Systematic Review of Intra Parotid Facial Nerve Schwannoma and a Case Report

Abstract

To evaluate the clinico-epidemiological aspects, pathological features, diagnostic methods, management protocol and functional outcome of the intra-parotid facial nerve schwannoma (IFNS) and to present a case report on intra parotid facial nerve schwannoma. PubMed, ProQuest, Google scholar, Science direct and Scopus were screened for studies. Article selection and data extraction was done by one investigator and other investigator confirmed its accuracy. After abstract and text screening a total of 69 articles were finally selected for the study with the inclusion and exclusion criteria of the systematic review as per PRISMA guidelines. With addition of one case reported to our department. The mean age of diagnosis was 43 ± 16 years with a slight female predominance. The mean duration of the tumour was 29.5 months and the mean size of the tumour on initial diagnosis was 3.6 ± 1.67 cm. Pleomorphic adenoma was the primary diagnosis in 44 cases. Superficial parotidectomy was done in 64 cases followed by resection in 47 cases. Reconstructive treatment was carried out by an end-to-end anastomosis in 3 patients and by facial-hypoglossal anastomosis in 16 patients, GAN cable grafting in 5 patients, a greater auricular nerve graft was done in18 patients and end-to-side interposed sural nerve graft in 8 patients. The type D tumours are treated by extended resection of the facial nerve, which is difficult to reconstruct and also employs a nerve graft that does not often give acceptable recovery of facial function. Facial nerve schwannomas being a rare entity poses a dilemma in diagnosis and management. Managing the lesions is also difficult as intraoperative adherence to the nerve makes a tumour free margin difficult without sacrificing the nerve. At present there is no consensus regarding the management of various types of intra-parotid facial nerve shwannoma.

Introduction

Schwannomas are one of the most common peripheral nerve sheath tumors. They are benign, well-circumscribed, encapsulated tumors of neuroectodermal origin, arising from the nerve sheath at any part of the peripheral nervous system [1, 2]. Facial nerve schwannomas are painless, slow growing tumors, of which, 9% of the cases have been reported to be intra-parotid. On the whole, schwannomas account for about 0.5–1.2% of all parotid gland tumors [3, 4]. Even though most of the head and neck schwannomas arise from the facial nerve, intra-parotid schwannomas are a rare entity [2]. The rarity of these lesions makes their early diagnosis difficult because their presentation mimics other benign tumors of the parotid gland [4]. In 1927, Ibarz reported the first case of an intra-parotid facial nerve schwannoma [IFNS], however, the first complete case report was published by O’Keefe, after 20 years. To date, approximately 87 studies have been published in world literature, reporting a total of 275 cases. Pre-operative diagnosis is very important in these cases, since misdiagnosis and mismanagement might result in life-long morbidity for the patient. Marchioni et al. proposed a classification of intraparotid schwannomas based on anatomical and pathological evaluation. Type A included those which could be safely dissected from the tumor, type B includes those which leads to partial acrifice of the facial nerve involving one of the peripheral branches, type C includes sacrifice of the main trunk, whereas type D required sacrifice of the facial nerve involving main trunk and at least one of the temporo-facial or cervico-facial branches [2]. The management of intra-parotid schwannoma is a topic of debate since last two decades. Some authors advocate surgical management, whereas, others support ‘wait and watch’ approach for cases with minimal or no facial nerve dysfunction and no intra-temporal extension. Review of literature revealed that most of the studies are case reports or a series of few cases, through which the authors have expressed their own perspective of diagnosis and management according to their observation from those cases. However, a strong evidence-based guideline for the diagnosis and management of the disease has not been reported yet. There has been no research study conducted on this topic with a reasonable sample size to report the management and its outcome. Hence, the only way to get a clear picture of the disease characteristics, treatment modalities, efficacy of various treatment methods and prognosis, is to review all the studies that has been reported till date. Therefore, we conducted a systematic review of all the studies that has been published in this regard, to date, with the aim of establishing the specifications of the disease and its management protocol. In addition, we also present the case of a 40-year-old male with a seven-year-old swelling of the parotid gland.

Materials and Methods

The substructure of the systematic review is based on PRISMA Statement [5]. All studies published on or before March 2020 were included. Based on institutional guidelines, the study was granted exemption from institutional ethic committee (Ref no Dean/2020/EC/2257(A) dated 07/12/2020).

Eligibility Criteria

Inclusion criteria: All published studies in English language reporting the cases with IFNS as final histopathological diagnosis were included. No time restriction was applied.

Exclusion criteria: Exclusion criteria included articles published in other languages like Chinese, Spanish, Italian, French etc., review articles without any case reports, unclear histological diagnosis like tumors with dual findings of pleomorphic adenoma and schwannoma, Parotid schwannomas arising from peripheral nerves other than facial nerve.

Information Sources

The following databases were incorporated in the systematic search for relevant literature: PubMed, ProQuest, Google scholar, Science direct and Scopus. All searches were conducted from in March 2020.

Search Terms

The following search terms were used “intra-parotid facial nerve schwannoma”. Other nomenclature for schwannoma like neurinoma and neurilemoma which were used in earlier articles were also included in search.

Study Selection

Two authors independently performed screening of all published articles obtained from the electronic databases.

In 1st phase of selection- the titles and abstracts were screened and evaluated.

In the 2nd phase of selection- Full text were screened and study which have the inclusion and exclusion criteria were selected (Fig. 1).

Fig. 1.

Flow chart showing the process of identification and screening of articles and cases reviewed

Total article in pubmed on search of key words “Intraparotid facial nerve schwanomma, neurilemoma, neurinoma—87.

Total cases reported—275.

Articles included in study—69.

Articles Excluded (chinese, Italian, Spanish, polish, French)—18.

Collection Process

For all the included studies, following descriptive characteristics were recorded: age, sex, duration, site, tumour dimensions, sign, symptoms, preoperative facial nerve status, initial diagnosis, treatment, nerve reconstruction performed, postoperative facial nerve status, follow up and recurrences (Table 1).

Table 1.

List of included studies and its main characteristics

S.no	Authors	Cases (L:R)	Age/Mean Age(in years)	Sex (M:F)	Size range	Duration (months)	Preoperative facial function
1	O’Keefe 1949 An Otol, Rhino, Laryngol [6]	1(L)	57	M	4 × 3 × 2	2 years	Mild paresis
2	Wade 1951 Br J Surg [7]	1(L)	52	F	3.5 cm	8 months	Complete Facial paralysis
3	Ackerman et al. 1956. Ann Surg [8]	6 (left-3) 3-NA	48.5 (35–60)	1:5	4–6 cm	2–17 yrs	Weakness-1
4	Gibson and Hora 1970 An Otol, Rhino, Laryngol [9]	1(R)	64	F	2.5 cm	1 year	N
5	Avery et al. laryngoscope 1972 [10]	2 (1:1)	51	2:0	2–6 cm	3 years	N-1 Paralysis-1
6	Aston Archives Surg 1975 [11]	2 (1:1)	34 (21–47)	1:1	1.5–4	2 months-11 years	N
7	Mabogunje J Ped Surg 1977 [12]	1(R)	14	M	4 × 4	4yrs	N
8	Kavanagh and Panje 1982 Am J Otolaryngol [13]	1(R)	50	F	3 cm	6 months	N
9	Bretlau et al. Acta Otolaryngologica 1983 [14]	1(R)	42	F	3 × 3	2 years	N
10	Balle and Greison 1984 Ann Otol Rhinol Laryngol [15]	2 (1:1)	23.25	2:0	2 × 3 cm	3 months–5 years	N
11	Prasad et al. 1993. Otolaryngol Head & neck Surg [16]	1(R)	39	M	1 × 2 cm	6 months	N
12	Elahi et al. J Otolaryngol 1995 [17]	1	47	M	ND	ND	N-HBGI
13	Kumar et al. J Laryngol otol 1996 [18]	1(L)	8	F	2 × 1 cm	1.5 months	N
14	Shah et al. 1997. J Postgrad Med [19]	1(L)	30	F	3 × 4	6 months	N
15	Sarela et al. 1997. Br J Oral Maxillofac Surg [20]	2 (1:1)	30 (25.35)	1:1	3–5 cm	2–6 months	N
16	Jayaraj et al. 1997 [21]	1(L)	42	M	3 cm	10 years	N
17	Prager and Klesper 1998 Int J Oral Maxillofac Surg [22]	1(R)	37	M	ND	ND	N
18	Chong et al. 2000. ANZ J Surg [23]	5	29–65	3:2	3–4 cm	3 months–1 years	N
19	Segas et al. 2001 ENT J [24]	1(L)	44	F	2 × 3	2 months	N
20	Chiang et al. 2001. Annals of oto, rhino, laryngol [25]	1(R)	27	F	3.5 × 3.5 Multilobular (8 multiple tumours)	3 months	N
21	Jaehne and Ussmuller 2001. HNO [26]	22	46.3 yrs (17–77)	14:8	2–6 cm	6 months-11 years	Facial paresis-6
22	Oncel et al. 2002 J Laryngol Otol [27]	1(L)	32	M	2 × 2.5 cm	6 months	N
23	Vellin JF et al. Ann Otolaryngol Chir Cervicofac 2003 [28]	1(L)	89	F	ND	ND	Yes
24	Maly B et al. Acta Cytologica 2003 [29]	1(L)	22	M	2 × 2	6 months	N
25	Caughey et al. 2004. Otolaryngol head Neck Surg [30]	8/29 (7:22)	44 (7–78)	11:18 total	ND	10.9	5 pts- normal average HBG- 1.5/6
26	Asaad et al. 2004 Diagn cytopathol [31]	2(1:1)	62.5 (50–75)	0:2	1.5-4 cm	3 months – 18 months	ND
27	Ulku et al. 2004. Am J otolaryngol [32]	1(R)	20	F	3 cm	1 year	HBGI
28	Chung et al. 2004. Surg Neurol [33]	2 (1:1)	39 (31–47)	1:1	2 × 4 cm	1–2 years	HBGI, HBGIV one case with paresis
29	Shimizu et al. AJNR AM J Neuroradiol 2005 [34]	5(R)	57.4 (50–70)	2:3	1.7–2.8 cm	ND	Weakness-1
30	Bayindir et al. 2006. J Craniomaxillofac Surg [35]	1(R)	41	F	ND	5 years	N
31	Marchioni et al. 2007. J Laryngol otol [2]	1(R)	74	F	3 × 1 cm	3 months	Weakness (HBGII)
32	Kreeft et al. Clin Otolaryngol 2007 [36]	2 (2:0)	50 (44–56)	2:0	2 × 2.5 cm	4 months(3–5)	N
33	Kang et al. Ann Acad Med Singapore 2007 [37]	4 (2:2)	49 (41–64)	2:2	ND	8.5 months(3 months-1 year)	N
34	Fyrmpas et al. Eur Arch Otorhinolaryngol 2008 [38]	4	47.7 (35–62)	3:1	ND	4.5 years(2–7)	Normal -2 Weakness-2(IV,V)
35	Mehta et al. Am J Otolaryngol 2008 [39]	1(L)	72	M	2.3 cm	ND	N
36	Salemis et al. Int J Oral Maxillofac Surg 2008 [40]	1(R)	32	F	5 × 4	ND	HBG-IV
37	Kizil et al. Kulak Burun Bogaz Ihtis Derg 2008 [41]	1	7	M	3 × 3	3 years	N
38	Guzzo et al. Tumori 2009 [42]	8 (2-L) Rest ND	38 (20–61)	6:2	1.4–4 cm	2–3 years	All normal
39	Ma et al. J Craniomaxillofac Surg 2010 [4]	4 (ND)	50.5 (42–64)	2:2	1.8–4 cm	10 days-2 years	Normal-3 HBG2-1
40	Back et al. Acta Otolaryngol 2010 [43]	5 (ND)	42.6 (19–75)	4:1	ND	ND	N-4 Weakness-1
41	Villatoro et al. 2011 Acta Otorrhinolaringol Esp [44]	2(R)	51.5 yrs	1:1	4 cm	3–4 months	N
42	Chan et al. Pathology 2011[45]	1(L)	46	F	1.7 cm	1	N
43	Irfan et al. Med J Malaysia 2011 [46]	1(L)	39	F	6 × 6 cm	1.5 years	Weakness (HBGIV)
44	Zhong et al. 2011 JOMS [Accessory Parotid] [47]	3 (1:2)	23.6 (14–39)	1:2	1.5–4 cm	(6 months–10 years)	N
45	Gross et al. Am J Otolaryngol 2012 [48]	15 (NA)	41 (27–66)	7:8	ND	38.3 months (4 months–20 years)	N
46	Li et al. Acta Otolaryngol 2012 [49]	7 (2:5)	40.9 (21–62)	5:2	1.5–3.5	4.14 (1–10) years	3- facial paresis(III)
47	De Ceulaer et al. B-ENT 2012 [50]	1(R)	68	F	ND	ND	Frontal branch palsy
48	Mena-Dominguez et al. Acta Otorhinolaryngol 2013 [51]	1(R)	63	M	Multiple –3.4 and 4.3 cm	ND	N
49	Lee et al. 2013, Int J Oral Maxillofac Surg [52]	15 (Not specified)	40 (28–69)	6:9	3.7 (1.4–8) cm	ND	N
50	Bacciu et al. 2013 Audiol and Neurotol [53]	3 (1:2)	36 (25–47)	2:1	> 1.5 cm	ND	HBGI-2 HBGII-1
51	Ingrosso et al. 2013 Am J Otolaryngol [54]	1(R)	48	F	1.79 ml	5 months	HBGII
52	Serhrouchni et al. 2014 Diagn Pathol [55]	1(R)	62	M	5 × 4 cm	2 years	N
53	Cho et al. 2014. Arch Craniofac Surg [56]	1(R)	59	M	3 × 1.5 cm	5 years	N (Zygomatic branch)
54	Jaiswal et al. World J Clin Cases 2015 [57]	1(L)	27	F	3 × 2 cm	1 year	N
55	Rigante 2015. Acta Otorhinolaryngol Ital [58]	1(L)	51	F	3.2 × 3.5 cm	6 yrs	N
56	Khilnani 2015. Int J Appl Basic Med Res [59]	1(R)	7	F	10 × 9 × 7 cm	1 year	N
57	Damar et al. 2016. Case rep otolaryngol [60]	1(L)	55	M	3 × 3.5 cm	3 months	N
58	Zheng et.al. 2016. J Cranio-Maxillofac Surg [61]	28 (12:16)	43 (14–66)	7:21	2.69 (1.5–4)	37.6 months (9–40 yrs)	N
59	Zhang et al. 2016. J Oral Maxillofac Surg [62]	9 (3:6)	35.8 (13–49)	3:6	2 × 3–7 × 6	(0.5–10) years	N
60	Carlson et al. 2016 Mayo Clin Proc [63]	18	ND	ND	ND	ND	4-facial paresis
61	Khalele 2016 Future dental Journal [64]	1(R)	48	M	ND	ND	N
62	Bhattacharya 2017 J Cytol [65]	1(L)	41	F	10 × 6	1 year	Facial weakness
63	Simone et al. 2018 Acta otorhinolaryngol [66]	2(Lt)	39, 45	1:1	ND	2 years, 3 years	N
64	Sah et al. 2018 Neurology India [67]	3 (2:1)	36 (26–48)	2:1	1.5–4 cm	3.6(2–5)	N
65	Ungari et al. 2018An di stomatologia [68]	1(R)	76	F	5 × 4	10 months	N
66	Verma et al. 2019. Ind J Surg Oncol [69]	4 (L:R-	34, 19, 37,45	M:F – 1:3	1.5–8 cm	ND	N:P – 3:1
67	Li et al. 2019. Acta Otolaryngol [70]	42 (L:R- 27:15)	44.5(13–71)	16:26	2.69+ –1.14	8.5(0.1–240)	39:3
68	Seo 2019. Arch Craniofac Surg [71]	1(R)	57	F	3 × 3	3 years	N
69	Gumussoy 2019. J Craniofac Surg [72]	1(R)	9	M	2 × 2 cm	10 months	N
70	Present case	1(R)	40	M	3.5 × 2.3 × 1.5 cm	7 years	N

Preoperative diagnosis	Treatment	Facial nerve weakness	Nerve grafting	Follow up
Adenoma	Total parotidectomy with nerve sacrifice	Complete paralysis	No	NA
PA	SP	Yes HBGVI	No	15 months HBG VI
ND	Enucleation-5 Biopsy/drained-1	Partial sacrifice-3 Total sacrifice-2	No	1 year
ND	Superficial parotidectomy	NO	No	1 yr
ND	Superficial parotidectomy	Weakness-1 recovered partially after 4 years Complete paralysis-1	Anastomosis-1	4 years
Benign tumor	Parotidectomy with neurectomy	Yes	Primary anastomosis	18 months, recovered
PA	SP	No	No	NA
Frozen section- infiltrating sarcoma/malignant schwanomma	TP + TM + VII neurectomy	Yes	GAN cable grafting	Benign schwanomma
Inconclusive	Superficial parotid lobectomy	No	No	9 months
FNAC- 1- inconclusive 2-adenolymphoma Frozen- benign mesenchymal tumor	Case 1- SP with neurectomy Case 2- TM + SP + neurectomy	Yes	End to end- GAN graft anastomosis	3 years Case 1- HBGIV Case 2- HBGIII
FNAC- not done Frozen – Neurilemmoma	SP + TM + Neurectomy	Yes	GAN cable grafting Gold implant in upper eyelid	1 year HBG-III
FNAC-inconclusive Frozen-schwanomma	Superficial parotidectomy	NO	No	6 months HBGI
FNAC-Inconclusive Frozen proven	Superficial parotidectomy	Temporal	No	3 months- HBGI
ND	Superficial parotidectomy	Yes(upper half)	No	3 months (HBG-II)
FNAC- inconclusive	Enucleation	Case 1- NO Case 2- buccal branch sacrifice	NO	Case 1– HBGI- 2 yrs Case 2- slight weakness recovered in 6 months (18 months)
FNAC-PA	SP	NO	NO	ND
Inconclusive Frozen- Neurinoma	SP	NO HBGI	NO	ND
FNAC- inconclusive	SP + TM  + NG- 2 SP only-1 SP + NG-1 TP + TM + NG-1	Yes	4- greater auricular	5 months–28 months HBGII-2 HBGIII-2 HBG V-1
Chronic sialadenitis-FNAC	Total parotidectomy	Complete paralysis	After 6 months- Facial-hypoglossal anastomosis	2 yrs sufficient recovery
ND	Superficial parotidectomy with segmental neurectomy	HBGV	Greater auricular nerve	ND
Frozen section- 4 schwanomma	SP + segmental nerve resection- 9 Enucleation -7 Total Parotidectomy + nerve resection 6	Yes	GAN- 3 Hypoglossal- facial anastomosis-3	(1–6 yrs)
FNAC- inconclusive	SP	Postop paralysis TZ branch	NO	2 months
ND	Superficial parotidectomy (segment of nerve sacrificed)	Yes	Greater auricular nerve	ND
FNAC proved schwanomma	Superficial parotidectomy with nerve preservation	No	No	NA
Mixed tumor MRI showed—7 cases with both temporal and parotid 1 with only parotid	S. Parotidectomy-6 Transmastoid –transparotid-1 No details-1	4.4/6 One case with total paralysis	6 had nerve repair (HBG-III)	1 year
Mesenchymal tumor of neural origin	SP	ND	ND	ND
FNAC-inconclusive	SP	Marginal mandibular paresis	NO	2 years HBG!
Inconclusive	SP	Case i- neurectomy	Case i- End to end- GAN	HBG III- 6 years HBGIV- 30 months
MRI- 3 pts showed target sign on T2 weighted images	Resection wioth nerve grafting-1 Enucleation-3 Biopsy-1	3	Greater auricular and transverse cervical	ND
FNAC- inconclusive	TP with preservation of FN	NO	No	HBGI, 2 years
Inconclusive	Superficial parotidectomy with mastoidectomy	HBGVI	Greater auricular nerve	6 months- HBGV
FNAC- 1-inconclusive Schwanomma	Superficial parotidectomy-1 Biopsy-1	1(HBGVI)	Secondary grafting with sural nerve graft-facial hypoglossal jump anastomosis	1.5 years(HBG-III)
PA	Superficial parotidectomy -3 Total parotidectomy with nerve grafting-1	4(HBG III-3 HBGIV-1)	2- greater auricular	1.5 years(6 months-2 years 8 months)
inconclusive	Superficial parotidectomy -2 Biopsy without tumor resection-2	2 (HBG III,IV	2- greater auricular	3.5 yrs
Inconclusive FNAC	Biopsy ( conservative)	No	No	ND
Inconclusive	Superficial parotidectomy	HBG-VI	Facial reanimation with muscle transfer	ND
ND	Superficial parotidectomy	No	No	6 months
FNAC-PA in 1 case Other inconclusive Intraop frozen- schwanomma-2	Total parotidectomy-5 Superficial parotidectomy-2 Conservative-1	Nerve transected-2 Postop HBGI-5 HBGV-1 HBGVI-2	ND	10.5 years (2–28 years)
3- PA 1-Cyst	Superficial parotidectomy	1(HB-6)	1	5 (1.5–8)
FNAC-PA-2 Inconclusive-2	SP-2 TP with neurectomy-2 Conservative-1	HBG-I-1 HBG-II-1 HBG-III-1 HBGIV-2	Sural graft-2	24.2 months (9–50)
FNAC- PA One case – epitheloid schwanomma	Subtotal parotidectomy	Case-1- HBGV Case 2- transient paresis	No	2 years
Inconclusive Epitheloid schwanomma on HP and IHC	Superficial parotidectomy with enucleation of deep lobe tumor	ND	ND	ND
Inconclusive	Total parotidectomy with nerve monitoring	Same-4	No	5 months
Frozen – Schwanomma	Resection- 2 Stripping-1	Postoperative NO facial palsy	GAN graft in case 1	1–21 months
FNAC-4 ( PA)	Superficial parotidectomy – 11 Total-4 (6-mastoidectomy)	9 HBG1-6 HBG-2–1 HBG3-3 HBG4-2 HBG5-1 HBG6-2	Of 6 mastoidectomy cases- 5- sural/GAN Facial- hypoglossal end to side -1	24 months (0–17 years)
H/p	Tumor resection-5 Biopsy and decompression-2	3	Greater auricular-1	40 months
ND	Total parotidectomy with neurectmy	Yes	Great auricular nerve	ND
PA	Parotidectomy	HB IV	No	1 month
USG FNAC- Inconclusive-8 Schwanomma-5 PA-2	Sleeve operation- 12 Debulking- 2 Observation-1	HBI-14 HBII-1	ND	24 months
ND	TM + TP- 2 TM + MCF + TP-1	HBGIII-2 HBGIV-1	Cable grafting –Sural nerve	14–34 months
MRI- intraparotid and intratemporal extension	SP + FSRT (fractionated stereotactic RT)	Yes	ND	30.2 months HBGIII
H/P confirmed	Total conservative parotidectomy	ND	ND	ND
Intraoperative frozen-Schwanomma	Excision of mass	HB-I	No	1 month
PA MRI showed String Sign	Superficial parotidectomy	Mild weakness	ND	ND
Spindle cell lesion mesenchymal origin	Intracapsular microenucleation	HB-IV	N	6 months
PA	Superficial Parotidectomy	1[HB-III]	N	3 months
Inconclusive FNAC	Parotidectomy with temporofacial division neurectomy	Y	N	ND
27(PA/WT) 1-IFNS	Intracapsular microenucleation- 12 Complete resection- 14 Biopsy-2	5	5	5.75 years
5-PA 4-WT	Total parotidectomy-2 Total parotidectomy with nerve sparing-4 Superficial parotidectomy-3	ND	ND	6.2 (1–16) yrs
ND	Observation-9 Resection-8 Multimodality -1	ND	ND	ND
Trucut- PA	Superficial parotidectomy	No	NO	18 months
FNAC-Schwanomma	Resection	ND	ND	ND
ND	Supercial parotidectomy	1	Hypoglossal-1	2.5 yrs
2-PA Inconclusive-1	Superficial parotidectomy with FN transected	Case-1,3- HBGII Case-2 HBGIV	NO	Case-1- after 5 months- HBGI Case2- HBGI(6 months) Case 3- HBGI (3 months)
FNAC- inconclusive	Superficial parotidectomy	NO	NO	6 months
ND	Superficial parotidectomy	2	1 case – greater auricular nerve	ND
Surgery history -10 FNAC-2 CT scan-2 False diagnosed -28	Stripping-17 Intracapsular enucleation – 9 Resection and reconstruction – 13 Resection without reconstruction -3	Spared -26 Sacrificed -3 Reconstructed Anastomosis -9 Nerve graft -4	ND	3.37+ –2.69
ND	Extracapsular enucleation without parotidectomy	No	ND	6 months
PA	Superficial parotidectomy	ND	ND	ND
PA	Superficial Parotidectomy	HBG- IV	No	12 months Improved to HBG-I

L Left, R Right, M Male, F Female, N Normal. P Paresis, ND Not documented, PA Pleomorphic adenoma, WT Warthin’s tumour, FNAC Fine needle aspiration cytology, CT Computed tomography, MRI Magentic resonance imaging, USG Ultrasonography, HBG House Brackmann grading, SP Superficial parotidectomy, TP Total Parotidectomy, TM Transmastoid, NG Nerve grafting, GAN Greater auricular nerve, FSRT Fractionated stereotactic radiotherapy, MCF Middle cranial fossa, H/p Histopathology, IHC Immunohistochemistry

Risk of Bias

This systematic review is based on case reports and case series. Although few articles have not documented complete information required but still, they were reviewed to support the current incidence.

Case Report

A 40-year-old patient presented in our outdoor department with a 7-year-old painless slowly growing mass over his right preauricular region. The swelling is not associated with any pain, local rise of temperature, cervical lymphadenopathy or facial nerve paresis. Physical examination revealed a 3 × 2 cm firm mass over his right parotid region (Fig. 2). No facial nerve weakness was noted on preliminary examination and the patient was classified of having grade 1 House Brackmann (HB) grading system. A fine needle aspiration cytology revealed pleomorphic adenoma as the diagnosis. A contrast enhanced computed tomography was done to radiologically evaluate the lesion which also reported of being a benign tumor of the parotid gland measuring approximately 3.5 × 2.3 × 1.5 cm (Fig. 3). The lesion only involved the superficial lobe with no involvement of deep lobe or parapharyngeal space. A routine blood investigation and pre admission clinics was done for the patient and the patient gave consent for a superficial parotidectomy.

Fig. 2.

Visible swelling over right parotid region

Fig. 3.

A. Axial section of CECT face showing extension of tumour mass B. coronal sections of CECT face showing extension of tumour mass

A lazy S incision was undertaken for the superficial lobectomy of the parotid gland and a sub–Superficial Muscular Aponeurotic System (SMAS) flap was reflected (Fig. 4). The facial nerve trunk was identified and tumor was dissected out from all the five branches of the facial nerve (Fig. 5). The SMAS layer was mobilized and a layer wise closure was performed with insertion of a vacuum drain. Post operatively the patient exhibited a mild-weakness of the temporal and zygomatic branches of the facial nerve (HB Grade IV) which improved over the period of next few months. The final histopathological report gave a diagnosis of Schwannoma with areas of Antoni A and Antoni B and IHC marker revealed the presence of S-100 protein confirming the diagnosis. After one year of follow up (Fig. 6), the patient reported with complete improvement in the facial nerve weakness to HB grade I and gustatory sweating over the preauricular region suggestive of Frey’s syndrome.The patient was reassured regarding the condition and was managed with anti-cholinergic drugs but shown no significant improvement noted.

Fig. 4.

A. Sub SMAS flap B. Exposed tumour mass with branches of facial nerve

Fig. 5.

Specimen showing tumour and superficial lobe of parotid

Fig. 6.

A. One year follow-up showing fully recovered surgical site B. normal facial nerve function

Result

The descriptive characteristics of the included studies are shown in the Table 1. A total of 87 articles were found in the various scientific database with search expressions relevant to this study. After abstract and text screening a total of 69 articles were finally selected for the study with the inclusion and exclusion criteria of the systematic review. The selection process of the include study is shown in Fig. 1. The review of 69 eligible articles came out with a total of 275 cases reported in literature (including the case report). The mean age at diagnosis of IFNS was 43 years ± 16 years, the male to female ratio was 126:134, IFNS has female sex preponderance, Parotid gland was involved in all the cases and 99 cases did not report the affected side. Type A tumours would comprise neoplasms resectable without sacrifice of the facial nerve. From the review, this would include 7 cases. Type B tumours would be resectable only with partial sacrifice of the facial nerve, involving one of the peripheral branches or its distal divisions. From the review, this would include 13 cases. Type C tumours would be resectable only with sacrifice of the main trunk of the facial nerve, with extratemporal extent (subtype e) or intra-extratemporal extent (subtype i), the total number of type C cases included were 12. Type D tumours would be resectable only with sacrifice of the main trunk of the facial nerve and at least one of the temporo-facial or cervico-facial branches, the total number of cases of type included were 6. The mean duration of tumour at the time of presentation was 29.46 months, the mean size of tumour at initial diagnosis was 3.55 ± 1.67 cm. Most of the studies reported IFNS sign and symptoms as painless mass with progressive increase in size and few studies reported it as a painful mass, mild facial paresis was seen in 47cases and complete paralysis was seen in 1 patient. Pleomorphic adenoma was the primary diagnosis in 44 cases. Reconstructive treatment was carried out by an end-to-end anastomosis in 3 patients and by facial-hypoglossal anastomosis in 16 patients, GAN cable grafting in 5 patients, a greater auricular nerve graft was done in18 patients and end-to-side interposed sural nerve graft in 8 patients. The type D tumours are treated by extended resection of the facial nerve, which is difficult to reconstruct and also employs a nerve graft that does not often give acceptable recovery of facial function. Superficial parotidectomy was done in 64 cases followed by resection in 47 cases. A summary of the results of the included studies are shown in the (Tables 2, 3, 4, 5, 6).

Table 2.

Demographic data

Total number of cases		287
Involved site	Left side	80
	Right side	108
	ND	99
Mean age of the patient		42.99 ± 16.11 years
Sex (M: F)		126:134 (1: 1.06)
Average size of the lesion		3.55 ± 1.67 cm
Mean duration of the lesion		29.46 months

Table 3.

Classification of intra-parotid schwannomas based on anatomical and pathological evaluation (based on Marchioni et al. classification)

Types	No. of cases
Main trunk	2
A	38
B	26
C	11
D	15
N.D	195

Table 4.

Pre-op Facial nerve function and diagnosis

Pre-op facial nerve function	Normal		104
	Mild paresis/weakness	47
	Complete paralysis (HBG VI)	1
	ND	1
Pre- op diagnosis	Pleomorphic adenoma (PA)	44
	Benign tumor/cyst/lesion	3
	FNAC	Inconclusive	39
		Pleomorphic adenoma	13
		Chronic sialadenitis	1
		Adenolymphoma	3
		Schwannoma	8
	Frozen section	Malignant schwannoma	14
		Benign tumor	2
		Neurilemmoma	1
		Neurinoma	1
	MRI	Mixed Tumor	8
		Target sign	3
		String Sign	1

Table 5.

Treatment and nerve grafting

Treatment	Superficial Parotidectomy	− Neurectomy	64
		+ Neurectomy	15
	Total parotidectomy	+ Nerve preservation	32
		+ Nerve sacrifice	4
	Enucleation	Extracapsular	18
		Intracapsular micronucleation	22
	Resection		47
	Stripping		18
	Sleeve operation		12
	Debulking		2
	Biopsy		10
	Observation		10
	Multimodality		1
	ND		1
Nerve grafting	Anastomosis		58
	Cable nerve grafting		7
	Facial reanimation with muscle transfer		1
	Not done		30
	ND		12

Table 6.

Recurrence

Present	2
Absent	90
Died	1
Stable disease	1
ND	29

Discussion

Intra-parotid schwannomas imitate other benign parotid tumors in presentation. The diagnosis becomes challenging as the number of reported cases are limited [4, 73]. Radiologically schwannomas lack any pathognomonic features although the study by Shimizu et al. states that 3 out of 5 lesions exhibit a target like appearance with a peripheral increased signal intensity and central decreased signal intensity on T2 weighted MR images [74, 75]. In the included studies of this systematic review MRI showed mixed tumor in 8 patients. The findings in MRI in various included studies showed the tumour mass located below stylomastoid foramen produce characteristic “string sign” which is formed due to vertical orientation of soft tissue on either side of mass. The string is actually a representation of entering and exiting nerve that is in continuity with nerve sheath tumour.

Ultrasonography guided FNAC although one of the first diagnostic tools to be used in case of parotid swelling is of limited accuracy when it comes to diagnosing schwannomas with only 17.6% of the cases with an accurate diagnosis [25], in our included studies only for 8 patients FNAC results came as schwannoma. Intraoperative presentation of schwannomas is also varied, with some being easily separated from the nerve while most being coherent to the nerve [30, 76, 77]. The gross appearance of the tumor does not differ significantly from other parotid tumors; however, a characteristic feature is difficulty in identifying the main trunk [4].

Marchioni et al. proposed a classification of intraparotid schwannomas based on anatomical and pathological evaluation. Type A included those which could be safely dissected from the tumor and type B, C and D required sacrifice of the nerve and reconstructive measures [2]. In the present study, 38 cases was categorized as type A, 26 cases type B, 11 cases as type C, 15 cases as type D and for other 195 cases no information was available.

Histologically, arrangements of Antoni A, with typical Verocay bodies, and Antoni B are typically seen in IPFNS. Antoni B architecture is considered degenerated areas of Antoni A where myxoid stroma, microcystic degenerative changes and several xanthoma cells can be observed. Although Verocay bodies are frequently seen in schwannomas, they can also be present in other lesions. So, endothelial vessels with ectasia, thrombosis or perivascular hyalinization must be combined with such Antoni arrangements and Verocay bodies to establish the diagnosis of schwannoma [72].

Controversy exists regarding the management of facial nerve schwannomas. Alicandri-Ciufelli et al. suggested several factors are to be considered in the management of the facial nerve schwannomas including the localisation and adherences of the tumour, the relationship with the facial nerve and the pre-operative nerve function. In patients with a parotid mass, associated facial nerve palsy generally indicates malignancy. But it can also be seen in benign parotid masses such as pleomorphic adenoma and Warthin’s tumour, in our included studies only one patient developed complete paralysis. A routine follow- up with MRI is required in patients in whom a wait and watch approach are applied with close monitoring of the facial nerve function. A surgical approach is to be considered whenever the tumour size is appreciable or facial nerve function is being compromised [72], in the included studies of our systematic review superficial parotidectomy was done in 64 cases followed by resection in 47 cases. If the schwannoma is extending into the intracranial portion of facial nerve then trans mastoid approach is also required to achieve complete excision which may further requires nerve grafting.

Conclusion

Intra-parotid facial nerve schwannoma is very rare and also clinically difficult to distinguish from other parotid tumors. When there is an asymptomatic parotid mass, careful attention is required to avoid misdiagnosis of Intra-parotid facial nerve schwannoma. When it involves the facial nerve or its branches, the facial nerve resection is unavoidable, which should be followed by nerve reconstruction procedures. A conservative approach if followed should consider for regular follow ups of the patient. Schwannomas are benign tumors and hence whenever possible preservation of the facial nerve and facial aesthetics should be considered while surgically managing the patient. However, there is a lack of consensus regarding the management of the different types of IFNS, which necessitates prospective studies with large sample size in future.

Declarations

Conflict of interest

The authors declares that they have no conflict of interest.