The most likely diagnosis is lymphangioleiomyomatosis (LAM). LAM is a very uncommon disorder that occurs in association with the genetic changes found in tuberous sclerosis complex, and a sporadic form that is seen almost exclusively in women during childbearing years. Histopathology shows infiltration of atypical smooth muscle cells into the pulmonary interstitium caused by activation of the mammalian target of rapamycin (mTOR) signaling pathway. This results in the development of thin-walled cysts scattered throughout the pulmonary parenchyma and increases the risk of spontaneous pneumothorax. Diagnosis is based on imaging studies showing the characteristic diffuse cystic changes and elevated levels of vascular endothelial growth factor-D (VEGF-D). Hormonal therapy, which was used in the past, is not effective in altering the disease course. Sirolimus, an mTOR inhibitor, has shown promise in stabilizing pulmonary function in patients with LAM and is increasingly used to treat patients with progressive lung disease.

Organizing pneumonia is a noninfectious diffuse parenchymal lung disease that may occur in association with other underlying conditions (such as collagen vascular diseases or use of certain drugs), but may also occur in the absence of another condition or exposure (cryptogenic organizing pneumonia). Onset is typically over 4 to 6 weeks and symptoms rarely persist for longer than 6 months; its presentation may mimic community-acquired pneumonia. Chest imaging typically shows patchy airspace disease with consolidation and ground-glass opacities but no cystic changes. This patient's presentation and imaging findings are not consistent with a diagnosis of organizing pneumonia.

Pulmonary Langerhans cell histiocytosis (PLCH), which involves an increased number of Langerhans and inflammatory cells in the lung interstitium, may present with nonspecific respiratory symptoms and a history of spontaneous pneumothorax. Most cases occur in young adults between 20 and 40 years of age. There is also a very strong association with smoking. The duration of symptoms is usually less than 1 year before the diagnosis is made. Although pulmonary cysts are found in PLCH, they tend to be thicker-walled and are accompanied by interstitial thickening and nodularity seen in radiographic findings. This patient's clinical course and imaging studies make a diagnosis of PLCH unlikely.

Respiratory bronchiolitis–associated interstitial lung disease results from inflammation of bronchioles and occurs primarily in smokers. It results in characteristic radiographic findings of centrilobular nodules with air-trapping and scattered ground-glass attenuation. This patient's absence of a smoking history and CT findings do not support this diagnosis.