Objective: To review the diagnosis of primary papillary carcinoma of ectopic thyroid tissue within branchial cleft cysts, and to discuss the diagnostic challenge of differentiating this condition from metastatic disease when an occult microcarcinoma is found in the thyroid gland.
Methods: These comprise a case report and a literature review. We present the case of a 75-year-old woman with papillary thyroid carcinoma within the wall of a recurrent, 15 cm, lateral neck cyst.
Results: Histological examination of the patient's thyroid gland found a 0.5 mm papillary thyroid microcarcinoma.
Conclusion: Our differential diagnosis was primary papillary carcinoma arising from ectopic thyroid tissue, or metastatic cystic degeneration of a lateral lymph node. We make an argument for the former.