Definition
• Most common primary neoplasm of the cardiac muscle in adults commonly arising from the endocardium, ranging in size from 1 cm to 10 cm
• Majority develop from the fossa ovalis in the left atrium, followed by the right atrium
• Rarely grows on both sides of fossa ovalis
• Ventricular or valvular sites are rare
• Tumor embolization is common and can be deadly
Clinical features
Epidemiology
• No known sex predilection
• Mean age at presentation is 50 years
• Unknown etiology; majority are sporadic; 10% associated with Carney syndrome
Presentation
• Presents with a clinical triad of valvular obstruction (tricuspid or bicuspid) with valvular damage, tumor emboli, and constitutional symptoms
• Arrhythmias leading to sudden death and abnormalities of atrioventricular conduction are seen because of disruption of the nodal or septal conduction system by the tumor
• If part of the Carney syndrome, it is more likely to be seen at a younger age, in atypical locations, and with increased risk of recurrence
Prognosis and treatment
• Complete surgical resection is curative, when possible
• Despite complete resection, risk of sudden death remains due to damage to the conduction system
• If the tumor is too large to resect, cardiac transplantation can be considered
Pathology
Gross
• Pale solitary, soft, gelatinous polypoid mass at fossa ovalis
• Can be sessile or pedunculated
• Cut surface may be variegated or diffusely calcified
• Some with surface thrombus
Histology
• Stellate or globular myxoma cells with abundant eosinophilic cytoplasm and indistinct cell borders arranged in cords, nests, rings, or poorly formed glands usually surrounding blood vessels
• Cells with oval nuclei, open chromatin, and indistinct nucleoli
• More cellular with mitotic activity near the surface; variable fibrosis and calcification
• Stroma consists of abundant myxoid substance containing chondroitin sulfate and hyaluronic acid
• Inflammation and hemorrhage are common
• Occasional Gamna-Gandy bodies (composed of fibrous tissue and elastic fibers with deposition of iron and calcium salts, completely disrupting the local architecture)
• Rarely, will have ossification, extramedullary hematopoiesis, mucin-forming glands, atypia, thymic rests
• May embolize to peripheral arteries
Immunopathology/special stains
• Positive for CD31, CD34, calretinin (cytoplasmic and nuclear staining), S100, vimentin
• Glandular components may be positive for keratin
• Negative for CD68, cytokeratin (except for glandular elements)
Main differential diagnoses
• Mural myxoid thrombi (no nests, cords, or rings; calretinin negative)
• Left atrial appendage thrombus
• Metastatic carcinoma
• Myxoid sarcoma
• Papillary fibroelastoma (on valve cusps, avascular papillary fronds)
Fig 1 Cardiac myxoma. Stellate or globular cells with abundant eosinophilic cytoplasm and indistinct cell borders arranged in cords, nests, rings, or poorly formed glands usually surrounding blood vessels: low- (A) and high- (B)power images.
Fig 2 Cardiac myxoma. Cardiac myxoma with mild chronic inflammation.
Fig 3 Cardiac myxoma. Calretinin immunostain highlights the myxoma cells.