Differential Diagnosis for Pneumonia Mimicking Cancer Metastases on Chest Imaging

• Single most likely diagnosis:
  • Round Pneumonia: This condition can present with rounded, well-defined masses on chest imaging, mimicking metastatic cancer. It is often caused by Streptococcus pneumoniae and typically responds well to antibiotic treatment.
• Other Likely diagnoses:
  • Lymphocytic Interstitial Pneumonia (LIP): Part of a spectrum of lung diseases associated with connective tissue disorders or immunodeficiency, LIP can show multiple nodular opacities that might be confused with metastases.
  • Cryptogenic Organizing Pneumonia (COP): COP can manifest with multiple nodules or masses on imaging, which could be mistaken for cancer metastases. It is characterized by the presence of organizing pneumonia in the lung.
• Do Not Miss diagnoses:
  • Tuberculosis (TB): Although less common in some regions, TB can present with a wide range of pulmonary manifestations, including nodular or mass-like lesions that could be mistaken for metastatic disease. Missing TB could lead to delayed treatment and significant morbidity.
  • Fungal Infections (e.g., Histoplasmosis, Coccidioidomycosis): In endemic areas, fungal infections can cause pulmonary lesions that mimic cancer. These infections can be severe and require specific antifungal treatment.
• Rare diagnoses:
  • Eosinophilic Pneumonia: Characterized by an accumulation of eosinophils in the lung, this condition can present with various imaging patterns, including nodules or masses, although it is less common.
  • Plasmacytoma: A rare tumor composed of plasma cells, plasmacytoma can present as a solitary mass in the lung, potentially mimicking a metastasis or primary lung cancer.