What diagnosis is most likely in a patient presenting with dyspnea, ascites, and elevated jugular venous pressure after radiation therapy?

The presence of dyspnea, ascites, and elevated jugular venous pressure in a patient who has recently undergone radiation therapy points toward constrictive pericarditis. Radiation therapy can lead to fibrosis and scarring of the pericardium, which can restrict the heart's ability to fill properly during diastole. This mechanical restriction results in symptoms associated with heart failure, such as shortness of breath (dyspnea) and fluid buildup both in the abdomen (ascites) and within the venous system, evidenced by elevated jugular venous pressure.

In constrictive pericarditis, the heart is physically limited by the thickened pericardium, causing a reduction in cardiac output and leading to congestion, which effectively explains the observed signs and symptoms. This condition is a well-recognized late complication of radiation therapy, particularly when the chest area is targeted, affecting not only the lungs but also the pericardium.

The other conditions listed do not align as well with this combination of symptoms after radiation exposure. For instance, pulmonary hypertension might cause dyspnea, but it typically does not lead to significant ascites or elevated jugular venous pressure to the same degree as constrictive pericarditis.