Patterns of Emphysema Heterogeneity

Abstract

Background: Although lobar patterns of emphysema heterogeneity are indicative of optimal target sites for lung volume reduction (LVR) strategies, the presence of segmental, or sublobar, heterogeneity is often underappreciated.

Objective: The aim of this study was to understand lobar and segmental patterns of emphysema heterogeneity, which may more precisely indicate optimal target sites for LVR procedures.

Methods: Patterns of emphysema heterogeneity were evaluated in a representative cohort of 150 severe (GOLD stage III/IV) chronic obstructive pulmonary disease (COPD) patients from the COPDGene study. High-resolution computerized tomography analysis software was used to measure tissue destruction throughout the lungs to compute heterogeneity (≥15% difference in tissue destruction) between (inter-) and within (intra-) lobes for each patient. Emphysema tissue destruction was characterized segmentally to define patterns of heterogeneity.

Results: Segmental tissue destruction revealed interlobar heterogeneity in the left lung (57%) and right lung (52%). Intralobar heterogeneity was observed in at least one lobe of all patients. No patient presented true homogeneity at a segmental level. There was true homogeneity across both lungs in 3% of the cohort when defining heterogeneity as ≥30% difference in tissue destruction.

Conclusion: Many LVR technologies for treatment of emphysema have focused on interlobar heterogeneity and target an entire lobe per procedure. Our observations suggest that a high proportion of patients with emphysema are affected by interlobar as well as intralobar heterogeneity. These findings prompt the need for a segmental approach to LVR in the majority of patients to treat only the most diseased segments and preserve healthier ones.

Fig. 1

Representation of sublobar segmentation from the VIDA Apollo software. Density and heterogeneity measurements are computed at the lobar and segmental levels.

Fig. 2

Equations for three different heterogeneity indices.

Fig. 3

Example patient with intralobar heterogeneous emphysema. The right upper lobe is perceived to be interlobar heterogeneous but is not considered to be truly interlobar heterogeneous because not all right upper lobe segments are more diseased than the lower lobe. The left upper lobe is truly interlobar heterogeneous because all left upper lobe segments are more diseased than the lower lobe.

Fig. 4

Frequency of disease heterogeneity and homogeneity in the study cohort for each upper and lower lobe. HI = Heterogeneity index; RUL = right upper lobe; LUL = left upper lobe; RLL = right lower lobe; LLL = left lower lobe.

Fig. 5

Example patient with intralobar heterogeneous emphysema. The left lung is interlobar homogenous but exhibits intralobar heterogeneity. The right upper lobe is perceived to be interlobar heterogeneous but is not considered to be truly interlobar heterogeneous because not all segments are more diseased than the lower lobe.