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Table of Contents
REVIEW ARTICLE
Year : 2020  |  Volume : 3  |  Issue : 3  |  Page : 517-525

Schwannomas of the head and neck region: A report of two cases with a narrative review of the literature


1 Consultant Head and Neck Oncosurgeon/Reconstruction Surgeon, Nagpur, Maharashtra, India
2 Consultant Oral and Facio-maxillary Surgeon, Nagpur, Maharashtra, India
3 Consultant Oral and Maxillofacial Surgeon, Indore, Madhya Pradesh, India

Date of Submission11-Apr-2020
Date of Decision10-May-2020
Date of Acceptance14-Jul-2020
Date of Web Publication19-Sep-2020

Correspondence Address:
Akheel Mohammad
Consultant Head and Neck Oncosurgeon/Reconstruction Surgeon, Flat 1002, Bliss 1, Skye luxuria, Nipaniya, Indore, Madhya Pradesh - 452 010
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/CRST.CRST_149_20

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  Abstract 


Schwannomas are slow-growing, encapsulated, benign tumors that can originate from any nerve covered with a sheath of Schwann cells. These tumors can originate from the cranial, peripheral, or autonomic nerves; about 25%–45% of schwannomas originate in the head-and-neck region, of which about 10% originate from either the vagal or sympathetic nervous system. They are rare tumors and are often asymptomatic, but depending on the location, they may produce secondary symptoms, such as swelling in the neck, dysphagia, and hoarseness of voice. The preoperative diagnosis of schwannomas is usually difficult because they often do not present with associated neurological deficits and can be misdiagnosed as other pathological conditions. Schwannomas should, therefore, be considered in the differential diagnosis of unilateral and slow-growing masses in the head and neck. The preferred modality for the treatment of schwannomas is surgical excision, and the recurrence of the tumor after complete resection is very rare. Vagal nerve injury is a common complication associated with surgical excision despite preserving nerve integrity. Therefore, the patients should be counseled preoperatively regarding the risk of developing neurological deficits. We searched in PubMed for articles related to schwannomas of the head and neck region, and extracted information regarding the symptoms, workup, management, and postoperative outcomes. We also discuss two cases, one with vagus nerve schwannoma and the other with supraclavicular cervical plexus schwannoma.

Keywords: Cervical schwannoma, schwannoma, vagus nerve schwannoma


How to cite this article:
Mohammad A, Iqbal MA, Wadhwania A. Schwannomas of the head and neck region: A report of two cases with a narrative review of the literature. Cancer Res Stat Treat 2020;3:517-25

How to cite this URL:
Mohammad A, Iqbal MA, Wadhwania A. Schwannomas of the head and neck region: A report of two cases with a narrative review of the literature. Cancer Res Stat Treat [serial online] 2020 [cited 2020 Oct 28];3:517-25. Available from: https://www.crstonline.com/text.asp?2020/3/3/517/295531




  Introduction Top


Schwannomas are nerve sheath neoplasms with sporadic malignant degeneration arising from either the peripheral, cranial or autonomic nervous sheath (ANS) cells of the body.[1] In 1935, Stout first coined the term “schwannoma,” also known as neurilemmoma or neuroma. Around 25%–45% of the schwannomas are located in the head-and-neck region, and about 10% of these originate from either the vagus or the sympathetic nervous system. They may involve the cranial nerves V, VI, VII, and X to XII, or the peripheral and sympathetic nerves.[2],[3],[4] These benign tumors are usually painless, slow-growing, and insidious and can occur regardless of age.[5],[6] Malignant transformation of schwannomas is very rare. The most common sites for the occurrence of schwannomas are the lateral neck, parapharyngeal space, and the temporal bone[7] and a commonly exhibited clinical sign is a lump in the neck with dysphagia and pain. Imaging modalities such as magnetic resonance imaging (MRI) and computed tomography (CT) scans can help in the diagnosis of schwannomas. The preferred treatment for schwannomas comprises complete surgical excision of the tumor, followed by a postoperative histopathological examination to establish the final diagnosis. In this review article, we aim to present a comprehensive literature review on schwannomas of the head-and-neck region, and also discuss two cases that we had managed at our hospital.


  Materials and Methods Top


We searched PubMed for keywords like “schwannoma,” “vagus nerve,” “cervical schwannoma,” and “neck mass.” Articles reporting schwannomas occurring in the head and neck region were selected. A total of 8 review articles published between 1995 and 2019 were included in the review. We recorded and analyzed the clinical symptoms, treatment approaches, and postoperative outcomes of the cases [Figure 1]. In addition, we report two cases of schwannomas that presented to our hospital, one originating from the vagal nerve and the other from the supraclavicular cervical plexus.
Figure 1: The search strategy to identify studies related to schwannomas in the head and neck regions

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  Case 1 Top


A 19-year-old boy presented to our hospital with a swelling in the lower part of the right side of the neck that had persisted for a year and was gradually increasing in size. The patient had no past medical or dental history. On clinical examination, a soft, oval swelling, 7 cm × 6 cm in size, was seen, which was movable in the horizontal, but not in the vertical direction. A provisional diagnosis of a nerve sheath tumor or paraganglioma was made. Fine-needle aspiration cytology (FNAC) indicated a schwannoma. A CT scan was done to assess the extent of the lesion. The swelling was around 8 cm × 6 cm in size, just above the clavicle on the right side of the neck below the sternomastoid muscle, laterally and medially displacing the internal jugular vein and carotid vessels, respectively [Figure 2]a. The cytologic findings of schwannomas usually correspond to the histologic findings of the Antoni Type A tissue. The Antoni Type A tissue comprises fragments of tightly cohesive fascicles with variable cellularity. The lesion showed dense fibrillary substances with palisading nuclei and the Verocay bodies [Figure 2]b.
Figure 2: (a) Computed tomography scan showed 8 cm × 6 cm swelling just above the clavicle in right side, below the sternomastoid muscle and displacing the internal jugular vein and carotid vessels, (b) Dense fibrillary substances were observed along with palisading nuclei and Verocay bodies and Antoni A cells seen with tightly cohesive fascicles with variable cellularity. (c) The vagus nerve was enclosed in the capsule of the lesion

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The patient was scheduled for surgical resection of the tumor under general anesthesia. A horizontal neck incision was made 4 cm above the clavicle. Dissection was done in layers. The sternocleidomastoid muscle was cut, and the lesion was approached. The vagus nerve was enclosed in the capsule of the lesion [Figure 2]c. The nerve was dissected, preserving anatomical integrity. Intraoperative neuromonitoring was not done because this facility was not available. Intraoperatively there was fluctuation in the heart rate probably due to vagal manipulation, but it was managed well by the experienced anesthetist. The lesion was freed from all the sides and was lifted very carefully from the carotid vessels. The internal jugular vein was surrounded by the capsule and had to be ligated. The tumor was removed in toto without disturbing the capsule of the lesion [Figure 3]a. The vagus nerve was saved [Figure 3]b, and the closure was done in layers. The final histopathological diagnosis was a vagus nerve schwannoma. Mild hoarseness of voice was observed postoperatively, which gradually improved over a period of 3 months. This patient neither had any family history of schwannomas nor underwent any molecular testing.
Figure 3: (a) The tumor was removed in toto without disturbing the capsule of the lesion. (b) The vagus nerve was saved

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  Case 2 Top


A 61-year-old woman presented to our hospital with a swelling in the lower part of the left side of the neck that grew slowly. The swelling had persisted for 3 years and then suddenly stopped growing. There was no past medical history. On clinical examination, a 5 cm × 4 cm, round, nontender, soft swelling was seen on the posterior region on the left side of the neck [Figure 4]a. It was provisionally diagnosed as a nerve sheath tumor or paraganglioma. The FNAC indicated a schwannoma with cytologic findings similar to those observed in the first case. However, a CT scan could not be performed because of the poor financial condition of the patient. Ultrasonography of the neck revealed a well-circumscribed lesion on the left side of the neck, away from the jugular vein and the carotid vessels.
Figure 4: (a) A 5 cm × 4 cm, round, nontender, soft swelling was seen on the left posterior region of the neck. (b) Tumor was removed in-toto without disturbing the capsule of the lesion

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The patient underwent surgery under general anesthesia. A horizontal neck incision was made 3 cm above the clavicle; dissection was done in layers. The sternocleidomastoid muscle was retracted anteriorly, and the lesion was approached. The cervical plexus was seen enclosed in the capsule of the lesion. The nerve plexus had to be sacrificed to separate the lesion for its removal. The tumor was removed in toto without disturbing the capsule of the lesion [Figure 4]b. The closure was done in layers. The final histopathological diagnosis was a supraclavicular cervical plexus schwannoma. Postoperatively, there was a sensory deficit on the skin of the left side of the neck and a pain in the shoulder, which was managed by physiotherapy for 3 months. The patient did not have a family history of schwannomas and had not undergone any molecular testing.


  Discussion Top


Origin and epidemiology

The neural crest, which differentiates into the sympathicoblasts and Schwann cells, gives rise to neurogenic tumors. Neurilemmomas, also known as schwannomas and neurofibromas, originate from the Schwann cells.[8] A schwannoma can arise from any nerve except for the two cranial nerves, the optic, and olfactory nerves.[9] Varocay in 1908 established schwannoma as a pathological entity, and in 1910 coined the term neurinoma. Later in 1935, Stout coined the term neurilemmoma.[10] The incidence of schwannomas is reported to be 1.2/100,000 people per year. About 90% of the cases are sporadic, 3% are associated with neurofibromatosis type 2 (NF2), 2% with schwannomatosis, and 5% with meningiomatosis with or without NF2.[11] Schwannomas do not have a predilection for any sex, race, or age. However, Leu et al., in their study on 52 patients, reported a predilection of schwannomas for men.[12] The extracranial schwannomas of the head and neck region most commonly occur in the parapharyngeal space.[12],[13] Fiji et al., in 1933, reported the very first case of schwannoma of the parapharyngeal space. The occurrence of schwannomas in other regions of the head and neck, such as the paranasal sinuses, submandibular space, oral cavity, cheek, etc., is rare.[14]

Genetic syndromes

Schwannomas can either occur sporadically or may be associated with genetic syndromes such as NF2, schwannomatosis, and Carney's complex. Considering the genetic predisposition to schwannomas, recording thorough family history is important as 50% of the probands may have parents affected by schwannomatosis, and 20% may have parents affected by NF2. A lack of symptoms in the parents does not establish the absence of these genetic disorders, and therefore, molecular testing is recommended. This also emphasizes the importance of genetic counseling for patients and their families, as it provides essential information about the inheritance, nature, and the implications of genetic disorders. This, in turn, helps them make informed personal and treatment-related decisions. The best time for genetic counseling is before planning a pregnancy.[15],[16]

Neurofibromatosis 2

This is a dominantly inherited syndrome that occurs as a result of mutations in the NF2 gene which encodes the Merlin protein. About 50% of the patients harbor de novo mutations in the NF2 gene, whereas a third of them are mosaics. The phenotypic manifestation of nonsense or frameshift mutations is more severe than that of in-frame deletions. Mutations in this gene cause a loss of the Merlin protein, which has several isoforms with the predominant ones being tumor suppressive in nature. Mutations in the NF2 gene are consistently present in cases of sporadic and NF2-related schwannomas. The diagnosis of NF2 can be made based on the Manchester criteria, which also helps us understand various other tumors associated with this syndrome. In addition, a patchy loss of SMARCB1 (INI-1) immunoreactivity and neurofilament-positive nerve fibers occasionally traversing the tumor may be observed, features that are not common among the sporadic cases.[14],[15],[16]

Schwannomatosis

This occurs as a result of mutations in the SMARCB1 and LZTR1 genes. In this genetic disorder, patients present with multiple painful schwannomas, most of which are found in the neck, trunk, and extremities. The vestibular nerve is rarely involved, and the involvement is usually unilateral. Schwannomatosis can be distinguished from NF2 by the absence of vestibular schwannomas, ocular pathology, and ependymomas. Germline mutations in the SMARCB1 gene (chromosome locus 22q11.23) have been reported to occur toward the end of the gene. SMARCB1 plays a role in the development of the central nervous system and functions as a tumor suppressor by inducing cell cycle arrest and mediating the downregulation of cyclin D1 and upregulation of p16. It has recently been shown that loss of function mutations in the LZTR1 gene (chromosome locus 22q11.21) in the germline are associated with schwannomatosis devoid of SMARCB1 gene mutations. Thus, schwannomatosis has its primary mutation in either SMARCB1 or LZTR1, and additionally, there may be a loss of heterozygosity in the chromosome 22q region or somatic mutations in the NF2 gene.[14],[15],[16]

Kehrer-Sawatzki et al. have suggested the following clinical and a combination of clinical and molecular criteria for the diagnosis of schwannomatosis in a proband.[17]

Clinical criteria

Either of the following:

  • Two or more nonintradermal schwannomas, of which at least one is confirmed by biopsy and no evidence of bilateral vestibular schwannomas by high-quality MRI and detailed examination of the internal auditory canal (with and without gadolinium and with slices ≤3 mm)


Note: The diagnosis cannot be excluded because of the presence of a unilateral vestibular schwannoma or meningioma (s).

  • A pathologically confirmed schwannoma, intracranial meningioma, or unilateral vestibular schwannoma, along with a first-degree relative affected with schwannomatosis.


Combined molecular and clinical criteria

Either of the following:

  • A germline mutation in the SMARCB1 or LZTR1 genes and a pathologically confirmed meningioma or schwannoma
  • Two or more tumors (schwannoma, meningioma) each with chromosome 22q loss of heterozygosity and each with a different somatic pathogenic variant of NF2 (the 22q deletions should have different breakpoints indicative of independent events)
  • Two or more pathologically confirmed meningiomas or schwannomas and none of the exclusion criteria.


Exclusion criteria

Any of the following:

  • A clinical diagnosis of NF2
  • A germline NF2 pathogenic variant
  • Schwannomas only within a radiation treatment field.


Carney's complex

This is a combination of mucosal and conjunctival lentigines; schwannomas; endocrine abnormalities, including Cushing's syndrome, Sertoli cell tumors, acromegaly; and myxomas (including cardiac).[18] Schwannomas in Carney's complex often arise in the upper gastrointestinal tract and sympathetic chain and have characteristics of the melanotic variant.[18]

Nerve of origin

Calcaterra et al., in their study, observed that the origin of a schwannoma from a nerve is often unidentifiable.[19] Batsakis et al. reported that schwannomas arise mainly from the intranasal nerves, maxillary and ophthalmic branches of the trigeminal nerve, and branches of the autonomic nervous system (ANS) in the nose and paranasal sinuses. In their study, based on the nerve of origin, the schwannomas of the neck region were divided into the lateral and medial groups. The medial group comprised schwannomas arising from the last four cranial nerves (IX, X, XI, and XII) along with the cervical sympathetic chain, and the lateral group comprised those arising from the cervical plexus, cervical neck trunk, and brachial plexus.[11] Rajan et al. reported that the vagus nerve, cervical sympathetic chain, or glossopharyngeal nerve might give rise to the schwannomas of the parapharyngeal space.[20] Ahad reported a case of a schwannoma originating from a lingual nerve in the submandibular region.[21]

Signs and symptoms

Cervical schwannomas characteristically present as well-circumscribed, well-encapsulated, and asymptomatic masses,[22] with a growth rate as slow as 2.5–3 mm per year.[18] They intimately adhere to the nerve of origin, the cervical vagus nerve, displacing the internal jugular vein and the carotid artery laterally and medially, respectively.[23] The vagus nerve schwannomas grow between the common or internal carotid artery and the internal jugular vein, thus separating these two major vessels. Large schwannomas may anterolaterally displace the internal carotid artery and the vagus nerve or the internal carotid artery along with the internal jugular vein.[24]

Hoarseness of voice is a specific and common symptom occurring as a result of vocal cord palsy, whereas a paroxysmal cough due to vagal stimulation during palpation of the mass is a pathognomonic sign of vagal schwannomas.[21] These masses are often nonmalignant, and malignancy, if present, is primarily associated with neurofibromatosis Type 1.[25],[26] The difference in the rate of progression and the associated pain and neurological deficit can guide us in differentiating a benign schwannoma from a malignant one. Any presenting case that shows a change in its clinical course indicates a potentially malignant tumor.[27]

Clinical features

The preoperative diagnosis of the schwannomas of the head and neck region is challenging because of their slow growth and paucity of symptoms. Moreover, many of them do not present with neurological deficits and can be confused with various other pathologies. Schwannomas are mobile in the transverse direction, but relatively immobile longitudinally due to their nested intraneural location. Depending on the origin of the tumor, the neurogenic signs and symptoms related to the schwannomas of the head and neck can include pain; tenderness; cough upon exerting pressure on the tumor with a finger (a characteristic feature of the vagal schwannomas); tinnitus or hearing loss; cranial nerve palsies, especially involving the V, VII, and XII nerves; Horner's syndrome; and headache.[2],[4] Schwannomas rarely produce a motor deficit, but when they do, they are highly likely to be malignant.[19]

A study by Ahad suggested that a fine-needle aspiration biopsy (FNAB) could help in the diagnosis of schwannomas.[18] FNAB can diagnose soft tissue tumors, both malignant and benign, but it is less accurate in diagnosing neural tumors.[18] Symptoms such as pain, growth in the lesion, changes in the texture, and presence of neurological deficit call for a surgical biopsy according to an international consensus statement on malignant peripheral nerve sheath tumors (MPNSTs).[23]

Imaging

MRI and CT scans may be very helpful in diagnosing schwannomas. The imaging findings, such as displacement of the local structures, circumscribed margins, and smooth expansion of the osseous foramina reflect the slow growth of schwannomas. Profound knowledge about the complex network of cranial nerves is indispensable for an image-based diagnosis of this entity. Literature suggests both biphasic and homogenous presentation of schwannomas on CT scan and MRI. The biphasic appearance is caused by the Antoni A and B tissues [Table 1], which are the hypercellular and hypocellular portions, respectively [Figure 5].[24]
Table 1: Special cells in schwannomas

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Figure 5: The biphasic appearance is because of the presence of Antoni A and B which are the hypercellular and hypocellular portions repectivelly

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Shoss et al., in their study, proposed that a high-resolution CT scan may be used to determine the anatomical extent, size and degree of vascularity of the tumor along with differentiating between benign and malignant lesions.[25] For such tumors, a differential diagnosis of inflammatory adenopathies, branchial cleft cyst, paraganglioma, metastatic cervical lymphadenopathies, submandibular salivary gland tumors, malignant lymphoma, and carotid artery aneurysm must be considered.[27],[28] The target sign seen on axial T2-weighted images depicts the central area of hypo intensity with a hyperintense periphery. It has high specificity but low sensitivity for schwannomas. Larger lesions evince cystic spaces and hemosiderin foci caused by internal microhemorrhage.[24] End-organ compromise such as muscle denervation exhibiting either edema or atrophy and replacement by fat can be perceived as high-intensity on T2-weighted MR Images and as high-intensity on T1-weighted MR images with reduced bulk, respectively. Vocal cord paresis in the cranial nerve X can be considered as medialization and nerve atrophy.[29]

Differentiating MPNSTs from benign tumors based on imaging can be challenging. Though features such as target, fascicular and split fat signs are absent, bony destruction and tumor peripheral edema are present in MPNSTs on MRI, but they are inconsistent. In recent years positron emission tomography with 18F-fluorodeoxyglucose, a glucose analog, has been instrumental in characterizing MPNSTs. This technique abets the quantification and visualization of glucose metabolism in cells, which is often increased in the case of malignant soft tissue tumors. The quantitative scanning exhibits high specific uptake values in MPNSTs, low in neurofibromas, and low to moderate in schwannomas. Tovmassian et al. reported a mean maximum standard uptake value (SUVmax) of 1.93 for benign neurofibromas and 7.48 for MPNST. Recently, Salomon et al. suggested an SUVmax cut-off value of >5.5 to achieve a sensitivity and specificity of 95% and 85%, respectively.[30],[31]

Pathological features

Histopathologically, schwannomas appear well-circumscribed and have a surrounding capsule. They comprise fascicles of Schwann cells with spindle cell morphology (Antoni A pattern) that either amalgamate with or abruptly transition to microcytic or other more loosely textured areas (Antoni B pattern). Antoni A is rich in laminin (secreted by the Schwann cells), which helps in the diagnosis of schwannomas by immunohistochemistry. It is named after the Swedish neurologist Nils Antoni who first described the entity in 1920. A portion of it may have nuclear palisades forming parallel nuclear arrays called the Verocay body. These Schwann cells are usually positively immunoreactive for the cytoplasmic as well as nuclear S-100 protein and are negative for the neurofilament protein. Schwannomas may also be positively immunoreactive for antibodies against the glial fibrillary acidic protein.[32]

The following are the histological variants of schwannomas.

Cellular schwannoma

These are highly cellular and locally aggressive but do not have malignant potential. Majority of the times, they are sporadic and occur primarily in the spinal and paraspinal regions. They predominantly exhibit the Antoni A pattern with <4 mitoses per 10 high power fields. They lack Verocay bodies but have a diffuse and strong expression of the S100 protein and pericellular collagen IV. Their local recurrence rate is as high as 40%, which is more than that of conventional schwannomas. This high recurrence rate can be attributed to the location of these tumors; they are generally deep-seated and cannot undergo complete resection. Yet, these recurrences are not fatal.[33]

Plexiform schwannomas

This variant occurs superficially, that is in the cutaneous and subcutaneous regions, with 5% of cases being associated with a syndrome. It has an intraneural nodular pattern. It may be poorly encapsulated or be completely devoid of a capsule. Proclivity to high recurrence is exhibited by an infiltrative subtype that is commonly seen in infants and children, but a uniform S100 immunoreactivity is reassuring.[33]

Melanotic schwannoma

These are pigmented schwannomas that comprise both spindle and epithelioid cells. A review on melanotic schwannomas reported the rates of local recurrence and metastasis to be 35% and 44%, respectively. In addition, the authors suggested the reclassification of melanotic schwannomas as malignant tumors. A subset of this variant called psammomatousmelanoticschwannoma contains psammoma bodies, wherein 50% of them are associated with Carney's complex.[20],[33]

Treatment

Surgical resection

Despite the possibility of vagal nerve injury arising from the fact that schwannomas originate directly from the nerve fibers, surgical resection remains the mainstay of treatment of schwannomas.[35 - 39] After a successful en bloc removal, the recurrence of the tumor is very rare, as has been reported by Khanna et al.[29]

Intraoperative electrophysiologic testing has been used for many years and has consistently produced better neuronal results. In the present times, there is an emphasis on the importance of preoperative electrodiagnostic studies for estimating the surgical outcomes. However, the available literature suggests that there is limited value to electrodiagnostic testing. Kunert et al., in 2019, conducted a study in 176 patients with vestibular schwannoma to assess the utility of preoperative electrophysiological testing of the facial nerve. It was observed that the most significant predictors of postoperative facial nerve function were factors related to the tumor size. However, a reduction in the amplitude by 50% compared to the healthy side was found to be an independent risk factor for the unsatisfactory function of the cranial nerve VII during the early and long-term follow-ups.[40]

Cavallaro et al., in their reviews on studies reporting a total of 53 patients with neck vagal schwannoma, observed that the technique preferred by the majority of the surgeons was intracapsular enucleation (64.9%), followed by extracapsular resection (32.4%) and debulking of the tumor (2.7%). For 24 of these patients, a description of the surgical technique was not available. The authors also stated that the outcomes with intracapsular enucleation and extracapsular resection were similar. A transverse cervical incision was the approach of choice for almost 93% of the patients in these studies, whereas transaxillary and postauricular approaches were used in the remaining patients for aesthetic reasons. For a total of 24 patients reported in 6 studies, the site of incision was not specified.[41] The vagus (X) nerve was sacrificed in four patients, but was reconstructed with an end-to-end microanastomosis in one patient; malignant transformations were noted in the remaining three patients: One with a neurogenic sarcoma and two with angiosarcomas originating from within the schwannoma (one of these patients had neurofibromatosis Type 1).[42]

About 26% of the patients reported no postoperative complications; hoarseness was a predominantly reported (22.6%) postoperative symptom, with or without other less frequent symptoms like coughing, facial palsy, Horner's syndrome, secretions and choking while eating. Postoperative symptoms were not described for about half of the patients. In 19 (35.8%) patients, laryngoscopy was used to confirm the diagnosis of vocal cord palsy. Of these, 9 patients had partial or complete recovery, and seven patients (36.8%) had a permanent injury. For 3 patients, the follow-up information was not available.[43] Cervical vagus nerve schwannoma is a rare entity with few non-specific symptoms. As a result of its slow growth rate benign nature, it is essential to ensure nerve preservation during the surgical excision, despite the challenges.

Even though the complete functionality of the nerve cannot always be achieved, most surgeons prefer a careful and meticulous intracapsular enucleation to avoid nerve injury.[34],[44] Valentino et al., in their review, have stated that complete excision of cervical schwannomas could be achieved in only 56% of the cases; of these, 29% showed transitory neuronal deficit and 64% showed permanent neuronal deficit; intracapsular enucleation or debulking of the tumor, on the other hand, showed transitory and permanent neuronal deficits in 43% and 29% of the patients, respectively.[44]

Pezzullo et al., showed that the primary treatment modality for cervical schwannomas is surgery and the preferred technique is intracapsular enucleation with the preservation of the anatomical nerve continuity in an attempt to achieve adequate nerve function.[45]

Management of unresectable schwannoma

There are rare cases of unresectable schwannomas involving the skull base when multiple cranial nerves are affected precluding surgery due to morbidity. Such cases can be treated with radiotherapy along with symptomatic treatment for pain. A rate of local control ranging between 92% and 94% and quality of life better than that of patients who undergo surgery has been reported for acoustic schwannoma. There is increasing evidence that radiotherapy can result in local control rates ranging between 90% and 100% for schwannomas arising from other cranial nerves, such as III, IV, V, and VI, in patients who cannot undergo surgery. Therefore, radiotherapy must be considered in such patients. Also, with large tumors comes the associated neuropathic pain that needs to be treated symptomatically. Medications like calcium channel alpha 2 delta ligands such as gabapentin, serotonin-norepinephrine reuptake inhibitors such as venlafaxine, and tricyclic antidepressants such as amitriptyline can be used. Even though these medications may not provide enough pain relief, their use has been suggested by various studies.[47]

A new strategy to wait and scan is now driving the treatment of schwannomas. This is based on the low growth rate of the tumor (0.4–2.9 mm/year) and also the involution seen in 3.8% of the cases. Tos et al. in 1988 suggested that this strategy could be used for tumors up to 15 mm in size. Huang et al. in 2013 suggested that it could be used in vestibular schwannomas with an extrameatal diameter of up to 20 mm. The strategy can be changed to active treatment in case of significant tumor growth. Until now, eight countries, including the United States of America, South Korea, Netherlands, Norway, Australia, Italy, Finland, and Denmark, have reported conservative management for vestibular schwannomas. In a study by Jufas et al., a better quality of life was observed with the wait and scan approach than the surgical treatment.[46]

Valentino et al. in their study reported that the neurologic deficit was definitely higher with extracapsular surgical resection of schwannomas whereby 64% of the patients had permanent and 29% had a transitory neuronal deficit. For patients who underwent intracapsular enucleation or debulking, the permanent and transitory neuronal deficit was reported to be 29% and 43%, respectively, Recurrence is rare but a few cases have been documented, whereas recurrence of different variants has been mentioned elsewhere in the article.[47]

Clinical trials

Presently, several drugs are undergoing trials for the treatment of schwannomas. Histone deacetylase inhibitors (HDACis) are an emerging class of antitumor drugs owing to their ability to promote differentiation, induce cell cycle arrest, and cause apoptosis. They inhibit the Akt pathway, which results in the suppression of the growth of schwannomas and meningiomas. Bevacizumab, a vascular endothelial growth factor inhibitor, is being tested in clinical trials and has been reported to improve hearing and reduce the tumor volume, or both in some, but not all patients who were at risk for complete loss of hearing or compression of the brain-stem due to the growing vestibular schwannoma.[48],[49]

Prognosis

Overall, the prognosis for benign tumors is good, with no effect on the lifespan. However, for malignant tumors, the prognosis is poor regardless of the treatment modality, with overall 5-year survival of 15%.[49]


  Conclusion Top


Extracranial schwannomas of the head and neck are rare tumors that usually present as solitary and asymptomatic masses. Although rare, they should be considered in the differential diagnosis of unilateral and slow-growing masses in the head and neck. The preoperative clinical diagnosis of schwannomas may often be challenging. The diagnosis can only be confirmed after a histopathological examination following the surgical resection. Complete or total surgical excision with an appropriate approach is the main treatment modality for head and neck schwannomas. However, patients must be thoroughly counseled preoperatively to inform them about the potential risk of developing neurological deficits.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patients have given their consent for their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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