Mediastinal masses evaluation and management

🗺️ Anatomy - Mediastinal Geography

• Definition: Central compartment of the thoracic cavity, located between the two pleural sacs.
• Boundaries:
  • Superior: Thoracic inlet
  • Inferior: Diaphragm
  • Anterior: Sternum
  • Posterior: Vertebral column

• Clinical Divisions (Felson Method):
  • Anterior: From sternum to anterior border of heart/trachea.
    • Contents: Thymus, lymph nodes, internal mammary vessels.
    • 📌 Mnemonic (Masses): The 4 T's - Thymoma, Terrible lymphoma, Teratoma, Thyroid (ectopic).
  • Middle: Contains heart, pericardium, great vessels, trachea, main bronchi, phrenic nerves.
  • Posterior: Behind the heart/trachea, before the vertebral column.
    • Contents: Esophagus, descending aorta, vagus nerves, thoracic duct.

⭐ High-Yield: The phrenic nerve runs anterior to the lung hilum, while the vagus nerve runs posterior to it. (Mnemonic: AP = Anterior Phrenic).

🩺 Clinical Manifestations - Compressive Syndromes

• Superior Vena Cava (SVC) Syndrome: Facial/neck swelling (plethora), jugular venous distention (JVD), headache, dilated chest wall veins.
  • 💡 Pemberton's sign: Facial flushing/JVD on raising arms.

• Airway Compression: Dyspnea, cough, stridor, wheezing. Symptoms may worsen when supine.
• Esophageal Compression: Dysphagia (solids > liquids).
• Nerve Compression:
  • Recurrent Laryngeal: Hoarseness.
  • Phrenic: Diaphragmatic paralysis (elevated hemidiaphragm on CXR), dyspnea.
  • Sympathetic Chain: Horner's Syndrome (ptosis, miosis, anhidrosis).

⭐ Malignancy (e.g., lung cancer, lymphoma) is the cause of SVC syndrome in >80% of cases.

🩺 Diagnosis - The Workup Algorithm

• Initial Imaging: Chest X-ray (often incidental finding) → CT chest with IV contrast is the gold standard to delineate mass location, size, and characteristics (e.g., cystic, solid, vascularity, invasion).
• Biochemical Markers: Guided by CT location.
  • Anterior: Serum AFP and β-hCG for suspected germ cell tumors.
  • Posterior: Urine/plasma metanephrines for suspected neurogenic tumors (paraganglioma).
  • Thymoma suspicion: Acetylcholine receptor (AChR) antibodies for myasthenia gravis.

⭐ Pure seminomas may have an elevated β-hCG, but NEVER an elevated AFP. If AFP is elevated, it signifies a non-seminomatous germ cell tumor (NSGCT) component.

🔪 Management - Treatment Blueprints

• General Principle: Treatment is histology-dependent. Biopsy is key before definitive therapy, unless resection is both diagnostic and therapeutic (e.g., suspected benign cyst).

• Anterior Mediastinum:

  • Thymoma: Complete surgical resection. Pre-op optimization for Myasthenia Gravis (if present).
  • Germ Cell Tumors (GCTs):
    • Seminoma: Primarily radiation/chemotherapy.
    • Non-seminoma: Chemotherapy (e.g., BEP) followed by surgical resection of any residual mass.
  • Lymphoma: Chemotherapy +/- Radiation. ⚠️ Surgery is for biopsy ONLY.

• Middle & Posterior Mediastinum:

  • Symptomatic Cysts (Bronchogenic, Pericardial): Surgical resection.
  • Neurogenic Tumors: Complete surgical resection.

⭐ For suspected lymphoma, an excisional biopsy (e.g., via mediastinoscopy) is preferred over fine-needle aspiration (FNA) to preserve lymph node architecture for accurate subtyping.

⚡ Biggest Takeaways

• The anterior mediastinum is home to the "4 T's": Thymoma, Teratoma (GCTs), ectopic Thyroid, and "Terrible" Lymphoma.
• Always associate thymoma with Myasthenia Gravis; check for AChR antibodies.
• Evaluate suspected germ cell tumors with serum AFP and β-hCG.
• Posterior mediastinal masses are overwhelmingly neurogenic tumors (e.g., schwannoma).
• The middle mediastinum contains lymphadenopathy (lymphoma, sarcoidosis) and congenital cysts.
• CT with contrast is the primary imaging modality; definitive management is often surgical resection, except for lymphoma.