title: Microscopic-sized "microthymoma" in patients with myasthenia gravis.
abstract: BACKGROUND
  In 2005, Cheuk et al reported two patients with microscopic-sized thymomas and proposed the term microthymoma to distinguish it from the nodular hyperplasia of thymic epithelium, so-called microscopic thymoma. Here, we present microthymomas that were found in 196 patients with myasthenia gravis (MG) who had undergone thymectomy.
  
  
  METHODS
  Thymic tissues in 196 patients with MG who underwent thymectomy or thymothymomectomy were examined. Of these patients, 73 patients had thymoma indicated by CT before surgery, and the other 123 patients had no mediastinal tumors. From the resected thymic tissues, an average of 14 hematoxylin-eosin-stained sections (range, 4 to 55 sections) were prepared for microscopic examination. The histologic type of the thymoma was classified according to the World Health Organization (WHO) classification.
  
  
  RESULTS
  From the 196 patients, we found three microthymomas in 3 patients (1.5%). While these three tumors could not be seen grossly in pathology section, they were found microscopically (range, 2 to 4 mm). The histologic subtype according to the WHO classification system was B1 in one patient and B2 in two patients.
  
  
  CONCLUSIONS
  Microthymoma was found in 3 of 196 patients (1.5%) with MG. Microthymoma might exist in thymus of patients with MG, even in patients who have no thymoma indicated by CT.
authors.affiliation: Department of Thoracic Surgery, Kumamoto University Hospital, 1-1-1 Honjo, Kumamoto 860-8556, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Mori
authors.affiliation: Department of Thoracic Surgery, Kumamoto University Hospital, 1-1-1 Honjo, Kumamoto 860-8556, Japan. Electronic address: hnomori@qk9.so-net.ne.jp.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Nomori
authors.affiliation: Department of Thoracic Surgery, Kumamoto University Hospital, 1-1-1 Honjo, Kumamoto 860-8556, Japan.
authors.forename: Koei
authors.initials: K
authors.lastname: Ikeda
authors.affiliation: Department of Thoracic Surgery, Kumamoto University Hospital, 1-1-1 Honjo, Kumamoto 860-8556, Japan.
authors.forename: Hironori
authors.initials: H
authors.lastname: Kobayashi
authors.affiliation: Department of Thoracic Surgery, Kumamoto University Hospital, 1-1-1 Honjo, Kumamoto 860-8556, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Iwatani
authors.affiliation: Department of Thoracic Surgery, Kumamoto University Hospital, 1-1-1 Honjo, Kumamoto 860-8556, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Yoshioka
authors.affiliation: Graduate School of Medical Sciences, and Department of Surgical Pathology, Kumamoto University Hospital, 1-1-1 Honjo, Kumamoto 860-8556, Japan.
authors.forename: Ken-Ichi
authors.initials: KI
authors.lastname: Iyama
mesh_terms: D000328:Adult; D000368:Aged; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008297:Male; D008853:Microscopy; D009157:Myasthenia Gravis / Q000473:pathology* / Q000601:surgery; D013934:Thymectomy; D013945:Thymoma / Q000473:pathology* / Q000601:surgery; D013950:Thymus Gland / Q000473:pathology; D013953:Thymus Neoplasms / Q000473:pathology* / Q000601:surgery