Benign tumors / other nonneoplastic
Cystic tumor of the atrioventricular node

Topic Completed: 1 November 2013

Minor changes: 24 August 2020

Copyright: 2007-2019, PathologyOutlines.com, Inc.

PubMed Search: Atrioventricular node tumor

Nat Pernick, M.D.
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Cite this page: Pernick N. Cystic tumor of the atrioventricular node. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/hearttumormesotheliomaofAVnode.html. Accessed October 20th, 2020.
Definition / general
  • Also called cystic tumor of AV node or mesothelioma of AV node but does not appear to have mesothelial origin
  • Rare; usually identified at autopsy
  • May be congenital rests of endodermal origin (Arch Pathol Lab Med 1990;114:1057) or ultimobranchial heterotopia identical to solid cell nests of thyroid (Am J Clin Pathol 2005;123:369)
  • Associated with other congenital anomalies
  • Often causes heart block and sudden death
  • Mean age 38 years, 75% female
  • Should examine conduction system in all patients with sudden death, particularly if a history of arrhythmia or heart block
Case reports
Radiology images

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MRI of the thorax showing tumor

  • Pacemaker implantation, anti-arrhythmic drugs, possibly surgical excision (Heart 2000;83:E6)
Gross description
  • May not be visible due to small size (2 to 20 mm)
  • Multicystic lesion in area of atrioventricular node and membranous septum
Gross images
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Tumor outlined by
arrowheads (RA-right
atrium, RV-right ventricle,
TV-tricuspid valve)

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Figures 1/2: nodule
of atrioventricular
node fig 3: elastic
and trichrome stains
Microscopic (histologic) description
  • Must sample conduction system
  • Solid and cystic areas lined by nonciliated, epithelial appearing cuboidal cells (main cells), mixed with occasional clear cells (neuroendocrine or C cells)
  • Lumina contains PAS+ diastase resistant material which may calcify
  • May have inflammatory cells and fibrosis
  • No smooth muscle, no mitotic figures, no atypia
Microscopic (histologic) images
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Normal anatomy (no tumor) with
IAS-interatrial septum (tumors are
located inferiorly), TV-tricuspid
valve and VS-ventricular septum
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Large cysts
filled with
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Multiple small cysts not visible to naked eye

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Cysts with irregular shape surrounded by fibrous stroma

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Cyst may have two
cell lining, with inner
lining composed of
small cuboidal cells

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Tumor nests and
cysts replace muscle
bundles in inferior
interatrial septum
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Cuboidal cells and clear, sebaceous-type cells

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Squamous differentiation and calcification of luminal debris

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Nests of cells resembling urothelium

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H&E and AE1/AE3+

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Cyst wall showing the large
cyst lining of simple
cuboidal epithelium
Positive stains
Electron microscopy description
  • Cells form solid nests with well formed basement membranes, cytoplasmic tonofilaments and desmosomes or glandular structures with desmosomes, electron dense material and short microvilli
Differential diagnosis
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