Cardiac Masses: Myxoma, Intracardiac Thrombus & Nonbacterial Endocarditis

Overview: tumor, thrombus or vegetation

Metastases come first. Secondary tumors are roughly 20–40 times more common than primary cardiac tumors. Lung and breast carcinoma, lymphoma and leukemia are the usual sources, and melanoma has the highest propensity of any cancer to reach the heart. Most metastases involve the pericardium and present as a hemorrhagic effusion or tamponade; renal cell and hepatocellular carcinoma can grow up the IVC into the right atrium.

Primary tumors are rare. About three-quarters are benign. Angiosarcoma, usually in the right atrium, is the most common primary malignant cardiac tumor in adults and carries a poor prognosis.

Atrial myxoma

Anatomy. Myxoma is the most common primary cardiac tumor in adults. About 75–80% arise in the left atrium, hanging on a stalk from the interatrial septum near the fossa ovalis; most patients are women aged 30–60. Histology shows stellate (lepidic) cells in a myxoid, mucopolysaccharide-rich stroma.

Obstruction. The mobile tumor prolapses into the mitral orifice during diastole, causing dyspnea, orthopnea, presyncope or syncope that change with body position, and occasionally sudden death. The exam mimics mitral stenosis — a diastolic rumble plus an early diastolic tumor plop, heard slightly later than an opening snap — but in sinus rhythm, without a rheumatic history, and varying with posture.

Embolism. Tumor fragments or surface thrombus embolize in roughly a third of patients, causing stroke or TIA in a young adult in sinus rhythm, retinal artery occlusion, or limb and visceral ischemia; right-sided myxomas embolize to the lungs. An unexplained embolic stroke in a young patient calls for echocardiography.

Constitutional features. Myxoma cells secrete IL-6, producing fever, weight loss, fatigue, arthralgias, anemia, a high ESR and CRP, and hypergammaglobulinemia. The picture mimics endocarditis, vasculitis or lymphoma and resolves after excision.

Diagnosis and treatment. TTE is the first test; TEE or cardiac MRI defines the attachment and tissue character. Resect promptly, including the stalk base, because embolism or obstruction can occur while waiting; biopsy is unnecessary. Periodic echo follows surgery — sporadic myxomas rarely recur, familial ones often do.

Carney complex. This autosomal dominant syndrome from PRKAR1A mutations causes multiple, recurrent myxomas in any chamber, at a young age and in either sex, together with spotty pigmentation (lentigines, blue nevi), cutaneous myxomas and endocrine overactivity: primary pigmented nodular adrenocortical disease (ACTH-independent Cushing syndrome), GH-secreting pituitary adenoma and testicular Sertoli cell tumors. First-degree relatives are screened.

A young patient with a myxoma outside the left atrium, more than one myxoma, or a recurrence should be evaluated for Carney complex.

Papillary fibroelastoma and rhabdomyoma

Papillary fibroelastoma. The most common valve tumor, found on the aortic more often than the mitral valve, is usually smaller than 1–1.5 cm and looks like a frond-like sea anemone on echo. Often incidental in older adults, it can embolize to cause stroke or TIA, or occlude a coronary ostium and cause MI. Excise it if it has caused symptoms, is mobile, or measures ≥1 cm.

Rhabdomyoma. The most common primary cardiac tumor of infants and children. These ventricular hamartomas, often multiple and septal, are strongly associated with tuberous sclerosis (TSC1/TSC2) and may be the first sign of it on fetal echo. They can obstruct outflow or cause arrhythmias, including WPW, but most regress spontaneously, so observation is standard unless they are hemodynamically significant. Look for ash-leaf spots, facial angiofibromas, infantile spasms, cortical tubers and renal angiomyolipomas.

Intracardiac thrombus

LV thrombus. Stasis over injured endocardium forms mural thrombus after a large anterior MI with apical akinesis or aneurysm, usually within the first 2 weeks, and in dilated cardiomyopathy with a very low EF. Contrast echo detects most thrombi; cardiac MRI is the most sensitive test. Treat with oral anticoagulation — warfarin (INR 2–3) or a DOAC — for about 3 months, then re-image; antiplatelet therapy alone is inadequate, and fibrinolysis or surgical removal is not indicated. Location helps: thrombus sits at an akinetic LV apex (or in the left atrial appendage in AF), whereas a myxoma hangs from the atrial septum.

Nonbacterial endocarditis

Marantic (nonbacterial thrombotic) endocarditis. Small, friable, sterile platelet–fibrin vegetations form along the closure line of the mitral or aortic leaflets in hypercoagulable states — mucin-secreting adenocarcinoma (pancreas, lung, stomach, ovary), DIC and sepsis. The leaflets are not destroyed, patients are often afebrile, and blood cultures are negative; the presentation is systemic embolism, often multiple strokes in different territories. TEE shows the vegetations. Treat with heparin (unfractionated or low-molecular-weight), which prevents recurrent emboli better than antiplatelet therapy, and search for and treat the underlying cancer.

Libman–Sacks endocarditis. In SLE, especially with antiphospholipid antibodies, small sterile verrucous vegetations form on both surfaces of the mitral leaflets (and less often the aortic), causing regurgitation and embolic stroke. Treat the lupus, anticoagulate with warfarin when antiphospholipid syndrome or embolism is present, and reserve surgery for severe valve dysfunction.