Solid Cell Nests Hyperplasia (Ultimobranchial Body Remnants) of the Thyroid: A Pitfall

Abstract

Abstract Introduction/Objective Solid cell nests (SCN) are small epithelial cell nests interspersed within thyroid parenchyma, resembling squamous/transitional epithelium. SCNs, which are ultimobranchial remnants, are popularly considered pluripotent stem-cells responsible for developing follicular and C-cells. While SCNs are not an uncommon incidental findings in thyroid, solid cell nest hyperplasia is rare. SCNs are often mistaken for benign entities such as C-cell hyperplasia (CCH) or malignant lesions such as papillary thyroid carcinoma (PTC), metastatic squamous cell carcinoma, or medullary thyroid microcarcinoma (MTC). Methods/Case Report To reiterate this diagnostic dilemma, we present a case of a 57-year-old male with a six-year history of Hashimoto thyroiditis and multiple bilateral thyroid nodules. Ultrasonography revealed two nodules, one in each lobe, measuring 2.0x1.9x1.8cm(right) and 1.6x1.5x1.5cm(left). Both were solid, hypoechoic nodules with smooth margins and no echogenic foci. Fine-needle aspiration of right nodule was suspicious for follicular neoplasm, Hürthle- cell type, and the left nodule was atypia of unknown significance. Right-hemithyroidectomy specimen revealed follicular adenoma and oncocytic adenomatous nodules in a background of florid lymphocytic thyroiditis (Hashimoto). In two blocks, small solid nests of cells were identified, largest focus measuring 0.5 cm. The cells were polygonal to epithelioid with moderate amphophilic cytoplasm. Nuclei were centrally located, irregular to oval with occasional grooves. While nests had a squamoid appearance, they did not have intercellular bridges. Although nuclear grooves and evenly dispersed chromatin and chromocenters were noted, they lacked optical clearing or intra-nuclear inclusions characteristic for PTC. Thus, excluding these two possibilities, primary diagnostic considerations were SCN versus CCH. Immunohistochemical analysis showed cells positive for P63 and CK5/6 and negative for PAX-8, TTF-1, thyroglobulin, CEA, and calcitonin. Results (if a Case Study enter NA) NA Conclusion If wrongly diagnosed as CCH, patients may be placed in a high-risk category for possible development of MTC. It is, thus, necessary to be aware of SCN, which can occasionally become hyperplastic, to prevent misdiagnosis.