Pulmonary Hypertension Due to Capillary Hemangiomatosis

The pulmonary circulation is a high-compliance, low-resistance vascular bed with enormous volume reserve capacity. These characteristics allow it to accommodate the entire cardiac output while being subjected to a low mean pulmonary artery pressure (mPAP) of 25 mmHg. Elevations in mPAP beyond 25 mmHg at rest or 30 mmHg during exer- cise are signs of pulmonary hypertension (PH), a devastating disorder that can affect individuals of all ages worldwide. Given the diverse pathophysiological manifestations, causes, and clinical management strategies of PH, it has been divided into five categories on the basis of the modified World Health Organization (WHO) Evian classification. Pulmonary arterial hypertension (PAH), or WHO group 1, consists of all forms of PH which are of unknown cause and involve extensive arteriopathy or loss/remodeling of the pulmonary arterial vasculature. This chapter will focus on an extremely rare form of PAH referred to as pulmonary capillary hemangiom- atosis (PCH). Unlike other forms of PAH where changes in the pulmonary vasculature are limited solely to the arteries, PCH is a very intriguing disease of uncontrolled endothelial cell growth that although specific to the lung involves proliferation of capillary-sized blood vessels.