Description
Cardiac rhabdomyoma is a benign cardiac tumour primarily seen in infants and children. It is composed of large polygonal cells with a characteristic central striation pattern. Rhabdomyomas account for the majority of primary cardiac tumours in the paediatric population, and they often present with symptoms related to their size and location.
Pathogenesis
The pathogenesis of cardiac rhabdomyoma is not completely understood. They are thought to arise from cardiac muscle cells (myocytes) but the triggers for their proliferation remain unclear. There is a significant association with tuberous sclerosis complex (TSC), a genetic disorder characterised by the growth of benign tumours in multiple organ systems, suggesting a role for the TSC genes in their development.
Epidemiology, Risk Factors & Associations
- Cardiac rhabdomyomas are the most common cardiac tumours in children, accounting for more than 60% of cases.
- Most rhabdomyomas are diagnosed before the age of 1 year, and there is no significant gender predilection.
- Approximately half of the cases are associated with tuberous sclerosis complex (TSC).
- Other less common associations include Bourneville’s disease and multiple lentigines syndrome.
Clinical Features
- Asymptomatic: Many cardiac rhabdomyomas are incidentally found due to their often asymptomatic nature.
- Cardiac symptoms: Due to obstruction, valve dysfunction or arrhythmias. These can include breathlessness, cyanosis, heart murmurs or palpitations.
- Systemic symptoms: In cases associated with tuberous sclerosis, systemic symptoms such as seizures, developmental delay and skin lesions may be present.
Complications
- Outflow tract obstruction
- Cardiac arrhythmias
- Valve dysfunction
- Sudden cardiac death
Subtypes
There are no specific subtypes of cardiac rhabdomyoma.
Pathological Features
Morphology
Cardiac rhabdomyomas are typically large, solitary, and well-demarcated masses, although multiple tumours can occur. They are most commonly found in the ventricles but can be found in any part of the heart.
Histopathology
Histologically, cardiac rhabdomyomas are composed of large polygonal cells with a central striation pattern, known as “spider cells”. There is abundant eosinophilic cytoplasm and centrally located nuclei.
Genetics
Cardiac rhabdomyomas are strongly associated with mutations in the TSC1 and TSC2 genes, which are involved in the regulation of the mTOR pathway, a key cellular growth and proliferation pathway.
Radiological Features
Echo
- Initial imaging modality for identifying cardiac rhabdomyomas.
- Visualises homogeneous, echogenic masses within the myocardium.
- Optimal for identifying small (< 5-mm) or completely intramural lesions.
CT
- Presents well-demarcated, homogeneous masses.
- Isoattenuating to the adjacent myocardium with minimal or no differential contrast enhancement.
- In patients with tuberous sclerosis, these tumours may exhibit fatty degeneration.
- Tumours can originate in the ventricular septum, the free wall of the left/right ventricle, or the papillary muscles.
MRI
- Offers detailed assessment of the tumour and surrounding structures.
- Tumours are typically isointense to myocardium on T1-weighted images and mildly hyperintense on T2-weighted images.
- Tumours show homogeneous enhancement and are hypointense to myocardium during the perfusion phase.
- In tuberous sclerosis patients, myocardial fatty foci (MFF) due to lipoma or angiomyolipoma can be seen, exhibiting high T1 and T2 signals with fat saturation and chemical shift in steady-state free precession (SSFP).
- Superior to echocardiography for detecting intracavitary lesions and determining extracardiac extension.
Grading and Staging
Grading and staging systems are not typically used in the context of cardiac rhabdomyoma as they are benign tumours.
Differential Diagnosis
- Cardiac fibroma: These are often more heterogeneous and may not show the homogeneous enhancement seen in rhabdomyomas.
- Cardiac teratoma: Teratomas are typically located in the pericardial space and show fat and calcifications.
- Intracardiac thrombus: These can mimic rhabdomyomas but usually occur in patients with predisposing factors and do not enhance after contrast administration.
Management
- In many cases, no treatment is necessary as the tumours often regress spontaneously.
- However, in cases where the tumour is causing significant symptoms or complications, surgical resection may be necessary.
- For patients with associated TSC, genetic counselling is recommended.
- The diagnosis is usually confirmed via imaging, and biopsy is rarely needed.