title: Cystic tumor of the atrioventricular node: rare antemortem diagnosis.
abstract: BACKGROUND
  The cystic tumor of the atrioventricular node (TAV) is a rare, congenital cardiac tumor, typically located at the base of the atrial septum. Histologically benign, this multicystic mass is a tumor of the conduction system and is considered the smallest tumor capable of causing sudden and unexpected death. TAV has shown a predilection for women with a mean age at presentation of 38 years. The majority of cases are diagnosed incidentally at autopsy, while antemortem surgical excision is rare, with ours being the fifth and sixth reported cases in the medical literature.
  
  
  METHODS
  We present two cases, in 33- and 29-year-old women who were admitted for complaints of dyspnea, dizziness, palpitation or numbness, along with a review of the literature. One was known to have complete congenital heart block and ventricular septal defect, where an intraoperative transesophageal echocardiogram revealed a right atrial mass. The other patient had a right atrial mass visible on magnetic resonance imaging, which led to surgical resection and permanent pacemaker insertion.
  
  
  RESULTS
  Histopathological examination revealed a tumor composed of cysts, some lined by squamous epithelium, and others by transitional epithelium. Irregular proliferation of glandular structures with squamoid nests within a fibrous stroma, with sebaceous-type differentiation, was also observed. A chronic inflammatory component with secondary lymphoid follicles was also noted.
  
  
  CONCLUSIONS
  These cases are presented, along with a review of the four previously reported cases of TAV diagnosed antemortem. Awareness regarding this lesion could improve gross and microscopic characterization of TAV and increase antemortem diagnoses.
authors.affiliation: Department of Pathology, Toronto General Hospital/University Health Network, 200 Elizabeth Street, Toronto, Ontario, Canada.
authors.forename: Kelsey B
authors.initials: KB
authors.lastname: Law
authors.forename: Tianshu
authors.initials: T
authors.lastname: Feng
authors.forename: Vidhya
authors.initials: V
authors.lastname: Nair
authors.forename: Robert James
authors.initials: RJ
authors.lastname: Cusimano
authors.forename: Jagdish
authors.initials: J
authors.lastname: Butany
mesh_terms: D000328:Adult; D001283:Atrioventricular Node / Q000473:pathology* / Q000601:surgery; D003560:Cysts / Q000175:diagnosis* / Q000601:surgery; D004452:Echocardiography; D005260:Female; D006338:Heart Neoplasms / Q000175:diagnosis* / Q000601:surgery; D006801:Humans; D016896:Treatment Outcome