title: Fine-needle aspiration cytology of hyalinizing trabecular adenoma of the thyroid in a patient with Hashimoto's thyroiditis: a case report.
abstract: BACKGROUND
  Hyalinizing trabecular adenoma (HTA) is a rare benign epithelial tumor of the thyroid which shows a prominent trabecular growth pattern and stromal hyalinization. On fine-needle aspiration cytology, HTA is frequently misdiagnosed as either papillary thyroid carcinoma (PTC) or medullary carcinoma. We present both the cytologic and the histopathologic features of HTA in a patient with Hashimoto's thyroiditis.
  
  
  METHODS
  Cytologically, the tumor cells showed a low nucleocytoplasmic ratio and eccentrically located nuclei, nuclear grooves, and eosinophilic pseudoinclusions. Lymphocyte-dominant inflammatory cells were present in the background, raising the possibility of thyroiditis. Histologically, the tumor was a 0.5 × 0.4 cm-sized mass and showed a trabecular and nested pattern of tumor cells separated by scant hyaline material in the background of Hashimoto's thyroiditis. Tumor cells showed abundant eosinophilic granular cytoplasms, nuclear grooves, and pseudoinclusions, as well as immunoreactivity for MIB-1 on the cell membrane. We diagnosed this lesion as HTA in a patient with Hashimoto's thyroiditis.
  
  
  CONCLUSIONS
  Although distinction of HTA from PTC in the cytologic specimen is difficult, especially in cases associated with Hashimoto's thyroiditis, cohesive cell aggregates with a low nucleocytoplasmic ratio and eccentrically located nuclei may be helpful to consider the possibility of HTA.
authors: Department of Pathology, Chonbuk National University Medical School and Hospital, Jeonju, South Korea.
authors: Tack Kune
authors: TK
authors: You
authors: Kyu Yun
authors: KY
authors: Jang
authors: Woo Sung
authors: WS
authors: Moon
authors: Myoung Ja
authors: MJ
authors: Chung
authors: Myoung Jae
authors: MJ
authors: Kang
authors: Dong Geun
authors: DG
authors: Lee
authors: Ho Sung
authors: HS
authors: Park
mesh_terms: D000236:Adenoma / Q000150:complications* / Q000473:pathology*; D000368:Aged; D044963:Biopsy, Fine-Needle; D005260:Female; D050031:Hashimoto Disease / Q000150:complications*; D006801:Humans; D016606:Thyroid Nodule / Q000150:complications* / Q000473:pathology*