title: Clinical characteristics of papillary thyroid carcinoma arising from the pyramidal lobe.
abstract: OBJECTIVE
  Papillary thyroid carcinoma (PTC) arising from the pyramidal lobe is rare; therefore, clinicopathologic evaluation is lacking. In addition, the rate of occult malignancy in the pyramidal lobe after thyroid surgery is unclear. This study is to evaluate the clinical characteristics of PTCs that involve the pyramidal lobe.
  
  
  METHODS
  The study enrolled 1,107 patients who underwent thyroid surgery for PTC at Seoul National University Hospital from 2006 to 2015. Pyramidal lobe status in pathologic reports was clear in all cases. "Pyramidal lobe-dominant PTC" was defined as single pyramidal lobe cancer or multifocal cancer with larger pyramidal lobe tumor. "Incidental pyramidal lobe PTC" was defined as occult cancer identified after thyroidectomy or as multifocal cancer with smaller pyramidal lobe tumor.
  
  
  RESULTS
  Ten patients were included in the pyramidal lobe-dominant PTC group. The mean age was 58 ± 12.5 years, and the mean tumor size was 0.7 ± 0.7 cm. Cervical lymph node metastasis was found in 5 patients (50%). Three patients had microscopic lymphatic invasion, and 7 had advanced American Joint Comitee on Cancer (AJCC) stage disease (5 with stage III and 2 with stage IV). Compared with conventional PTC (n = 1,058), pyramidal lobe-dominant PTC was significantly associated with lymphatic invasion (P = 0.031) and advanced AJCC stage (P = 0.022). The prevalence of incidental pyramidal lobe PTC was 3.56%.
  
  
  CONCLUSIONS
  Pyramidal lobe PTC is relatively small in size; however, the rate of extrathyroidal extension and lymph node metastasis is high. Preoperative evaluation of nodal status is important, and the extent of surgery should be determined in accordance with the preoperative diagnosis.
authors.affiliation: Department of Surgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Sang Gab
authors.initials: SG
authors.lastname: Yoon
authors.affiliation: Department of Surgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.; Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Jin Wook
authors.initials: JW
authors.lastname: Yi
authors.affiliation: Department of Surgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Chan-Yong
authors.initials: CY
authors.lastname: Seong
authors.affiliation: Department of Surgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Jong-Kyu
authors.initials: JK
authors.lastname: Kim
authors.affiliation: Department of Surgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.; Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Su-Jin
authors.initials: SJ
authors.lastname: Kim
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea.; Department of Surgery, Seoul National University Boramae Medical Center, Seoul, Korea.
authors.forename: Young Jun
authors.initials: YJ
authors.lastname: Chai
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea.; Department of Surgery, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea.
authors.forename: June Young
authors.initials: JY
authors.lastname: Choi
authors.affiliation: Department of Surgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.; Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Kyu Eun
authors.initials: KE
authors.lastname: Lee
keywords: Lymphatic metastasis; Papillary thyroid carcinoma; Pyramidal; Thyroid; Thyroid neoplasms