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FNAC before RFA. 4 microm-thick H&E stained sections from the cell-block show a highly cellular sample, with a typical papillary architecture; thyrocytes show irregular, large and clear nuclei. A diagnosis of Papillary Thyroid Carcinoma (TIR5 according to the Italian SIAPEC-IAP classification of thyroid cytology) was formulated (A, magnification x200; B, x400).
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Given the suspicious US features and the 18FDG-PET uptake, a US-guided fine needle aspiration cytology (FNAC) was performed, being consistent with PTC (Tir 5 according to SIAPEC/IAP classification of thyroid cytology or category VI according to the Bethesda System) ( Figure 1 ).
Ultrasound features of the nodule before and after RFA. Before RFA (A), the nodulation has a solid, irregular, hypoechoic structure, with slightly spiculated margins and microcalcifications. At control 12 months after RFA only a small nodular, hypoechoic and homogeneous area is appreciable (B); it is in contact with the thyroid capsule that appears slightly retracted but with no signs of extra-thyroidal extension.
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The echostructure was solid, irregular, hypoechoic, with slightly spiculated margins and with microcalcifications ( Figure 2 ). After 12 months, only a small nodular area in the site of the previous treatment was appreciable, with a maximum size of about 4 mm, hypoechoic, homogeneous, without significant vascularization under ECD investigation ( Figure 2 ).
FNAC after RFA H&E (A) or Giemsa (B) stained smears and H&E stained section from cell-block (C) exhibit a poorly cellular sample with sparse inflammatory elements or multinucleated giant cells in a background of thick colloid and fibrosis (magnification x400).
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The FNAC (both smears and cell-block) yielded a poorly cellular sample containing inflammatory cells (histiocytes and multinucleated cells), necrotic debris, fibrotic tissue, thick colloid and scattered thyrocytes, the latter showing no significant nuclear atypia (regular nuclear margins without groovings or pseudoinclusions) ( Figure 3 ).