Lung microstructure in adolescent idiopathic scoliosis before and after posterior spinal fusion

Abstract

Adolescent idiopathic scoliosis (AIS) is associated with decreased respiratory quality of life and impaired diaphragm function. Recent hyperpolarized helium (HHe) MRI studies show alveolarization continues throughout adolescence, and mechanical forces are known to impact alveolarization. We therefore hypothesized that patients with AIS would have alterations in alveolar size, alveolar number, or alveolar septal dimensions compared to adolescents without AIS, and that posterior spinal fusion (PSF) might reverse these differences. We conducted a prospective observational trial using HHe MRI to test for changes in alveolar microstructure in control and AIS subjects at baseline and one year. After obtaining written informed consent from subjects' legal guardians and assent from the subjects, we performed HHe and proton MRI in 14 AIS and 16 control subjects aged 8-21 years. The mean age of control subjects (12.9 years) was significantly less than AIS (14.9 years, p = 0.003). At baseline, there were no significant differences in alveolar size, number, or alveolar duct morphometry between AIS and control subjects or between the concave (compressed) and convex (expanded) lungs of AIS subjects. At one year after PSF AIS subjects had an increase in alveolar density in the formerly convex lung (p = 0.05), likely reflecting a change in thoracic anatomy, but there were no other significant changes in lung microstructure. Modeling of alveolar size over time demonstrated similar rates of alveolar growth in control and AIS subjects in both right and left lungs pre- and post-PSF. Although this study suffered from poor age-matching, we found no evidence that AIS or PSF impacts lung microstructure. Trial registration: Clinical trial registration number NCT03539770.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. HHe MRI overview.

(A) Schematic of a single HHe atom that is measured at to sequential time points. In a normal alveolar duct (top), although the atom diffuses the same total distance (dashed line) measurement is limited to the measured distance (Δx) and is relatively small. In dilated ducts, diffusion is less restricted and Δxis larger. (B) Schematic representation of the outer alveolar duct radius (R), the inner duct radius (r), and the septal height (h). (C) Representative axial images of the raw HHe data (top), directly measured apparent diffusion coefficients (ADC), calculated mean linear intercept (Lm) values, derived alveolar density (N) values. Manual segmentation of right and left lung values was performed to obtain unilateral values for right-left comparisons.

Fig 2. Impact of AIS on distal lung architecture.

(A) All AIS subjects had levoscoliosis. The mean linear intercept (Lm) values were no different in left/concave vs right/convex lungs. (B) Alveolar surface to volume ratio decreased with age as expected since alveolar size increases and neoalveolarization slows during adolescence. There was no discernible difference between control and AIS groups or between right and left lungs with regard to this derived value.

Fig 3. Change in alveolar size at one year.

(A) In the left/concave and (B) right/convex lungs of control and AIS subjects, there was the expected increase in alveolar size over time without significant differences between them. Lines connect subjects and the shaded regions indicate standard error for both the first and 1-year HHe images as determined using generalized linear modeling.