All the following statements about chronic constrictive pericarditis are true except

Ref Harrison 19 th ed pg 1575 CHRONIC CONSTRICTIVE PERICARDITIS This disorder results when the healing of an acute fibrinous or serofi- brinous pericarditis or the resorption of a chronic pericardial effusion is followed by obliteration of the pericardial cavity with the formation of granulation tissue. The latter gradually contracts and forms a firm scar encasing the hea, which may be calcified. In developing nations where the condition is prevalent, a high percentage of cases are of tuberculous origin, but this is now an uncommon cause in Noh America. Chronic constrictive pericarditis may follow acute or relaps- ing viral or idiopathic pericarditis, trauma with organized blood clot, or cardiac surgery of any type or result from mediastinal irradiation,