Introduction
Schwannomas, or neurilemmomas, are benign neoplasms that arise from Schwann cells
that surround the peripheral, cranial, or autonomic nerve sheaths.[1 ] These slow-growing, benign, encapsulated tumors arise when proliferating Schwann
cells form a tumor that encompasses the nerve sheath.[1 ]
[2 ] Although the etiology is unknown, some causative factors such as spontaneous growth,
external injury, chronic irritation, or exposure to radiation have been hypothesized.[2 ] Typically these growths are solitary lesions with no genetic or gender predisposition,
although they may rarely occur in multiples when associated with neurofibromatosis.[3 ]
Approximately 25–48% of reported schwannomas occur in the head and neck region of
patients between 20–50 years of age.[2 ]
[4 ] However, only 1% originate in the intraoral cavity, mostly involving the tongue.[4 ] Schwannomas of the tongue present as a painless mass with conventional histology
demonstrating Antoni A patterns of nuclear palisades surrounding Verocay bodies with
alternating Antoni B patterns.[5 ] The presence of S-100 protein in immune-histochemical staining is a classic marker
for diagnostic confirmation and magnetic resonance imaging (MRI) is the gold standard
for preoperative imaging.[6 ] As schwannomas are typically benign, well circumscribed, and minimally invasive
tumors, complete surgical excision is the standard of care for ensuring no recurrence.[7 ]
Intraoral schwannomas commonly produce symptoms of throat discomfort, dysphagia, dysarthria,
snoring, and impaired breathing. Complete surgical excision leads to favorable outcomes
with no recurrence.[2 ]
[8 ] About 130 cases of tongue schwannoma have been reported in the English literature,
and of those, only 19 cases have been documented at the base of the tongue.[5 ] Surgical resection of schwannomas located at the base of the tongue are inherently
difficult due to limited operative exposure amidst intricate neurovascular anatomy,
which may cause significant morbidity when damaged, such as impaired speech, aspiration,
dysarthria, and dysphagia.[9 ] Due to the rarity of this lesion and the difficulties inherent in complete excision,
surgical complications may occur, including airway management, nerve preservation,
and anesthetic complications.[1 ]
[10 ]
The present article will review and comprehensively analyze relevant literature and
patient data to more definitely explain the treatment options and optimal surgical
approaches for base of tongue schwannomas.
Review of Literature
Literature Search
We systematically searched the National Library of Medicine's PubMed database up to
June 2016. The following search terms were used: “tongue” and “lingual” combined with
“schwannoma,” “neurilemmoma,” “nerve sheath tumor,” and “Schwann cell tumor.” We screened
titles and abstracts for possible inclusion, and subsequently, retrieved the full
text of potentially relevant articles for review. We chosen articles based on the
following criteria: it must be written in English, report cases using primary human
subjects, and discuss malignancies of the base of the tongue only, not of the palate,
cheek, and other tongue regions. All other articles were effectively excluded.
Results
Initial search of PubMed returned 293 articles (see [Fig. 1 ]). After screening the titles and abstracts for relevance, the full text of 14 articles
were retrieved for review. Upon completion of full text review, we excluded one article
because it was a literature review. Ultimately, 13 articles were included in this
review, consisting of 15 cases total. All included articles were case reports (N = 11) or case series (N = 2). The highest number of cases was reported in India (N = 4), followed by the United States of America and Taiwan (both N = 3). Summary of the study characteristics are reported in [Table 1 ].
Table 1
Study characteristics and patient demographics
Country
Studies (Cases)
India
4 (4)
Brazil
1 (1)
USA
3 (3)
Spain
1 (1)
England
1 (1)
Netherlands
1 (1)
Sweden
1 (1)
Taiwan
1 (3)
Study Design
Case report
11 (11)
Case series
2 (4)
Demographics
N (range)
Total patients
15
Mean Age
28.6 (9–49)
Gender
Male
7
Female
8
Fig. 1 Systematic search of PubMed returned 293 studies. After review of the titles, abstracts,
and full-text, 13 studies were included in the present review.
Clinical Presentation
The mean patient age was 28.6 years (range 9–49 years), and gender distribution nearly
equal with 8 female patients (53.3%) and 7 male patients (46.7%). The clinical presentation
of included cases is summarized in [Table 2 ]. All cases presented as a single nodule on the base of the tongue and all were symptomatic
(N = 15, 100%). Patients presented with either non-tender masses (N = 9, 60%) or painful lesions (N = 6, 40%) with reported discomfort at the back of the throat. Physical examination
of the lesions revealed that the majority were smooth (N = 9, 60%), non-ulcerated (N = 13, 86.7%), round (N = 3, 20%), well-defined and/or encapsulated (N = 13, 86.7%) tumors. The most common symptomatic complaint was noticeable swelling
(N = 13, 86.7%) frequently causing dysphagia (N = 7, 46.7%), discomfort (N = 6, 40%), dysarthria/change in voice (N = 5, 33.3%), snoring (N = 5, 33.3%), compromised airway and difficult nasal breathing (N = 3, 20%), and impaired tongue mobility (N = 2, 13.3%). Other symptoms during presentation included hemorrhage (N = 2, 13.3%), cosmetic deformity (N = 1, 6.7%), paresthesia (N = 1, 6.7%), bilateral otalgia (N = 1, 6.7%), and necrosis (N = 1, 6.7%). A delayed visit to a medical professional was commonly seen, with a mean
of 13.3 months (range 0.03–36 months) after the onset of symptoms to presentation.
Table 2
Clinical presentation of tongue base schwannoma (N = 15)
Number of nodules
N (%)
Single
15 (100%)
Well Defined
13 (86.7%)
Non tender/painful
9 (60%)
Pain/discomfort
6 (40%)
Smooth
9 (60%)
Submucosal
4 (26.7%)
Firm
4 (26.7%)
Symptoms
Swelling
13 (86.7%)
Dysphagia
7 (46.7%)
Dysarthria
5 (33.3%)
Snoring
5 (33.3%)
Compromised Airway
3 (20%)
Impaired tongue mobility
2 (13.3%)
Hemorrhage
2 (13.3%)
Paresthesis
1 (6.7%)
Otalgia
1 (6.7%)
Mean duration , months (N = 12)
13.3 (range, 0.03–36)
Workup
Blood and urine chemistries were rarely reported in these case reports. The two cases
in which blood and/or urine analyses were performed reported that all tests returned
within normal limits. Biopsy was performed in 11 cases, the majority of which were
done via excisional biopsy (N = 8; 72.7%) and the rest via fine needle aspiration (N = 3; 27.3%). All lesions were determined to be benign and none were graded as malignant
tumors.
Of the cases that performed histological analyses, histological findings, shown in
[Fig. 2 ] and [Fig. 3 ], of the biopsied tumors included spindle shaped or elongated cells (N = 13, 100%) that were often palisading (N = 10, 83.3%). Antoni A pattern was observed in 12 cases (N = 12; 100%) and Antoni B pattern was reported in 11 of those cases (91.7%). Verocay
bodies were found in 10 cases of those tumors that underwent biopsy examination (N = 10; 100%). All of the cases were encapsulated, well-defined tumors (N = 15, 100%) with four cases demonstrating dilated and congested vessels characteristic
of schwannomas (N = 4, 50% present when checked for). Nine cases reported the use of immunostaining
during evaluation. All cases stained positive for S100, while fewer cases stained
positive for vimentin (N = 1, 11%). No cases stained positive for actin, desmin, smooth muscle antigen, neuron
specific enolase, or epithelial membrane antigen. The histological characteristics
of tongue base schwannoma are outlined in [Table 3 ].
Table 3
Histological characteristics of tongue base schwannoma
Histology (N varies by info reported)
N (%)
Spindle/elongated cells
13/13 (100%)
Antoni A pattern or Verocay bodies
12/12 (100%)
Palisading
10/12 (83.3%)
Antoni B
11/12 (91.7%)
Well delineated and/or encapsulated
15/15 (100%)
Necrosis
1/15 (6.7%)
Hemorrhagic
2/15 (13.3%)
Dilated, congested vessels
4/8 (50%)
Immunostaining (
N
= 15)
Positive S100; S100 diffuse staining
15/15 (100%)
Radiology (
N
= 13)
T2 Hyperintense
8/13 (61.5%)
Hypointense T1
3/13 (23%)
Isointense to muscle
3/13 (23%)
Fig. 2 Schwannoma of the tongue under low power, with underlying lymphocytic infiltrate
and well-defined hypocellular lesion. Reproduced under CC-NC-ND from Badar et al (2016).[15 ]
Fig. 3 Schwannoma of the tongue is composed of spindled cells with hypocellular and hypercellular
regions in addition to focal nuclear-palisading areas (Verocay bodies). Reproduced
under CC-NC-ND from Badar et al (2016).[15 ]
MRIs are the preferred imaging technique for diagnosing base of the tongue base schwannomas
over other modalities due to higher spatial resolution and tissue contrast.[3 ] Some form of imaging was performed in 13 cases, with MRI being the most common modality
used (N = 9, 69.2%). Magnetic resonance imagining, see [Fig. 4 ], revealed well-delineated, rounded lesions that were T2 hyperintense (N = 8, 61.5%), T1 hypointense (N = 3, 23%), and isointense to muscle (N = 3, 23%), all of which are enhancement patterns characteristic of schwannomas. Less
common image findings included necrosis and blooming, indicating hemorrhage. All cases
had well-defined margins, were well-encapsulated, and revealed no indication of invasion.
Computed tomography was reported in 4 cases, and was primarily used to rule out metastases
(N = 4).
Fig. 4 Sagittal STIR MRI image of the head and neck (A ) reveals a well-defined hyperintense mass (red arrow) within the base of the tongue.
A coronal postcontrast fat-saturated image (B ) shows heterogeneous enhancement of the lesion abutting the right submandibular gland.
Reproduced under CC-NC-ND from Badar et al (2016).[15 ]
Outcome
In a majority of the cases, preservation of nerve function was a primary concern during
complete surgical resection. Despite a wide variety of surgical techniques utilized
in the 15 cases, all postoperative recoveries were uneventful with no post-surgical
complications such as loss of tongue function, sensation, or nerve damage. Of the
papers that reported follow-up for their patients (N = 9), the mean follow-up period was 13 months (range 1.5 months- 60 months) with
no evidence of recurrence in any of the cases.
The most common route used in resecting tongue base schwannomas was trans-orally (N = 7), which resulted in successful, short postoperative recovery times with no visible
scarring, nerve damage, or loss of tongue function.
Another surgical approach was transcervical incision with blunt dissection (N = 1), resulting in a simple, quick procedure that protected surrounding nerves. Advantages
to this approach included minimal morbidity, adequate exposure, no bony cuts, and
minimal postoperative care.
One case utilized a suprahyoid pharyngotomy procedure (N = 1), during which a tracheotomy was first performed followed by an incision made
at the hyoid bone, lacerating the platysma muscle, and enabling the removal of the
suprahyoid muscles from the hyoid bone. This surgical technique led to a long postoperative
period of 8 days and a more extensive and arduous recovery.
Other surgical approaches that were reported included mandibulotomy with lip splitting
and mandibular swing (N = 1), which is unfavorable as it leaves aesthetically deforming scars around the
mouth. Alternatively, the submandibular approach (N = 1) leaves a less noticeable scar below the mandible. Despite a resulting visible
scar, the transhyoid approach (N = 1) allowed adequate resection and access to the base of the tongue with no morbidity
and acceptable functional results. Excision via transoral laser microsurgery (N = 2) was used without any complication and the patient was discharged that same day
post-surgery. Fiber optic bronchoscope (FOB)-guided awake nasotracheal intubation
followed by general anesthesia was utilized in one case. The patient in this case
was successfully intubated with no other complications following the procedure.
Discussion
The overall clinical presentation of tongue base schwannoma is fairly consistent,
generally presenting as an encapsulated, well-defined mass at the back of the tongue.
Oftentimes patients will delay seeking medical attention until the airway is compromised,
presenting with symptoms of snoring, sleep apnea, difficulty breathing, dysphagia,
and dysarthria.[8 ]
[9 ]
[10 ]
[11 ] Generally, blood and urine chemistries are within normal limits.[8 ] Biopsies and further histological analyses show characteristic histology of a schwannoma,
revealing spindle shaped cells that are often palisading in a mixture of Antoni A
and Antoni B patterns.[5 ]
[12 ] MRI investigation usually demonstrates a well-delineated, encapsulated lesion with
enhancement patterns characteristic of schwannomas such as T2 hyperintensity, T1 hypointensity,
and isointensity to muscle.[11 ] All cases stain positively for S100.[13 ] Complete surgical excision is the gold standard of treatment for schwannomas, leading
to very low rates of recurrence.[9 ]
[13 ]
Surgical treatment of tongue base schwannomas is difficult due to limited operative
exposure.[9 ]
[10 ]
[14 ] Several surgical techniques are employed to remove schwannomas at the base of the
tongue due to varying levels of surgical difficulty based on tumor size and location.[14 ] Traditional surgical techniques for treatment of lesions at the base of the tongue
include transoral excision, suprahyoid pharyngotomy, submandibular approach, and mandibulotomy
with lip splitting.[1 ]
[2 ]
[3 ]
[4 ]
[5 ]
[6 ]
[8 ]
[9 ]
[10 ]
[11 ]
[12 ]
[13 ]
[14 ] The transoral surgical approach is the most common and preferred method for small,
well-encapsulated tumors, which do not cause any distortion of the airway.[13 ] While transoral operations eliminate cosmetic disfigurement from scars, this technique
is more likely to cause postoperative bleeding and swelling, especially in cases of
larger, deeper lesions.[14 ] Of the traditional surgical methods used to treat tongue schwannomas, the transoral
approach is recommended in favor of suprahyoid pharyngotomy and the submandibular
approach, which should be reserved for schwannomas that are malignant or deemed too
difficult to approach transorally.[10 ]
[11 ] Although mandibulotomy with lip splitting is frequently used for treatment of larger
schwannomas due to better exposure, this approach has a higher risk of damaging the
intricate neurovasculature within this region and can cause significant morbidity.[9 ]
The utilization of laser treatment in tumor excision is an emerging alternative to
traditional surgical methods. A CO2 laser surgery has high organ and nerve function preservation, minimal postoperative
care and complications, and bypasses difficulties posed by excessive bleeding and
obstruction of the lesion site.[7 ] Laser surgery is very precise and readily seals any blood vessels, providing a dry
field during dissection; however, higher cost and inadequate training of professionals
limit this technique.[7 ]
Another surgical challenge inherent in tongue base schwannoma treatment is difficult
intubation. Fiber optic bronchoscope-guided awake nasotracheal intubation followed
by general anesthesia proved advantageous for schwannomas that profoundly obstructed
the airway (N = 2).[1 ]
[5 ] This technique was performed to preserve the airway anatomy and permit intact muscle
tone to keep airway structures open, leading to easier visualization of the upper
airway.[1 ]
[5 ] Postoperative bleeding and swelling in the pharyngeal cavity and mouth floor is
a common complication that can lead to dangerous obstruction of the airway after excision.[1 ]
[5 ] Thus, nasal intubation and careful postoperative monitoring is recommended to maintain
a viable airway even after a successful, complete excision.[14 ] Proper anesthetic management for surgical excision of schwannoma of the tongue depends
on the location, size, and surgical approach.[1 ] Swellings located at the base of the tongue, though asymptomatic, may cause a distorted
airway upon operative proceedings, causing life threatening airway obstruction after
the induction of anesthesia.[1 ]
The methodology of this review was designed a priori with explicit procedures to reduce
bias in article selection, appraisal, and data extraction and analysis. However, there
exist limitations to the present review. Use of a single search database is one limiting
factor. Additionally, the study is limited by the consistency of the literature in
reporting data, even with thorough extraction of available data.
Final Comments
Tongue base schwannoma is a rare neoplasm with an excellent prognosis. The clinicopathological
characteristics are consistent with that of benign peripheral nerve sheath tumors.
Surgical removal is the primary mode of treatment with excellent postoperative prognosis
and rare instances of recurrence. Preservation of lingual function and minimal postoperative
complications, however still remain a challenge. Traditional surgical techniques,
though routinely performed as the primary treatment, frequently result in poor potential
outcomes such as swelling, scarring, bleeding, and longer recovery period. CO2 laser surgery is a new, upcoming treatment option that has been performed in several
cases with excellent results. Investigation into the efficacy of this modality on
primary lesions should be further explored as a minimally invasive alternative to
traditional surgical treatment is highly desirable.
