Introduction

Brachial cleft cysts are commonly encountered in lateral neck swelling in clinical practice, however, the presence of ectopic thyroid tissue with papillary thyroid carcinoma (PTC) is extremely rare [1]. PTC primarily arising in brachial cleft cyst is indistinguishable from metastatic papillary carcinoma in the cyst and the diagnosis can only be confirmed after total thyroidectomy to exclude occult primary [2]. The first case of PTC in ectopic thyroid of the branchial cyst was reported in 1992 by Balasubramanniam et al [3]. We hereby report a very rare case of papillary thyroid carcinoma incidentally arising in a branchial cleft cyst. To the best of our knowledge, only seventeen cases have reported PTC arising in a branchial cyst without a primary in the thyroid [3], [4], [5], [6].

Case Report

A 70-year-old male presented with a painless right-sided lateral neck mass. Physical examination revealed a 4 cm mass on right side of neck. No significant cervical lymphadenopathy or thyroid mass was noted. Contrast-enhanced computed tomography (CECT) of neck showed a well-demarcated walled, solid cystic-enhancing mass lesion in right carotid space of neck. The solid component was measuring 2.6 mm in size and showed peripheral foci of calcifications. No cervical lymphadenopathy was detected. The differential diagnosis offered in radiology were vagal schwannoma, nerve sheath tumor and paraganglioma. The patient underwent surgical excision of mass and histopathological examination revealed a 5 cm cystic mass with keratin debris confirming a branchial cleft cyst. A solid area measuring 2 x 1.5 cm was identified. Microscopic examination revealed a cyst wall lined by cuboidal epithelium and stratified squamous epithelium with a fibrotic wall showing dense lymphoid infiltrate. The wall also showed few foci of normal thyroid tissue and classical type papillary carcinoma comprising of tumour arranged in form of papillae lined by cells showing nuclear overcrowding, grooving and intranuclear inclusions. Psammoma bodies were also identified. No areas of necrosis were identified. On immunohistochemistry, tumour cells were positive for TTF-1, PAX-8, p-16 and were immunonegative for p63. Two out of four lymph nodes in wall showed metastatic deposits of papillary carcinoma.

however, most of these reports are from thyroglossal duct cysts, lingual thyroid and struma ovarii. Primary papillary carcinoma of the thyroid arising in branchial cysts is rare. Cochrane search shows only 17 cases have been reported in the literature as PTC arising from branchial cysts without a primary in the thyroid [6]. Two of these cases presented with metastatic lymph node disease at diagnosis. The usual diagnostic dilemma in such situations is that carcinoma in the cyst is a primary or metastatic disease with missed/occult primary in the thyroid. Sidhu et al. proposed the following criteria for diagnosing papillary thyroid carcinoma in branchial cysts [8].

1. an epithelial lining layer with subepithelial lymphoid tissue collection,
2. normal thyroid tissue adjacent to the focus of papillary carcinoma within the wall,
3. and no evidence of papillary carcinoma in the thyroid or other areas.

In our case, tumor showed morphological features of papillary thyroid carcinoma and fulfilled all the above criteria. Metastases in neck nodes are detected in about 20% of cases as per the available evidence and distant metastasis has not been reported [9], [10]. Immunohistochemical positive staining for TTF-1, PAX-8 and thyroglobulin can help in the identification of a PTC, however, it cannot distinguish between primary and metastatic tumors. CT, MRI and scintigraphy imaging can help in detecting ectopic thyroid tissue, however histopathological examination is the gold standard.

Conclusion

In conclusion, we have reported a very rare case of primary PTC located in the branchial cyst. Clinicians should always keep the possibility of ectopic thyroid tissue while dealing with the management of lateral neck mass. The diagnosis of this rare entity requires a multidisciplinary team comprising of radiologists, surgeons and pathologists.

References