Summary of "Thorax 7 - Médiastin postérieur : œsophage, aorte descendante, conduit thoracique [Mediastinum 2]"

Summary of “Thorax 7 - Médiastin postérieur : œsophage, aorte descendante, conduit thoracique [Mediastinum 2]”

This detailed lecture focuses on the anatomy, relationships, and clinical relevance of the posterior mediastinum, particularly emphasizing the esophagus, descending thoracic aorta, and thoracic duct. The lesson also integrates anatomical structures surrounding these organs, including nerves, vessels, and the diaphragm, and concludes with clinical applications in cardiac imaging.

Main Ideas and Concepts

1. Overview of the Posterior Mediastinum

Located behind the tracheal plane.
Contains key structures: descending thoracic aorta, esophagus, and thoracic duct.
Focuses on the relationship of the posterior mediastinum to the thoracic segment of the digestive tract, mainly the esophagus.

2. Esophagus Anatomy and Course

Muscular-fibrous tube connecting the pharynx (cervical region) to the stomach (abdominal region).
Divided into three segments:
- Cervical segment ~5-6 cm long, starts opposite C6 vertebra, behind the trachea, with a narrowing called Killian’s mouth (upper esophageal sphincter area).
- Thoracic segment ~25 cm long, vertical, behind the trachea in the superior mediastinum, forming the tracheoesophageal angle, then passing behind the heart in the inferior mediastinum. Narrowed at two points:
  - Opposite the aortic arch (aortic impression).
  - At the esophageal hiatus of the diaphragm.
- Abdominal segment 2-3 cm long, passes through the esophageal hiatus of the diaphragm to join the stomach at the cardia.
The esophagus curves forward and leftward near the T10 vertebra to cross the thoracic aorta.

3. Esophageal Sphincter Mechanism

Formed by circular muscle fibers from the right diaphragmatic crus wrapping around the esophagus at the hiatus.
Acts as an anti-reflux sphincter, contracting during inspiration to prevent gastric contents reflux.
Dysfunction leads to gastroesophageal reflux disease (GERD), causing symptoms like heartburn.

4. Histological Structure of the Esophagus

Lumen lined by mucosa with stratified squamous epithelium transitioning sharply to gastric mucosa at the Z-line.
Submucosa contains glands.
Muscular layer:
- Upper third: striated muscle (continuous with pharynx).
- Middle and lower thirds: smooth muscle.
Outer layer: adventitia connecting esophagus to surrounding tissues.
Pathological changes (e.g., mucosal metaplasia in GERD) can lead to Barrett’s esophagus, increasing cancer risk.

5. Anatomical Relationships and Surrounding Structures

Posterior mediastinum includes:
- Esophagus (right of aorta in thorax).
- Descending thoracic aorta (left of vertebral column).
- Thoracic duct (ascends anterior to vertebral bodies, drains lymph into left venous angle).
- Posterior intercostal arteries and veins.
- Sympathetic chain ganglia.
- Pleura (parietal layers on each side).
Nerves:
- Vagus nerves:
  - Right vagus: gives right recurrent laryngeal nerve at right subclavian artery, runs posterior to esophagus.
  - Left vagus: gives left recurrent laryngeal nerve looping under aortic arch, runs anterior to esophagus.
  - Both form the esophageal (vagal) plexus providing parasympathetic innervation.
- Phrenic nerves:
  - Right phrenic runs along right heart border to right diaphragm.
  - Left phrenic crosses aortic arch, runs along left heart border to left diaphragm.
The diaphragm:
- Has an aortic hiatus at T12 vertebral level, formed by the median arcuate ligament and right/left crura, allowing passage of the aorta and esophagus.
- Diaphragmatic fibers contribute to the esophageal sphincter.

6. Vascular Anatomy

Aortic arch gives off three main branches:
- Brachiocephalic trunk (right side) → right common carotid and right subclavian arteries.
- Left common carotid artery.
- Left subclavian artery.
Superior vena cava formed by union of brachiocephalic veins, drains into right atrium.
Pulmonary trunk and arteries located anteriorly to esophagus and aorta.
Venous drainage includes azygos vein system connecting superior and inferior vena cava.

7. Imaging and Clinical Relevance

Horizontal cross-sections at various thoracic vertebral levels (T3, T4, T5, T6-T8) help identify mediastinal structures on CT scans.
The heart occupies the middle and inferior mediastinum, with right and left atria and ventricles, valves, and pericardium described.
Transesophageal echocardiography (TEE):
- Ultrasound probe inserted into esophagus provides close imaging of left heart chambers, superior to transthoracic ultrasound for detecting left atrial thrombi or valvular lesions.
- Important in clinical cardiology for stroke risk assessment and endocarditis evaluation.

Methodology / Key Instructional Points

Anatomical Construction Approach:
- Begin with the trachea as the central axis.
- Place superior mediastinal structures above tracheal bifurcation.
- Place inferior mediastinal structures below bifurcation.
- Identify vertebral levels as landmarks (C6, T3, T4, T5, T6-T8, T10, T12).
- Use anterior, posterior, and lateral views for spatial orientation.
- Recognize vascular and nervous structures in relation to the esophagus and aorta.
Histological Study:
- Identify mucosal layers and transition zones.
- Understand muscle fiber types and their distribution.
Clinical Application:
- Use anatomical knowledge to interpret CT scans and echocardiography.
- Understand the clinical significance of esophageal sphincter dysfunction.
- Appreciate the advantages of TEE in cardiac diagnostics.

Speakers / Sources Featured

Primary Lecturer: Unnamed professor delivering the anatomy lecture.
References to Other Educators:
- Mrs. Debénath du Jardin (esophageal anatomy).
- Fabienne Reuzeau (histology of esophagus).
- Fabienne Jo and Théo Haye (transesophageal echocardiography).

This summary captures the key anatomical, physiological, and clinical insights from the lecture on the posterior mediastinum, emphasizing the esophagus, thoracic aorta, thoracic duct, and related neurovascular structures.