Cardiac Rhabdomyoma

Etiology

Genetic modification during the development of striated muscle may be the cause of rhabdomyoma. There are no other identified causes. Between 80% and 90 % of the cardiac rhabdomyomas are associated with tuberous sclerosis.[2][3][4]

Epidemiology

Primary cardiac tumors are extremely rare and occur in 0.2% of children.[5] Cardiac rhabdomyomas are the most common cardiac tumor in children (45%).[5] It is observed both in men and women, without any predilection for races.

Pathophysiology

Cardiac rhabdomyoma belongs to the hamartomatous subtype. It is most often identifiable in 20 to 30 weeks of gestation. Tumors are identified more in the fetal series than in the postnatal series. With the advent of imaging technology, the rate of fetal detection is on the rise. The interventricular septum, the left and right ventricles, and the atrioventricular valves are usually involved. It grows in the myocardium of the cardiac muscle. It can be sporadic, but a strong clinical association exists between cardiac rhabdomyoma and tuberous sclerosis [6] - an autosomal dominant condition characterized by benign hamartomas in multiple organ systems. Diagnosis of tuberous sclerosis is usually clinical, and further genetic testing looking for TSC1 and TSC2 gene mutations is confirmatory. 

Histopathology

Cardiac rhabdomyomas are comprised of cells resembling embryonic cardiac muscle cells. The histopathology reveals abnormal myocyte architecture, vacuolization, and spider cells (pathognomic).[7]

History and Physical

Cardiac rhabdomyoma can be identified as a mass in utero using ultrasonography. The presentation can vary from heart blocks, hydrops fetalis, or pericardial effusion.[7] If the tumor is large enough, intrauterine fetal demise can also be present. After birth, they are usually asymptomatic; if symptomatic, they typically present with signs and symptoms of heart failure and ventricular dysfunction from the obstruction of the outflow or inflow of blood. Dyspnea is one of the major initial patient complaints. Tumors are diagnosed more commonly in fetal series than in postnatal series, resulting in an increased sensitivity of fetal echocardiograms.[8] Due to its close association with tuberous sclerosis, physical findings of tuberous sclerosis-like ash leaf macules, shagreen patches, or sebaceous adenoma can also be in the patient presentation.

Evaluation

As cardiac rhabdomyoma most commonly correlates with tuberous sclerosis, a baseline 12-lead electrocardiogram (EKG) is necessary at the time of diagnosis, even without any cardiac symptoms, with routine EKGs every 2 to 5 years thereafter. The imaging modality of choice is echocardiography (ECHO). Cardiac rhabdomyoma presents as multiple, echogenic, and nodular masses in the ventricular myocardium. Cardiac rhabdomyoma can also protrude into the ventricular cavity. They are more homogenous and hyperechoic than the normal myocardium. The findings can be misinterpreted as a different cardiac tumor-like atrial myxoma if the location is atypical (atria) or there is a single large solitary tumor. Other imaging modalities like cardiac magnetic resonance imaging (MRI) can also be used as an adjunct to ECHO in cases of equivocal findings. The MRI gives a better delineation of the tumor and can be very helpful in cases of planned surgical resection. It also provides a more reliable estimate of ventricular systolic function.[7]

Treatment / Management

Cardiac rhabdomyomas are asymptomatic and regress spontaneously. In rare instances of hemodynamic compromise and congestive heart failure, pharmacotherapy with angiotensin-converting (ACE) enzyme inhibitors, digitalis, and diuretics is indicated. Prostaglandin E can be used to manage hemodynamic instability in a critically ill newborn. Antiarrhythmics are useful when there are conduction defects or any other ventricular arrhythmia. Partial or complete surgical resection of the mass is indicated in cases of hemodynamic compromise and congestive heart failure due to a large tumor.[9] Partial resection is preferred if there is a high risk of damage to the myocardial mass or vital structure by complete excision. Orthotopic heart transplantation is considered in extremely rare events when the tumor is so large that it has replaced the normal myocardial tissue. (B2)

Differential Diagnosis

The differential diagnosis includes:

• Cardiac fibroma
• Atrial myxoma
• Hemangioma
• Teratoma
• Thrombus
• Inflammatory myofibroblastic tumor

Treatment Planning

If the patient is asymptomatic, watchful waiting is advised as most tumors regress on their own. If symptomatic, the patient requires admission to the cardiac intensive care unit. The mTOR inhibitors are a consideration in cases associated with tuberous sclerosis. 

Prognosis

The patients who have had surgery for the removal of rhabdomyoma have a fair to good prognosis. The highest risk is among cardiac rhabdomyomas. They may grow and obstruct the left ventricular outflow tract, thus causing abnormalities in the flow, or may cause ventricular tachycardias or heart blocks.[7] The presence of fetal cardiac rhabdomyoma may be a sign of tuberous sclerosis, and thus, one should evaluate other structures ie, the renal or brain parenchyma for tumors; this is because cardiac rhabdomyoma is often the first symptom of tuberous sclerosis, followed by neurological involvement and impairment.[10]

Complications

The complications of cardiac rhabdomyoma include the following:

• Infections
• Arrhythmias (bradycardia and tachycardia)
• Congestive heart failure
• Hemodynamic compromise