Background
Atrial myxomas are the most common primary heart tumors. Because of nonspecific symptoms, early diagnosis may be a challenge. Left atrial myxoma may or may not produce characteristic findings on auscultation. Two-dimensional echocardiography is the diagnostic procedure of choice. Most atrial myxomas are benign and can be removed by surgical resection.
Pathophysiology
Myxomas account for 40-50% of primary cardiac tumors. Approximately 90% are solitary and pedunculated, and 75-85% occur in the left atrial cavity. Up to 25% of cases are found in the right atrium. Most cases are sporadic. Approximately 10% are familial and are transmitted in an autosomal dominant mode. Multiple tumors occur in approximately 50% of familial cases and are more frequently located in the ventricle (13% vs 2% in sporadic cases).
Myxomas are polypoid, round, or oval. They are gelatinous with a smooth or lobulated surface and usually are white, yellowish, or brown. The most common site of attachment is at the border of the fossa ovalis in the left atrium, although myxomas can also originate from the posterior atrial wall, the anterior atrial wall, or the atrial appendage. The mobility of the tumor depends upon the extent of attachment to the interatrial septum and the length of the stalk.
Although atrial myxomas are typically benign, local recurrence due to inadequate resection or malignant change has been reported. Occasionally, atrial myxomas recur at a distant site because of intravascular tumor embolization. The risk of recurrence is higher in the familial myxoma syndrome. [1]
Symptoms from a cardiac myxoma are produced by mechanical interference with cardiac function or embolization and more pronounced when the myxomas are left-sided, racemose, and over 5 cm in diameter. [2] Because the tumors are intravascular and friable, myxomas account for most cases of tumor embolism, which occurs in about 30-40% of patients. The site of embolism is dependent on the tumor location (left or right atrium) and the presence of an intracardiac shunt. A case of multiple peripheral pulmonary artery aneurysms has been reported in association with a right atrial myxoma. [3] Most of the aneurysms had thrombi and became smaller following disappearance of thrombi after resection of the right atrial myxoma. However, some aneurysms became slightly larger. [3]
Ha and associates reported a more frequent occurrence of systemic embolism in polypoid tumors as compared to round (58% vs 0%). [4] Also, polypoid tumors more frequently prolapse into the ventricle. Prolapse of a tumor through the mitral or tricuspid valve may result in the destruction of the annulus or valve leaflets. In one study, 19% of the patients had atrial fibrillation associated with large atrial myxomas. Tumors vary widely in size, ranging from 1 to 15 cm in diameter, with the rate of growth not exactly known. In one case report, right atrial myxomas had a growth rate of 1.36 × 0.03 cm/mo. The myxomas are vascular tumors and may be neovascularized by a branch of a coronary artery. [5] A case of hemorrhage in a left atrial myxoma has been reported. [6]
Myxomas have been demonstrated to produce numerous growth factors and cytokines, including vascular endothelial growth factor, resulting in angiogenesis and tumor growth and an increased expression of the inflammatory cytokine, interleukin-6. [7, 8, 9]
Etiology
Most cases of atrial myxoma are sporadic, and the exact etiology is unknown.
Familial atrial myxomas have an autosomal dominant transmission.
Carney syndrome is genetically heterogenous and is caused by a defect in more than one gene. It is estimated to account for 7% of all atrial myxomas without any predilection for age or sex. Abnormalities in the short arm of chromosome 2 (Carney) and chromosome 12 (Ki-ras oncogene) have been described. In one case report, a frame-shift mutation was found in exon 2 in the causative gene of Carney complex, protein kinase A regulatory subunit 1 alpha (PRKAR1A). [10]
At present, there does not appear to be an association between cardiac myxomas and herpes simplex types 1 and 2. [11]
Epidemiology
United States statistics
Based upon the data of 22 large autopsy series, the prevalence of primary cardiac tumors is approximately 0.02% (200 tumors per million autopsies). About 75% of primary tumors are benign, and 50% of benign tumors are myxomas, resulting in 75 cases of myxoma per million autopsies.
International statistics
Surgical incidence in the Republic of Ireland from 1977-1991 was 0.50 atrial myxomas per million population per year.
Sex- and age-related demographics
Approximately 75% of sporadic myxomas occur in females. In a series of 66 cardiac myxomas, the female-to-male ratio was 2.7:1. [12] However, female sex predominance is less pronounced in familial atrial myxomas. In a retrospective analysis of 367 patients, there were 28 cases of right atrial myxoma, of which 16 occurred in males and 12 in females. [13]
Myxomas have been reported in patients aged 3-83 years. The mean age for sporadic cases is 56 years; whereas it is 25 years for familial cases. In a retrospective review of 171 patients from India, the mean age of presentation was 37.1 years. Most of these patients were symptomatic; dyspnea was the most common symptom. [14]
Prognosis
Morbidity/mortality
Atrial myxomas are histologically benign but can be dangerous owing to the potential for systemic and cerebral embolism. [15] Factors associated with an increased risk of embolism in those with left atrial myxoma include the presence of atrial fibrillation, an irregular tumor surface, a larger tumor size, and an increased left atrial diameter. [15]
Sudden death may occur in 15% patients with atrial myxoma, typically caused by coronary or systemic embolization or by obstruction of blood flow at the mitral or tricuspid valve.
Morbidity is related to symptoms produced by tumor embolism, heart failure, mechanical valvular obstruction, and various constitutional symptoms.
In a single-center study of 62 patients with cardiac myxoma, actuarial survival was 96.8 ± 1.8% at 10 years. Most patients were asymptomatic following the surgery, without recurrence. Recurrence occurred only in two familial cases of left atrial myxoma. Freedom from reoperation was 98.4 ± 1.3% at 5 years and 96.8 ± 1.8% at 10 years. [16]
Complications
Complications of atrial myxoma include the following:
-
Atrial myxoma. This is an apical 4-chamber echocardiographic view.
-
Atrial myxoma. This is a transesophageal echocardiogram.
