Great auricular nerve schwannoma: a rare presentation and literature review

Abstract

Head and neck schwannomas are a rare form of tumour arising from the nerve sheath. They are often slow growing and asymptomatic, posing a diagnostic challenge for clinicians. The great auricular nerve (GAN) provides cutaneous innervation to the lower pinna, ear lobule and the inferior periauricular area. Hence, surgical management of GAN schwannomas can have sensory and functional dysfunction postoperatively, necessitating good counselling and communication with the patient. We present the first documented case of GAN schwannoma in the West, with literature review and considerations for surgical management.

Background

Schwannomas are tumours originating from Schwann cells present in the sheath of peripheral nerves. Although rare, the head and neck is the most common site for these tumours with up to 25%–45% of all extracranial schwannomas occurring in this region, especially from the last four cranial nerves.¹ The majority of schwannomas are benign; however, malignant tumours are also rarely encountered.²

Due to its rarity, head and neck schwannomas present a difficult conundrum for the clinician. Differential diagnoses for a slow growing, often asymptomatic, unilateral neck lump are diverse with risk of misdiagnosis. Here, we present the first documented case of great auricular nerve (GAN) schwannoma in the West, with a literature review and considerations for surgical management.

Case presentation

A 76-year-old woman was referred to the Ear, Nose and Throat surgery department for assessment of a left neck lump. The mass had been slowly increasing in size over the past 4 years but was otherwise asymptomatic. The patient had a medical history of early-stage endometrial cancer and bladder cancer; both successfully treated surgically.

On examination, there was a soft and smooth, mobile lesion overlying the superior part of the sternocleidomastoid muscle (SCM). There was full range of neck movement and no palpable lymphadenopathy.

Investigations

A previous ultrasound scan (USS) diagnosed the lump as a sebaceous cyst and it was hence conservatively managed. On second presentation, a repeat USS confirmed that the lump had increased in size to 20×12 mm (figure 1). Fine needle aspiration cytology showed inflammatory cells; however, the aspirate was paucicellular and was deemed inadequate for diagnosis. A contrast-enhanced CT (CECT) scan of the neck showed a smooth rounded lesion with internal vascularity (figure 2).

Figure 1.

Ultrasound imaging of the left neck lump showing well-defined hypoechoic mass lesion with internal vascularity.

Figure 2.

Contrast-enhanced computed tomographic image showing axial (A) and coronal (B) views of rounded lesion overlying the left sternocleidomastoid muscle with interval vascularity (arrow).

Treatment

Diagnostic excisional biopsy was therefore recommended considering the increase in size and the internal vascularity. The lesion was planned for excision under local anaesthetic infiltration. Intraoperatively, the lump was discovered to be a solid, well-encapsulated lesion arising within a nerve sheath in the GAN territory (figure 3). These findings were explained to the patient on table. As it was likely that the mass was arising from a sensory nerve, she was counselled that removing the lesion would involve dividing the nerve. Consequently, this may lead to permanent sensory disturbance in the ear and neck region. The patient agreed for excision and the decision was made to ligate and divide the nerve above and below the lesion. The patient reported feeling neuropathic-type pain in the GAN territory when the nerve was divided proximal to the lesion. Postoperatively, the patient had complete anaesthesia in the GAN territory.

Figure 3.

Intraoperative photograph showing well-encapsulated tumour within the great auricular nerve sheath (black tie).

Outcome and follow-up

Histological examination revealed a benign nerve sheath tumour with a hypercellular component (Antoni A) and a myxoid hypocellular component (Antoni B) confirming the diagnosis of benign schwannoma of the GAN. Postoperatively, the patient recovered well and was discharged the same day. The patient felt relieved that the mass was benign. She still had sensory anaesthesia to the ipsilateral ear at 6 months post-op; however, this was not detrimental to her quality of life (QOL). Overall, the patient was satisfied with the decision to fully excise the schwannoma.

Discussion

The GAN is a pure cutaneous nerve, arising from the ventral rami of C2 and C3 cervical nerves.³ It usually loops around the posterior border of the SCM and divides on the muscle into its anterior and posterior branches as it courses superiorly. Both branches provide cutaneous innervation to the lower pinna, ear lobule and the inferior periauricular area.

A comprehensive literature search in Medline and Embase databases using the search terms (great auricular nerve) AND (tumour OR tumor OR schwannoma) revealed 111 results. Title, abstract review and thorough reference search only identified three previous cases of GAN schwannoma. All were reported from Southeast Asia.^4–6

The four cases of the GAN schwannoma, including our case, had striking similarities in presentation and clinical course (table 1). The median age at presentation was 49 years (range 29–76), with male:female ratio of 1:3. All cases but one presented with a painless lateral neck swelling. The case reported by Fukasawa et al had a tender swelling in the parotid space with regional neuropathic pain in the GAN territory.⁵ All cases had cross-sectional imaging before the excision. MRI suspected GAN tumour in two cases, based on the findings of benign-looking inhomogeneous lesions within the GAN territory. MRI signal intensity was variable between different reports and hence differences between T1 and T2 signals are unlikely diagnostic. In our case, a CECT did highlight the likely benign nature of the lesion and the internal vascularity, but failed to suspect GAN schwannoma as a preoperative differential diagnosis.

Table 1.

Characteristics of great auricular nerve schwannoma cases

Author	Year	Country	Age (years)	Sex	Presenting symptoms	Cross-sectional imaging	Schwannoma suspected pre-op	Treatment	Post-op anaesthesia
Ishikura et al4	1996	Japan	32	F	Painless lateral neck swelling	CEMRI: T1 hyperintense, T2 hypointense (inhomogeneous)	Unknown	Tumour and nerve excision (GA)	Yes
Fukasawa et al5	2008	Japan	66	M	Painful parotid space swelling and regional neuropathic pain	CEMRI: T1 hypointense, T2: hyperintense (inhomogeneous)	Yes (clinically and radiologically)	Tumour and nerve excision (GA)	Yes
Xu et al6	2019	China	29	F	Painless lateral neck swelling	CEMRI: Intermediate signal at both T1 and T2 (inhomogeneous)	Yes (radiologically)	Subcapsular enucleation (LA)	Yes
Present case	2020	UK	76	F	Painless lateral neck swelling	CECT: Smooth rounded lesion with internal vascularity	No	Tumour and nerve excision (LA)	Yes*

*Anaesthesia improved in follow-up 6 months post resection.

CECT, contrast-enhanced CT; CEMRI, contrast-enhanced MRI; F, female; GA, general anaesthesia; LA, local anaesthesia; M, male.

Three cases were treated surgically with total excision of the nerve section including the tumour, with only one case treated with tumour enucleation aiming to preserve the nerve function.⁶ All patients however encountered postoperative anaesthesia in the GAN territory.

Histopathology is considered the gold standard for a diagnosis of GAN schwannoma. Wavy nuclear contours, S-100 protein expression and a well-formed collagenous capsule are consistent findings.⁷ The lesions are composed of cellular-rich areas called Antoni A, showing haphazard arrangement of bland cells with spindled and oval nuclei, and loose less cellular areas called Antoni B, showing only a loose mucinous stroma with fibrillar collagen.⁷

Because of its location, GAN schwannomas can pose a surgical challenge. Division or injury of the nerve can cause regional numbness of the auricular, mastoid and parotid areas. That can lead to not only discomfort but also functional deficits such as difficulty wearing jewellery or answering the phone.⁸ Moreover, Xu et al argued that GAN sacrifice may increase the risk of litigation and patient dissatisfaction postoperatively and recommended to include a thorough discussion with the patient during the consent process for all lesions in the nerve territory.⁶

While division of the anterior branch of the GAN is often necessary for access during parotidectomy, some surgeons also routinely sacrifice the posterior branch. Research into the sensory outcomes and QOL in patients with and without GAN preservation has demonstrated minimal long-term impact.⁹ Sensory function largely improves, and initial differences are not statistically significant whether the GAN is preserved or not.¹⁰

Learning points.

• Great auricular nerve (GAN) schwannomas are rare and usually present as a slow growing, unilateral neck lump.

• Clinicians should include this as a differential in their workup, especially for upper lateral neck lesions.

• Patients should be counselled and consented for the possibility of GAN injury and sensory dysfunction in its territory prior to surgical excision.

• Good counselling and management of patient expectations will lower potential medicolegal risk for the operating surgeon.

Ethics statements

Patient consent for publication

Obtained.