Cystic schwannoma of cervical sympathetic chain masquerading as type II second branchial cleft cyst

INTRODUCTION

Brachial cleft cyst is a common differential for benign lateral neck mass. Other differentials can be necrotic lymphadenopathy, epidermoid cyst, carotid body tumors, lymphangioma and rarely schwannomas. Schwannomas are benign, capsulated, firm and slow growing tumours arising from schwann cell of myelinated nerves. More than 25 percent of schwannomas are found in head and neck but less than 5 percent are cystic in nature.¹ Rarely these tumors can masqurades as brachial cleft cyst.

CASE REPORT

A 22 year old female patient presented to our OPD with painless right side neck swelling since 4 years ago. On examination a 5 cm× 4 cm swelling on right side of neck extending from 1 cm below mastoid tip up to level of cricoid non tender soft mobile. No pulsations were felt on palpation.

On oral examination patient had a tongue tie. No obvious bulge or displacement of peritonsillar structures seen. On 70°scopy B/L vocal cords were mobile.

USG revealed a 5.6 cm × 4.1 cm × 3.7 cm well-defined heteroechoic lesion on right side in subcutaneous plane in upper cervical region suggestive of branchial cyst.

CT scan with contrast showed an encapsulated 3 cm × 4 cm cystic mass with focus of enhancing nodule along it’s medial aspect suggestive of branchial cyst.

Multiple FNAC yielded blood cells only hence inconclusive.

Patient was taken under general anaesthesia cervical incision taken and meticulous dissection done. The attachment was traced up to the sympathetic chain. A cystic mass was excised in situ with nerve of attachment. Patient developed Horner’s syndrome postoperatively.

The gross specimen was smooth fusiform cystic 5 cm × 4 cm with thin nerve attached. The specimen was cut open chocolate brown thick fluid was expressed. Cut specimen showed median raphe.

Histology showed benign spindle cells of neurogenic origin. Spindle cells had bland morphology and surrounded by myxoid matrix. Hypocellular & hypercellular (Antoni A and Antoni B) areas were seen, suggestive of schwannoma.

DISCUSSION

Most common differential for benign neck masses is brachial cleft cyst and necrotic lymphadenopathy.² Other differentials are carotid body tumors, lymphangioma, epidermoid cyst and schwannomas. Gold standard for pre-operative fine needle aspiration cytology in conjuction with radiological imaging.³

Schwannomas are benign encapsulated tumors which arise from schwann cells. These tumours were first described by Verocay in 1910. 25-40% of all schwannomas are found in head and neck area. These tumors are slow growing tumors which may manifest as a painless, smooth regular mass. FNAC in schwannomas may be inconclusive due to haemarhagic aspirate or inadequate cellular materials.⁴ In our case FNAC was suggestive of brachial cleft cyst.

The gold standard pre-operative investigation in cases of schwannoma is diffusion weighted gadolinium contrast MRI. On T1 weighted images, they are low signal intensity and on T2 weighted images, it is high signal intensity. On contrast administration, these tumours are homogenously enhancing. It shows low intensity flow void giving characterstic “salt and pepper” appearance and has delayed wash out time on diffusion weighted imaging.⁴ CT scans show a homogenous regular hypodense swelling which slightly enhance on contrast.

In our case, CT neck with contrast depicted a cystic heterogenous mass with smooth borders which was abutting internal carotid artery suggestive of type II brachial cleft cyst by Bailey’s classification. Bailey postulated following classification for second brachial cleft cyst type I: deep to platysma, anterior to sternocleidomastoid (SCM) type II: abutting internal carotid artery and adherent to internal jugular vein (most common) type III: extending between internal and external carotid arteries. Visualization of the cyst’s extension or “tail” between the internal carotid artery and external carotid artery has been considered pathognomonic for type III BCCs type IV: abutting pharyngeal wall and potentially extending superiorly to skull base.⁵

Meticulous surgical dissection for complete excision of the tumor with tracing the origin of the swelling can help in the diagnosis. In our case, on surgical dissection we found that the mass was arising from cervical sympathetic chain behind the carotid vessels and there was no tract between the carotid as is expected in brachial cysts. This hinted towards a schwannoma arising from the cervical sympathetic chain.

Histologically, two tissue forms have been described. The Antoni type A tissue shows well-developed cylindrical bands of Schwann’s cells and connective tissue fibres with a tendency towards pallisading of the nuclei about a central mass of cytoplasm (Verocay bodies). Antoni type B tissue is a loosely arranged stroma in which the fibres and cells form no distinctive pattern. Between these palisades are the regions that are devoid of nuclei termed Verocay bodies. On immunohistochemistry, schwannomas are intensely S-100 positive along with capsular epithelial membrane antigen and CD34.⁶ Hence, histopathology report with immunohistochemistry is the gold standard for confirmation of the diagnosis of schwannoma.

To the best of our knowledge and after extensive research of English medical literature, there are 4 reported cases of cystic schwannoma mimicking brachial cleft and all of the had origin from vagus nerve. In this case, the cystic schwannoma was arising from cervical sympathetic chain which never been reported in the literature.⁷

CONCLUSION

Cystic schwannomas can present as brachial cyst radiologically but meticulous surgical dissection and tracing the site of the origin of the mass and final histopathological report will guide towards correct diagnosis. Complete surgical excision is treatment of choice.⁸

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: Not required

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