Pulmonary Arterial Hypertension (PAH)

Pathophysiology:  Any process that effectively leads to an increased intrapulmonary vascular resistance can cause PAH.  Traditionally, etiologies divided into capillary, pre-capillary, and post-capillary causes.

Classification:

(1) Idiopathic or Primary Pulmonary Hypertension: no known cause

(2) Secondary Pulmonary Hypertension: Etiologies include:

precapillary causes: pulmonary vasculitis, collagen vascular diseases, multiple pulmonary emboli; rarely, multiple vascular tumor emboli, pulmonary endarteritis obliterans often aggravated by underlying PAH, marked emphysema or bullous emphysema which may attenuate the smaller pulmonary arteries, post-surgical or radiation elimination of sufficient pulmonary arterial bed, drugs

capillary causes: any diffuse, infiltrative lung disease involving numerous alveolar septae

post-capillary causes: valvular heart disease especially mitral stenosis, chronic heart disease, left atrial myxomas, tumors or blood clots

Commonest Causes: severe COLD/emphysema, sleep apnea

Clinical Clues: Progressive dyspnea, decreasing exercise tolerance, tachypnea and tachycardia, right ventricular strain on ECG, congestive heart failure and cor pulmonale.

CXR Findings:

1.      prominent central pulmonary arteries ie. big hila

2.      thinning and attenuation of pulmonary arterial branches

3.      abrupt cut-off or squaring of pulmonary arteries

4.      increase in vascular-free peripheral lung zone

5.      right ventricular dilatation and cardiomegaly

6.      any underlying lung pathology that may be a cause

“Aunt Sophies”:  the main mimickers are other causes of large central hila

1.      Hilar adenopathy of any cause **

2.      Idiopathic dilatation of the pulmonary arteries, seen in asymptomatic young women; this is only a CXR problem, not a physiologic one.