Rhabdomyomas aregray-whitemassesuptoseveralcentimetersindiameterthatprotrudeintotheventricularchambers.Histologicexaminationshowsamixedpopulationofcells;mostcharacteristic,however,arelarge,rounded,orpolygonalcellscontainingnumerousglycogen-ladenvacuolesseparatedbystrandsofcytoplasmrunningfromtheplasmamembranetothecentrallylocatednucleus,so-called“spidercells”.
The major clinical manifestations of myxomas are due to valvular “ball-valve” obstruction, embolization, or a syndrome of constitutional signs and symptoms including fever and malaise. This syndrome is caused by elaboration of the cytokine interleukin-6 by the tumor cells, a major mediator of the acute-phase response. Echocardiography is the diagnostic modality of choice, and surgical resection is almost uniformly curative.
With enhanced patient survival due to diagnostic and therapeutic advances, significant cardiovascular effects of non-cardiac neoplasms and their therapy are increasingly encountered (
Table 11.6 ). The pathologic consequences include direct tumor metastasis or infiltration, effects of circulating mediators, and therapeutic complications.
The most frequent metastatic tumors involving the heart are carcinomas of the lung and breast, melanomas, leukemias, and lymphomas. Metastases can reach the heart and pericardium by retrograde lymphatic extension (carcinomas), by hematogenous seeding (many tumors), by direct contiguous extension (primary carcinoma of the lung, breast, or esophagus), or by venous extension (tumors of the kidney or liver). Clinical symptoms are most often associated with pericardial spread, which can cause symptomatic pericardial effusions or a mass-effect that is sufficient to restrict cardiac filling. Bronchogenic carcinoma or malignant lymphoma may infiltrate the mediastinum extensively, causing encasement, compression, or invasion of the superior vena cava and obstruction to blood flow from the head and upper extremities (superior vena cava syndrome). Renal cell carcinoma often invades the renal vein and may grow as a continuous column of tumor up the inferior vena cava and into the right atrium, blocking venous return to the heart.
Noncardiac tumors also may affect cardiac function indirectly, sometimes via circulating tumor-derived substances. The consequences include nonbacterial thrombotic endocarditis, carcinoid heart disease, pheochromocytomaassociated myocardial damage, and myeloma-associated AL-type amyloidosis.
Complications of chemotherapy were discussed earlier in this chapter. Radiation used to treat breast, lung, or mediastinal neoplasms can cause pericarditis, pericardial effusion, myocardial fibrosis, and chronic pericardial disorders. Other cardiac effects of radiation therapy include accelerated coronary artery disease and mural and valvular endocardial fibrosis.