title: Heterotopic intrathymic thyroid tissue.
abstract: Heterotopic intrathymic thyroid tissue is an extremely rare condition, but it is important to distinguish it from metastases of clinically undetected thyroid carcinoma because metastatic papillary thyroid carcinoma is often so well differentiated, simulating normal thyroid tissue. Described herein are histological findings of heterotopic intrathymic thyroid tissue that was incidentally identified in a woman with papillary thyroid carcinoma during histological examination of a radical neck dissection specimen. These findings emphasize that this rare incidence may occur and should be differentiated from metastatic papillary carcinoma. Histologically, the patient's intrathymic thyroid follicles were identical to the normal thyroid follicles, having flat cuboidal cells with uniformly small nuclei without nuclear grooves or inclusions. The follicular cells had a low Ki-67 labeling index close to zero, and immunonegativity for galectin-3, HBME-1, and RET oncoprotein, in contrast to the tumor cells in primary papillary thyroid carcinoma of the patient. To the authors' knowledge this is the first case report of intrathymic heterotopic thyroid tissue posing a diagnostic difficulty in a patient with papillary thyroid carcinoma.
authors.affiliation: Department of Pathology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea.
authors.forename: Ilseon
authors.initials: I
authors.lastname: Hwang
authors.forename: Seung-Koo
authors.initials: SK
authors.lastname: Lee
authors.forename: Kyung-Ja
authors.initials: KJ
authors.lastname: Cho
authors.forename: Kyu-Rae
authors.initials: KR
authors.lastname: Kim
mesh_terms: D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism; D002291:Carcinoma, Papillary / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002828:Choristoma / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D003937:Diagnosis, Differential; D005260:Female; D037502:Galectin 3 / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D019394:Ki-67 Antigen / Q000235:genetics / Q000378:metabolism; D008206:Lymphatic Diseases / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D008875:Middle Aged; D051096:Proto-Oncogene Proteins c-ret / Q000235:genetics / Q000378:metabolism; D013950:Thymus Gland / Q000378:metabolism / Q000473:pathology*; D013961:Thyroid Gland; D013964:Thyroid Neoplasms / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D000951:Antigens, Neoplasm
chemical_list: D014408:Biomarkers, Tumor; D037502:Galectin 3; D019394:Ki-67 Antigen; D051096:Proto-Oncogene Proteins c-ret; C432845:HBME-1 antigen; D000951:Antigens, Neoplasm; C099282:RET protein, human