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A 38-year-old woman presents to her physician complaining of shortness of breath. An echocardiogram revealed a mass in the left atrium. Received for intraoperative consultation is a 1.8 cm broad-based, soft, hemorrhagic mass.
Archive Case and Diagnosis:
This case first appeared as Performance Improvement Program in Surgical Pathology (PIP) 2007, Case 19 and is a cardiac myxoma.
Criteria for Diagnosis and Comments:
Although controversial at one time, cardiac myxoma has been classified as a true neoplasm. Its designation as such is supported by studies demonstrating the presence of numerous chromosomal abnormalities, microsatellite instability, and aneuploid DNA content. Cardiac myxoma is one of the most common benign tumors of the heart, having a propensity to arise on the endomyocardial surface of the atria. The clinical setting of this tumor may be either sporadic or familial (syndromic) and will influence prognosis. In some series, cardiac myxoma represents 20% to 40% of primary cardiac tumors. The vast majority of patients (~90%) are between the ages of 30 to 60 years, with a mean age of 50 and a range from 2 – 97 years. In sporadic cases, cardiac myxoma is usually single, more common in women than men (2:1 ratio), and located in the left atrium near the fossa ovalis. In contrast, familial cases are seen in younger patients, may involve multiple sites, are slightly more common in men, and are likely to be located at intracardiac sites other than the left atrium.
The configuration and location of the tumor often influences clinical presentation and symptoms. Clinical presentations are generally of three types: cardiac symptoms; embolic symptoms; and systemic symptoms. The cardiac symptoms are most common, and are associated with valvular obstruction or stenosis. Embolic events are most often associated with tumors with a polypoid configuration, presenting as multiple systemic or pulmonary emboli (depending on the location of the myxoma). The diagnosis of cardiac myxoma may occasionally be made by histologic examination of the removed embolus. Systemic symptoms, thought to be due to tumor cell IL-6 production, includes myalgia, muscle weakness, arthralgia, fever, fatigue, and weight loss.
Gross examination of cardiac myxoma reveals a friable mass that may be broad based or stalked. The cut surface is pale yellow to grey, or hemorrhagic with a glistening gelatinous quality. The outer surface of the myxoma often is smooth-surfaced papillary nodules.
The histologic features on H&E sections include cytologically bland mesenchymal cells with stellate to polygonal eosinophilic cytoplasmic borders embedded in a pale grey-blue abundant myxoid stroma. The nucleus is usually small, round, and lacks atypia. Mitotic figures are extremely rare. The architecture of the suspended cellular growth can be seen as single cells, cords, or in characteristic concentric rings of stroma and cells around vessels. The blood vessels within the myxoma are frequently rudimentary, ranging from capillary size to large dilated thin walled vessels. Necrosis is not usually identified. Free-floating hemosiderin deposits within the stroma can be seen. The myxoid stroma contains abundant proteoglycans, which will stain with Alcian-blue and are resistant to predigestion with hyaluronidase. The cardiac myxoma cells are negative for cytokeratin, as well as variably positive for S100, smooth muscle, or endothelial markers (CD34 and CD31). Calretinin, interestingly, is positive in approximately 75% of cardiac myxomas. Because of the variable immunohistochemistry, the histogenesis of the tumor has been controversial but there is a growing consensus that it is derived from remnants of the endocardial cushions. This would also correlate with the common location of the tumor in the interatrial septum.
Microscopic variations reported in cardiac myxoma include cartilaginous tissue, ossification (“petrified” myxoma), thymic remnants, and foregut remnants. The foregut remnants are mucin producing glands that have been reported in about 20% of myxomas. These foregut remnants should not be mistaken for metastatic adenocarcinoma. The glands will stain for cytokeratins (cytokeratin 7, 34ß E12, CAM 5.2 and focally for cytokeratin 20), EMA, and CEA. Although occurring in less than 10% of cardiac myxomas, extramedullary hematopoiesis has been described.
Cardiac myxoma has been associated with a myxoma complex called Carney syndrome. A gene located at 17q24 (PRKAR1A) with mutations has been reported in three patients with this syndrome. This syndrome is a constellation of cardiac myxoma, abnormal skin pigmentations, calcifying Sertoli cell testicular tumors, cutaneous myxomas, myxoid breast fibroadenomas, pigmented adrenal cortical hyperplasia, pituitary hyperactivity, psammomatous melanotic schwannoma, and thyroid tumors. Carney syndrome is inherited as an autosomal dominant trait. Familial cardiac myxomas account for 7% of atrial myxomas, seen more commonly in the right atrium. Patients with inherited cardiac myxoma are prone to recurrent myxomas as compared to patients with sporadic myxoma.
The differential diagnosis for cardiac myxoma includes organized mural thrombus, hemangioma, and papillary fibroelastoma. Organizing mural thrombus has well formed abundant vessels seen as capillary ingrowth from the periphery of a thrombus and does not contain the prominent myxoid stroma. The hemangioma may present as an intracavitary mass but usually involve the ventricles. Hemangiomas will have dilated vessels with variably developed wall components such as smooth muscle and a myxoid background. However, true myxoid stroma with the characteristic stellate cells and growth patterns are not identified. The papillary fibroelastoma is usually a lesion located on the cardiac valves, has an avascular stalk which is confluent with valvular tissue and covered by radiating medusa like surface of papillary fronds. The lesion is composed of an array of elastic fibers easily demonstrated with an elastin stain.