CC BY-NC-ND 4.0 · Int Arch Otorhinolaryngol 2019; 23(03): e360-e370
DOI: 10.1055/s-0039-1692635
Systematic Review
Thieme Revinter Publicações Ltda Rio de Janeiro, Brazil

Palatal Schwannoma: An Analysis of 45 Literature Reports and of an Illustrative Case

1   Department of Ear, Nose, and Throat, Krishna Institute of Medical Sciences Deemed University, Karad, Maharashtra, India
,
Anagha Rajguru
1   Department of Ear, Nose, and Throat, Krishna Institute of Medical Sciences Deemed University, Karad, Maharashtra, India
,
Vishwakarma Mayashankar
2   Department of Ear, Nose, and Throat, HBT Medical College and Dr RN Cooper Municipal General Hospital, Juhu, Mumbai, Maharashtra, India
,
Indranil Mukherjee
3   Department of Ear, Nose, and Throat, Gouri Devi Institute of Medical Sciences and Hospital, Rajbandh, Durgapur, West Bengal, India
,
Bhagyashree Jaipuria
4   Department of Ear, Nose, and Throat, Lokmanya Tilak Municipal Medical College and Hospital, Sion, Mumbai, Maharashtra, India
,
Devika Shere
5   Department of Ear, Nose, and Throat, Rajiv Gandhi Medical College, Thane, Maharashtra, India
› Author Affiliations
Further Information

Address for correspondence

Vivek Dokania, MBBS, MS
Department of Ear, Nose, and Throat, Krishna Institute of Medical Sciences, Deemed University
Karad 415110, Maharashtra
India   

Publication History

22 March 2019

13 April 2019

Publication Date:
26 July 2019 (online)

 

Abstract

Introduction Schwannomas are benign tumors originating from differentiated Schwann cells. Being the least common intraoral neoplasm of neural origin, it is rarely seen in the palate. The literature lacks an extensive review of intraoral schwannoma confined to the palate.

Objective To review previously reported cases of palatal schwannoma along with an illustrative case, and to provide a better insight regarding clinicopathological and radiological features of this neural tumor in a rare intraoral site.

Data Synthesis We present a case of palatal schwannoma in a 16-year-old female. An additional 45 cases were identified in 2 medical database searches (PubMed and Google Scholar) published from the year 1985 onwards, and from 13 countries, in the 5 continents. The ages of the patients ranged from 3 to 84 years old. Palatal schwannoma showed a slight predilection to females, with a male/female ratio of ∼ 1:1.81. Hard palate involvement is almost twice greater than soft palate involvement. Surgical excision was employed in almost all of the cases, and recurrence was reported only once.

Conclusion Palatal schwannomas, although rare, have been reported both over the hard and the soft palate. They mostly present as a painless, firm, well-encapsulated, slow-growing solitary lesion over the lateral palatal aspect.

Imaging can add to suspicion and can delineate a differential diagnosis, but the diagnosis is confirmed by pathological examination. Fine-needle aspiration cytology (FNAC) is almost always inconclusive. Immunohistochemistry can assist in confirming a diagnosis, but is more important to rule out close differentials. Complete surgical excision is the treatment of choice, and recurrence or malignant transformation are extremely rare.


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Introduction

Schwannoma or neurilemmoma is a benign tumor of neuroectodermal origin that is derived from Schwann cells of the neural sheath.[1] [2] [3] In 1910, Verocay first described the microscopic features of this tumor under the term neurinoma.[4] The term schwannoma was introduced by Masson in 1932.[5] Later, in 1935, Stout[3] used the term, neurilemmoma, and further detailed its histopathology. In 1940, Tarlov described the tumor to be of fibroblastic origin and coined the term perineural fibroblastoma.[6] About between 25 and 45% of all schwannomas are found in the head and neck region, and only between 1 and 12% of them have an intraoral origin.[7] [8] [9] However, the palatal location is rare. The present article presents a specific systematic review of the published literature on palatal schwannomas, along with an illustrative case.


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Review of the Literature

Case Presentation

A 16-year-old female presented with a complaint of a painless swelling over the palatal region. She first noticed a small nodule 2 months before, which was gradually increasing in size. She was otherwise healthy and did not report a history of alcohol consumption or of smoking. No genetic or syndromic abnormalities were reported from her family. Her laboratory reports were unremarkable. In the intraoral examination, a solitary, nontender, firm swelling, ∼ 2.5 × 2 cm in dimension, was noted over the left soft palate. The tumor had a whitish-yellow appearance, and the overlying mucosa was ulcerated ([Fig. 1]). A computed tomography (CT) scan revealed a well-defined, hypodense, soft tissue lesion measuring 27.8 × 21.6 × 18.2 mm involving the left side of the soft palate ([Fig. 2]). With a probable clinical diagnosis of benign salivary gland tumor, the lesion was completely excised and the defect was allowed to heal by secondary intention. The histological examination of the lesion revealed a predominant presence of Antoni A areas with spindle-shaped cells arranged in a palisading pattern and central acellular areas representing Verocay bodies ([Figs. 3] and [4]). Some areas also showed a hypocellular and less organized arrangement, as seen in the Antoni B type. The immunohistochemical (IHC) examination with S-100 protein revealed intense positivity in the cells of the tumor ([Fig. 5]). The tumor cells also showed positive expression of SRY-related HMG-box 10 (SOX-10) protein ([Fig. 6]). Based on the clinical behavior, as well as on the histological and IHC findings, the final diagnosis was of a benign schwannoma of the soft palate (conventional variant).

Zoom Image
Fig. 1 Painless swelling over the left soft palate with ulceration of the overlying mucosa.
Zoom Image
Fig. 2 Computed tomography shows a hypodense, soft tissue lesion involving the soft palate on left side (red arrow).
Zoom Image
Fig. 3 Section showing a spindle cell tumor and areas of collagenization (Hematoxylin and eosin staining; 100x).
Zoom Image
Fig. 4 Section showing proliferating fusiform cells arranged in palisading pattern and areas of acellular eosinophilic regions representing Verocay bodies (Hematoxylin and eosin staining; 200x).
Zoom Image
Fig. 5 Section showing tumor cells expressing strong nuclear and cytoplasmic S-100.
Zoom Image
Fig. 6 Section showing tumor cells expressing SRY-related HMG-box 10 (SOX-10).

#

Methodology

A systematic review of the literature was performed in August 2018 on 2 different databases (PubMed and Google Scholar). The database was searched for full-length articles and abstracts using the following Medical Subject Headings (MeSH): palate, AND schwannoma, AND/OR neurilemoma, AND/OR neurilemmoma AND hard AND/OR soft palate, AND/OR intraoral MINUS tongue, vestibule and other intraoral anatomical locations. The search included synonymous terms and was confined to studies or reports in humans. The review included isolated case reports or articles with up to 2 cases of palatal schwannomas published after 1984 in English, German or Japanese. Articles containing > 2 cases of palatal schwannoma, or larger case series, were not included. Cases diagnosed as malignant schwannoma at the initial presentation were not included. No age limits were applied. Information from the included articles was collected in a predesigned Microsoft Excel (Microsoft Corporation, Redmond, WA, USA) spreadsheet.


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#

Result

A total of 46 cases (45 published cases and an illustrative case) of palatal schwannoma were included in the present review. From the included articles, clinical, histopathological, radiological, and treatment findings were charted ([Tables 1] and [2]).[10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54]

Table 1

Review of previously reported palatal schwannomas

Case authors

Year

Age/gender

Country

Lesion duration (months)

Clinical symptoms

Lesion size (cm)

Site

Surgical procedure

IHC

F/U

Recurrence

MT

Variant

Yamashita et al[10]

1985

19/F

Japan

NI

swelling

1.5 × 1.2

RSP

CEN

S-100  + ve

NI

no

no

cv

Jones et al[11]

1987

29/F

UK

24

painless swelling

2.5

RSP

CEN

NI

3 years

no

no

cv

Hieda et al[12]

1987

44/M

Japan

4

tumor

1.5 × 1.2

RHP

WLE & tumor resected en bloc

S-100  + ve

4 months

no

no

cv

Krolls et al[13]

1994

21/F

USA

12

tumor, discomfort during eating and talking

NI

LHP

Excision Bx

NI

3 years

yes

no

plx

Amir et al[14]

2002

40/M

USA

3

FB sensation, dysphagia, garbled speech

5 × 4

EHP

WLE; secondary intention closure

S-100  + ve

NI

no

no

cv

Rabbels et al[ 15]

2005

11/F

Germany

3

painless swelling

2 × 2

RHP

WLE; collagen closure

S-100, Vimentin & NSE  + ve

2 years

no

no

cv

López-Carriches et al[16]

2009

15/M

Spain

3

swelling

1 × 1.5

LHP

Incision Bx-CEN

S-100  + ve

2 years

no

no

cv

Baliga et al[17]

2009

40/F

India

recently

painless swelling

NI

LSP

FNAC (IC)-WLE; collagen closure

NI

10 years

no

no

cv

Murthy et al[18]

2009

28/F

India

4

swelling, bleeding, with tongue pressure

1.5 × 1.5

LHP

Incision Bx- CEN

NI

NI

no

no

cv

Lollar et al[19]

2010

33/M

USA

3

enlarging mass

2 × 2

MHP

Shave Bx- WLE

S-100 & Vimentin  + ve

NI

no

no

cv

Parikh et al[20]

2010

64/F

India

36

enlarging mass

2 × 2

MHP

CEN

NI

NI

no

no

cv

Isildak et al[21]

2010

45/F

Turkey

180

enlarging mass

2 × 2

RHP

WLE

S-100 + ve; Actin - ve

NI

no

no

cv with NFLA

Santos et al[22]

2010

41/F

Brazil

60

painless nodule

3 × 1

RHP

CEN

NI

NI

no

no

cv

Santos et al[22]

2010

53/F

Brazil

6

painless swelling

3 × 3

HP

CEN

S-100  + ve

NI

no

no

cv

Chawla et al[23]

2011

9/M

UK

0.75

(3 weeks)

painless swelling, difficulty in eating and swallowing

1 × 1

RSP

CEN

NI

1 year

no

no

cv

dos Santos et al[24]

2011

3/F

Brazil

6

enlarging painless mass

1.6

RHP

CEN

S-100, Vimentin, EMA, GFAP, CD-57 & CD-56 + ve, NF; AE1/AE3, & Calponin - ve

1 year

no

no

plx

Dhupar et al[25]

2012

10/M

India

5

swelling, dysphagia, garbled speech, bleeding

3 × 2

MHP

WLE; palatal splinting

NI

NI

no

no

cv

Handschel et al[26]

2012

32/M

Germany

24

enlarging nodule

1 × 2

RHP

Incision Bx-WLE; prosthesis placement

S-100 +ve

6 months

no

no

cv

Shetty et al[27]

2012

70/F

India

24

enlarging painless mass, discomfort on mastication

2 × 2

RHP

FNAC (IC)-CEN

NI

8 months

no

no

cv

Prasanna Kumar et al[28]

2012

18/m

India

22

enlarging painless mass

3 × 2.5

LHP

CEN

NI

NI

no

no

cv

Kapetanakis et al[29]

2012

21/F

Greece

14

enlarging painless mass

1.5 × 2

SP

WLE

S-100 + ve

NI

no

no

plx

Rahpeyma et al[30]

2012

12/F

Iran

3

enlarging painless mass

3

RSP

Incision Bx-CEN; buccinators myomucosal flap closure

S-100 + ve

6 months

no

no

cv

Venkatachala et al[31]

2013

43/M

India

1

swelling and dysphagia

2 × 2

RSP

CEN

S-100 + ve

NI

no

no

cv

Gainza-Cirauqui et al[32]

2013

35/F

Spain

60

enlarging tumor

2 × 1.5

MHP

FNAC(IC)-CEN

S-100 + ve

2 years

no

no

ancient

Chikhale et al[33]

2013

42/F

India

ID

ID

2 × 2

LHP

CEN

NI

NI

no

no

cv

Moradzadeh Khiavi et al[34]

2014

21/M

Iran

2

painless mass

2 × 2

MHP

Incision Bx-CEN

S-100 + ve

6 months

no

no

cv

Aboh et al[35]

2014

49/F

Italy

240

enlarging mass, difficulty with oral hygiene, phonation and dyspnea

4 × 3

LHP

CEN

NI

1 year

no

no

cv

Parhar et al[36]

2014

34/F

India

12

enlarging painless mass

2 × 1.5

RHP

Incision Bx - CEN

NI

NI

no

no

cv

Sahoo et al[37]

2014

28/M

India

48

enlarging mass, pain since 3 months

3

LHP

FNAC -WLE

S-100 + ve, SMA - ve

10 months

no

no

cv

Kudoh et al[38]

2015

84/M

Japan

ID

ID

3

LHP

Incision Bx-partial maxillectomy; split-thickness skin graft

S-100 + ve, Ki-67 + ve rate 1%

29 months

no

no

cv

Meundi et al[39]

2015

20/F

India

ID

ID

1 × 3

LHP

FNAC(IC)-CEN

NI

2 months

no

no

cv

Tibbetts et al[40]

2015

11/F

USA

12

enlarging mass

1

RSP

WLE

NI

1 month

no

no

cv

Yaga et al[41]

2015

28/M

India

12

enlarging nodule, dysphagia

4 × 4

RSP

FNAC-CEN

NI

NI

no

no

cv

Karatas et al[42]

2015

36/F

Turkey

36

enlarging mass

3 × 5

RHP

CEN

S-100 & Vimentin + ve

18 months

no

no

cv

Morgan et al[43]

2015

16/F

India

12

painless swelling

2 × 3

RHP

FNAC (IC)- CEN

NI

NI

no

no

cv

Sicca et al[44]

2015

13/F

Italy

couple of weeks

rapidly growing mass

1.5

LSP

Incision Bx- CEN

S-100 + ve

6 months

no

no

cv

Barhmi et al[45]

2016

13/NI

Morocco

6

painless swelling

2

RSP

Incision Bx-CEN

S-100 + ve

2 years

no

no

cv

Shi et al[46]

2016

56/F

USA

ID

ID

1.6 × 2

LSP

Incision Bx-CEN

S-100 + ve; AE1/AE3 cytokeratin -ve

11 days

no

no

cv

Eroglu et al[47]

2017

29/M

Turkey

ID

ID

2 × 2

LHP

Enucleated (y-shaped incision); primary closure

NI

18 months

no

no

cv

Poonja et al[48]

2017

30/F

India

8

swelling

1 × 1

MHP

FNAC (IC)-CEN

S-100 + ve

1 year

no

no

cellular

Vera- Sirera et al[49]

2017

26/F

Spain

>10

painless swelling

3 × 2

LSP

FNAC (IC)- CEN

S-100, CD-34, EMA, CD-117 & FVIII-RA + ve

14 months

no

no

ancient

Gueiros et al[50]

2017

26/M

Brazil

1/6 (5 days)

painless nodule

2 × 2

RHP

Incision Bx-CEN

NI

30 months

no

no

cv

Melo et al[51]

2018

18/m

Brazil

36

painless lesion

3.5 × 3

RHP

Incision Bx-CEN

S-100 + ve

1 year

no

no

cv

Khalele et al[52]

2018

33/F

Egypt

28

painless swelling, discomfort in mastication

2 × 3

RHP

FNAC(IC)-CEN

S-100 + ve; NF -ve

NI

no

no

cv

Murakami et al[53]

2018

17/F

Japan

12

swelling, pharyngeal pain and redness

2 × 1.9

MSP

WLE; buccinator myomucosal flap closure

S-100 + ve

6 months

no

no

cv

Present case

2016

16/F

India

2

painless swelling

2.5 × 2

LSP

CEN

S-100 + ve & SOX-10 + ve

1 year

no

no

cv

Abbreviations: +ve, positive; Bx, biopsy; CEN, complete excision with narrow margin; cv, conventional variant; EHP, entire hard palate; EMA, epithelial membrane antigen; F/U, follow-up duration; F, female; FB, foreign body; FNAC, fine needle aspiration cytology; GFAP, glial fibrillary acidic protein; HP, hard palate; IC, inconclusive; ID, Incidentally detected; IHC, immunohistochemistry; LHP, left hard palate; LSP, left soft palate; M, male; MHP, midline hard palate; mo, month/months; MSP, midline soft palate; MT, malignant transformation; NF, neurofilament; NFLA, neurofibroma-like areas; NI, not informed; NSE, neuron specific enolase; plx, plexiform variant; RHP, right hard palate; RSP, right soft palate; SMA, smooth muscle actin; SOX-10, SRY-related HMG-box 10; SP, soft palate; -ve, negative; WLE, wide local excision; yr, year/years.


Table 2

Updated clinical profile of reported cases of palatal schwannomas

Clinical features of 46 patients with palatal schwannomas

Feature

Data[a]

Number of cases amenable to analysis

Female

29 (64%)

45

Mean age at time of initial evaluation, years old

30.04 (range: 3–84)

46

Mean duration of lesion, months

25.63 (range: 5 days– 20 years)

38

Cases reported from India

15 (32.6%)

46

Hard palate involvement

31 (67.4%)

46

Soft palate involvement

15 (32.6%)

46

Mean size of lesion, centimeters

2.4 (range: 1–5)

44

Symptomatic cases

41 (89%)

46

Asymptomatic cases/ cases detected incidentally

5 (11%)

46

Symptoms at initial presentation

 Painless swelling/nodule

40 (87%)

46

 Painful lesion/ pharynx pain

2 (4.3%)

46

 Dysphagia

5 (10.9%)

46

 Dysphonia

3 (6.5%)

46

 Dyspnea

1 (2.2%)

46

 Difficulty in mastication

4 (8.7%)

46

 Bleeding from tumor

2 (4.3%)

46

 Foreign body sensation

1 (2.2%)

46

 Pharyngeal erythema

1 (2.2%)

46

Signs at initial presentation

 Tenderness over lesion

2 (4.3%)

46

 Soft on palpation

4 (8.7%)

46

 Ulcerated overlying mucosa

8 (17.4%)

46

Histological variant

 Conventional

40 (87%)

46

 Plexiform

3 (6.5%)

46

 Ancient

2 (4.3%)

46

 Cellular

1 (2.2%)

46

IHC positive staining

27[b]

 S-100

27 (100%)

 Vimentin

3 (11.1%)

 EMA

2 (3.7%)

 SOX-10

1 (3.7%)

 NSE

1 (3.7%)

 GFAP

1 (3.7%)

 CD-56 & CD-57

1 (3.7%)

 CD-34 & CD-117

1 (3.7%)

Surgical treatment

46

 Enucleation/complete excision with

 narrow margin/excision biopsy

33 (71.7%)

 Wide margin excision

11 (24%)

 Partial maxillectomy

1 (2.2%)

 En bloc resection

1 (2.2%)

Prognosis

46

 Recurrence

1 (2.2%)

 Malignant transformation

0 (0%)

Abbreviations: EMA, epithelial membrane antigen; GFAP, glial fibrillary acidic protein; SOX-10, SRY-related HMG-box 10.


a Number (%) unless otherwise specified.


b Number of cases in which some form of immunohistochemistry staining was performed.


Out of 46 compiled cases, 29 were female (64%), and 16 were male (in 1 case, no gender was reported).[45] The ages ranged from 3 to 84 years old, with an average of 30.04 years old. The mean duration of the lesion from 38 reported cases was of 25.63 months (range: 5days–20 years), while in the remaining 8 cases no information about the duration of the tumor could be retrieved (either the exact numerical duration was not stated, or the lesion was incidentally detected).[10] [17] [33] [38] [39] [44] [46] [47] Some articles reported the duration of onset in days, weeks or years. Therefore, the approximate lesional age was converted and charted into months. The incorporated cases were reported from 13 countries: India (n = 15), USA (n = 5), Brazil (n = 5), Japan (n = 4), Spain (n = 3), Turkey (n = 3), UK (n = 2), Germany (n = 2), Iran (n = 2), Italy (n = 2), Greece (n = 1), Morocco (n = 1), and Egypt (n = 1) ([Fig. 7]). The majority of the cases has been reported from India, indicating either a high prevalence or a greater awareness about the disease in that country.

Zoom Image
Fig. 7 Worldwide distribution of reported cases of palatal schwannomas.

The tumor involved the soft and the hard palate in 15 (32.6%) and in 31 (67.4%) subjects, respectively. Among the 15 soft palatal lesions, 8 involved the right side, 5 involved the left side, 1 was in the midline, and no specific site over the soft palate was mentioned in 1 case.[22] Out of 31 hard palatal lesions, 13 were confined to the right hard palate, 11 involved the left side, 5 were in the midline, 1 involved the entire hard palate, and no specific hard palatal location was reported in 1 case.[29]

Most of the articles mentioned the width and length of the lesion, but the depth dimension is rarely reported. The largest diameter/dimensions of the tumor ranged from 5 cm to 1 cm, with an average of 2.4 cm (no information about the dimension of the lesion was reported in 2 cases).[13] [17] When studying for an association between the duration of the lesion and lesion size, we found a weak positive correlation (r = 0.25). However, the correlation is statistically insignificant (p = 0.13) ([Fig. 8]).

Zoom Image
Fig. 8 Relationship between lesion size and duration of lesion.

Symptoms were commented in 41 cases (89%). The remaining 5 cases were incidentally detected or asymptomatic. Painless swelling/nodule was the most common symptom, present in 40 cases (87%). One case reported delayed pain over the tumor[37] while in another patient, pharyngeal pain was present.[53] Other symptoms were reported in the following frequency: dysphagia (n = 5) [14] [ 23] [ 25] [ 31] [ 41] dysphonia/garbled speech (n = 3)[ 14] [25] [35], dyspnea (n = 1) [35], difficult mastication (n = 4) [13] [ 23] [ 27] [52], occasional bleeding (n = 2) [18] [ 25], foreign body sensation (n = 1) [14], difficulty in oral hygiene (n = 1)[ 35] and pharyngeal redness (n = 1) [53].

Clinically, most of the lesions were reported as nontender and/or firm/hard. Tenderness was elicited only twice[21] [ 37], while soft swelling on palpation was reported in four cases [18] [ 38] [ 43] [ 44]. Jones et al reported a cystic component in the lesion.[11] Most of the lesions had a healthy overlying mucosa without any obvious ulceration. Ulceration of the overlying mucosa was noted in seven other cases apart from present case.[13] [ 23] [ 30] [ 31] [34] [37] [44] The low frequency of ulceration reflects a good encapsulation of this tumor.

Of the histological variant, the conventional subtype dominated and was reported in 40 cases (87%). It was followed by plexiform-3,[13] [24] [29] ancient-2,[32] [49] and cellular variant- 1.[48] Almost all of the cases with conventional phenotype exhibited Verocay bodies and a predominance of Antoni A areas over Antoni B areas. The additional presence of acute and chronic inflammatory infiltrate,[23] areas of hyalinization, and thin blood vessels with/without thrombus/fibrin,[11] [28] [30] [31] [46] and areas containing epithelioid cells have also been reported from cases with conventional phenotypes.[46] In one report, a note was made about the predominance of neurofibroma-like areas.[21]

Various IHC staining were performed in 27 patients. S-100 staining was employed in all of the 27 amenable cases, and showed strong immunoreactivity in all of the employed cases. Other authors revealed varying degrees of positive immunoreactivity with different stains: vimentin,[15] [19] [42] epithelial membrane antigen (EMA),[24] [49] SOX-10 (present case), neuron specific enolase (NSE),[15] glial fibrillary acidic protein (GFAP),[24] CD-56 and CD-57,[24] and CD-34 and CD-117.[49] Immunonegative results were noted with the following stains: actin,[21] neurofilament protein (NFP),[24] [52] smooth muscle antigen,[37] cytokeratin,[46] AE1/AE3,[24] and Calponin.[24]

Various imaging modalities capable of revealing abnormal palatal morphologies were performed on 36 patients, including simple X-ray scan in 1, panoramic radiography (orthopantomogram [OPG]) in 6, maxillary occlusal radiography in 7, CT scan (with or without contrast) in 20, magnetic resonance imaging (MRI) in 7, and positron emission tomography (PET) scan in 1 patient. The principal CT scan finding was an isodense-hypodense soft tissue lesion without any bony erosion/resorption. Partial/complete bony erosion was noted in 6 instances.[15] [16] [ 33] [37] [38] [51] The lesion was seen eroding into the right maxillary sinus through the floor of the sinus in one case;[15] while in another patient, the mass was seen invading the nasal cavity through the palatal bone.[38] Orthopantomogramand maxillary occlusal radiography showed mostly a radiolucent lesion, without any bony alteration or periapical changes. In MRI exams, the mass appeared hypo-to-isointense on T1-weighted images and hyperintense on T2-weighted images, in almost all of the cases. Small foci of central calcification were evident on MRI in one occasion.[40]

With the exception of two cases, all of the lesions were treated with simple surgical removal, either with enucleation, with wide local excision with a good margin, or with a complete resection without incorporating a wide margin. The remaining two cases were treated by partial maxillectomy,[38] and by en bloc resection.[12] The defect was either closed primarily or was allowed to heal by secondary intention. Otherwise, large defects were closed with some form of prosthesis, splints, grafts or flaps. Reconstruction using buccinator myomucosal pedicle flap,[30] [53] split-thickness skin graft,[38] palatal splint,[25] and collagen sheet have been reported by various authors.[15] [17]

Preoperative fine-needle aspiration cytology (FNAC) was performed in 10 cases, while incisional biopsy was performed in 13 cases. Fine-needle aspiration cytology was inconclusive in almost all of the cases.

Postoperative follow-up was performed in 29 cases, and the follow-up duration ranged from 11 days to a decade. Recurrence was noted only once,[13] while none of the included cases reported malignant transformation.


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Discussion

Schwannoma is synonymous with neurinoma, neurilemmoma, and perineural fibroblastoma.[22] It arises from cranial, peripheral, or autonomic nerves that contain Schwann cells. It never arises from cranial nerves I and II, since they lack Schwann cells.[16] Sensory nerve is more common, with rare involvement of motor nerve.[54]

About 25 to 45% of all schwannomas are found in the head and neck region, and only between 1 to 12% of them have an intraoral origin.[7] [8] [9] However, the palatal location is rare. In a review of 52 cases of schwannomas of the head and neck region, only 1 case of schwannoma over the hard palate was reported.[55] A review of the literature on oral, as well as on head and neck schwannomas, showed varying results about the gender predilection of the tumor. Williams et al showed a male predominance of the tumor; for Lucas et al, there was a greater predilection for females,[56] [57] while other authors reported no gender predilection.[58] [59] Although reported in all age groups, schwannomas are more common in the 2nd and 3rd decades of life.[21]

Intraoral and palatal schwannomas are mostly solitary lesions.[34] Multiple nerve schwannomas require evaluation for Von-Reklinghausen disease, while bilateral vestibular schwannomas raise suspicion for neurofibromatosis-II.[30] The majority of palatal schwannomas have been reported on the lateral aspect of the palate.

Based on its location, schwannomas have been classified either as central (bone) or peripheral (soft tissue) type. The tumor may arise centrally in the bone, may arise within the nutrient canal, or a soft tissue tumor may secondarily erode into the bony tissue.[60] There are two clinical forms of oral schwannomas: the encapsulated form, surrounded by dense fibrous connective tissue, and the pediculate/nonencapsulated form, in which the tumor is located just below the mucous membrane.[61]

Although the etiology of schwannomas is unknown, trauma is considered to be an unclear etiological cause.[2] There are various theories about its onset: 1) ectodermal tumor derived from Schwann cells; and 2) mesodermal tumor arising from the perineurium.[38]

Most of the cases are asymptomatic, while most of the lesions are slow-growing. A sudden increase in size may be due to internal hemorrhage.[16] The clinical presentation depends upon the site of the tumor, the size of the tumor, and upon the anatomy of the affected nerve.[32]

There are four major histological types of schwannoma: conventional, plexiform, cellular, and ancient variant. According to Erlandson, schwannomas are classified into seven subtypes: conventional, cellular, plexiform, cranial nerve, melanotic, ancient, and granular cell schwannomas.[62] However, they have mainly two distinct histological patterns: Antoni types A and B. Antoni patterns were first described by Prof. Nils Ragnar Eugene Antoni. Antoni A areas consist of a hypercellular proliferation of fusiform cells, often arranged in a palisading pattern around a central acellular eosinophilic area known as Verocay bodies, while Antoni B areas are hypocellular and less organized.

The conventional variant consists mostly of Antoni A areas and Verocay bodies, with the occasional presence of Antoni B areas. The additional presence of acute/chronic inflammatory infiltrate, areas of hyalinization, and thin vessels containing thrombin are noted in the conventional variant.[22] The cellular variant is characterized by a marked increase in cellularity, with a compact arrangement of spindle cells in fascicles, variable nuclear hyperchromasia and pleomorphism, lack of Verocay bodies, and a predominance of Antoni A areas.[48] [64] The cellular variant, due to the increased mitotic activity and to the high potential for body destruction, is often confused with sarcoma.[65]

The ancient variant is characterized by degenerative changes, such as calcification, mild pleomorphism and bizarre nuclei, microcyst formation, dilated vessels, and hemorrhagic phenomena. Some authors believe that the absence of symptoms and the long history of the lesion are the probable cause of transformation into an ancient variant.[32] The plexiform type consists of both Antoni A and B regions with prominent Verocay bodies, like the conventional variant; however, the Schwann cells show a nodular arrangement with capsular delineation.[24]

Immunohistochemistry is important to distinguish schwannoma from other close differentials, and can aid in its diagnosis; however, it is not mandatory to confirm the diagnosis. S-100 is undoubtedly the first immunostaining that comes into mind when dealing with suspected peripheral nerve tumors. Both schwannomas and neurofibromas show moderate to strong reactivity to S-100. However, S-100 has low specificity for diagnosing peripheral nerve cell tumors. One study has found Sox-10 to be more sensitive and specific than S-100 for peripheral nerve tumors.[66] Diffuse staining with CD-34 is seen in neurofibromas, while schwannomas only occasionally show some focal staining in noncellular (Antoni-B) areas. Calretinin staining is found to be highly specific for schwannoma and useful in differentiating it from neurofibroma.[67] [68] Intensive staining with CD-57 is noted in traumatic neuromas.[69] Schwannomas also stain positive with Leu-7antigen, GFAP, and vimentin.[18] The presence of axons in palisaded encapsulated neuroma (PEN) and, therefore, positive staining with NFP, distinguishes it from schwannomas.[70] Staining with AE1/AE3 and with calponin can help rule out salivary gland tumors.[24]

The major differentials are benign salivary gland tumors, benign peripheral nerve tumors (neurofibroma, traumatic neuroma, and PEN), other benign mesenchymal tumors (lipoma and hemangiomas), and odontogenic tumors. Salivary gland tumors are the most common differential in our review, and were considered in 25 cases (54.3%).

Imaging modalities such as CT and MRI are useful during the initial workup to know the extent of the tumor, to delineate any bony erosion, to identify the nerve of origin, and to narrow the differentials.[14] [16] [19] [21] Yamazaki et al reported a case of a rapid growing lesion which was found in MRI to be originating from the mental nerve; therefore, the imaging exam assisted in the preoperative diagnosis of a peripheral nerve tumor that was otherwise considered a malignant lesion.[71] Schwannomas mostly appear iso- to hypointense on T1-weighted MRI images and hyperintense on T2-weighed MRI images. Computed tomography scans generally show a well-circumscribed, soft tissue lesion without any bony erosion. However, schwannomas can occasionally cause pressure erosion of the bone.[42] [72] The proportion of Antoni-A and B areas has been reported to have a significant influence on the imaging findings. Gomez-Brouchet et al reported that vestibular schwannomas with a homogeneous appearance on MRI were predominantly made of Antoni-A tissues, while those with heterogeneous/cystic features were predominantly composed of Antoni-B/mixed tissues.[73]

The therapy of choice consists of complete surgical removal. Schwannomas do not recur if they are completely removed. Only one case of benign palatal schwannoma has been found to recur after excision.[13] Malignant transformation of head and neck schwannomas are exceedingly unusual, although it has been reported.[74] [75]


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Final Comments

There is barely any paper in the literature focusing extensively on palatal schwannomas, and tackling this benign tumor as an individual entity. Despite divergent inferences from different articles, the following conclusions can be drawn:

  • Predominance in females, and involvement of the hard palate is twice the involvement of the soft palate.

  • Although reported in all age groups, schwannomas commonly present during the 2nd or 3rd decades of life.

  • Slow-growing tumor with a mean lesion duration of 25.63 months.

  • Mostly present on the lateral aspect of the palate, with occasional reports of midpalatal or panpalatal lesions.

  • Almost always a solitary tumor, presenting as a painless, nontender, and firm swelling.

  • The conventional variant is the most common histological phenotype.

  • Imaging can add to suspicion and can delineate a differential diagnosis, but the diagnosis is confirmed by pathological examination.

  • Benign tumor of the salivary gland is the most common clinical differential.

  • Fine-needle aspiration cytology is mostly inconclusive. Immunohistochemistry can assist in confirming a diagnosis, but is more helpful to rule out close differentials.

  • Complete surgical removal is the treatment of choice.

  • Recurrence and malignant transformation are extremely rare.


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Conflicts of Interests

The authors have no conflicts of interests to declare.


Address for correspondence

Vivek Dokania, MBBS, MS
Department of Ear, Nose, and Throat, Krishna Institute of Medical Sciences, Deemed University
Karad 415110, Maharashtra
India   


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Fig. 1 Painless swelling over the left soft palate with ulceration of the overlying mucosa.
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Fig. 2 Computed tomography shows a hypodense, soft tissue lesion involving the soft palate on left side (red arrow).
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Fig. 3 Section showing a spindle cell tumor and areas of collagenization (Hematoxylin and eosin staining; 100x).
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Fig. 4 Section showing proliferating fusiform cells arranged in palisading pattern and areas of acellular eosinophilic regions representing Verocay bodies (Hematoxylin and eosin staining; 200x).
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Fig. 5 Section showing tumor cells expressing strong nuclear and cytoplasmic S-100.
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Fig. 6 Section showing tumor cells expressing SRY-related HMG-box 10 (SOX-10).
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Fig. 7 Worldwide distribution of reported cases of palatal schwannomas.
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Fig. 8 Relationship between lesion size and duration of lesion.