Auricle Schwannoma: Presentation of a Rare Case and Review of Existing Literature

Abstract

Schwannomas are extremely rare over auricle. Despite the extensive somatogenic neural innervations of the pinna, schwannomas are never amongst the differentials for a benign auricular mass. Previously published articles have all agreed on the rarity of this lesion occurring over the auricle. However, none of the articles have tackled and extensively reviewed the auricle schwannomas (AS) as an individual entity. The article aim to review previously published cases of AS along with an illustrative case, and provide a better insight regarding demographic, clinicopathological and immunohistochemical features of this neural tumor in a rare site. A systemic review of English literature was performed after using a sensitive search strategy involving three different databases (PubMed, Google Scholar and Embase). A total of nine cases were included. They mostly presented in young adults as a slow growing tumor (mean duration: 3.17 years) and showed a slightly higher male predominance (male/female ratio 1.25:1). They were mostly located over lateral surface (66.67%) with a predilection for left ear (77.78%). Conventional histological variant has only been reported. Complete surgical excision was performed for all the cases without any reports of recurrence or malignant transformation. AS present as a solitary, painless, firm and well-encapsulated lesion, mostly over the lateral auricle surface. Preoperative clinical diagnosis is difficult and radiological investigations do not hold much importance. FNAC is inconclusive and diagnosis mandates histopathologic examination. The nerve of tumor origin is difficult to precisely identify. Complete surgical excision is the treatment of choice. Post-operative prognosis is excellent.

Introduction

A neurilemmoma or schwannoma is an ectodermal derived benign tumor originating from the Schwann cells of the neural sheath [1–3]. Verocay first described the microscopic features of this tumor and Masson introduced the term schwannoma [4, 5]. The term “Neurilemmoma” was first used by Stout in 1935 [3]. About 25–45% of all schwannomas have been reported in the head and neck region [6–8]. In the outer ear, it is mostly found in the external auditory canal, and pinna involvement is extremely rare [9–12]. The first case of an auricular schwannoma was reported by Fodor et al. [9].

Review of Literature

Case Presentation

A 45-year-old female presented with a 6-month history of a slowly enlarging, painless mass over the right auricle. She was otherwise healthy and did not report any history of local trauma. No genetic or syndromic abnormalities were reported from her family. Laboratory reports were unremarkable. Physical examination revealed a firm, oval-round, well circumscribed, relatively mobile, non-tender mass with a broad base over the middle third of the dorsal surface of right pinna. The lesion measured approximately 1.5 × 1.1 cm (Fig. 1).

Fig. 1.

Painless lesion over the dorsal surface of right auricle (black arrow)

With a probable clinical diagnosis of lipoma, the lesion was completely excised under local anesthesia and sent for histopathologic examination. The mass was easily dissected from the underlying perichondrium and overlying skin flaps. The skin flaps were then placed in the midline and sutured. The sutures were removed on the seventh postoperative day, revealing a healthy wound.

The histological examination of the lesion revealed a predominance of Antoni A areas with spindle-shaped cells arranged in a palisading pattern and central acellular areas representing Verocay bodies. Some areas also showed a hypocellular and less organized arrangement, as seen in the Antoni B type (Fig. 2). The immunohistochemical (IHC) examination with S-100 protein revealed intense positivity in the cells of the tumor (Fig. 3). The tumor cells also showed positive expression of SRY-related HMG-box 10 (SOX-10) protein (Fig. 4). The tumor was finally diagnosed as auricular schwannoma.

Fig. 2.

Section showing spindle cell tumor arranged in palisading pattern representing Antoni A region (bold arrow) and an area of acellular eosinophilic region representing verocay body (arrowhead). Also seen is a hypocellular and less organized region representing Antoni B area (thin arrow) (Hematoxylin and eosin staining; 200×)

Fig. 3.

Section showing tumor cells expressing strong nuclear and cytoplasmic S-100 (400×)

Fig. 4.

Section showing tumor cells expressing SRY-related HMG-box 10 (SOX-10) (400×)

Methodology

An extensive search of three medical databases (PubMed, Google Scholar and Embase) was performed in the month of December 2019. The databases were searched for full-length articles and abstracts published in the English language and confined to human subjects, using the following Medical Subject Headings (MeSH): “Schwannoma” AND/OR “Neurilemmoma” AND/OR “Auricle” AND/OR “Pinna” AND/OR “Ear”. Included articles were either an isolated case report or a single case report with review of literature, and only reported a lesion confined to the pinna. Case reports with a lesion extending to surrounding structures such as the external auditory canal or post-auricular region were excluded. No age, race or demographic filters were applied. Information from the included articles was collected in a predesigned Microsoft Excel (Microsoft Corporation, USA) spreadsheet.

Results

A total of nine cases are included in the current review (eight published cases and one illustrative case). From the included articles clinical, histopathologic and treatment findings were documented (Tables 1, 2) [9–16].

Table 1.

Updated review of cases of auricle schwannoma

Case authors (Ref. #)	Year	Country	Age/sex	Lesion duration (years)	Lesion size (mm)	Side/surface/site	Clinical symptoms	Clinical signs	Surgical procedure	IHC	Database	D/D	Variant
Fodor et al. [9]	1977	USA	14/F	3	30 × 15	LE/VS/Cavum concha	painless swelling	Firm, non-tender, mobile, broad-based	CLE	S-100 + ve	GS + PM	NI	CV
Carter et al. [10]	2008	UK	80/F	2	7 × 4	RE/VS/Superior crus of antihelix	Intermittent painful swelling	Firm, translucent, tender	CLE	NI/NP	GS + PM	NI	CV
Lai et al. [11]	2010	Taiwan	47/M	2	NI/NIO	LE/VS/Concha	Painless swelling	NI/NIO	CLE	NI/NIO	GS + PM	NI/NIO	NI/NIO
Lee et al. [12]	2012	Korea	40/M	10	13 × 12	LE/VS/Cavum Concha	Painless swelling	Soft, non-tender	CLE	S-100 + ve	GS	Epidermal cyst or Lipoma	CV
Thakur et al. [13]	2013	India	25/F	6	12 × 8	LE/Junction of DS and VS/Helix near darwin tubercle	Painless swelling	Soft-firm, non-tender, mobile	CLE	S-100 + ve	GS	Chondroma	CV
Bajpai et al. [14]	2016	Cyprus	27/M	1	30 × 30	LE/DS/Scaphoid eminence	Painless swelling	Mobile	FNAC (IC)- CLE	S-100 + ve	GS + PM	Benign adnexal tumor	CV
Chhetri et al. [15]	2017	Nepal	28/M	1	20 x10	LE/VS/Junction of cymba concha and Inferior crus antihelix	Painless swelling	Firm, non-tender, mobile	FNAC (IC)- CLE	S-100 + ve	GS	Follicular infundibular cyst	CV
Testa et al. [16]	2019	Italy	23/M	3	30 × 15	LE/VS/Root of helix	Painless swelling	Firm, non-tender, mobile	CLE with CO2 laser	S-100 + ve	GS + PM	Chondroma	CV
Present case	2019	India	45/F	0.5	15 × 11	RE/DS/Junction of antihelix groove and conchal eminence	Painless swelling	Firm, non-tender, mobile	CLE	S-100 + ve and SOX-10 + ve		Lipoma	CV

F female; M male; NI not informed; NIO no information obtained; NP not performed; RE right ear; LE left ear; VS ventral surface; DS dorsal surface; CLE complete local excision; FNAC fine needle aspiration cytology; IC inconclusive; IHC immunohistochemistry; + ve positive; F/U follow up duration; GS Google Scholar; PM PubMed; D/D differential diagnosis; CV conventional variant

Table 2.

Clinical features of nine patients with auricle schwannoma

Feature	Dataa	Number of cases amenable to analysis
Male	5 (55.56%)	9
Mean patient age at the time of initial evaluation, years	36.56 (range 14–80)	9
Mean duration of lesion, years	3.17 (range 0.5–10)	9
Left ear involvement	7 (77.8%)	9
Right ear involvement	2 (22.2%)	9
Mean size of lesion, millimeters	19.63 (range 7–30)	8
Size range, millimeters
0–10	1 (12.5%)
11–20	4 (50%)
21–30	3 (37.5%)
Symptoms at initial presentation
Painless swelling/nodule	8 (88.9%)	9
Intermittent pain	1 (11.1%)	9
Signs at initial presentation
Tenderness over lesion	1 (12.5%)	8
Soft or soft-firm on palpation	2 (25%)	8
Ulcerated overlying mucosa	0 (0%)	8
Histological variant		8
Conventional	8 (100%)
Plexiform/ancient/cellular	0 (0%)
IHC positive staining		7b
S-100	7 (100%)
SOX-10	1 (14.3%)
Surgical treatment		9
Traditional complete local excision	8 (88.9%)
CO2 laser assisted excision	1 (11.1%)
Prognosis		9
Recurrence	0 (0%)
Malignant transformation	0 (0%)

^aNumber (%) unless otherwise specified

^bNumber of cases in which some form of IHC staining was done

The cases were reported from eight different countries: India (n = 2), USA (n = 1), UK (n = 1), Italy (n = 1), Nepal (n = 1), Taiwan (n = 1), Cyprus (n = 1), and Korea (n = 1). Out of nine included cases, five were males (55.56%), and four were females. The ages ranged from 14 to 80 years (mean 36.56, SD 18.47). The mean duration of lesion was 3.17 years (range 6 months–10 years, SD 2.87). Dimension of the lesion was obtained/reported in all cases except one [11]. The mean largest dimension/diameter of the eight lesions was 19.63 mm (range 7–30 mm, SD 8.70).

The tumor involved the medial and lateral surface of pinna in two (22.22%) and six (66.67%) subjects, respectively. In one case, the lesion was located at the junction of the medial and lateral surfaces of the left pinna over the helix, close to Darwin tubercle [13].

Among the six laterally placed lesions, two involved the cavum concha, one involved the root of helix, one involved the superior crus of the antihelix, and one involved the cymba concha with an extension to the inferior crus of the antihelix. In one case a full-text of the article could not be obtained and the specific site over the concha was not provided in the abstract (Lai et al.). Among the two medially located lesions one was present at the scaphoid eminence (Bajpai et al.) and one was present at the junction of antihelix groove and conchal eminence (present case).

The lesion involved the left ear in seven (77.78%) and the right ear in two (22.22%) of the subjects.

All cases, with the exception of one, presented symptomatically with a painless swelling. Carter et al. reported intermittent pain over the tumor site. There were no reports of other neurological symptoms such as tingling or numbness, and no reports of aural symptoms such as altered hearing, tinnitus, vertigo, aural fullness or autophony.

A majority of the lesions were firm, non-tender and/or mobile. Tenderness over the tumor site was reported from one case (Carter et al.), and a soft/soft-firm lesion on palpation was reported twice [12, 13]. Overlying skin ulceration was not noted in any lesion. These observations imply a good encapsulation of the tumor in all of the cases.

Various pre-operative differentials were considered by the authors; these included chondroma (Thakur et al., and Testa et al.), benign adnexal tumor (Bajpai et al.), epidermal cyst (Lee et al.), follicular infundibular cyst (Chhetri et al.), and lipoma (Lee et al., and present case).

Since none of the lesions were huge or aggressive, preoperative radiological investigations were not considered or performed. Fine needle aspiration (FNA) was performed in two of the cases and yielded an inconclusive result in both [14, 15].

One article reported a history of trauma (ear piercing) [13]. There were no reports of prior trauma, surgery or infection in the other cases; this reflects an idiopathic etiology of the tumor.

In all of the cases, microscopic examination yielded a conventional variant of schwannoma with varying amounts of Antoni A and B areas. There was no cellular atypia seen in any of the lesions. Other findings included areas of focal hemorrhage (Bajpai et al.), internal vascularity (Bajpai et al.), and hemosiderin-laden macrophages (Carter et al.).

Seven out of nine cases revealed a strong immunoreactivity with S-100 staining. In one case the S-100 staining was not performed (Carter et al.). For the other case no information could be obtained regarding immunohistochemistry (IHC) staining (Lai et al.). In our case, we also performed a SOX-10 staining, which demonstrated a strong reactivity as well.

Complete surgical excision was employed in all the cases, and no recurrence or malignant transformations were reported. Traditional excision was done in all cases, except in one case where CO₂ laser-assisted tumor excision was performed [16].

The nerve of tumor origin was not precisely identified for any case. The lesion in our case was present over the middle-third of the dorsal surface of the auricle. Therefore the most likely nerves of origin for the tumor was one amongst the auricular branch of vagus nerve, the great auricular nerve, or the lesser occipital nerve [17].

Discussion

The term schwannoma is synonymous with neurilemmoma, neurinoma, and perineural fibroblastoma and can arise from the Schwann cells covering the cranial, peripheral, or autonomic nerves [18]. Schwannomas never arise from cranial nerves I and II since they lack Schwann cells [19]. Sensory nerve involvement is more common; there are rare instances of motor nerve involvement [20].

Approximately 25–45% of all schwannomas are found in the head and neck region, with a few reports of primary external ear schwannomas [6–8]. In the outer ear it is mostly found in external auditory canal, with rare involvement of the pinna [9–12].

Auricle schwannomas are mostly asymptomatic, and most patients present with a painless solitary swelling and/or aesthetic alteration of the pinna [16]. Sensory neurological symptoms including neuralgia and paresthesia are present in up to one-third of the lesions [21]. Altered hearing, tinnitus, vertigo, aural fullness, recurrent otitis externa and autophony have been reported from schwannomas of external auditory canal (EAC), tympanic membrane, and postaural schwannomas occluding EAC [22–26]; however none of these symptoms were reported from previously published cases of isolated primary auricle schwannoma [9–16].

Schwannomas, including auricular schwannomas, are benign, slow-growing and well-encapsulated lesions. They are generally non-tender, firm and/or mobile. Their soft consistency can be attributed to internal hemorrhage or degenerative changes [12]. Owing to the benign and well-encapsulated nature, they barely ulcerate overlying skin or erode surrounding structures. However, there is a report of EAC schwannoma, accompanied by mastoid bone erosion [23].

Primary auricle and EAC schwannomas are mostly solitary lesions [9–16, 22–24]. Bilateral vestibular schwannomas raise suspicion for neurofibromatosis-II, while multiple-nerve schwannomas require evaluation for Von-Reklinghausen disease [27]. A majority of auricle schwannomas have been reported on the ventral/anterior aspect of the pinna.

None of the reported cases of isolated primary auricle schwannoma mandated any form of radiological investigation due to their small/moderate size, non-aggressive nature and absence of neurological symptoms.

None of the authors precisely located or found the nerve of origin for the auricle schwannomas. However, a few authors determined a probable nerve of origin based on tumor site and theoretical knowledge of the neural supply of the pinna [13, 15]. The somatogenic innervation of the pinna involves four nerves: the auricular branch of vagus nerve, the great auricular nerve, auriculotemporal nerve and the lesser occipital nerve. There is an extensive innervation overlap over both lateral and medial surface of the pinna; therefore we presume that it is tough to precisely comment with certainty regarding a particular nerve of origin solely based on the location of the tumor over the auricle [17].

The exact etiology behind the development of an auricle schwannoma is unknown. There are various theories regarding its onset: (1) mesodermal origin from the perineurium; and (2) ectodermal tumor derived from Schwann cells. A history of prior trauma is reported by few authors [13, 28–30].

Histopathological examination is mandatory to confirm a diagnosis. Erlandson classified schwannomas into 7 subtypes: conventional, cellular, plexiform, melanotic, cranial nerve, ancient and granular cell schwannomas [31]. However, there are 4 major histological variants: conventional, plexiform, cellular and ancient [32]. All the variants mainly have two distinct histological patterns: Antoni types A and B.

IHC can aid in the diagnosis, but is more useful to rule out close differentials [32]. S-100 is highly sensitive and most common immunostain used when dealing with a suspected peripheral nerve tumor. Both schwannomas and neurofibromas show moderate/strong reactivity to S-100. However S-100 has low specificity for diagnosing peripheral nerve cell tumors. SOX-10 staining is considered more sensitive and specific than S-100 for peripheral nerve tumors [33]. Diffuse staining with CD-34 is seen in neurofibromas, while schwannomas only show occasional focal staining in non-cellular (Antoni-B) areas. Calretinin staining has high specificity for schwannoma and is helpful in differentiating it from neurofibroma [34, 35]. Intensive staining with CD-57 is noted in traumatic neuromas [36]. Schwannomas also stain positive with Leu-7antigen, glial fibrillary acidic protein (GFAP), and vimentin [37]. A positive neurofilament protein (NFP) staining of axons distinguishes a palisaded encapsulated neuroma from a schwannoma [38].

According to Jung et al., the differentials of a benign auricular tumor include: epidermal cysts (25.3%), hypertrophic scar (12.6%), fibrous tissue-accessory ear (9.5%), chronic inflammation-nevus (7.9%), keloid (6.3%), hemangioma (4.7%), and skin tag-seborrheic keratosis (3.1%) [21]. Benign peripheral nerve tumors, including neurilemmomas, do not generally fall in the differentials of an auricular mass and there are only sporadic reports of asyndromic solitary benign neural tumors over the pinna.

Complete surgical excision is considered the treatment of choice. Good encapsulation and non-adherence to adjacent perichondrium/cartilage/skin makes it easy to excise an auricular schwannoma from surrounding structure and remove it completely in toto [13, 16].

The prognosis after removal of a pinna schwannoma is excellent, and to the best of our knowledge there are no reports of post-operative recurrence/malignant transformation of an auricle schwannoma.

Conclusion

• Auricle schwannomas are almost equally distributed amongst male and female, and shows predominance for the left ear (77.78%).

• The tumor involves the lateral auricle surface three times more frequently than the medial surface.

• AS are small-moderate in size with a mean largest dimension of approximately 2 cm.

• Indolent slow-growing tumor and mean lesion duration of 3.17 years.

• Almost always solitary tumor, and presents as a painless, firm and well-encapsulated lesion.

• Only conventional histological variant has been reported from all previously published articles of AS.

• Preoperative clinical diagnosis is difficult while radiological investigations do not hold much importance. Diagnosis is confirmed by histopathologic examination

• FNAC is mostly inconclusive. Immunohistochemistry can assist in confirming a diagnosis, but is more helpful to rule out close differentials.

• Despite the extensive neural innervations of the auricle, the nerve of tumor origin is tough to precisely identify.

• Complete surgical excision is the treatment of choice, and recurrence or progression to malignant transformation is extremely rare.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Compliance with Ethical Standards

Conflict of interest

The authors declare that there is no conflict of interest.

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