Cystic lung diseases in the daily routine: a comprehensive step-wise algorithm for the radiological diagnosis of cystic lung lesions and diffuse cystic lung diseases

Background: Cystic lung lesions and diseases represent a wide range of entities that are challenging for radiologists to diagnose. This difficulty arises from ambiguous terminology, similar imaging appearances, and the frequent coexistence of multiple disease entities. Purpose: To describe a comprehensive, step-wise algorithm enabling radiologists to accurately describe cystic lung lesions and support the correct diagnosis of diseases presenting with lung cysts or cyst-like findings. Methods: A refined diagnostic algorithm is proposed based on the authors' clinical experience and a comprehensive literature search (PubMed). Results: Our recommended approach to cystic lung lesions guides radiologists through three key steps: (1) Confirmation whether a lesion meets the definition of a true pulmonary cyst (thin-walled ≤ 2mm, well-circumscribed, air-containing structure) and distinguishing true cysts from mimicking lesions; (2) Evaluation of possible etiologies: congenital, inflammatory, senescent, neoplastic, diffuse cystic lung diseases; and (3) Identification of diffuse cystic lung diseases (DCLDs) including lymphangioleiomyomatosis, Birt-Hogg-Dubé syndrome, pulmonary Langerhans cell histiocytosis, lymphoid interstitial pneumonia, light-chain deposition disease, and neurofibromatosis type 1, using key CT features and associated thoracic and extra-thoracic findings. Conclusion: Radiologists should be familiar with cystic lung lesions and their common mimics to ensure accurate classification. The spectrum of cases is broad, ranging from congenital, to age-related and neoplastic as well as diffuse cystic lung diseases. A clear and step-wise approach assists radiologists in addressing cystic lung lesions and DCLDs and thus improves clinical decision-making and patient management. Key Points: · Differentiation between true lung cysts and mimicking lesions.. · Assessment of a broad spectrum of etiologies of cystic lung lesions.. · Diagnosis of diffuse cystic lung diseases.. Clinical relevance of the study: · Radiologists should be familiar with the terminology of cystic lung lesions to reduce ambiguity in reports, thereby improving communication with clinicians.. · Following a step-wise structured approach to cystic lung lesions and their mimics can contribute to safer radiological diagnoses.. · Recognizing specific radiologic patterns in cystic lung diseases facilitates diagnosis and, when necessary, timely referral for multidisciplinary evaluation.. Citation Format: · Martin Mens A, Andreisek G, Müller MA. Cystic lung diseases in the daily routine: a comprehensive step-wise algorithm for the radiological diagnosis of cystic lung lesions and diffuse cystic lung diseases. Rofo 2026; DOI 10.1055/a-2804-9147.