Objective: The aim of the study is to present the unusual changes that a lymph node metastasis of papillary thyroid carcinoma (PTC) underwent after radioiodine therapy, leading to the confusion with a parathyroid adenoma (PA).
Patient and methods: Eight years after a total thyroidectomy and radioiodine ablation with 73.35 mCurie 131I for PTC, a 67-year-old female presented with an enlarged, painless, nodular mass in the left lateral neck region. Clinical examination revealed a firm nodule located on the site of the left inferior parathyroid gland. Elevated serum parathyroid hormone level (120 pg/mL) and parathyroid scintigraphy led to a suspicion of PA. A minimally invasive surgical procedure was performed to remove the mass, which was sent to the Department of Pathology, Emergency County Hospital, Tirgu Mures, Romania, as left PA. It was fixed and processed for microscopic evaluation.
Results: On macroscopic examination, the surgical specimen was oval; it had 13 mm at the largest diameter and weighted 2 g. On microscopy, the lesion appeared as a fibro-hyaline, intensely acidophilic, acellular mass, with calcifications. It was limited by a delicate capsule in which one typical psammoma body was present. At the periphery, on one single level, a small mass of cells of indefinite origin was noticed. Immunohistochemistry (IHC) was done to ascertain the origin of these cells: they were negative for Pan-Cytokeratin AE1/AE2, Parathormone and Thyroglobulin antibodies, but positive for Leukocyte Common Antigen (LCA) antibody, proving that they were lymphocytes, most likely residual from a lymph node.
Conclusions: These IHC data, together with the microscopic feature, the presence of the psammoma body and the patient's history, excluded a PA and led to a diagnosis of fibro-hyaline involution of a PTC metastasis in a lymph node, consecutive to radioiodine therapy. Without careful microscopic examination and accurate clinical information, this lesion could represent a real diagnostic challenge.