An adult presents to a physician because of repeated episodes of fainting. EKG fails to disclose an arrhythmia. Echocardiogram shows a mass in the left atrium that is acting like a "ball valve" to produce intermittent obstruction of flow. Which of the following would most likely be seen on microscopic examination of the resected mass?

The most common primary cardiac tumor of adults is the benign atrial myxoma. 90% of these lesions involve the left atrium, where they can produce intermittent obstruction when they flop onto the mitral valve. Resection is curative. Neither benign (adenomas) nor malignant (adenocarcinomas) primary glandular tumors usually involve the hea. If adenocarcinoma is seen, suspect metastatic disease. The rhabdomyoma is the benign tumor with striated muscle differentiation (choice C) that can involve the hea. This tumor is the most common cardiac tumor of children. Ref: Wyatt C., Butterwoh IV J.F., Moos P.J., Mackey D.C., Brown T.G. (2008). Chapter 10. Cardiac Pathology. In C. Wyatt, J.F. Butterwoh IV, P.J. Moos, D.C. Mackey, T.G. Brown (Eds), Pathology: The Big Picture.