Congenital cystic tumors of the atrio-ventricular node: successful demonstration by an abbreviated dissection of the conduction system

Cystic tumor of the atrioventricular node: a review of the literature

Primary cardiac tumors are uncommon clinical entities with an incidence of 0.0017% to 0.03% of all autopsies. Cystic tumor of the atrioventricular (AV) node, also known as mesothelioma of the AV node, is a benign congenital tumor that is located in the triangle of Koch in the AV nodal region of the atrial septum of the heart. It comprises of 2.7% of cardiac tumors and is the most common primary cardiac tumor causing sudden death. We herein review the etiology, presentation, differential diagnosis, diagnosis, management, surgical approaches and outcomes of this rare tumor.

Cystic tumor of the atrioventricular node: rare antemortem diagnosis

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.

CONCLUSION

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.

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

SUMMARY

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.

CONTEXT

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.

DESIGN

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.

RESULTS

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.

CONCLUSIONS

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.

Endodermal heterotopia of the atrioventricular node associated with transposition of the great arteries

A 13-year-old girl with surgically corrected complete transposition of the great arteries died suddenly while walking to school. Postmortem examination revealed endodermal heterotopia of the atrioventricular node, a condition not previously associated with transposition of the great arteries. New immunohistochemical observations are described, and the embryogenesis of the condition and its association with complete transposition are discussed.