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ORIGINAL ARTICLE
Year : 2019  |  Volume : 15  |  Issue : 3  |  Page : 659-664

Clinicopathological analysis of extracranial head and neck schwannoma: A case series


1 Department of Pathology, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India
2 Department of Radiodiagnosis, All India Institute of Medical Sciences, New Delhi, India

Date of Web Publication29-May-2019

Correspondence Address:
Dr. Surbhi Goyal
4th Floor, College Building, Department of Pathology, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi - 110 029
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jcrt.JCRT_1125_16

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 > Abstract 


Background: Extracranial head and neck schwannomas are rare tumors which are often clinically misdiagnosed. Preoperative diagnosis of these tumors is challenging but imperative for surgeons so as to avoid nerve damage during excision.
Materials and Methods: Sixteen patients diagnosed with extracranial head and neck schwannomas over a period of 2 years were retrospectively analyzed. Clinical details including preoperative fine-needle aspiration cytology (FNAC) and/or computed tomography (CT)/magnetic resonance imaging (MRI) findings were retrieved. FNAC smears and formalin-fixed paraffin-embedded sections were evaluated.
Results: Among these 16 tumors, 6 (37.5%) were located in the lateral aspect of neck, 4 (25%) in scalp, 2 (12.5%) in orbit, and one each (6.25%) in palate, tongue, submandibular gland and parotid gland. The mean patient age was 31.3 years. FNAC was performed in 14 cases, of which 8 cases (58.3%) showed features of benign nerve sheath tumor (BNST), two cases (14.2%) were inconclusive with possibility of mesenchymal lesion, two cases (14.2%) were inadequate, one case (8.3%) showed features suggestive of schwannoma, and a diagnosis of nerve sheath tumor inconclusive for malignancy was rendered in a single case. The sensitivity of FNAC in diagnosis of BNST was 71.4%. CT or MRI was performed in five cases, of which an accurate diagnosis was rendered only in one case of orbital schwannoma.
Conclusion: Imaging has a limited role in the preoperative diagnosis of head and neck schwannomas owing to nonspecific radiological features. Cellular aspirate smears are helpful in accurate diagnosis even at unusual locations.

Keywords: Extracranial, fine-needle aspiration cytology, neurilemmoma, S-100, schwannoma


How to cite this article:
Sharma P, Zaheer S, Goyal S, Ahluwalia C, Goyal A, Bhuyan G, Mandal AK. Clinicopathological analysis of extracranial head and neck schwannoma: A case series. J Can Res Ther 2019;15:659-64

How to cite this URL:
Sharma P, Zaheer S, Goyal S, Ahluwalia C, Goyal A, Bhuyan G, Mandal AK. Clinicopathological analysis of extracranial head and neck schwannoma: A case series. J Can Res Ther [serial online] 2019 [cited 2019 Dec 13];15:659-64. Available from: http://www.cancerjournal.net/text.asp?2019/15/3/659/243469




 > Introduction Top


Neurogenic tumors comprise a very small percentage of all neoplastic lesions in the head and neck region.[1] These mainly include neurofibromas and schwannomas (neurilemmomas).[2] The latter are rare, benign, encapsulated, slow-growing tumors that arise from Schwann cells of myelinated nerves. These are reported most commonly in the parapharyngeal region followed by paranasal sinuses, nasal cavity, scalp, submandibular region, larynx, epiglottis, and oral cavity.[3],[4],[5]

Considering the rarity and nonspecific clinicoradiological features, these tumors masquerade other nonneoplastic and neoplastic entities. These include soft-tissue tumors such as paraganglioma, benign salivary gland neoplasms, fibroma, lipoma, leiomyoma, reactive or neoplastic lymphadenopathy in the neck, and intraoral mucus retention cyst. An accurate diagnosis is imperative before therapeutic intervention as it prevents radical surgery and prepares a surgeon for neural reconstruction following excision.

On literature search, there is no large study or case series on the incidence, distribution, and clinicopathological features of schwannoma in the head and neck region. Keeping in view these considerations, we retrospectively analyzed cases of extracranial head and neck schwannomas diagnosed on histopathology over a period of 2 years in a tertiary care setting. Our study describes the clinicopathological features of extracranial head and neck schwannomas, highlighting the diagnostic utility of preoperative investigations such as fine-needle aspiration cytology (FNAC) and imaging.


 > Materials and Methods Top


This study was in accordance with the ethical standards of institutional committee. The archives of the department of histopathology were retrospectively reviewed from January 2014 to January 2016. Of the 31,220 pathology case records reviewed, 230 cases of neurogenic tumors were retrieved. Of these, 16 patients of extracranial head and neck schwannoma who underwent surgical excision were included in the study and medical records of these patients were reviewed. Clinical details including preoperative FNAC and/or radiological findings on computed tomography (CT)/magnetic resonance imaging (MRI) were also noted. FNAC was performed in all the cases except inaccessible sites. A repeat aspiration was performed if the first FNA attempt was nondiagnostic or yielded inadequate material. Aspirates were smeared on clean glass slides, air-dried, and stained by May–Grünwald–Giemsa stain. Following surgical excision, the specimen was fixed in 10% neutral-buffered formalin and sent for histopathological evaluation. Diagnosis was confirmed on paraffin-embedded hematoxylin and eosin-stained (H and E) sections and supported by S-100 immunohistochemical (IHC) staining. IHC was performed by streptavidin-biotinylated horseradish peroxidase method. Tumor cells showing cytoplasmic staining were considered as positive. FNAC smears and H and E sections of all the cases were reviewed by two pathologists and correlated with the clinical findings including radiology.


 > Results Top


Of 31,220 cases received, we found only 16 cases (0.05%) of extracranial head and neck schwannomas [Table 1]. The mean patient age at the time of surgery was 31.3 years (range 19–49 years). There were 12 male and 4 female patients with a male: female ratio of 3:1. The mean tumor size was 2.6 cm (range 2–5 cm). Among these 16 tumors, 6 (37.5%) were located in the neck, 4 (25%) in scalp, 2 (12.5%) in orbit, and one each (6.25%) in palate, tongue, submandibular gland, and parotid gland. Eleven patients (68.7%) presented with a gradually increasing asymptomatic palpable mass, two patients (13.3%) presented with neck pain, two patients with proptosis, and one patient (6.2%) presented with Horner's syndrome.
Table 1: Clinicoradiological and fine-needle aspiration cytology findings in 16 cases of extracranial head and neck schwannomas

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In the preoperative workup, FNAC was performed in 14 cases of which 2 cases (14.2%) were inconclusive as the aspirates revealed paucicellular smears comprising loosely scattered spindle cells with a possibility of mesenchymal lesion. Repeated FNA attempts from lingual and palatal swellings were nondiagnostic due to scant cellularity in a hemorrhagic background. In eight cases (58.3%), aspirate showed moderately cellular smears comprising clusters of spindle-shaped cells embedded in a pink fibrillary matrix [Figure 4]a. The individual cells had scant cytoplasm and slender, wavy hyperchromatic nuclei with pointed ends [Figure 4]b. No foci of necrosis or mitosis were seen. Diagnosis of mesenchymal lesion with possibility of benign nerve sheath tumor (BNST) was rendered in these eight cases. Aspirate from a submandibular swelling (8.3%) showed characteristic nuclear palisading and Verocay bodies, suggestive of schwannoma [Figure 4]c. Moderate degree of pleomorphism and nuclear atypia was seen in the aspirate smears of one patient with lateral neck swelling [Figure 4]d. A probable diagnosis of mesenchymal tumor with neural differentiation inconclusive for malignancy was rendered, and excision biopsy was advised for confirmation and categorization. FNAC was not attempted in two orbital swellings owing to risk of bleeding and inaccessibility.
Figure 1: Axial contrast-enhanced computed tomographic images, (a) soft-tissue window and (b) cerebral window showing a well-defined homogeneously enhancing mass lesion (arrows) in the medial extraconal space of left orbit, abutting the medial rectus muscle and oriented anteroposteriorly. Possibilities included schwannoma and hemangioma. (c and d): Axial T2-weighted and coronal fluid-attenuated inversion recovery magnetic resonance images demonstrate a well-defined spherical mass lesion (arrows) in the right retroocular space, causing proptosis. Further, there is indentation of the posterior sclera due to mass effect. The lesion is heterogeneously hyperintense on T2-weighted images. Possibility of orbital hemangioma was kept on imaging

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Figure 2: Axial contrast-enhanced computed tomography image showing a well-defined mass lesion (arrow) within the left parotid gland, involving both superficial and deep lobes. The mass is showing heterogeneous but intense contrast enhancement. No extension beyond the parotid gland is seen. No foci of calcification. Possibility of a vascular, neoplastic mass (pleomorphic adenoma/hemangioma) was suggested on computed tomography. (b) Photograph of excised specimen showing a well encapsulated, solid, homogenous tumor with a gray, white glistening cut surface, suggestive of a neural tumor

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Figure 3: (a) A 41-year-old woman presented with a mass in the left submandibular region for the past 1 year with pain over the swelling for 4 months. (b) Axial contrast-enhanced computed tomography image shows a small lobulated mass lesion (2.3 cm × 2.2 cm × 1.8 cm) just anterior to the left submandibular gland. The lesion shows tiny areas of necrosis within. No foci of calcification seen. Possibilities included metastatic lymphadenopathy, minor salivary gland neoplasm and neurogenic tumor. (c) Intraoperative photograph of tumor showing close relation to the mandibular nerve

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Figure 4: May–Grünwald–Giemsa smears showing (a) Moderately cellular aspirate smear comprising clusters of spindle-shaped cells embedded in a pink fibrillary matrix, suggestive of mesenchymal tumor with possibility of benign nerve sheath tumor (×200). (b) Higher magnification showing cells having scant amount of cytoplasm and slender, wavy, hyperchromatic nuclei with pointed ends (×400). (c) Fine-needle aspiration smears showing characteristic nuclear palisading and Verocay bodies, suggestive of schwannoma (×200). (d) Photomicrograph showing moderate degree of pleomorphism and nuclear atypia in the aspirate smears, suggestive of nerve sheath tumor, inconclusive for malignancy (×400)

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Contrast-enhanced CT (CECT) was performed in two cases of orbital swelling and one case each of parotid, submandibular region, and palatal schwannoma. Of these, only one case of orbital schwannoma was accurately diagnosed on CECT imaging, and an alternative diagnosis was suggested in the remaining four cases [Table 1].

All patients included in the study underwent complete intracapsular excision while preserving the nerve of origin. H and E sections revealed a well-encapsulated tumor comprising alternating cellular (Antoni A areas) and hypocellular areas (Antoni B areas) [Figure 5]a. Antoni A areas showed the presence of nuclear palisading and formation of Verocay bodies [Figure 5]b. The cells were spindle shaped, had mild to moderate amount of eosinophilic cytoplasm, and had spindle-shaped, wavy, hyperchromatic nucleus with pointed ends. Moderate degree of pleomorphism and nuclear atypia was noted in a single case of schwannoma of the neck. No atypical mitosis or necrosis was seen. On IHC, the cells were diffusely positive for S-100 in all cases.
Figure 5: (a) Section showing a well-encapsulated tumor comprising Antoni A hypercellular areas with nuclear palisading and formation of numerous Verocay bodies (×200), (b) Photomicrograph showing Verocay bodies (arrow). The spindle-shaped cells have moderate amount of eosinophilic cytoplasm with spindle-shaped, wavy, and hyperchromatic nucleus (H and E, ×400)

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In the preoperative workup of patients who presented with lateral neck swelling, radiology was not performed and FNAC was suggestive of BNST, with one case being inconclusive for malignancy owing to marked pleomorphism and atypia. Preoperative workup included only FNAC in four patients who presented with a scalp swelling. Possibility of BNST was suggested in two of these patients, while aspirates in the remaining two cases were inconclusive with a possibility of mesenchymal lesion.


 > Discussion Top


The head and neck regions account for 25%–45% of schwannomas and usually affect patients in their fifth decade. Liu and Fagan et al[6], Das et al[7] and Caughey et al[8] have independently reported the mean patient age of 42 years, 32.6 years and 45 years respectively. In our study, the mean patient age was 31.4 years which is similar to the data published for developing countries.

The most common site of extracranial schwannomas in the head and neck is the parapharyngeal region, with submandibular region, parotid region, and intraoral and paranasal sinus localization being relatively uncommon.[9],[10],[11] In our study, lateral aspect of neck (parapharyngeal region) was the most common site accounting for 37.5% of cases which is in concordance with the literature. Among the unusual sites, we encountered two cases of the intraoral region (tongue and palate) and two cases involving the salivary glands (parotid gland and submandibular gland). Only 1% of all extracranial schwannomas are described in oral cavity, with tongue being the most common site followed by palate and buccal mucosa.[12],[13],[14]

Patients usually present with an insidious-onset gradually progressive swelling which may or may not be accompanied by paresthesia. Clinically, schwannomas are often misdiagnosed as other common benign lesions such as pleomorphic adenomas, fibromas, or mucous retention cysts on account of their slow growth. FNAC has little diagnostic utility in the preoperative diagnosis of intraoral lesions due to diversity of lesion types, lack of technical expertise in intraoral aspiration, and increased risk of bleeding.[15] In our study, we reviewed two cases of intraoral schwannomas on the dorsal surface of tongue and hard palate, respectively. Repeated FNA attempts were nondiagnostic in both the cases possibly attributed to difficulty in accessing and aspirating intraoral mucosal swellings.

Schwannoma arising in the salivary gland is a rare event with very few cases reported in English literature. Around 170 cases of intraparotid schwannoma have been described, of which only 23 cases were accurately diagnosed on preoperative evaluation by FNAC (15 cases) and/or radiology (8 cases).[16],[17] Patients most commonly present with a gradually increasing asymptomatic mass with a normal nerve function. Clinicoradiologically, schwannoma is known to masquerade benign salivary gland tumors such as pleomorphic adenoma and Warthin's tumor, as seen in our study. The signal intensity and enhancement characteristics are variable, and therefore, the preoperative diagnosis of schwannoma within salivary gland is challenging. On CT and MRI, schwannomas present as spherical or ovoid enhancing mass lesions and may have areas of necrosis/hemorrhage within. Central nonenhancing area may give rise to target appearance, but this is more commonly seen in neurofibromas.[7],[17] Characteristic cytomorphology in the cellular aspirate smears can render a diagnosis of schwannoma even in such unusual locations. With this possibility, the surgeon should carefully look for close association of the tumor with the nerve during surgery and try to preserve it.

Orbital schwannomas are rare and account for only 1%–6% of all orbital tumors. These are usually unilateral and solitary however can have variable clinical and radiological presentations, making diagnosis difficult for an ophthalmologist. Anteroposterior orientation, extraconal location, and intense contrast enhancement may suggest the diagnosis, but these features are not pathognomonic. Cavernous hemangioma is an important differential, but it is usually intraconal and retrobulbar in location, whereas anteroposterior orientation favors schwannomas.[7] The enhancement is in schwannoma typically more homogeneous compared with nodular enhancement of orbital hemangioma but may be similar. Histopathological examination thereby remains the gold standard for the diagnosis. One of these cases was quite challenging as radiology was suggestive of a vascular etiology. Subsequently, FNAC was not performed assuming the vascular nature of the lesion and owing to risk of bleeding. Even though rare, orbital schwannoma should be considered as a preoperative differential diagnosis of a unilateral slow-growing orbital mass in an adult and prompt management is warranted to prevent vision-threatening complications.

Among preoperative investigations, ultrasound is the first modality to localize and characterize these lesions. CECT is the next step to better evaluate the deeper extent and relationship with the surrounding structures. MRI has superior contrast resolution and may provide additional information in case of orbital masses, detection of smaller lesions, and better evaluate the involvement of neural structures.[18],[19] Furthermore, the nerve of origin can be better appreciated on MRI than CT. These are usually hyperintense on T2-weighted images, similar to hemangiomas, paragangliomas, and pleomorphic adenomas. Paragangliomas show multiple flow voids and salt and pepper appearance on MRI. Metastatic lymph nodes also constitute an important differential. In our study, an accurate radiological diagnosis was made only in one case out of five cases of schwannoma. A major limitation of our study was its retrospective evaluation, and that radiology was not performed in all the 16 cases.

On the other hand, FNAC is a simple, minimally invasive, and cost-effective, first-line outpatient department investigation which can render a preoperative diagnosis of schwannoma. However, intraoral lesions pose a diagnostic difficulty owing to the inaccessibility and technical difficulty in performing mucosal FNAC and often yield hemorrhagic/inadequate aspirates as seen in two of our cases. It is usually difficult to characterize and differentiate schwannoma from neurofibroma on FNAC unless characteristic Verocay bodies are seen. Various authors have reported the sensitivity of FNAC varying from 6% to 20% in the diagnosis of head and neck schwannomas.[20],[21]

In our study, of the 14 cases, FNAC was diagnostic of nerve sheath tumor in 10 cases (71.4%), of which only one case (0.04%) showed features consistent with schwannoma. Categorization of spindle cell tumor as benign or malignant on cytology is difficult. Further, some degree of cellular and nuclear atypia is commonly observed in aspirate smears from schwannomas which should not be misdiagnosed as malignancy. This warrants a careful search for mitotic figures and necrosis. Whenever in doubt owing to cytological or nuclear atypia, such lesions should be categorized as inconclusive for malignancy and advised for excision.

Most common histopathological mimics of schwannoma include other mesenchymal tumors such as neurofibroma, traumatic neuroma, fibroma, and leiomyoma. Antoni A and Antoni B areas along with Verocay bodies distinctly characterize the morphology of schwannoma. Furthermore, diffuse and strong immunoreactivity against anti-S100 antibody aid in making a definitive diagnosis.

As schwannomas are benign and radioresistant, the mainstay of treatment is intracapsular enucleation with the preservation of nerve function. In neurofibromas, on the other hand, tumor resection is performed with a safety margin. While two small-scale series have reported no recurrence after intracapsular dissection,[22],[23] one case of intraparotid facial nerve schwannoma recurred 6 months after surgery.[8]


 > Conclusion Top


Extracranial head and neck schwannomas are rare, benign tumors. The preoperative diagnostic role of imaging is limited as CT and MRI were unable to differentiate schwannoma from other neoplastic differential diagnosis of head and neck masses. Therefore, the preoperative diagnosis is difficult for the clinicians as well as radiologists. If adequately cellular smears are available, FNAC can be extremely helpful in the diagnosis even in unusual locations. The sensitivity of FNAC was 71.4% in our study, with intraoral and orbital swellings being the main limitations due to inaccessibility.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Singh S, Garg N, Gupta S, Marwah N, Kalra R, Singh V, et al. Fine needle aspiration cytology in lesions of oral and maxillofacial region: Diagnostic pitfalls. J Cytol 2011;28:93-7.  Back to cited text no. 15
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Bhaker P, Chatterjee D, Gochhait D, Radotra BD, Dey P. Schwannoma of the parotid gland: Diagnosis by fine-needle aspiration cytology. J Cytol 2014;31:196-8.  Back to cited text no. 16
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Anil G, Tan TY. Imaging characteristics of schwannoma of the cervical sympathetic chain: A review of 12 cases. AJNR Am J Neuroradiol 2010;31:1408-12.  Back to cited text no. 18
    
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