Schwannoma of the extracranial portion of the accessory nerve presenting as spinal adenopathy

Abstract

Schwannomas are benign tumours arising from Schwann cells in the peripheral nerve. The schwannoma of the accessory nerve is a very rare entity. We report a case of Schwannoma of the extracranial accessory nerve. A 22-year-old man presented with a slow-growing mass, located on the right upper neck. The patient did not have any neurological deficit. CT scan showed a hypodense mass behind sternocleidomastoid muscle. The suspected diagnosis was an adenopathy of the accessory spinal chain. Surgery was done via transcervical approach. The histopathological analysis concluded with a diagnosis of schwannoma. No recurrence was noted at the follow-up examination 29 months after surgery.

Background

Schwannomas are benign tumours arising from Schwann cells in the peripheral nerve. At the head and neck area, they have a predilection for the origin of the vagus nerve in the neck and the cervical sympathetic chain.^{1 2} The schwannoma of the accessory nerve is a very rare entity. When arising from the accessory nerve, the schwannoma is usually found in the intracranial and spinal portions.³ We report a case of a swelling in the right upper neck, which highlights an atypical presentation of this tumour. We discuss clinical presentation, radiographic finding, surgical management and long-term outcome.

Case presentation

A 22-year-old man was observed a swelling mass in the right upper lateral neck, which has been growing for 5 years painlessly and slowly. There was no history of cervical paresis. Physical examination revealed a 4×4 cm mass behind the right sternocleidomastoid muscle. It was firm and immobile. There was no associated palpable cervical lymphadenopathy. Cranial nerve examination was normal. The cutaneous examination of the cephalic area and the nasofibroscopic exploration were both normal.

Investigations

CT scan showed an oval mass on the right side of his neck. It was behind sternocleidomastoid muscle. The lesion was hypodense and 4.3 cm in size with necrotic areas and calcification tissues (figures 1 and 2). Zeihl Neelsen staining of sputum samples and chest X-ray were normal. The diameter of induration after tuberculin skin test was 8 mm.

Figure 1.

Axial CT scan of the patient showing a mass in the upper right neck.

Figure 2.

Sagittal CT scan of the patient showing a mass in the upper neck (black arrow).

Differential diagnosis

The differential diagnosis was an adenopathy of the accessory spinal chain, especially cervical node tuberculosis or cervical node metastasis of nasopharyngeal carcinoma.

Treatment

Prior to the operation, the patient was informed about the surgery and its possible complications. Surgery was done by transcervical approach under general anaesthesia. Complete enucleation with preservation of the involved accessory nerve was performed. The histopathological analysis concluded of schwannoma (figure 3).

Figure 3.

Histopathological section showing Verocay bodies with nuclear palisading (H&E stain, ×200).

Outcome and follow-up

The postoperative course was uneventful except for neck pain and oedema. These symptoms disappeared within 2 weeks. No recurrence was noted at the follow-up examination 29 months after surgery.

Discussion

Schwannomas are usually solitary and slow growing tumours. They are composed of Schwann cells that make up the myelin sheath. The myelin sheath covers the periphery of the nerve. Schwannomas do not invade the nerve fibbers but push them back. Schwannomas are equally distributed between the genders. In terms of age, the greatest incidence is between the second and fifth decades.⁴ The symptomatology is dominated by the tumour syndrome. There are few neurological signs.¹ History and clinical examination of Schwannomas are non-specific so they usually represent a diagnostic challenge. The unilateral asymptomatic neck mass is often diagnosed clinically incorrectly as an enlarged lymph node.⁵ Our country has endemic tuberculosis and high prevalence of nasopharyngeal carcinoma. That is why we performed diagnosis tests for tuberculosis and nasofibroscopy.

Cervical CT is the appropriate test for diagnosis and localisation of the tumour. Schwannomas appear hypodense, well limited and cause a displacement of the sternocleidomastoid muscle and the vascular sheath forward. CT scan assists in differential diagnosis like congenital cyst or a paraganglioma of the X nerve. MRI is not essential but allows to better show the nerve from which the schwannoma originated.^{4 6} According to Kang et al,⁵ imaging evokes diagnosis in 73% of cases. Fine-needle aspiration cytology of a cervical schwannoma is not very contributive to the diagnosis. The specificity is about 20%–25%.^{2 3 7}

The most commonly used therapeutic management is surgery. However, it is important to study the benefit/risk ratio with the informed consent of the patient.³ Extracapsular complete excision is the only guarantee of non-recurrence but with the risk of nerve damage.⁷ In our case, the risk was paralysis of the sternocleidomastoid and the trapezius muscle. Nerve function can be preserved by intracapsular dissection.⁷

Learning points.

• The schwannoma of the accessory nerve is a benign and rare tumour.

• The differential diagnosis is challenging particularly with diseases in endemic areas like tuberculosis or nasopharyngeal carcinoma.

• Surgical treatment should be adapted to avoid invalidating postoperative complications.