Radiologic Approach to Cystic Lung Diseases: From Cyst Definition to Diagnosis.

Cystic lung diseases represent a heterogeneous group of conditions characterized by the presence of multiple pulmonary cysts. Accurate recognition and differentiation of true cysts from their mimics (such as cavities, emphysema, bullae, blebs, and honeycombing) are essential, as management strategies and prognoses vary significantly. This review provides a systematic approach to the radiologic evaluation of cystic lung diseases, beginning with the definition and pathogenesis of pulmonary cysts and progressing through a structured diagnostic algorithm. We detail the characteristic imaging findings and clinical associations for major cystic lung diseases, including lymphangioleiomyomatosis (LAM), Birt-Hogg-Dubé syndrome (BHD), light-chain deposition disease (LCDD), lymphocytic interstitial pneumonia (LIP), desquamative interstitial pneumonia (DIP), pulmonary Langerhans cell histiocytosis (PLCH), and amyloidosis. Additionally, we discuss uncommon etiologies, such as cystic metastases, hypersensitivity pneumonitis, and cystic changes associated with genetic syndromes like neurofibromatosis type 1 (NF-1) and trisomy 21. The review emphasizes key imaging clues, such as cyst distribution, wall characteristics, associated nodules, and parenchymal abnormalities, that aid in narrowing the differential diagnosis. With the growing use of CT imaging, cystic lung diseases are increasingly identified in both symptomatic and asymptomatic patients. Familiarity with their imaging patterns, clinical contexts, and distinguishing features is essential for radiologists and clinicians alike. By following a stepwise, pattern-based approach, early and accurate diagnosis can be achieved, potentially improving patient outcomes through timely surveillance and targeted management.