Infarction in a thyroid nodule after fine needle aspiration: report of 2 cases with a discussion of the cause of pitfalls in the histopathologic diagnosis of papillary thyroid carcinoma.

Background: In case of difficulty in the interpretation of fine needle aspiration (FNA) smears of a thyroid nodule, histopathologic examination is advised to arrive at a definitive diagnosis. On rare occasions, a specific diagnosis may be given based on cytologic examination, but FNA is followed by infarction of the thyroid nodule, with resultant difficulty in interpretation or even misinterpretation of bistopathologic material. We report 2 such cases.

Methods: Two cases were diagnosed as papillary thyroid carcinoma (PTC) by FNA cytology, but histopathology reports indicated colloid goiters with infarcted nodules. Review of histopathologic material showed features of PTC in the viable tissue at the periphery of nodules. Immunohistochemical study for galectin-3 and CD44 in 1 of the cases supported the diagnosis of PTC.

Conclusions: We suggest that while reporting on an infarcted nodule in paraffin sections of a thyroidectomy specimen, the histopathologist should be careful to look thoroughly at its periphery for the surviving cells and their detailed morphologic features, especially if there is a prior FNA cytology report of a neoplasm.