Idiopathic pulmonary arterial hypertension is uncommon, representing only a tiny fraction of all cases of pulmonary arterial hypertension, which has a very long list of secondary causes (see causes of pulmonary arterial hypertension).
Older terms for this entity include primary pulmonary arterial hypertension and plexogenic pulmonary arteniopathy, which should no longer be used.
Epidemiology
Typically this entity is seen in young women, with diagnosis most frequently made between 20 and 30 years of age 1. While a majority are sporadic a small proportion have a familial inheritance 5 .
Clinical presentation
Exertional dyspnoea, fatigue, chest pains and syncope are the most common presenting complaints. Haemoptysis may also occur and may be of high volume 1.
Pathology
The plexiform lesion which characterises this entity is a tuft of endothelium lined channels and are associated with over-expression of angiogenesis-related molecules 4.
Radiographic features
Radiographic features are those of pulmonary arterial hypertension, with no other cause identified.
Treatment and prognosis
Treatment and prognosis is discussed in the parent article on pulmonary arterial hypertension.
Differential diagnoses
The differential is essentially that of secondary pulmonary arterial hypertension with idiopathic pulmonary arterial hypertension being a diagnosis of exclusion.
There are also numerous causes of an enlarged pulmonary artery (main segment) on chest radiography.

Primary Pulmonary Arterial Hypertension
Article Source : Dr Frank Gaillard, Radiopaedia
References
* 1. Randall PA, Heitzman ER, Bull MJ et-al. Pulmonary arterial hypertension: a contemporary review. Radiographics. 1989;9 (5): 905-27. Radiographics (abstract) [pubmed citation]
* 2. Galiè N, Torbicki A, Barst R et-al. Guidelines on diagnosis and treatment of pulmonary arterial hypertension. The Task Force on Diagnosis and Treatment of Pulmonary Arterial Hypertension of the European Society of Cardiology. Eur. Heart J. 2004;25 (24): 2243-78. doi:10.1016/j.ehj.2004.09.014 [pubmed citation]
* 3. Mehta S, Shoemaker GJ. Improving survival in idiopathic pulmonary arterial hypertension: revisiting the "kingdom of the near-dead". Thorax. 2005;60 (12): 981-3. doi:10.1136/thx.2005.045674 [free text at pubmed] [pubmed citation]
* 4. Voelkel NF, Douglas IS, Nicolls M. Angiogenesis in chronic lung disease. Chest. 2007;131 (3): 874-9. doi:10.1378/chest.06-2453 [pubmed citation]
* 5. I Shohet et.al, Familial persistent pulmonary hypertension, Arch Dis Child 1984;59:783-785 doi:10.1136/adc.59.8.783