A, Light microscopy view of open lung biopsy showed diffuse over-expansion and simplification of alveolar spaces (asterisk) with well-preserved lung parenchyma including small bronchioles (Br) and pulmonary arteries (PA) with no evidence of septal wall thickening. B, Low magnification EM view of lung biopsy showed interalveolar septum delineated by alveolar spaces (Alv), some with alveolar type 2 cells (white arrow) containing several vacuolated interstitial storage cells (asterisk) characteristic of MPS. C, Higher magnification of interstitial storage cells, some with nucleus (ν) and cytoplasm filled with mucopolysaccharide appearing as empty spaces owing to extraction (asterisk). Interstitial collagen (Col).