Differential Diagnosis for Mediastinal Masses Incidental Pick Up on CT

When a mediastinal mass is incidentally found on a CT scan, it's crucial to consider a wide range of potential diagnoses due to the variety of structures and tissues present in the mediastinum. The differential diagnoses can be categorized as follows:

• Single Most Likely Diagnosis
  • Thymoma: This is often considered because thymomas are common anterior mediastinal masses, especially in adults. They can be benign or malignant and may be associated with myasthenia gravis or other paraneoplastic syndromes.
• Other Likely Diagnoses
  • Lymphoma: Both Hodgkin and non-Hodgkin lymphoma can present as mediastinal masses, often in the anterior or middle mediastinum. Lymphadenopathy may also be present.
  • Teratoma: These are germ cell tumors that can contain several different types of tissues and are typically found in the anterior mediastinum. They are more common in younger adults.
  • Cystic Lesions (e.g., Bronchogenic Cysts, Pericardial Cysts): These are congenital anomalies that can appear as fluid-filled structures in the mediastinum on CT scans.
• Do Not Miss Diagnoses
  • Malignant Germ Cell Tumors: While less common than teratomas, these tumors (such as seminomas and non-seminomatous germ cell tumors) are aggressive and require prompt treatment.
  • Mediastinal Involvement by Lung Cancer: Direct extension or metastasis from lung cancer can present as a mediastinal mass, emphasizing the importance of evaluating the lungs in the context of a mediastinal mass.
  • Lymphadenopathy from Infection or Inflammation: Conditions like tuberculosis or sarcoidosis can cause significant lymphadenopathy in the mediastinum, which might be mistaken for a mass.
• Rare Diagnoses
  • Pheochromocytoma: Although more commonly associated with the adrenal glands, extra-adrenal pheochromocytomas (paragangliomas) can occur in the mediastinum.
  • Neurogenic Tumors (e.g., Neurofibromas, Schwannomas): Typically found in the posterior mediastinum, these tumors arise from nerve tissues.
  • Mesenchymal Tumors (e.g., Lipomas, Leiomyomas): These are rare tumors of the mediastinum that originate from mesenchymal cells.

Each of these diagnoses has different implications for patient management and prognosis, highlighting the importance of a thorough diagnostic workup following the incidental discovery of a mediastinal mass on CT.