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The Anatomy of the Mediastinum Lecture 6 24 January 2023 Presented by Shaarika Munshi Learning Objectives 2 mins Structure of Overview: Layout, organisation, boundaries 10 mins the session and anatomical landmarks of the mediastinum The Superior mediastinum 10 mins KEY POINT The Anterior Mediastinum 5 mins The Middle Mediastinum 10 mins EXTRA MATERIAL The Posterior Mediastinum 20 mins REVISION TIP Summary, Tips and Practice Questions 10 mins Surgical Society| Junior Anatomy Series Learning Objectives •Mediastinum: Describe the arrangement and contents of the superior, anterior, middle and posterior parts of the mediastinum. •The Aorta and the Vena Cava: Describe the course of the ascending aorta, the arch of the aorta and the descending thoracic aorta. Name their major branches and the structures they supply. Describe the origins, courses and relationships of the brachiocephalic veins, inferior and superior venae cavae and the azygos venous system. •The Nerves of the Mediastinum : Describe the distribution and function of the sympathetic chains and thoracic splanchnic nerves. Explain the mechanism of referred pain from T1-5 sympathetic afferents to the chest wall and relate it to the thoracic viscera. •The Oesophagus: Describe the course, major relations and neurovascular supply of the oesophagus within the thorax. •Lymphatics: Describe the course and major relations of the thoracic duct. Explain the lymph drainage within the thorax and its clinical significance. •Imaging: Identify major thoracic structures on standard diagnostic images e.g. CT, MRI, X-ray and ultrasound. Surgical Society | Junior Anatomy SeriesOverview of the Mediastinum • One of the 3 cavities found in the thorax • Situated between right and left pleural cavity • Contains all Thoracic structure except lungs and surrounding pleura. • Divided into Superior and Inferior Mediastinum • Inferior further divided into – Anterior, Middle and Posterior Mediastinum. Surgical Societyunior Anatomy Series KEY POINT Boundaries of the Mediastinum The Superior and Inferior Mediastinum are divided by the ‘STERNAL ANGLE’. Superiorly: Superior Thoracic Aperture (Rib 1+ Manubrium + T1 vertebrae). Inferiorly:Diaphragm (mobile structure therefore MS is a mobile cavity). Anteriorly: Sternum Posteriorly: 12 Thoracic Vertebrae Laterally:Lungs enveloped by Pleura Surgical SocietyJunior Anatomy Series Boundaries of the Mediastinum - Bound inferiorly by diaphragm- curved structure that contracts and relaxes during respiration. - Different regions of the Inferior mediastinum have different inferior aspects. - Certain components e.g. Pericardium are bound to the Diaphragm, therefore the move along with their attachments. - MOBILE CAVITY - Structures may move during times of pathology e.g. TENSION PNEUMOTHORAX Surgical Society Junior Anatomy SeriesRelevance to Clinical Practice - Structures may move during times of pathology e.g., TENSION PNEUMOTHORAX (collapsed lung). - Trachea deviates to OPPOSITE side - MEDICAL EMERGENCY REVISION TIP Causes of tracheal deviation is relevant to your Respiratory CPA exam Surgical Societyunior Anatomy SeriesImportant Anatomical Landmarks: STERNAL ANGLE - Also known as ‘ Angle of Louis’ - Divides the Superior and Inferior Mediastinum - Manubrium articulates with the Body of Sternum. - Easy identification of Intercostal spaces and ribs- allows for valve auscultation REVISION TIP Using surface markings for valve auscultation is relevant to your Cardiovascular CPA exam. Surgical SocietyJunior Anatomy Series STERNAL ANGLE - In line with T4 posteriorly - Dissects Aortic Arch (ascending vs descending thoracic aorta) - Trachea bifurcates into R and L primary bronchi - Where the azygous vein drains into the Superior Vena Cava - Allows for easy mapping of great vessels of the heart. Surgical SocietyJunior Anatomy SeriesThe Superior Mediastinum Superiorly: Superior Thoracic Aperture Inferiorly: Sternal Angle Plane Anteriorly: Manubrium Posteriorly: T1- T4 vertebrae Laterally: Mediastinal Pleura From a frontal view most structures obscured by Thymus Gland, a fatty connective tissue that is a resident inactive structure in adult. Most prominent during puberty. Inferior portion of gland projects downwards into anterior Inferior Mediastinum. Surgical SocietyJunior Anatomy Series The Superior Mediastinum: Blood Vessels - Arch of the aorta- 3 branches: - (see diagram).From right subclavian- Internal thoracic artery, travels down into inferior mediastinum. - Superior vena cava- Right and left brachiocephalic vein (each receive blood from internal jugular and subclavian veins). - Azygous vein drains into the superior vena cava at the level of the sternal angle. Brings deoxygenated blood from posterior walls of thorax and abdomen into the general circulation. Surgical Society Junior Anatomy SeriesThe Superior Mediastinum- Lymphatics - Thoracic duct drains into junction between left Internal Jugular vein and the left subclavian vein. - Travels up from posterior mediastinum into superior mediastinum. - Brings lymph from the lower limbs, abdomen, left side of the thorax, left upper limb and part of the head. - Travels through aortic hiatus (T12 behind the diaphragm). - Right lymphatic duct drains the right upper limb, right side of thorax and part of head into the junction between the right IJV and the subclavian vein. Surgical Society| Junior Anatomy SeriesThe Superior Mediastinum- Oesophagus and T rachea - Bifurcation of trachea at the level of sternal angle - Oesophagus travels behind the trachea. - Posterior most structure of all major structures in the superior mediastinum - Through the diaphragm via the Oesophageal Hiatus (T10) then enters the stomach. - Innervated by branches of the Vagus nerve (parasympathetic innervation). Surgical Societyunior Anatomy SeriesThe Superior Mediastinum- Nerves - Upper portions of the sympathetic trunk - Right and Left Vagus Nerve: Former crosses over right subclavian artery where the right recurrent laryngeal nerve branches off. Latter over the aortic arch where left recurrent laryngeal nerve branches off. - Superficial cardiac plexus- lies on Aortic arch. Formed by branches of Right and Left Vagus nerves (parasympathetic) and branches from T1-T4 sympathetic trunk. - Phrenic nerves travelling down to supply diaphragm. Surgical SocietyJunior Anatomy SeriesThe Inferior Mediastinum Superiorly: Sternal Angle Plane Inferiorly:Diaphragm Anteriorly: Body of Sternum Posteriorly:T5- T12 Laterally:Mediastinal Parietal Pleura Surgical SocietyJunior Anatomy SeriesThe Anterior Mediastinum Superiorly: Sternal Angle Plane Inferiorly:Diaphragm Anteriorly: Body of Sternum, costal cartilages and transversus thoracic muscles Posteriorly:Anterior Pericardium Laterally:Mediastinal Parietal Pleura Surgical SocietyJunior Anatomy SeriesThe Anterior Mediastinum - Inferior Portion of Thymus Gland - Sternopericardial Ligaments: Attaches anterior surface of pericardium to the sternum. - Lymph Nodes: Prepericardial and Parasternal Lymph Nodes ( drain a small portion of lymph from the breast). - Branches of Internal Thoracic artery- Perforating branches of ITA. Surgical Societynior Anatomy SeriesThe Anterior Mediastinum- Summary Surgical Society | Junior Anatomy SeriesThe Middle Mediastinum Superiorly: Sternal Angle Plane Inferiorly:Diaphragm Anteriorly: Anterior Pericardium Posteriorly:Posterior Pericardium Laterally:Mediastinal Parietal Pleura Surgical SocietyJunior Anatomy Series REVISION TIP Watch the JAS lecture on The Middle Mediastinum Thorax 3- The Heart to learn more. - Pericardium , containing heart and roots of great vessels (Ascending aorta, pulmonary trunk, Superior and Inferior Vena cava and Pulmonary veins). - Right and Left Primary Bronchi - Left and Right Phrenic Nerves - Pericardiophrenic artery and veins (internal thoracic artery and vein). - Deep Cardiac Plexus - Tracheobronchial Lymph Nodes Surgical SocietyJunior Anatomy SeriesThe Deep Cardiac Plexus - Lies on trachea slightly superior to the Tracheal Bifurcation - Formed Cardiac Branches of the Left and Right Vagus Nerves (parasympathetic) - Cardiac Branches of the sympathetic trunk (T1-T4). - Deep to the Superficial Cardiac plexus which lies on aortic arch. Surgical Societyunior Anatomy SeriesT racheobronchial Lymph Nodes - Lymph nodes lying on main bronchus and inferior trachea. EXTRA MATERIAL During cases of pathology these nodes can enlarged. May becomes necessary to perform a biopsy. A slit is made about the jugular notch to enter the superior mediastinum, travelling down the trachea until reaching the point of bifurcation where the nodes are found. Allows access to nodes without damaging lung tissue/ pleura. Surgical Society Junior Anatomy SeriesThe Posterior Mediastinum Superiorly: Sternal Angle Plane- T4 Inferiorly:Diaphragm Anteriorly: Back of Pericardium Posteriorly: Vertebral Bodies of T5- T12 Laterally:Mediastinal Parietal Pleura Anterior-most Structures: Descending Thoracic Aorta and Oesophagus. Posterior-most structures: Azygous System, Thoracic duct and sympathetic chains that sit either side of vertebral column. Surgical Society| Junior Anatomy Series REVISION TIP- Mneumonic I ate (8) ten eggs at 12: Diaphragm Recap I 8 (Inferior vena cava- T8) At 12 (Aortic- T12) T10) T8 T10 T12 Caval Hiatus Oesophageal Aortic Hiatus (through) Hiatus (Behind) (through) - Inferior Vena Cava - Oesophagus - Descending aorta - Branches of Right - Right and Left - Thoracic duct Phrenic Nerve Vagus nerves - Azygous Vein - Oesophageal Branches of left gastric artery and vein Surgical Society Junior Anatomy Series KEY POINT Begins atT5 and exits at (aortic hiatus) to become Descending Thoracic Aorta the Abdominal AortaLies to the left of the Thoracic Vertebral Bodies. Moves slightly towards midline as it descends but remains to the left of the Oesophagus. Branches of Thoracic Aorta: - Posterior Intercostal arteries (costal grooves of ribs) - Mediastinal branches which supply lymph nodes of posterior mediastinum - Pericardial Branches supplies posterior aspect of pericardium - Oesophageal branches to supply Oesophagus - Two superior phrenic arteries to supply diaphragm T5- T12 Surgical Society | Junior Anatomy Series Oesophagus - Travels through superior mediastinum posterior to trachea, down the midline, over the vertebral bodies before passing through oesophageal hiatus at T10 in diaphragm. - Supplied by oesophageal branches from descending Thoracic Aorta - Continuously supplies by right and left Vagus nerves which form oesophageal plexus. Converge to form anterior and posterior vagal trunks as it descends (parasympathetic supply). Surgical Societynior Anatomy Series Azygous System - Left-to-Right Venous shunting. - Azygous vein lies on the Right side of the thoracic vertebral bodies. Veins cross over midline to drain into azygous system before that drains into the superior vena cava (slightly to the right of thorax) - Drains posterior thoracic cavity - Formed from the union of the ascending lumbar vein and right subcostal vein (APP revision). Surgical Society Junior Anatomy Series KEY POINT Azygous System Azygous vein crosses over hilum of right lung and leaves an indentation in right lung where it lays before it drains into the SVC at the level of the sternal angle. - On RHS, Azygous vein drains majority of posterior intercostal veins except for the supreme intercostal veins (1 ICS) which drains into right brachiocephalic vein th - Hemiazygos vein drains 9 ICS- subcostal region (left).. Crosses the midline over the thoracic duct before entering the Azygous vein. - Accessory hemi-azygous vein drains posterior intercostal veins 4-8. Upper ICS on the left- hand side use the superior intercostal vein which drains into the left brachiocephalic veins (also crosses midline). Surgical Society Junior Anatomy Series Thoracic Duct - Begins as Cisterna Chyli, a dilation of lymphatic tissue formed by unison of intestinal and left and right lumbar ducts. - Brings lymph from Abdomen and Lower Limbs - Travels through Aortic Hiatus to enter thorax, over vertebral bodies and slightly to the left. Surgical Societyunior Anatomy Series Sympathetic Chains - Run down the lateral sides of thoracic vertebral bodies - Responsible for sympathetic outflow to the whole body - Sympathetic efferents from T– L2 travel up the chain into the cervical ganglion where it supplies head and neck with sympathetic innervation, vice versa for lower body - Made of Sympathetic ganglions and interganglionic branches. Surgical SocietyJunior Anatomy Series Sympathetic Chains - In Thorax this is the region where the splanchnic nerves arise: greater, lesser and least splanchnic nerves. - Travel through diaphragm to supply the viscera of the abdomen with sympathetic innervation. - Travel upwards as the upper sympathetic chains to supply cardiac branches (T1-T4). Sympathetic innervation to the heart. Surgical Societynior Anatomy Series [SBAs] PRACTICE QUESTION PRACTICE QUESTION PRACTICE QUESTION 1. What is the plane that divides 3. Which nerves contribute to the the superior and inferior superficial cardiac plexus? 5. Which of the following vessels does the azygous vein drain? mediastinum? • Phrenic nerves • Posterior intercostal veins • Epigastric plane • Left vagus nerves • Angle of Louis • Accessory nerves • Hemiazygos vein • Supracristal plane • Hypogastric nerve • Accessory hemi-azygous vein • Brachiocephalic vein • Coronal plane • T1- T4 sympathetic branches • Supreme Posterior intercostal • Subchondral plane • Right vagus nerve branches vein 2. Which of the following are 4. Which of these form part of the 6. At which Vertebral level is the branches of the aortic arch? border of the inferior Aortic Hiatus? mediastinum? • T8 • Internal thoracic artery • Superior thoracic aperture • T9 • Epigastric artery • Diaphragm • T10 • Subclavian artery • Pericardium • T11 • Left Common Carotid Artery • Mediastinal parietal pleura • T12 • Brachiocephalic Artery • Cervical vertebral bodies Surgical Society | Junior Anatomy Series [SBAs] PRACTICE QUESTION PRACTICE QUESTION PRACTICE QUESTION 1. What is the plane that divides 3. Which nerves contribute to the the superior and inferior superficial cardiac plexus? 5. Which of the following vessels does the azygous vein drain? mediastinum? • Phrenic nerves • Posterior intercostal veins • Epigastric plane • Left Vagus nerves • Angle of Louis • Accessory nerves • Hemiazygos vein • Supracristal plane • Hypogastric nerve • Accessory hemi-azygous vein • Brachiocephalic vein • Coronal plane • T1- T4 sympathetic branches • Supreme Posterior intercostal • Subchondral plane • Right Vagus nerve branches vein 2. Which of the following are 4. Which of these form part of the 6. At which Vertebral level is the branches of the aortic arch? border of the inferior Aortic Hiatus? mediastinum? • T8 • Internal thoracic artery • Superior thoracic aperture • T9 • Epigastric artery • Diaphragm • T10 • Subclavian artery • Pericardium • T11 • Left Common Carotid Artery • Mediastinal parietal pleura • T12 • Brachiocephalic Artery • Cervical vertebral bodies Surgical Society | Junior Anatomy SeriesQ1 Surgical Society | Junior Anatomy SeriesAnswer Apex of heart within the pericardium Surgical Societyunior Anatomy SeriesQ2 Surgical Society | Junior Anatomy SeriesAnswer Azygous Vein Surgical Societyunior Anatomy SeriesQ3 Surgical Society | Junior Anatomy SeriesAnswer Sympathetic trunk and and sympathetic Ganglion Surgical Societyunior Anatomy Series Useful Learning and Revision Resources - Complete Anatomy App - Acland’s Atlas of Human Anatomy- Videos and practice exams on various topics. - Grey’s Anatomy for Students - Rohen’s Color Atlas of Human Anatomy- Online pdf available for free - Teach me Anatomy (Website) - YouTube: The Noted Anatomist (especially good for cranial nerves) andAnatomy Zone (very good videos explaining the parasympathetic/ sympathetic nervous system). - Practice lots of flashcards !- Rohens flashcards and Gray’s Anatomy | Junior Anatomy Series Surgical SocietySurgical Society | Junior Anatomy Series Shaarika Munshi JAS LEADS Contact sm4619@ic.ac.uk Phase 1a: Anya Nanchahal (sn1119) Phase 1b: Andrea Perez Navarro (ap6618) CPA Lead: Defne Artun (da1019) Click to add text Feedback Please fill out the following feedback form in order to receive a copy of the slides on MedAll, along with bonus VSAQs to aid your revision! Form We hope you enjoyed this lecture! See you on Tuesday 31st January 2023 for our next lecture on Lower Limbs 1.