A Very Unusual Thyroid Tumor: a Nodule with Mature Fat Papillary Hyperplasia and Focal Atypia
A 51-years old man presented with a clinical diagnosis of multinodular goiter. The patient did not show evidence of autoimmune disorders or thyroiditis and the thyroid function was normal. He was referred to surgery and complete thyroidectomy with intraoperative histological examination was performed. The thyroid was enlarged with a weight of 55 g, measuring 5×4.5×4.5 cm in the right lobe and 5×3×3 cm in the left lobe. Macroscopically, the right lobe harboured a cystic-colloid hemorrhagic nodule 2.5 cm diameter while two colloid nodules of 2 cm and 3 cm respectively, were found in the left lobe. All of the aforementioned nodular lesions were examined intraoperatively. The cystic nodule in the right lobe showed a diffuse papillary architecture with slight overlapping and enlarged nuclei; as a consequence an intraoperative histological diagnosis of suspicious papillary thyroid carcinoma/papillary hyperplasia with atypia, was posed. The two nodules in the left lobe were considered benign, although one of them also showed cystic aspects with papillary architecture. The lesions were finally sampled, formalin fixed and paraffin embedded for the final histological evaluation. Microscopically two colloid-cystic nodules showed papillary structures with a delicate stroma and prominent intralesional mature fat (). Furthermore, the nodule in the right thyroid lobe showed cytological features suspicious for PTC. The nuclei in fact were sometimes enlarged, with scattered grooves, overlapping and clearing, but no nuclear pseudoinclusion or psammomabodies were found (). The lesion did not show a complete capsule and merged with the surrounding thyroid tissue. Neither mitotic figures nor necrosis were found. In the left nodule the nuclei were basally located with dark chromatin without atypical features. To exclude the diagnosis of a PTC and to better categorize these lesions, the expression of two well known thyroid cancer associated antigens namely Galectin-3 (Gal-3) and HBME-1 was evaluated by using immunohistochemical procedures. A biotin-free immunoperoxidase detection system was applied, and foamy macrophages were considered as internal positive control for Gal-3 immunostaining. The left nodule showed a faint and focal cytoplasmic immunoreactivity for Gal-3 (data not shown), while the suspicious lesion in the right thyroid lobe showed a variable immunoreactivity for Gal-3 with nuclear and cytoplasmatic pattern of staining. Interestingly galectin-3 expression was restricted to those cells showing atypical cytological features whereas HBME-1 immunostaining further highlighted the plasma membrane aspect of these atypical cells ( and ) However the larger part of the papillary lesion was unreactive with both Galectin-3 and HBME-1. On the basis of the morphological and immunophenotypical analysis we classified the lesion as an adenomatous nodule with fat-rich stroma and papillary atypical hyperplasia, with focal expression of Galectin-3 and HBME-1 reflecting an incipient transformation in PTC. To exclude the presence of a PTC, we carefully examined the rest of the thyroid for a total of 28 slides.