Definition, Incidence, and Prevalence

Myxomas are the most common primary cardiac tumors. They are benign. Although they have been reported in both sexes and in all age groups, they most often occur in women in the third to sixth decade of life. Myxomas are usually sporadic, but at least 7% occur as part of an autosomal dominant syndrome. In the latter situation, the myxoma is a component of a larger syndrome referred to as the Carney complex.⁶ In the Carney complex, myxomas are associated with spotty pigmentation of the skin and endocrine hyperactivity. Myxomas that arise as part of the Carney complex affect both sexes equally and at any age, arise as single or multiple lesions in all chambers of the heart, and tend to recur after surgical excision.⁷

Morphology

Arising from the endocardium, myxomas usually extend into a cardiac chamber. They are generally polypoid, pedunculated lesions with a smooth surface that may be covered with thrombus (Fig. 104-1). The tumors range in size from 1 to 15 cm, but they are most commonly about 5 cm in diameter with a weight of approximately 70 g.^8–11 Myxomas are thought to arise from pluripotent mesenchymal cells. Histologically, they consist of a matrix of acid mucopolysaccharide (Fig. 104-2).¹² The cells are polygonal or spindle-shaped and may form capillary-like channels that can communicate with arteries and veins located at the base of the tumor.¹⁰

Figure 104–1 Pedunculated atrial myxoma with atrial tissue at base.

Figure 104–2 Hematoxylin and eosin stain of myxoma. (See color version in the online edition through Expert Consult.)

Myxomas most commonly occur in the atria. Approximately 75% arise in the left atrium, and 15% to 20% arise in the right atrium.¹⁰ Most left atrial myxomas are located on the border of the fossa ovalis, but they can originate from any place on the atrial wall. The remainder of myxomas are located in the ventricles. Myxomas arising from cardiac valves are rare.

Clinical Characteristics

Patients with myxomas can have a variety of symptoms. In the sporadic form, classic findings include emboli, congestive heart failure caused by obstruction of cardiac blood flow, and constitutional symptoms. These sequelae are related to the location, size, and mobility of the tumor.

Because most myxomas arise in the left atrium, systemic embolization is common, occurring in 30% to 50% of cases.^13–15 Left ventricular myxomas have an even higher propensity to embolize.¹⁶ Right atrial myxomas rarely display clinical manifestations of emboli. Embolic material from myxomas can compromise blood flow to any organ, but the brain is most commonly affected. Myxoma should be included in the differential diagnosis of any systemic embolic event, and any embolic material removed should undergo histologic evaluation.

Myxomas also can display signs and symptoms related to cardiac obstruction. Typically, the findings are related to the tumor’s ability to impede filling of the ventricles; in such instances, signs and symptoms may mimic those of mitral or tricuspid valve stenosis. Less commonly, the tumors impede atrioventricular valve leaflet coaptation, causing valvular regurgitation. Much less frequently, ventricular tumors obstruct ventricular outflow and cause findings similar to those of aortic or pulmonic stenosis.

Constitutional symptoms include fever, malaise, rash, weight loss, and myalgia. Abnormal laboratory values, including elevated erythrocyte sedimentation rate, anemia, thrombocytopenia, and an elevated C-reactive protein, are common. These constitutional symptoms and laboratory findings are not related to tumor size or location.

Many patients with myxomas are asymptomatic. The myxoma may be detected by routine screening echocardiography performed for other indications. Asymptomatic myxomas should be excised to prevent emboli, valvar dysfunction, or constitutional symptoms.