Papillary carcinoma arising in thyroglossal duct cyst in the lateral neck.

The patient presented here, a 74-year-old female, had a 3-year history of a gradually enlarging painless nodule in the right submental lateral region of the neck. A neck CT scan showed a well-demarcated cystic lesion, measuring 25mm in diameter, but without any definite evidence of neoplastic foci in the lymph nodes, thyroid gland, or lung. Clinicians first interpreted it as branchial cleft cyst, and a cystectomy was performed. Gross examination revealed a unilocular cystic lesion filled with yellowish clear fluids, containing a markedly thinned fibrous wall with smooth inner surface, partly coexisting with tiny solid and papillary-like components. On microscopic examination, the cystic tumor was lined by mono-layered ciliated columnar or metaplastic stratified squamous epithelium with underlying ectopic thyroid follicles or lymphocytic infiltrate, reminiscent of thyroglossal duct cyst (TDC), partly adjacent to the compressed lymph node tissue. Its solid parts were composed of a proliferation of atypical cuboidal to columnar epithelial cells with occasional nuclear grooves or intranuclear inclusions, arranged in a papillary growth pattern with supporting delicate fibrovascular cores. Immunohistochemically, these atypical cells were positive for thyroid transcription factor 1, thyroglobulin, and cytokeratin 19. Therefore, we finally made a diagnosis of papillary carcinoma (PC) arising in TDC in the lateral neck. Although metastatic thyroid PC of cervical lymph node was an important differential diagnosis owing to various overlapping clinicopathological features, coexistent benign lining epithelium or thyroid follicles, a histological hallmark of TDC, were present in the current case.