While the presence of volume loss is not specific to fibrosis, it has value for identifying fibrotic ILD.10 The loss of lower-lobe volume is a useful supportive finding of the presence of interstitial fibrosis.10 This is particularly helpful when honeycombing or traction bronchiectasis are absent or equivocal.10 Lower-lobe volume loss is best determined by evaluating displacement of the major fissure inferiorly, which can be best observed on coronal and sagittal images.10
Here we have coronal images which were taken 2 years apart. The patient has subpleural, lower lobe-predominant disease, and over the course of 2 years, the degree of fibrosis has increased quite dramatically while there has been a reduction in lung volume. Volume loss has occurred in the lungs as a whole, and the emphasis of the volume loss is in the lower lobes where the fibrotic lung disease is most prevalent.