Significance of main pulmonary artery dilation on imaging studies

Abstract

Proper and early identification of patients who harbor serious occult illness is the first step in developing a disease-management strategy. Identification of illnesses through the use of noninvasive techniques provides assurance of patient safety and is ideal. PA dilation is easily measured noninvasively and is due to a variety of conditions, including pulmonary hypertension (PH). The clinician should be able to thoroughly assess the significance of PA dilation in each individual patient. This involves knowledge of the ability of PA dilation to accurately predict PH, understand the wide differential diagnosis of causes of PA dilation, and reverse its life-threatening complications. We found that although PA dilation is suggestive of PH, data remain inconclusive regarding its ability to accurately predict PH. At this point, data are insufficient to place PA dilation into a PH risk-score equation. Here we review the causes and complications of PA dilation, define normal and abnormal PA measurements, and summarize the data linking its association to PH, while suggesting an algorithm designed to assist clinicians in patient work-up after recognizing PA dilation.

Keywords: pulmonary arterial hypertension; pulmonary artery diameter; pulmonary artery enlargement.

Figure 1.

Dilated pulmonary artery (PA, indicated by the asterisk in each panel) on contrast-enhanced computed tomography (CT) of the chest. (A) A 22-year-old man with idiopathic pulmonary arterial hypertension (PAH). Mean PA pressure 83 mm Hg and pulmonary vascular resistance (PVR) 18.3 Wood units. Aorta and PA measure 21.8 and 39.5 mm, respectively. (B) A 46-year-old woman with PAH due to congenital heart disease had a ventricular septal defect corrected at the age of 5 years. Right heart catheterization at the time of CT scan showed mean PA pressure of 55 mm Hg with a PVR of 12 Wood units. Aorta and PA measure 29.3 and 44.9 mm, respectively. (C) A 64-year-old woman with chronic thromboembolic portopulmonary hypertension after pulmonary thromboendarterectomy. Due to severe (80%) extrinsic compression of the left main coronary trunk she required percutaneous coronary intervention with stent placement. Mean PA pressure 55 mm Hg and PVR 7.5 Wood units. Aorta and PA measure 31.5 and 80.0 mm, respectively.

Figure 2.

Algorithm for evaluation of dilated pulmonary artery (PA) in adult patients without interstitial lung disease. *We used the PA diameter cut-offs of 29 mm for men and 27 mm for women, following the upper limit of normal (90th percentile) proposed by the Framingham investigators (23). A ratio of main PA to aorta diameter cut-off of 0.9 is supported by the same study (23). A PA diameter cut-off of 33 mm and ratio of main PA to aorta diameter of greater than 1.1 had a specificity of 95 and 92%, respectively, for detecting pulmonary hypertension (PH) (24, 43). ^No recommendations are made regarding the frequency and method for follow-up, given the absence of data. Ao = aorta; BNP = brain natriuretic peptide; Dl_CO = diffusing capacity of carbon monoxide; RV = right ventricle; RVSP = right ventricle systolic pressure.