1354958 - Large Isolated Right Atrial Mass in a Neonate: A Diagnostic Dilemma

An otherwise, asymptomatic neonate was born at term with a prenatally diagnosed right atrial mass. Serial fetal echocardiograms in the third trimester demonstrated an isolated large right atrial mass without any obstruction to flow, that remained stable in size. The potential etiologies of intracardiac masses including fibroma, myxoma, hemangioma, rhabdomyoma and malignant tumor were discussed with mother. Fetal brain magnetic resonance imaging (MRI) performed in the third trimester was normal. Postnatal echocardiogram confirmed a large 1.3 X 1.1 cm homogenous immobile mass in the anterosuperior aspect of the right atrium without any obstruction to systemic venous inflow or tricuspid inflow. A postnatal brain MRI showed a focus in the subependymal area suspicious for nodule versus hemorrhage and a follow up scan was recommended. There were no clinical seizures or cardiac arrhythmias. Genetic testing for Tuberous Sclerosis returned negative for TSC1 and TSC2 gene. The diagnosis remained uncertain and etiologies other than rhabdomyoma were being considered.

Diagnostic Techniques and Their Most Important Findings:

A cardiac MRI was performed at 2 months of age for further assessment. On cine imaging, there was a large solitary, immobile and sessile mass (1.1 X 1.0 cm) in the anterosuperior aspect of the right atrium, near the right atrial appendage and SVC. On T1 weighted imaging with and without fat saturation, as well as on T2 weighted imaging, the mass was isointense. On first pass perfusion imaging, the mass remained hypointense. On early gadolinium enhancement sequences with long inversion time, the mass appeared dark. On delayed gadolinium imaging, there was no hyperenhancement of the mass. Based on these characteristics and given the clinical picture, the mass was most consistent with a rhabdomyoma. [1]. Subsequent brain MRI demonstrated a subependymal nodule. Despite negative genetic testing, a clinical diagnosis of Tuberous Sclerosis (TS) was made based on presence of 2 major criteria. [2] Given the diagnosis, no further cardiac intervention was recommended. The baby continues to be monitored clinically with a reduction in size of the mass and no arrhythmias at 9 months of age.

Learning Points from this Case:

Although cardiac rhabdomyomas are the most common pediatric intracardiac tumors, they tend to be multiple and are usually found in the ventricular myocardium. They are highly associated with TS and typically regress during early childhood. [3] While majority of patients with TS have a positive genetic test, a clinical diagnosis can be made in patients with a negative test. 2]  Differential diagnosis for right atrial mass in children includes a fibroma, myxoma, hemangioma, malignancy or thrombus. [1, 4] The management of these can include resection and treatment with medications. Thus, tissue characterization by cardiac MRI in this case was critical in establishing a diagnosis of rhabdomyoma and TS, despite negative genetic test. It aided in clinical decision making and altered the management strategy.