05 CB 041 Mediastinum

Introduction NGU School of Medicine Focus on unbounded thinking in medical education, fostering innovative approaches to understanding medical concepts and enhancing critical thinking skills in future healthcare professionals.

Mediastinum Overview General Description The mediastinum is the central compartment of the thoracic cavity and plays a crucial role in housing essential structures vital for respiratory and cardiovascular function.

Contains essential structures:

• Heart and its vessels: Including the aorta, pulmonary arteries, and veins.

• Esophagus: The muscular tube that transmits food from the throat to the stomach.

• Trachea: Airway leading into the lungs, bifurcating into the bronchi.

• Phrenic and cardiac nerves: Nerves essential for respiratory function and heart regulation.

• Thoracic duct: The main lymphatic vessel that drains lymph from the body into the bloodstream.

• Thymus: A gland involved in immune function, particularly during childhood.

• Lymph nodes: Critical for immune response and fluid balance.

Subdivisions of the Mediastinum

1. Superior Mediastinum: Contains structures above the pericardium, important for the transmission of signals and vessels.

2. Inferior Mediastinum: Divided further into:

   • Anterior Mediastinum: Contains remnants of the thymus and the sternopericardial ligaments, important for structural support.

   • Middle Mediastinum: Occupied by the pericardium as well as the heart and great vessels, critical for blood circulation.

   • Posterior Mediastinum: Contains the descending thoracic aorta, esophagus, thoracic duct, and sympathetic chains, integral for vasculature and autonomic nervous system signaling.

Objectives of the Teaching Session By the end of this topic, students should be able to:

• Indicate and diagram subdivisions of the thoracic cavity accurately.

• Describe the diverse contents of the mediastinum and their functions.

• Discuss the lymphatic drainage patterns of the thorax and their clinical implications.

• Diagram the distribution of the vagus nerve within the thorax and its relevance to cardiac and digestive functions.

• Describe the thoracic sympathetic trunk, its connections, and associated structures, particularly in stress responses.

• Detail the anatomical relations of the esophagus in the thorax and implications for diseases such as esophageal cancer.

• Recognize heart and mediastinal structures on CT images, enhancing diagnostic skills in radiology.

Detailed Anatomy of Mediastinum Contents Overview

• Superficial Structures: Encompasses the thymus, aortic arch, and great vessels such as the brachiocephalic trunk, contributing to their protective and supportive roles.

• Functional Structures: Includes the heart, lungs, and associated nerves responsible for respiration and circulation, highlighting their interdependence for physiological function.

Subdivisions and Structures

Superior Mediastinum

Contains:

• Thymus: Key for T-cell development in the immune system.

• Aortic arch: Major vessel supplying blood to the head, neck, and arms.

• Brachiocephalic vein: Drains blood from the head and arms back to the heart.

• Vagus nerves: Important for parasympathetic control of the heart and digestive tract.

• Phrenic nerve: Controls the diaphragm and is crucial for breathing.

Middle Mediastinum

Occupied by:

• Pericardium: The fibrous sac surrounding the heart, offering protection and anchoring.

• Heart and great vessels: Such as the aorta and pulmonary trunk, essential for systemic and pulmonary circulation.

Anterior Mediastinum

Contains remnants of the thymus and sternopericardial ligaments, which play crucial roles in providing structural integrity to the thorax.

Posterior Mediastinum

Contains:

• Descending thoracic aorta: Supplies blood to the chest wall and organs.

• Esophagus: Important for the passage of food, with potential for compression by mediastinal masses.

• Thoracic duct: Responsible for transporting lymph, with clinical significance in lymphatic drainage disorders.

• Left and right vagus nerves: Concerning their roles in autonomic control of thoracic organs.

• Sympathetic chains: Involved in the body's stress response and regulating visceral functions.

Neural and Vascular Structures

Vagus Nerve

• Left Vagus: Enters via thoracic inlet, runs between left common carotid and subclavian arteries, courses behind hilum of left lung affecting cardiac regulation.

• Right Vagus: Enters via thoracic inlet, runs alongside the trachea, and influences the right lung and heart functions.

Sympathetic Trunk and Nerves

The sympathetic trunk consists of ganglia linked through nerve fibers, crucial for the autonomic nervous system's response to stress.

• Thoracic sympathetic trunk: Has 12 ganglia, some generally fused. Contains:

• Greater splanchnic nerve (T5-T9): Supplies abdominal organs, involved in pain signaling.

• Lesser splanchnic nerve (T10-T11): Transmits autonomic signals.

• Least splanchnic nerve (T12): Relevant for renal blood flow regulation.

Clinical Significance

Mediastinal Conditions

• Mediastinal Syndrome: A collection of symptoms due to compression by masses; includes:

  • Dyspnea: Resulting from tracheal compression, affecting respiration.

  • Dysphagia: Esophageal compression leads to difficulty swallowing.

  • Hoarseness: Compression of recurrent laryngeal nerve impacting voice.

  • Ischemia: Resulting from aorta compression, presenting risks for ischemic heart disease.

  • Non-pitting edema: Thoracic duct compression leading to fluid accumulation.

• Aortic Aneurysm: Localized dilation which may manifest as mediastinal syndrome, requiring early intervention to prevent rupture.

• Coarctation of Aorta: A narrowing that can lead to differential blood pressures, preserving lower limb circulation through collateral channels, important for surgical considerations.

Conclusion Emphasis on understanding the anatomy and pathologies of the mediastinum in clinical settings is vital for improved diagnosis and management of thoracic conditions. Visualizing structures through imaging techniques and diagrams enhances comprehension and aids in effective clinical decision-making.