Pulmonary Artery Size in Interstitial Lung Disease and Pulmonary Hypertension: Association with Interstitial Lung Disease Severity and Diagnostic Utility

Abstract

Purpose: It is postulated that ILD causes PA dilatation independent of the presence of pulmonary hypertension (PH), so the use of PA size to screen for PH is not recommended. The aims of this study were to investigate the association of PA size with the presence and severity of ILD and to assess the diagnostic accuracy of PA size for detecting PH.

Methods: Incident patients referred to a tertiary PH centre underwent baseline thoracic CT, MRI and right heart catheterisation (RHC). Pulmonary artery diameter was measured on CT pulmonary angiography and pulmonary arterial areas on MRI. A thoracic radiologist scored the severity of ILD on CT from 0 to 4, 0 = absent, 1 = 1-25%, 2 = 26-50%, 3 = 51-75%, and 4 = 76-100% extent of involvement. Receiver operating characteristic analysis and linear regression were employed to assess diagnostic accuracy and independent associations of PA size.

Results: 110 had suspected PH due to ILD (age 65 years (SD 13), M:F 37:73) and 379 had suspected PH without ILD (age 64 years (SD 13), M:F 161:218). CT derived main PA diameter was accurate for detection of PH in patients both with and without ILD - AUC 0.873, p =< 0.001, and AUC 0.835, p =< 0.001, respectively, as was MRI diastolic PA area, AUC 0.897, p =< 0.001, and AUC 0.857, p =< 0.001, respectively Significant correlations were identified between mean pulmonary arterial pressure (mPAP) and PA diameter in ILD (r = 0.608, p < 0.001), and non-ILD cohort (r = 0.426, p < 0.001). PA size was independently associated with mPAP (p < 0.001) and BSA (p = 0.001), but not with forced vital capacity % predicted (p = 0.597), Transfer factor of the lungs for carbon monoxide (T_LCO) % predicted (p = 0.321) or the presence of ILD on CT (p = 0.905). The severity of ILD was not associated with pulmonary artery dilatation (r = 0.071, p = 0.459).

Conclusions: Pulmonary arterial pressure elevation leads to pulmonary arterial dilation, which is not independently influenced by the presence or severity of ILD measured by FVC, T_LCO, or disease severity on CT. Pulmonary arterial diameter has diagnostic value in patients with or without ILD and suspected PH.

Keywords: computed tomography (CT) scanning; interstitial lung disease; pulmonary artery diameter; pulmonary hypertension; right heart catheterisation.

Figure 1

CT images of pulmonary artery diameter measurements in patients with (A) a patient without PH (mean pulmonary arterial pressure of 20 mmHg), (B) a patient with PH with moderate elevation in pulmonary arterial pressure (mPAP 54 mmHg). Diameter measured where largest and most consistent - proximal to bifurcation, perpendicular to direction of vessel.

Figure 2

The Study Cohort. PH, pulmonary hypertension; CT, computed tomography scan; MRI, magnetic resonance imaging; MPA, main pulmonary artery; CTPA, computed tomography pulmonary angiogram; ILD, interstitial.

Figure 3

Correlations between mean PA pressure and PA diameter with pulmonary function tests and CT-derived severity score. Graphs (A) and (B) represent the association with ILD severity on CT in ILD cohort. Graphs (C) and (D) scatter plot showing the association of PA pressure and diameter with T_LCO %predicted and graphs (E) and (F) scatter plots showing the association of PA pressure and diameter with FVC %predicted.

Figure 4

Scatter distribution showing the relationship between mean PA pressure and PA diameter. Subgroups include ILD cohort (A), non-ILD (B), ILD with UIP pattern of disease (C) and ILD with NSIP pattern of disease (D).

Figure 5

ROC analysis showing the area under the curve for both ILD (A) and non-ILD (B) cohorts for the CT measured main pulmonary artery size (PA diameter and PA:AA Ratio)