Contents · 12 sections
- 1. Boundaries of the mediastinum
- 2. Classical division
- 3. Modern ITMIG classification
- 4. Contents of the middle mediastinum
- 5. Contents of the posterior mediastinum
- 6. Mass lesions by compartment ("4T rule" and others)
- 7. Clinical syndromes
- 8. Pneumomediastinum
- 9. Imaging modalities
- 10. Mediastinal lymph nodes
- 11. Surgical approaches
- 12. FAQ
In a nutshell. The mediastinum is the thoracic space between the pleural sacs, bounded anteriorly by the sternum, posteriorly by the spine, superiorly by the thoracic inlet, and inferiorly by the diaphragm. It is divided into the superior (above the Th4–sternal angle plane) and inferior (anterior, middle, posterior) mediastinum. The anterior contains the thymus; the middle contains the heart and pericardium; the posterior contains the descending thoracic aorta, esophagus, thoracic duct, azygos and hemiazygos veins, and sympathetic trunks. Clinically: mass lesions are categorized by compartment ("4T's" of the anterior: teratoma, thymoma, thyroid, terrible lymphoma), mediastinitis (Boerhaave syndrome, odontogenic), superior vena cava syndrome.
1. Boundaries of the mediastinum
- Anteriorly — sternum and costal cartilages.
- Posteriorly — bodies of the thoracic vertebrae (Th1–Th12).
- Laterally — mediastinal pleura.
- Superiorly — plane of the thoracic inlet (jugular notch + Th1).
- Inferiorly — diaphragm.
2. Classical division
Superior mediastinum
- From the thoracic inlet to the plane of Th4–sternal angle (Louis angle).
- Contains: thymus (in children, fibrous remnant in adults), aortic arch with its branches, brachiocephalic veins, superior vena cava (proximal part), trachea, esophagus (proximal part), thoracic duct, phrenic and vagus nerves, recurrent laryngeal nerve (right hooks around the subclavian artery, left around the aortic arch).
Inferior mediastinum
- Anterior — between the sternum and the pericardium; contains: thymic remnants, lymph nodes, adipose tissue, branches of the internal thoracic arteries.
- Middle — contains the heart with the pericardium, ascending aorta, pulmonary arteries and veins, main bronchi, tracheal bifurcation, phrenic nerves.
- Posterior — between the pericardium and the spine; contains: descending thoracic aorta, esophagus, thoracic duct, azygos and hemiazygos veins, sympathetic trunks, vagus nerves (distal branches), lymph nodes.
3. Modern ITMIG classification
- Adopted by the International Thymic Malignancy Interest Group (ITMIG) — 3 compartments:
- — Prevascular compartment (formerly anterior + major part of superior).
- — Visceral compartment (middle).
- — Paravertebral compartment (posterior).
- Boundaries defined on CT, without reference to the Louis line.
4. Contents of the middle mediastinum
- Heart with pericardium.
- Ascending aorta.
- Pulmonary trunk and main pulmonary arteries.
- Pulmonary veins (4 — two right, two left).
- Superior and inferior venae cavae within their pericardial reflections.
- Tracheal bifurcation, main bronchi.
- Phrenic nerves + pericardiacophrenic vessels.
- Lymph node stations 2–10 (paraesophageal, paratracheal, subcarinal).
5. Contents of the posterior mediastinum
- Descending thoracic aorta (Th4–Th12).
- Esophagus — crosses the aorta from right to left.
- Thoracic duct — empties into the left venous angle.
- Azygos vein on the right, hemiazygos vein on the left.
- Sympathetic trunks and greater splanchnic nerve.
- Vagus nerves (posterior branches) and esophageal branches.
- Posterior intercostal arteries.
- Lymphatic vessels and nodes.
6. Mass lesions by compartment ("4T rule" and others)
| Compartment | Typical masses |
|---|---|
| Anterior (superior) | Thymoma, teratoma / germ cell tumors, toxic goiter (retrosternal), terrible lymphoma (Hodgkin, non-Hodgkin) |
| Middle | Lymphomas, lymphadenopathy (sarcoidosis, tuberculosis, metastases), bronchogenic cyst, pericardial cyst |
| Posterior | Neurogenic tumors (schwannoma, neurofibroma, ganglioneuroma, pheochromocytoma), esophageal duplication cysts, hernias (Bochdalek) |
7. Clinical syndromes
Superior vena cava syndrome
- SVC obstruction by a mass in the anterior mediastinum (most commonly small-cell lung cancer, lymphoma, or post-catheter thrombosis).
- Clinical presentation: edema of the face, neck, and arms, distended veins, elevated venous pressure, headache.
- Diagnostics: CT angiography.
- Treatment: stenting, chemoradiotherapy, anticoagulants in case of thrombosis.
Mediastinitis
- Acute: following cardiac surgery, esophageal perforation (Boerhaave syndrome), odontogenic (descending from deep neck spaces).
- Clinical presentation: fever, chest pain, sepsis symptoms, subcutaneous emphysema.
- Diagnostics: CT, water-soluble contrast esophagography.
- Treatment: broad-spectrum antibiotics, drainage, esophageal repair, sternotomy for postoperative cases.
- Chronic: tuberculosis, histoplasmosis, sarcoidosis.
Horner's syndrome
- Involvement of the sympathetic chain (Pancoast tumor of the lung apex).
- Ptosis, miosis, anhidrosis, enophthalmos.
Hoarseness
- Involvement of the left recurrent laryngeal nerve (loops under the aortic arch) — anterior mediastinal tumors, aortic aneurysm, mitral stenosis (Ortner's syndrome).
Eisenmenger syndrome, pericardial tamponade
- Processes of the middle mediastinum.
8. Pneumomediastinum
- Causes: alveolar rupture (cough, asthma, mechanical ventilation barotrauma), esophageal perforation, trauma.
- Clinical presentation: retrosternal pain, neck crepitus, Hamman's sign (crunching sound synchronous with the heartbeat on auscultation).
- Diagnostics: radiography, CT.
- Treatment: addressing the underlying cause; usually self-limiting, decompression for tension pneumomediastinum.
9. Imaging methods
- Radiography — chest X-ray in 2 projections; mediastinal width, contours.
- Contrast-enhanced chest CT — gold standard.
- MRI — neurogenic tumors, vascular structures.
- PET/CT — lymphomas, staging.
- Endoscopic ultrasound (EUS/EBUS) + biopsy — lymph nodes, masses.
- Mediastinoscopy — biopsy of paratracheal nodes for lung cancer staging.
- Video-assisted thoracoscopic surgery (VATS) — diagnosis and treatment of masses.
10. Mediastinal lymph nodes
- IASLC classification — 14 stations (1–14).
- Used for lung cancer staging (N1–N3).
- Key stations: paratracheal (2, 4), aortopulmonary window (5), subaortic (6), subcarinal (7), paraesophageal (8), pulmonary ligaments (9).
11. Surgical approaches
- Median sternotomy — heart, anterior mediastinum.
- Lateral thoracotomy — middle and posterior mediastinum.
- VATS (video-assisted thoracoscopic surgery) — minimally invasive interventions.
- Cervical approach — superior mediastinum.
- Robotic surgery (DaVinci) — modern alternative.
12. FAQ
Why does the recurrent laryngeal nerve loop around different structures on the right and left?
Embryologically, the nerve hooked around the 6th branchial arch. On the left, it persists as the ligamentum arteriosum → the nerve loops around the aortic arch. On the right, the 6th arch disappears, and the nerve "ascends" to hook around the right subclavian artery.
What is Hamman's sign?
A heartbeat-synchronous crunching or clicking sound in pneumomediastinum — a classic sign, especially in the left lateral decubitus position.
When is the anterior mediastinum widened in young individuals?
Frequently due to persistent thymus tissue (normal up to age 20), Hodgkin lymphoma, or teratoma. In adults > 40 — thymoma.
How to determine the source of pneumomediastinum?
CT with oral water-soluble contrast and esophagoscopy — for esophageal rupture; CT + bronchoscopy — for bronchial injury; spontaneous pneumomediastinum is typically idiopathic.
How does a posterior mediastinal neurogenic tumor differ from others?
Typical location is paravertebral, in the costovertebral sulcus. MRI shows a "dumbbell" (hourglass) shape when extending through the intervertebral foramen. Dopamine/HVA/VMA are often elevated in pheochromocytoma and catecholamine-secreting paragangliomas.
See also: Aorta · Thymomas · Boerhaave syndrome · Lung cancer · Anatomy Catalog