Clinical primary pulmonary hypertension: three pathologic types.

Clinically, there is a group of patients with elevated pulmonary arterial pressure in whom the underlying cause is not apparent. The pulmonary arterial wedge pressure is not elevated. For such cases, the designation of primary pulmonary hypertension may be made clinically. From the clinical categorization of primary pulmonary hypertension, three distinct pathologic entities emerge, namely 1) plexogenic pulmonary arteriopathy, 2) recurrent pulmonary thromboembolism, and 3) pulmonary veno-occlusive disease. The plexogenic type is characterized initially by pulmonary arterial vasoconstriction with medial hypertrophy. Secondary proliferative intimal lesions, including the plexiform lesion, develop. Recurrent pulmonary thromboembolism is characterized by the presence of arterial thrombi of varying ages involving the microscopic-sized pulmonary arteries. Thrombi may be embolic in nature or may develop in situ. Pulmonary veno-occlusive disease is characterized by obstructive lesions of pulmonary veins and venules. The clinical presentation of the three pathologic types may be so similar that definitive diagnosis depends upon histologic examination of the lung from tissue obtained either by biopsy or at necropsy.