PMC4058903_01
Thyroid ultrasound: Left lobe nodule well circumscribed measuring 2.9 x 1.55 x 1.98 cm without calcifications but with peripheral vascularity
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F1
There was a 2.9 cm x 1.55 cm x 1.98 cm solid, isoechoic nodule, without calcifications, and with increased peripheral vascularity in the inferior pole of the left lobe [Figure 1] corresponding to the area of PET uptake.
Thyroid FNA ThinPrep: On the left are the mesothelioma cells, which are in three-dimensional groupings compared to the Hurthle cell population on the right, that forms two dimensional sheets. The mesothelioma cells have waxy cytoplasm with multiple nucleoli and more nuclear variation. The Hurthle cell population has abundant granular cytoplasm and generally one nucleolus. Papanicolaou stain x600
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F2
The FNA was diagnosed as suspicious for Hurthle cell neoplasm based on the presence of predominantly microfollicular groups of cells with abundant Hurthle-like cytoplasm [Figure 2].
Thyroid FNA cell block: Panel A shows two distinct populations, with Hurthle cells (thin arrow) and mesothelioma cells (open arrow). Panels B and C show calretinin and keratin 5/6 staining, respectively, in the mesothelioma cell population, but not in the Hurthle cell population. (H and E x400)
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F3
The cytology showed two distinctively different cell populations [Figure 3, panel A]. Material in the cell block was stained for cytokeratin (CK) 5/6 and calretinin and found to be positive in the potential mesothelial population but negative in the Hurthle cell population [Figure 3, panels B and C].
Surgical Resection: Panel A (x40) shows nodular thyroid tissue. Panel B (x40): Two populations of cells seen within the nodule. Hurthle cells (black arrow) shows abundant pink cytoplasm. However, the tissue contains mostly mesothelial cells (white arrow) which are smaller polygonal cells with less cytoplasm. Panel C (x100): Mesothelial cells are positive for keratin 5/6. Panel D (x100): Mesothelial cells are positive for calretinin. Other immunostains (not shown) that were positive in the mesothelial cells include CK7 and HBME1, while TTF-1 and Thyroglobulin were both negative
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F4
Final pathology confirmed the presence of multiple microscopic foci of metastatic mesothelioma that were again positive for immunostains CK 5/6 and calretinin, negative for TTF-1 and thyroglobulin [Figure 4].