Prenatal mTOR-Inhibitor Therapy for Fetal Cardiac Rhabdomyomas: Indications, Treatment Duration and Perinatal Outcomes

Background: Fetal cardiac rhabdomyomas are strongly associated with tuberous sclerosis complex (TSC). Although many remain asymptomatic and regress spontaneously, large tumors may cause ventricular inflow or outflow obstruction, arrhythmia, impaired ventricular function, pericardial effusion, hydrops fetalis and fetal demise. Transplacental mammalian target of rapamycin (mTOR) inhibition has emerged as a potential rescue therapy. Methods: We performed a narrative review of published reports on prenatal sirolimus or everolimus therapy for fetal cardiac rhabdomyomas in suspected or confirmed TSC. Data was extracted on treatment indication, gestational age at initiation, treatment duration, fetal echocardiographic response, maternal adverse effects, delivery and postnatal outcome. Results: Available evidence consists predominantly of case reports, small case series and retrospective cohorts; no prospective controlled trials were identified. Treatment was generally initiated for progressive or hemodynamically significant disease, particularly ventricular inflow or outflow obstruction, worsening valve regurgitation, arrhythmia, pericardial effusion, ventricular dysfunction or hydrops. Therapy was usually started in the late second or third trimester and continued until hemodynamic stabilization, delivery or planned transition to neonatal treatment. Most reports described tumor regression within 1–3 weeks, accompanied by improved cardiac function and high perinatal survival. However, rebound growth after treatment withdrawal, persistent arrhythmic risk and limited long-term safety data remain important concerns. Conclusions: Prenatal mTOR-inhibitor therapy should be considered an individualized rescue or stabilization strategy for fetuses with life-threatening or progressive cardiac compromise, rather than routine treatment for all fetal rhabdomyomas. Management should be multidisciplinary and guided by fetal hemodynamics, treatment response, maternal tolerance and gestational age.