Primary Papillary Thyroid Carcinoma Arising in a Branchial Cleft Cyst – Navigating a Hidden Malignancy on Histopathology

Abstract

Rationale: Papillary thyroid carcinoma arising from ectopic thyroid tissue within a branchial cleft cyst is extremely rare. To the best of our knowledge, only 17 cases have been reported as Papillary carcinoma in branchial cyst, being primary or secondary in the archives. Only 7 cases are reported as primary, with only 5 cases having regional lymph node metastasis. Patient Concerns: We present a case report of an Indian male in his 30s, presented with complaints of a progressively enlarging, non-tender swelling in the left cervical region for 1 year. Diagnosis: The Contrast - enhanced computed tomography & Fine needle aspiration performed in an outside laboratory showed findings suggestive of branchial cyst. A clinical diagnosis of “branchial cyst” was formed. Interventions: The Cyst excision was done and sent for histopathological examination(HPE) for confirmation. Outcomes: Microscopic examination revealed papillary carcinoma arising from branchial cleft cyst with three out of seven lymph nodes identified showing metastatic deposits. The remaining four lymph nodes showed marked fibrosis and sinus histiocytosis. Then the patient was subjected for total thyroidectomy, which showed no evidence of malignancy on HPE, followed by I-131 radioactive ablation. Lessons: Primary PTC arising in a branchial cleft cyst is an incidental, extremely rare entity and should be kept in mind while dealing with a lateral cervical cystic lesion. They bear a high risk of regional lymph node metastasis. FNAC and radiological investigations alone cannot warrant the diagnosis. Histopathological examination is the key to unlocking the diagnosis and is considered the “gold standard”. Complete cyst excision and regional lymph node removal, along with precautionary hemi- or total thyroidectomy, are highly suggested to reduce metastasis and increase survival rates.