E5050. Overcoming the Diagnostic Challenge of Cystic Lung Diseases Through a Stepwise Approach
  1. Pallavi Srivastava; UT Southwestern Medical Center
  2. Arzu Canan; UT Southwestern Medical Center
  3. Suhny Abbara; UT Southwestern Medical Center
  4. Asha Kandathil; UT Southwestern Medical Center
A wide spectrum of diseases may be associated with pulmonary cysts, imposing a diagnostic challenge to the radiologist. Since cystic lung diseases show characteristic CT pattern, a careful radiological approach, along with clinical features, may aid in diagnosis. Through this educational exhibit, the readers will be able to a) identify CT findings of common cystic lung diseases, b) learn a stepwise approach to differential diagnosis of cystic lung diseases, and c) differentiate true cysts from mimics.

Educational Goals / Teaching Points
- Cystic structures within the lung (terminology definition with imaging examples). 1. Cysts. 2. Cavity. 3. Bulla. 4. Pneumatocele. 5. Centrilobular emphysema - systematic approach to diagnose cystic lung diseases based on CT findings and clinical features. Step 1: Is it a true cyst? (or is it mimic?) Step 2: Location (subpleural or intraparenchymal). Step 3: Intraparenchymal - solitary (incidental cysts, pneumatocele, bronchogenic cysts), multifocal/diffuse (lymphangioleiomyomatosis [LAM], Birt-Hogg-Dube syndrome. Step 4: Is it associated with ground glass opacities or nodules? Ground glass opacities: desquamative interstitial pneumonia (DIP), Pneumocystis jirovecii Pneumonia (PJP). Nodules: Langerhans cell histiocytosis (LCH). Amyloidosis, cancers associated with cystic spaces. Both: Lymphocytic interstitial pneumonia (LIP), hypersensitivity pneumonitis (HP), ultrarare cystic lung diseases (chronic inflammatory bronchiolitis, light chain deposition disease, neurofibromatosis, COPA syndrome, Cowden syndrome).

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Case 1: 59-year-old woman with Birt Hogg Dube syndrome. Imaging pearl: CT findings of multiple thin-walled cysts, predominantly in peripheral lung zones at lung bases and along mediastinum. Compared to LAM, cysts are less profuse with intervening normal lung parenchyma. Clinical pearl: autosomal dominant disorder, lesions usually appear after age 20, and renal cancers occur in 25% of patients (chromophobe subtype). Case 2: 59-year-old woman with neurofibromatosis type 1 (NF1). Imaging pearl: neurofibromatosis associated lung disease may manifest as ground-glass opacities, bibasilar fibrosis, bulla, emphysema, and cysts. Clinical pearl: NF1 is characterized by the triad of pigmented hamartomas of the iris (Lisch nodules), cafe´-au-lait spots, and neurofibromas.

This stepwise approach based on CT findings provides a noninvasive diagnostic tool for characterization of cystic lung diseases.