Discussion
Cardiac rhabdomyoma is a benign tumor of striated muscle. In a study of 14,000 fetal echocardiograms, 17 patients were found to have cardiac rhabdomyoma, a prevalence of 0.12% [1]. In another study of obstetric ultrasounds, the prevalence of cardiac rhabdomyoma was approximately 1 in 9000 (11/97,867) [2]. Rhabdomyoma is the most common fetal cardiac tumor, occurring in 80-90% of cases [1,3].
In 1982, DeVore et al reported the first prenatal diagnosis of cardiac rhabdomyoma [4]. Ultrasound findings characteristic of cardiac rhabdomyoma are a non-vascular, round, homogenous, hyperechoic mass originating from the myocardium. They can be intramural, intracavitary, sometimes multiple, and predominantly in the ventricles. [5,6]. These cardiac tumors are more commonly detected after the 24th week of pregnancy, however approximately 14% are diagnosed earlier [5].
Cardiac rhabdomyoma are associated with tuberous sclerosis, which is an autosomal dominant systemic genetic disorder with variable penetrance that affects the central nervous system, skin, retina, kidneys and heart. It can occur from either inherited or de-novo mutations that inactivate the TSC1 and TSC2 genes encoding the proteins tuberin and hamartin [6]. In approximately 25% of cases, there is a positive family history [6]. In a review of the literature, cardiac rhabdomyomas are associated with tuberous sclerosis in 51-86% of cases [2,5,7], and more commonly in patients with multiple cardiac tumors [5]. Tuberous sclerosis can be suspected prenatally with third trimester MRI showing brain or renal tubers [5, 8]. Association of cardiac rhabdomyoma with congenital heart defects (3.6%) and extracardiac structural anomalies (1.4%) is rare [5].
The differential diagnosis for fetal cardiac tumors includes fibroma, myxoma, teratoma, lipoma and hemangioma [3,5,9]. Fibromas are hyperechoic, often associated with calcification and cystic degeneration. Teratoma are extracardiac masses located in the pericardial cavity, associated with pericardial effusion. Hemangiomas have a more complex echogenicity with cystic and solid parts mixed with calcifications and usually located in the right atrium [5].
Cardiac rhabdomyoma can have variable clinical outcomes. While a portion of tumors can regress or even resolve, larger tumors can cause mechanical obstruction, heart failure and death. Factors associated with negative fetal outcomes are tumors >20mm, fetal dysrhythmias, and hydrops [5]. Neonatal death occurs in approximately 10-15% of infants [2,3,5,8] and intrauterine death is also reported [5]. While these are benign tumors, surgical resection is indicated in cases with hemodynamic compromise [6]. Conversely, in at least two-thirds of cases, the tumor regresses and can even resolve spontaneously [5,6,10,11].
The presence of tuberous sclerosis affects clinical outcomes in these infants due to the associated neurologic sequelae. In a study of 51 fetuses with cardiac rhabdomyoma, 20 of which were followed postnatally, 45% were found to have adverse neurologic outcomes over a follow up period of approximately 5 years [8]. In another study, the prevalence of neurologic complications was higher with 80% of cases presenting with seizures and 29% presenting with mental retardation [6]. It is recommended to follow patients after birth with serial examination of the cardiac rhabdomyoma to ensure regression, and neurologic exam including MRI to exclude the development of tuberous sclerosis [5].
References
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