Cystic tumor of the atrioventricular node: an unexpected finding in an explanted heart

We report herein a unique case of cystic tumor of atrioventricular (AV) node (CTAVN), which, to our knowledge, is the first of its kind diagnosed in an explanted heart specimen and only the fourth diagnosed antemortem. Often, this rare tumor can only be diagnosed by careful gross examination and adequate sampling of AV node region. It is an important differential diagnosis in young patients with syncopal attacks and varying degrees of heart blocks.

CTAVN is a rare, benign tumor. Most cases have been reported in young females (mean age, 38 years). Patients typically present with conduction abnormalities including complete heart block leading to sudden cardiac death. Most cases have been identified at autopsy; no cases to our knowledge have been reported in an explanted heart.

A 19 year-old female presented to the cardiac transplant clinic for evaluation of severe congestive heart failure felt to be secondary to postpartum cardiomyopathy. The patient's history was significant for congenital heart block requiring placement of a permanent pacemaker at 12 years of age. At the time of this presentation, electrocardiogram revealed second-degree AV block, and two-dimensional echocardiogram showed lipomatous hypertrophy of the interatrial septum. Seven months later, orthotopic cardiac transplantation was performed.

On gross examination, the explanted heart weighed 500 g and had biventricular dilatation. Histologic sections of left and right ventricle revealed myocyte hypertrophy and interstitial fibrosis consistent with dilated cardiomyopathy. Sections from the AV node showed a lesion with morphological features of CTAVN. It was composed of cysts of varying sizes lined by transitional, cuboidal and squamous epithelium. Some cysts were filled with proteinaceous debris that were periodic acid Schiff-positive and diastase resistant.

CTAVN occurs exclusively in the area of the AV node, tricuspid valve, and inferior atrial septum. These lesions are now believed to be endodermal in origin, although mesothelial origin was earlier proposed. We report herein a case of CTAVN, the first of its kind diagnosed in an explanted heart specimen and only the fourth diagnosed antemortem.