Evidence for adult lung growth in humans

Abstract

A 33-year-old woman underwent a right-sided pneumonectomy in 1995 for treatment of a lung adenocarcinoma. As expected, there was an abrupt decrease in her vital capacity, but unexpectedly, it increased during the subsequent 15 years. Serial computed tomographic (CT) scans showed progressive enlargement of the remaining left lung and an increase in tissue density. Magnetic resonance imaging (MRI) with the use of hyperpolarized helium-3 gas showed overall acinar-airway dimensions that were consistent with an increase in the alveolar number rather than the enlargement of existing alveoli, but the alveoli in the growing lung were shallower than in normal lungs. This study provides evidence that new lung growth can occur in an adult human.

Figure 1. Three-Dimensional Reconstructions of Axial CT Images of the Left Lung after a Right-Sided Pneumonectomy

The reconstructions, shown in three projections, are based on CT scans of contiguous 10-mm sections in 1995 and 5-mm sections in 2010 and are presented with identical scaling.

Figure 2. Air, Tissue, and Total Lung Volumes Based on CT Images of the Left Lung Obtained before and after Pneumonectomy

Total lung volumes, as assessed by radiography, were fractionated into gas and tissue components. Data were obtained from CT scans with and without intravenous contrast material; one gas volume at total lung capacity (TLC) was measured by plethysmography. Early scans, digitized from radiographic film, permitted the measurement of total lung volume only. Within months after pneumonectomy (Pnx), the total lung volume increased and the lung density fell below normal (to 0.07 g per milliliter), suggesting simple hyperexpansion of the lung. Thereafter, the lung tissue volume progressively increased and the lung density returned to a level normally seen at full inspiration (0.13 g per milliliter), suggesting the growth of new lung tissue. Insertion of a volume expander (VolExp) in the right hemithorax on two occasions was followed by an increase in gas volume.

Figure 3. Acinar-Airway Dimensions on Transverse (Axial) Images Obtained with Hyperpolarized Helium-3 MRI in 2010

Panel A is a color map of the fractional deviations of the radial dimension of the acinar airway (R) relative to its mean R of 330 µm; similarly, Panel B shows the fractional deviations of the effective alveolar depth (h) relative to its mean h of 70 µm. Lung crossing the midline is indicated by arrows. Panels A and B are the central slices from five sequential axial images of R (Panel C) and h (Panel D), with the same color scale. The helium-3 MRI scan shows remarkable uniformity in R, which varied by less than 5% over the entire lung field — a finding inconsistent with regional expansion into the right hemithorax but compatible with true growth.