Young female patient, multiple thin walled air filled cysts

Answer: LAM (lymphangioleiomyomatosis)

LCH (Langerhans Cell Histiocytosis) is in the differential but you often see peribronchial nodules as they evolve in cavitated thick walled cysts and later numerous irregular cysts http://radiopaedia.org/articles/pulmonary-langerhans-cell-histiocytosis

Reference on LAM: http://radiopaedia.org/articles/lymphangioleiomyomatosis-1

and remember that LAM can be sporadic or commonly part of the Tuberous Sclerosis Complex, so don’t forget to consider that (Nice Radiographics article on Tuberous Sclerosis: http://pubs.rsna.org/doi/full/10.1148/rg.e32