A Case of Lateral Neck Cyst with Ectopic Thyroid Papillary Carcinoma

Thyroid develops from median rudiment which is a surface elevation dorsal to the tuberculam impar and forms by proliferation of endodermal cells. Lateral thyroid element of the fourth pouch contributes in the development of thyroid gland. Failure of the lateral thyroid element to fuse with the median element may result in a lateral ectopic thyroid gland. In the present case, patient initially presented with lateral neck cyst. There were two possibilities in the patient: a) a cystic degeneration of lymph node metastasis from an occult thyroid papillary carcinoma and b) thyroid papillary carcinoma arising from ectopic thyroid tissue within a branchial cleft cyst. Histological examination demonstrated foci of normal thyroid glands along with evidence of papillary thyroid carcinoma. These finding favours the possibility of malignant transformation of follicular epithelial cells of ectopic thyroid tissue within a branchial cleft cyst. There was a focus of papillary thyroid carcinoma in the resected total thyroidectomy specimen. So differentiation between two possibilities becomes difficult in this patient. A papillary thyroid carcinoma found with a cyst of the lateral neck represents a diagnostic and therapeutic dilemma.