Effect of lung volume and gravity on the attenuation and size of a pure ground-glass nodule.

Detecting potentially malignant changes in a pure ground-glass nodule (GGN) is challenging. The development of a solid component is a known sign, which may help in differentiating benign from malignant GGN. We report the case of a 58-year-old man presenting with a pure GGN in the posterior segment of the right lower lobe. Follow-up computed tomographic scan after 1 year showed marked increase in attenuation (from -319 HU to +27 HU), whereas the average size of the nodule decreased (from 7 to 4.7 mm). On a computed tomographic scan in the prone position the nodule seemed larger (7.8 mm) and appeared as a pure GGN (-406 HU). Such changes were attributed to the reduction of lung volume and gravity.