle cells with nuclear palisading forming Verocay bodies) and Antoni B areas (loosely arranged cells with a myxoid stroma). ¹ Tumor cells usually show strong diffuse positivity for S100 protein and are negative for markers such as desmin, helping to exclude other stromal or epithelial tumors.^1,7 Some tumors may show cystic degeneration or degenerative changes, including ancient change, which are related to long-standing tumor growth. ¹⁰

In terms of treatment, complete surgical excision remains the primary and most effective approach.^5,11 However, because the tumor originates from the vagus nerve, the risk of postoperative vocal cord paralysis is high. In a study by Ryu et al, the incidence of vocal cord paralysis was 44% in 18 cases. ⁵ Kim et al reported that more than half of patients developed this complication. ⁶ In addition to vocal cord paralysis, some patients may also experience dysphagia or persistent cough after surgery, requiring voice and swallowing rehabilitation to improve function. ¹²

Management of vagal schwannoma should be individualized according to tumor size, symptoms, patient age, comorbidities, and patient preference. Although complete surgical excision remains the standard treatment, observation may be considered in selected patients with small, asymptomatic tumors because these lesions typically grow slowly. When surgery is performed, the decision to preserve or sacrifice the vagus nerve remains controversial. If the boundary between the tumor and the nerve is clear, intracapsular excision or preservation of the nerve sheath may be attempted to minimize postoperative functional deficits. ⁹ However, conversion to extracapsular excision or partial nerve sacrifice may be necessary when the tumor is tightly adherent to the nerve or when intraoperative nerve signals deteriorate. Therefore, careful preoperative counseling and individualized risk-benefit assessment are essential, including discussion of observation versus surgery, the possibility of postoperative vagal dysfunction, and potential treatment options for persistent vocal cord paralysis. For patients who develop persistent vocal cord paralysis, treatment options include voice therapy, injection laryngoplasty with hyaluronic acid or fat injection, and medialization thyroplasty.

In the present case, the patient initially believed the lesion was a benign parotid tumor and was surprised to learn that it originated from the vagus nerve. Although postoperative hoarseness affected his daily communication, he understood the potential risks discussed before surgery. After structured voice rehabilitation, his symptoms gradually improved, and he was satisfied with the overall treatment outcome.

The strength of this report lies in the detailed clinical, radiological, surgical, and pathological documentation of a rare vagal schwannoma initially mimicking a parotid tumor. The case highlights important diagnostic clues and emphasizes perioperative counseling and rehabilitation. However, limitations include the single-case design and the absence of subjective and objective voice outcome measurements before the surgery.

Conclusion

In summary, this case is consistent with previous literature, showing that vagal schwannoma is difficult to diagnose due to non-specific clinical features. Imaging findings such as separation of the internal carotid artery and internal jugular vein, high signal intensity on T2-weighted images, and heterogeneous enhancement may provide diagnostic clues. However, definitive diagnosis still relies on pathological evidence, including Antoni A/B patterns and S100 positivity. Complete surgical excision provides favorable therapeutic outcomes, but postoperative vocal cord paralysis remains the most common complication, underscoring the importance of comprehensive preoperative counseling and postoperative rehabilitation.