# Case Report: Neonatal right atrial mass of uncertain etiology

## TL;DR

A preterm neonate had a right atrial mass that was difficult to diagnose as either a blood clot or a tumor, requiring surgery and highlighting the challenges in neonatal cardiac mass diagnosis.

## Contribution

This case report adds to the understanding of diagnostic challenges in neonatal intracardiac masses and emphasizes the need for multidisciplinary approaches.

## Key findings

- Multimodal imaging suggested a thrombus, but could not definitively identify the mass.
- Surgical excision was performed due to diagnostic uncertainty and risk of embolization.
- Histopathology could not distinguish between an organized thrombus and a regressed benign neoplasm.

## Abstract

Neonatal intracardiac masses are rare and pose significant diagnostic and therapeutic challenges, particularly in differentiating thrombi from tumors.

We present the case of a preterm neonate with a right atrial mass of uncertain etiology. Multimodal imaging, including echocardiography and cardiac MRI, suggested the presence of a thrombus—consistent with thrombi being the most common type of intracavitary cardiac mass. As a result, primary anticoagulation therapy was initiated. However, after 16 days without significant change in the mass and given the high risk of embolization and the possibility of a benign tumor, surgical excision was performed. Histopathological analysis of the excised tissue could not definitively distinguish between an organized thrombus and a regressed benign neoplasm, although no malignant cells were identified.

This case highlights the diagnostic uncertainty surrounding neonatal intracardiac masses and the limitations of imaging and pathology in achieving definitive diagnosis. A multidisciplinary approach and long-term follow-up are essential, particularly when the true nature of the mass remains unclear.