Differential Diagnosis for Left Upper Lobe Mass in an Adult

Single Most Likely Diagnosis

• Lung Cancer: This is the most common cause of a lung mass in adults, especially in those with a history of smoking. The left upper lobe is a common location for lung tumors.

Other Likely Diagnoses

• Pneumonia or Abscess: Infectious processes can cause masses in the lung, especially if they are complicated by abscess formation or significant inflammatory response.
• Tuberculosis (TB): TB can present as a mass in the upper lobes of the lung, particularly in individuals from endemic areas or with compromised immune systems.
• Hamartoma: A benign lung tumor that can appear as a mass on imaging, often containing fat and calcifications.

Do Not Miss Diagnoses

• Pulmonary Embolism (PE): Although less common as a cause of a discrete mass, a large PE can present as a mass in the lung, and missing this diagnosis can be fatal.
• Lymphoma: Both Hodgkin's and non-Hodgkin's lymphoma can involve the lung and present as masses, requiring prompt diagnosis and treatment.

Rare Diagnoses

• Pulmonary Arteriovenous Malformation (AVM): A rare congenital anomaly that can appear as a mass on imaging due to the abnormal vascular structure.
• Bronchogenic Cyst: A congenital anomaly that can present as a mass in the lung, often filled with fluid or air.
• Metastasis from Other Cancers: While less common than primary lung cancer, metastases from other primary sites (e.g., breast, colon, kidney) can present as lung masses.
• Inflammatory Pseudotumor (Myofibroblastic Tumor): A rare, benign tumor that can mimic malignant processes on imaging.
• Sarcoidosis: Can cause masses in the lung, particularly in the upper lobes, due to granulomatous inflammation.