Potential Pitfalls for False Suspicion of Papillary Thyroid Carcinoma: a Cytohistologic Review of 22 Cases

To evaluate the diagnostic pitfalls attributing to false suspicious interpretation of papillary thyroid carcinoma (PTC), we performed a retrospective cytohistologic review of thyroid nodules diagnosed as suspicious for papillary carcinoma with histology-proven false suspicion of PTC. A total of 22 thyroid fine needle aspirates along with the corresponding surgical specimens were reviewed. The presence and/or absence of PTC-associated morphologic features and their mimics were evaluated. One aspirate showed papillary-like fragments with honeycomb architecture. One aspirate contained rare syncytial-type fragments which were accompanied by honeycomb sheets of follicular cells and moderate amount of colloid. Intranuclear grooves presented occasionally in virtually all 22 aspirates. The grooves were noted mainly within round nuclei and appeared thin and/or incomplete. Rare intranuclear pseudoinclusions were detected in one otherwise benign-appearing aspirates. Eight aspirates contained various numbers of histiocytes, as well as atypical polygonal, epithelioid, elongate, or spindle cells in which intranuclear grooves were occasionally seen. Conspicuous fragments of fibrocollagenous tissue with entrapped follicular cells were detected in one aspirate. The corresponding histological specimen revealed counterpart of the cytological findings described. Other features associated with PTC were inconspicuous. The findings demonstrated that the following factors may contribute to the false suspicion of PTC: (1) misinterpretation of papillary-like tissue fragments with honeycomb arrangement and fragments offibrocollagenous tissue with entrapped follicular cells; (2) overinterpretation of suboptimal intranuclear grooves and rare intranuclear pseudoinclusion in the absence of the other features of PTC; (3) misinterpretation of the polygonal, epithelioid, elongate, or spindle cells that actually represented atypical cyst lining cells.