Diffuse Bilateral Pseudo-Cystic Pulmonary Lesions Revealing Metastatic Lung Adenocarcinoma: A Case Report and Literature Review.

Diffuse cystic lung diseases are a heterogeneous group of disorders with multiple etiologies, including rare malignant causes. We report the case of a 49-year-old non-smoking man presenting with a two-month history of dry cough without hemoptysis, dyspnea, or chest pain. Chest computed tomography (CT) revealed diffuse bilateral pseudo-cystic pulmonary lesions and scattered nodules. Bone window analysis identified osteolytic lesions of the sternum and the eighth thoracic vertebra. Additional CT scans demonstrated multiple secondary lesions involving the brain, spine, and left iliac bone. 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) showed hypermetabolic pulmonary, mediastinal, and skeletal lesions. Brain and spinal magnetic resonance imaging confirmed multiple cerebral and vertebral secondary localizations, with perimedullary tumoral epiduritis. A CT-guided biopsy of the sternal lytic lesion established the diagnosis of poorly differentiated lung adenocarcinoma. Tumor cells expressed thyroid transcription factor-1 and cytokeratin AE1/AE3, with programmed death-ligand 1 expression <1%. Molecular analysis revealed no mutations in EGFR, KRAS, BRAF, HER2, or MET. Systemic chemotherapy with carboplatin and pemetrexed was initiated, with pembrolizumab planned, and radiotherapy was administered for the vertebral lesion. This case highlights a rare pseudo-cystic radiological presentation of metastatic lung adenocarcinoma and underscores the importance of considering a neoplastic etiology in patients presenting with diffuse bilateral thin-walled pulmonary lesions.