Anthracosilicosis Mimicking Primary or Secondary Lung Malignancy in a Patient With a History of Treated Prostate Cancer

A 65-year-old male with a history of prostate adenocarcinoma treated with radical prostatectomy in 2013 was referred for evaluation of a new pulmonary lesion. Surveillance chest computed tomography (CT) revealed a newly developed 25 × 20 mm irregular parahilar mass in the right upper lobe. 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) showed intense uptake in the lesion (SUVmax 6.6) and mediastinal lymph nodes (SUVmax 12.4), raising concern for malignancy or metastatic recurrence. However, multiple bronchoscopic and mediastinoscopic biopsies were negative for malignancy. The patient subsequently underwent video-assisted thoracoscopic surgery (VATS) with partial pleural and parenchymal resection for definitive diagnosis. Histopathology showed fibrotic pleura, anthracotic pigment deposition, silica crystals under polarized light, and reactive sinus histiocytosis, confirming anthracosilicosis. No carcinoma was detected on pan-cytokeratin staining. A small right-sided pleural effusion persisted postoperatively but regressed gradually on follow-up imaging. This case highlights a diagnostic pitfall where FDG-PET/CT mimicked malignancy in a benign fibrosilicotic process, emphasizing the limitations of imaging alone and the critical importance of histopathologic confirmation before major surgical intervention.