Cystic tumors of the atrioventricular node (CTAVN), also known as endodermal heterotopia, refer to a benign mass lesion of the atrioventricular node that constitutes a developmental endodermal rest.
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Terminology
A term that is no longer recommended for use is ‘mesothelioma of the atrioventricular node’ 1.
Epidemiology
Cystic tumors of the atrioventricular node make up about 2.7% of cardiac tumors and are the most common tumors causing sudden cardiac death 1,2. They have been found in all age groups with a mean age of 38 years at the time of diagnosis 1. Women are more frequently affected 1.
Diagnosis
The final diagnosis is based on the histology with evidence of a cystic endodermal inclusion within Koch’s triangle or the atrioventricular septum 1.
A well-circumscribed lesion or tumor in the area of the atrioventricular septum might indicate the diagnosis.
Clinical presentation
Clinical signs and symptoms revolve around arrhythmia-related symptoms and include palpitations, dizziness, syncope, dyspnea, fatigue, partial or complete heart block. Tumors might be initially and temporarily asymptomatic 1.
Complications
Cystic tumors of the atrioventricular node might cause the following complications or sequelae 1,2:
- atrioventricular block
- ventricular tachycardia, ventricular fibrillation
- cardiac arrest
- sudden cardiac death
Pathology
Cystic tumors of the atrioventricular node are cystic endodermal residue that is believed to be a result of abnormal migration during embryogenesis 1.
Etiology
The exact etiology of cystic tumors of the atrioventricular node is unknown. They are thought to be congenital 1.
Location
Cystic tumors of the atrioventricular node are usually found at the base of the atrioventricular septum in the triangle of Koch possibly extending from the coronary sinus ostium to the membranous septum adjacent to the septal tricuspid leaflet 1-4.
Macroscopic appearance
Macroscopically the cystic or multicystic nature of the tumors might not always be apparent. They are usually small and might be seen as bulges within the atrioventricular septum. They might contain fluid or debris 1,2.
Microscopic appearance
Microscopically cystic tumors of the atrioventricular node are characterized by the following features 1-3:
- variably sized cysts with a columnar, squamous or transitional cell lining
- scattered neuroendocrine or C cells
- dense fibrous matrix
- rarely goblet or sebaceous cells
- no cellular atypia
- rare mitoses
Immunophenotype
Immunohistochemistry stains are positive for alcian blue and PAS. They are also usually positive for cytokeratins such as AE1 and/or AE3, CK5/CK7, epithelial membrane antigen and CEA. Neuroendocrine cells might show focal, scattered positivity for chromogranin and calcitonin 1,2.
Radiographic features
Echocardiography
Echocardiography might show a well-delineated lesion in the area of the atrioventricular node 4.
CT
Thoracic CT or cardiac CT might show a well-circumscribed hyperdense lesion or mass in the area of the atrioventricular node 5.
MRI
Cardiac MRI might demonstrate well-delineated cystic in the atrioventricular or proximal interatrial septum 3,4.
Signal characteristics
- T1: isointense
- T2: hyperintense
- T1C+ (Gd): heterogeneous enhancement
Angiography
A coronary angiogram might show an abnormality such as a ‘tumor flush’ of the AV nodal artery, which most commonly arises from the right coronary artery 2.
Radiology report
The radiological report should include a description of the following:
- lesion extent and location
- relation to adjacent structures
Treatment and prognosis
The occurrence of arrhythmias is apparently not related to the size of the tumors 1. Nevertheless, management usually includes surgery since a pacemaker does not reliably prevent arrhythmias and sudden cardiac death 2. Complete or partial excision, as well as minimally invasive techniques on cardiopulmonary bypass, have been described. Pacemaker implantation and medical antiarrhythmic treatment might still be necessary following surgery 2.
Recurrences have not been reported 2.
Differential diagnosis
Condition or tumors that might mimic the imaging appearance of cystic tumors of the atrioventricular node include 1:
- bronchogenic cysts (on the epicardial surface)
- mesothelial cysts (composed of endoderm and mesoderm, on the epicardial surface)
- teratomas (composed of all three germ layers)
- conduction system hamartoma (in infants)
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