FIG 52.10 Histologic section of a rhabdomyoma showing the typical features of the so-called spider cell FIG 52.11 Multiple rhabdomyomas occupying an intracavitary position and growing from the wall of the right ventricle and the adjacent right atrium Rhabdomyomas are readily visible on fetal or transthoracic echocardiography, with a homogenous and echobright appearance This homogeneity helps to distinguish rhabdomyomas from other common pediatric primary cardiac tumors, which tend to have heterogenic appearances.74 On MRI, the lesions appear bright on T2-weighted sequences and are relatively isointense to myocardium and nonenhancing on other sequences.54 Rhabdomyomas have been diagnosed as early as 15 weeks of gestation and continue to grow through approximately 32 weeks’ gestation Postnatally, spontaneous regression will occur in a majority of neonates during the first year of life Echocardiographic follow-up has shown regression within a period as short as 6 weeks (Fig 52.12).1,75–79 The frequency of lesions decreases in children older than 2 years De novo appearance of a rhabdomyoma with rapid growth at 2 years has been reported,80 as well as transient enlargement of tumors in both infancy and adolescence (see section later on myocardial fatty foci [MFF]).71,81,82 FIG 52.12 Regression of rhabdomyomas Apical four-chamber view shows multiple ventricular rhabdomyomas in a patient with tuberous sclerosis complex (A) as a neonate and (B) at 3 years of age The majority of patients with rhabdomyomas are asymptomatic from a cardiac standpoint, with the diagnosis made on screening fetal or postnatal echocardiography When present, symptoms, morbidity, and/or mortality are generally due to intracardiac obstruction, arrhythmia, or heart failure due to replacement of myocardium Extrinsic compression of coronary arteries has also been described In rare cases, large left ventricular lesions have been implicated in the development of hypoplastic left heart syndrome.83,84 In some patients, rhabdomyomas are an immediate cause of morbidity and/or mortality, with fetal demise or neonatal death One meta-analysis found prenatal tumor size greater than 20 mm and fetal arrhythmia to be significant predictors of intrauterine or neonatal death.85 However, other groups have noted that the location of a tumor and impact on blood flow plays a larger role than size in symptomatology.28 Arrhythmias were present in 28% of patients with rhabdomyomas in one large single-institution study.5 Nearly half of these patients had low-grade arrhythmia, followed by asymptomatic preexcitation, supraventricular tachycardia, and ventricular tachycardia Most patients were managed conservatively with resolution of arrhythmia or preexcitation with tumor regression Preexcitation and ectopic atrial tachycardia persisted into the teenage years in a minority of patients When needed, pharmacologic management, radiofrequency ablation of accessory pathways, and surgical resection of tumors were successful in nearly all patients Diffuse cardiac rhabdomyomatosis is an extremely rare entity where portions ... with a homogenous and echobright appearance This homogeneity helps to distinguish rhabdomyomas from other common pediatric primary cardiac tumors, which tend to have heterogenic appearances.74 On MRI, the lesions