Papillary carcinoma thyroid with anastomosing channels: An unusual morphology

Papillary thyroid carcinoma (PTC) is the most common thyroid malignancy, accounting for 70%-80% of all thyroid malignancies. It is biologically indolent and has an excellent prognosis. Variations in histopathologic patterns are known to influence prognosis and often result in a diagnostic dilemma. We report an unusual case of a 35-year-old female with papillary carcinoma of a thyroid isthmus showing anastomosing channels on histopathology, a distinctive pattern that has not been described in PTC. Similar to tumor cells, the lining cells of these channels were also positive for thyroid transcription factor 1, thyroglobulin, and cytokeratin-19 and negative for CD34 and CD31. The diagnosis of PTC should rely on nuclear morphology rather than architecture. Pathologists should be aware of different variants because some of these variants show aggressive behavior and poor outcome. The present report highlights the distinctive pattern of PTC, recognition of which is important to avoid any diagnostic pitfall.