Trichrome stain shows myocardium (red) interdigitating with a fibroma (blue). Though rare, fibromas are the second most common primary cardiac tumor in children. Fibrosarcomas can also occur.

Cardiac fibromas are well-circumscribed tumors composed of fibrous tissue. Grossly they appear well-circumscribed but, microscopically, the fibrous tissue intermingles with the surrounding myocardium. They are classified as benign based on pathologic characteristics and their failure to metastasize. However, as with other ‘benign’ cardiac tumors their clinical behavior can be malignant because of impaired cardiac function or involvement of the conduction system. Impaired cardiac function can result from impaired systolic or diastolic function, from obstruction of inflow or outflow of blood, or interference with valve function. Most common sites of involvement are the ventricular septum or left ventricular free wall. Fibromas are associated with Gorlin syndrome which is characterized by multiple nevoid basal cell carcinomas and ‘benign’ tumors in various locations including cardiac fibromas and rhabdomyomas.