7.5 Fetal Cardiac Tumors & Rare Lesions

Fetal Cardiac Tumors

Primary cardiac tumors in the fetus are rare, occurring in less than 0.2% of pregnancies. However, when detected during routine prenatal ultrasound, they warrant comprehensive echocardiographic evaluation due to their potential to cause hemodynamic compromise and their strong associations with underlying genetic syndromes.

Cardiac Rhabdomyomas

Rhabdomyomas are by far the most common fetal cardiac tumor, accounting for over 60-80% of all cases. They are benign, hamartomatous growths of striated cardiac muscle.

• Echocardiographic Appearance: Rhabdomyomas typically present as well-circumscribed, highly echogenic, homogenous solid masses. They are most commonly located intramurally within the ventricular myocardium or attached to the ventricular septum. Crucially, they are frequently multiple. While they can grow into the ventricular cavity, they rarely possess a distinct stalk.
• The Tuberous Sclerosis Connection: The discovery of a fetal cardiac rhabdomyoma, especially if multiple, demands immediate genetic counseling. There is a profound association—reported between 50% and over 80% in various studies—with Tuberous Sclerosis Complex (TSC). TSC is an autosomal dominant neurocutaneous disorder caused by mutations in the TSC1 or TSC2 genes. It is characterized by the formation of benign tumors in multiple organs, including the brain (cortical tubers, subependymal nodules), leading to severe postnatal complications such as intractable seizures and cognitive impairment.
• Fetal Complications: Most rhabdomyomas are small and asymptomatic. However, large tumors can cause mechanical obstruction to the left or right ventricular outflow tracts, interfere with atrioventricular valve closure leading to severe regurgitation, or compress the conduction system causing arrhythmias (like Wolff-Parkinson-White syndrome or ventricular tachycardia). Remarkably, rhabdomyomas often regress spontaneously during the third trimester or after birth.

Other Cardiac Tumors

• Cardiac Fibromas: These are the second most common tumors. Unlike rhabdomyomas, fibromas are almost always solitary. They typically present as a large, echogenic, sometimes calcified mass located in the left ventricular free wall or ventricular septum. They do not spontaneously regress and carry a higher risk of intractable arrhythmias and mechanical obstruction, sometimes necessitating postnatal surgical resection.
• Intrapericardial Teratomas: These rare tumors typically arise from the base of the great vessels and grow outwardly into the pericardial space. They are frequently accompanied by large, life-threatening pericardial effusions. The classic appearance is a complex, multilocular, heterogeneous mass containing cystic and solid components. They can cause severe cardiac tamponade in utero, sometimes requiring prenatal pericardiocentesis.

Pericardial Effusions

A pericardial effusion is the abnormal accumulation of fluid within the pericardial sac surrounding the heart. A tiny rim of fluid (less than 2 mm) is often seen normally in the third trimester.

Pathological effusions are significant and easily visualized on ultrasound as an anechoic (black) halo completely surrounding the heart. Large effusions can compromise cardiac filling, leading to cardiac tamponade and severely reduced cardiac output. Furthermore, a pericardial effusion is frequently an early herald sign of hydrops fetalis, prompting a thorough search for underlying causes such as severe fetal anemia, heart failure, arrhythmias, or viral infections (like Parvovirus B19).

Vascular Rings and Slings

Vascular rings are anomalies of the aortic arch system that completely encircle and potentially compress the trachea and esophagus. While often hemodynamically silent in utero, they can cause severe respiratory distress (stridor) or swallowing difficulties (dysphagia) postnatally.

• Double Aortic Arch: The most common true vascular ring. The ascending aorta bifurcates into two distinct arches (a right and a left) that run on either side of the trachea and esophagus before merging posteriorly to form the descending aorta. In the 3VT view, this creates an unmistakable "O" shape completely encircling the central trachea.
• Right Aortic Arch with Aberrant Left Subclavian Artery and Left Ductus Arteriosus: This combination forms a complete ring. The right-sided arch passes behind the trachea, and the ductus arteriosus connects the aberrant left subclavian artery to the left pulmonary artery, completing the vascular loop around the airway.
• Pulmonary Artery Sling: This is a non-aortic vascular anomaly where the left pulmonary artery arises abnormally from the right pulmonary artery, crossing over the right mainstem bronchus and coursing between the trachea and esophagus. It typically causes severe distal tracheal compression.

Prenatal diagnosis of vascular rings relies heavily on mastering the three-vessel and trachea view and carefully tracing the branching pattern of the aortic arch and the position of the ductus arteriosus relative to the trachea.