Disorders of the Mediastinum¶
Chapter 306 | Part 7: Respiratory System
KEY CLINICAL POINTS¶
- Mediastinal disorders encompass neoplasms, congenital malformations, infections, and fibrosing mediastinitis, classified by anatomical compartments.
- Tension pneumothorax is a life-threatening emergency requiring immediate needle decompression via the second intercostal space.
- Mediastinal masses are categorized into anterior (thymomas, teratomas), middle (lymphomas, metastases), and posterior (neurogenic tumors) compartments.
- Acute mediastinitis often follows esophageal perforation or sternotomy, with high mortality despite aggressive treatment.
- Fibrosing mediastinitis is associated with granulomatous infections (histoplasmosis, TB) and can cause SVC obstruction and airway compression.
1. DEFINITION & OVERVIEW¶
The mediastinum is the central compartment between the pleural sacs, bounded superiorly by the thoracic inlet and inferiorly by the diaphragm. It is divided into three compartments: anterior (thymus, lymph nodes), middle (heart, great vessels), and posterior (esophagus, thoracic spine). Disorders include neoplasms, congenital anomalies, infections, and inflammatory conditions.
Table 306-1 The Three Compartments of the Mediastinum¶
| Anatomical Boundaries | Contents | Common Abnormalities |
|---|---|---|
| Manubrium and sternum anteriorly; pericardium, aorta, and brachiocephalic vessels posteriorly | Thymus gland, anterior mediastinal lymph nodes, internal mammary arteries and veins | Thymoma, lymphomas, teratomatous neoplasms, thyroid masses, mesenchymal tumors |
| Anterior mediastinum anteriorly; posterior mediastinum posteriorly | Pericardium, heart, ascending and transverse arch of aorta, superior and inferior vena cavae, brachiocephalic arteries and veins, phrenic nerves, trachea, mainstem bronchi | Metastatic lymphadenopathy, granulomatous lymphadenopathy, bronchogenic cysts, vascular masses |
| Pericardium and trachea anteriorly; vertebral column posteriorly | Descending thoracic aorta, esophagus, thoracic duct, azygos and hemiazygos veins, posterior mediastinal lymph nodes | Neurogenic tumors, meningoceles, esophageal diverticula, extramedullary hematopoiesis |
1.1 Anatomical Compartments¶
Anterior: Thymus, lymph nodes, thyroid; Middle: Heart, great vessels, trachea; Posterior: Esophagus, thoracic spine, paravertebral structures.
1.2 Clinical Relevance¶
Compartment-specific pathologies dictate differential diagnosis and management (e.g., thymomas in anterior compartment vs. neurogenic tumors in posterior).
2. EPIDEMIOLOGY¶
Acute mediastinitis incidence after median sternotomy: 0.4–5.0%. Tension pneumothorax occurs in mechanically ventilated patients or during resuscitation. Mediastinal masses are more common in adults, with thymomas peaking in 30–50-year-olds. Fibrosing mediastinitis is rare but associated with chronic granulomatous infections.
2.1 Risk Factors¶
Esophageal perforation, post-sternotomy, immunocompromised states, prior radiation, and chronic infections (e.g., TB, histoplasmosis).
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Pneumothorax: Trauma, iatrogenic causes (thoracentesis), or lung disease. Mediastinal masses: Neoplasms (thymoma, germ cell tumors), congenital anomalies (bronchogenic cysts), or infections. Mediastinitis: Esophageal rupture, post-surgical, or ascending infections. Fibrosing mediastinitis: Granulomatous inflammation from fungal/bacterial infections.
3.1 Pathogenesis¶
Tension pneumothorax: Air accumulation in pleural space compresses mediastinum, reducing venous return. Fibrosing mediastinitis: Chronic granulomatous inflammation leads to fibrosis and vascular compression.
4. CLINICAL FEATURES¶
Pneumothorax: Chest pain, dyspnea, hyperresonance on percussion. Mediastinal masses: Asymptomatic or symptoms based on mass location (e.g., SVC obstruction, airway compression). Mediastinitis: Fever, chest pain, sepsis, widened mediastinum. Fibrosing mediastinitis: Dyspnea, SVC syndrome, hemoptysis.
5. DIFFERENTIAL DIAGNOSIS¶
Pneumothorax vs. pulmonary embolism; mediastinal masses vs. lymphadenopathy; acute mediastinitis vs. cardiac tamponade. Consider congenital anomalies (bronchogenic cysts) vs. neoplasms.
6. INVESTIGATIONS & DIAGNOSIS¶
Chest X-ray for pneumothorax; CT scan for mediastinal masses (attenuation of fat/water/calcium); mediastinoscopy for lymph node biopsy; bronchoscopy for mass evaluation. Fibrosing mediastinitis diagnosed via imaging and histopathology.
6.1 Imaging¶
CT: Best for mass characterization; MRI: Diffusion-weighted imaging aids in differentiating cystic vs. solid lesions. Ultrasound: For pleural effusion or guiding drainage.
7. MANAGEMENT & TREATMENT¶
Pneumothorax: Tube drainage, chemical pleurodesis, or surgical repair. Mediastinal masses: Surgical resection for thymomas/teratomas; chemotherapy/radiation for lymphomas. Mediastinitis: Debridement, antibiotics, and drainage. Fibrosing mediastinitis: Steroids, surgery for vascular compression.
8. PROGNOSIS & COMPLICATIONS¶
Tension pneumothorax: Rapid mortality without intervention. Fibrosing mediastinitis: Progressive airway compression and SVC obstruction. Mediastinal masses: Malignant potential (e.g., thymic carcinoma) with poor prognosis if unresectable.
9. SPECIAL CONSIDERATIONS¶
Pregnancy: Avoid radiation; use ultrasound for imaging. Pediatrics: Congenital anomalies (e.g., bronchogenic cysts) are common. Elderly: Higher risk of iatrogenic pneumothorax from procedures.
10. KEY POINTS & CLINICAL PEARLS¶
- Tension pneumothorax is a surgical emergency requiring immediate decompression.
- CT is essential for mediastinal mass characterization.
- Fibrosing mediastinitis is a chronic, progressive condition with fibrotic complications.
- Mediastinal masses require multidisciplinary evaluation for optimal management.
- Acute mediastinitis has high mortality despite aggressive treatment.