Papillary carcinoma with extensive squamous metaplasia arising from thyroglossal duct cyst in an 11-year-old girl: significance of differentiation from squamous cell carcinoma: a case report.

We report a case of papillary carcinoma (PC) with extensive squamous metaplasia arising from a thyroglossal duct cyst (TDC) that required differential diagnosis from squamous cell carcinoma (SCC). An 11-year-old Japanese girl presented with a 9-month history of an anterior-midline neck mass that was clinically diagnosed as TDC. Open neck biopsy revealed nested proliferation of atypical squamous cells within the cystic structures, and SCC arising from TDC was initially suspected. Further examination, however, including immunohistochemistry, revealed the tumor to be of thyroid cell origin. The patient underwent wide local resection of the thyroglossal duct carcinoma by Sistrunk procedure and cervical lymph node dissection. Microscopically, the diagnosis was of PC with extensive squamous metaplasia and metastasis to the medial submandibular lymph node. Distinction of squamous metaplasia in PC from SCC is sometimes difficult, but has a significant effect on postoperative management.