A 39-year-old woman was referred with a 3-month history of pleuritic chest discomfort, shortness of breath on exertion, and occasional palpitation and presyncope. Physical examination showed no abnormalities. ECG revealed sinus rhythm. Posteroanterior chest x-ray (Figure 1A) showed a large, rounded, right paracardiac mass. Transthoracic echocardiography showed a cystic mass as large as the heart at the right cardiophrenic angle (Figure 2), interposed between the diaphragm (and the liver), right atrium, and lung. The left ventricular size and function were normal, though some right atrial compression was noted. Contrast computerized tomography scan (Figure 1B) revealed a homogenous right pericardial mass, 10.0×8.0 cm in size, with a density greater than that of the usual simple cyst (Figure 2A), along with a thin capsule suggestive of a pericardial cyst. The patient underwent removal of the cyst, which was attached to the pericardium over a small area (diameter=1.5 cm). She made an uneventful recovery and was discharged on the fourth postoperative day.
The excised cyst weighed 510 g, with maximum dimensions of 13.5×10.5×7.5 cm. The outer surface was smooth with several small vessels coursing over its surface (Figure 2B). On sectioning, the cyst was unilocular; contained clear, straw-colored fluid; and had a focal, firm, yellow-white–colored solid area measuring 1.5×1.0 cm (Figure 3A). Histologically, this firm area (Figure 3B) showed a mixed lymphocyte and epithelial cell population, consistent with a benign thymoma of predominantly lymphocytic type (Lattes/Bernatz classification) (ie, predominantly cortical type [Muller Hermelink classification] or type B1 [World Health Organization classification]) (Figure 4A). The cystic portion of the lesion was lined by flattened squamoid to cuboidal thymic epithelium (AE1:AE3 positive/calretinin negative), with occasional subepithelial Hassall’s corpuscles evident (Figure 4B). We interpreted the combined findings to be those of a cystic thymoma, although the remote possibility that the lesion was a thymoma originating in the wall of a thymic cyst cannot be ruled out completely.
The editor of Images in Cardiovascular Medicine is Hugh A. McAllister, Jr, MD, Chief, Department of Pathology, St Luke’s Episcopal Hospital and Texas Heart Institute, and Clinical Professor of Pathology, University of Texas Medical School and Baylor College of Medicine.
Circulation encourages readers to submit cardiovascular images to the Circulation Editorial Office, St Luke’s Episcopal Hospital/Texas Heart Institute, 6720 Bertner Ave, MC1-267, Houston, TX 77030.