Cardiovascular: Mediastinum & Superficial Anatomy of the Heart (Nelson Mandela University) PDF

Cardiovascular: Mediastinum & Superficial Anatomy of the Heart YBOD200 Mr J Naidoo  Learning Objectives MEDIASTINUM Identify and describe the divisions of the mediastinum including borders and contents Describe the structures found in the mediastinum and their relati...

Cardiovascular: Mediastinum & Superficial Anatomy of the Heart YBOD200 Mr J Naidoo  Learning Objectives MEDIASTINUM Identify and describe the divisions of the mediastinum including borders and contents Describe the structures found in the mediastinum and their relations to each other from Anterior to Posterior Describe the anatomy of the azygos vein, thoracic duct, Vagus nerve, and oesophagus.  Learning Objectives SUPERFICIAL SURFACE OF THE HEART Describe the superficial anatomy of the heart: o Pericardial layers, reflections of serous pericardium The major vessels of the heart entering and leaving the heart, ie. vena cava, pulmonary trunk, pulmonary veins etc. Grooves on the surface of the heart and main blood vessels of the heart, viz. coronary arteries and cardiac veins trunk, pulmonary veins etc. The atria and ventricles Mediastinum  Mediastinum Broad central partition that separates the two laterally placed pleural cavities. BOUNDARIES: o Anteriorly – Body of sternum o Posteriorly – Vertebral bodies of thoracic vertebrae o Inferiorly – Diaphragm o Superiorly – Thoracic aperture Transverse plane between sternal angle and intervertebral disc at T4/T5 separates mediastinum into superior and inferior mediastinum Inferior mediastinum further divided into anterior, middle and posterior mediastinum Superior Mediastinum  Superior Mediastinum Centrally located in thoracic cavity Contains: Pericardium, heart, great vessels and nerves Superior Boundary: Oblique plane passing from jugular notch to superior border of T1 Inferior Boundary: Transverse plane between sternal angle and intervertebral disc at T4/T5 Lateral Boundary: Pleural cavities on either side Anterior boundary – Posterior surface of manubrium Posterior boundary – Body of first four thoracic vertebrae  Superior Mediastinum CONTENTS: o Thymus o Left and Right Brachiocephalic veins o Left Superior Intercostal vein o Superior vena cava o Arch of Aorta o Trachea and Oesophagus o Phrenic and Vagus nerves o Left recurrent branch of vagus nerve o Thoracic Duct  Superior Mediastinum Thymus Gland Most anterior component of superior mediastinum Immediately posterior to manubrium Asymmetrical, bilobed structure Involved in early development of immune system Left and Right Brachiocephalic veins Immediately posterior to thymus Left Superior Intercostal Vein Passes over left side of aortic arch Situated lateral to the vagus nerve and medial to the phrenic nerve  Superior Mediastinum Trachea and Oesophagus Trachea - midline structure o Palpable in jugular notch as it enters superior mediastinum Oesophagus o posterior to trachea, immediately anterior to vertebral bodies Both structures crossed laterally by azygos vein on right and arch of aorta on left Thoracic Duct Major lymphatic vessel in body Enters superior mediastinum inferiorly Continues upward posterior to arch of aorta between oesophagus and parietal pleura Anterior Mediastinum  Anterior Mediastinum Superior Boundary: Transverse plane between sternal angle and intervertebral disc at T4/T5 Inferior Boundary: Diaphragm Lateral Boundary: Pleural cavities on either side Anterior boundary – Body of sternum Posterior boundary – Pericardial sac Contents: 1. Inferior extension of thymus gland 2. Mediastinal branches of internal thoracic vessels 3. Sternopericardial ligaments Middle Mediastinum  Middle Mediastinum Centrally located in thoracic cavity Contains: Pericardium, heart, great vessels and nerves Superior Boundary: Transverse plane between sternal angle and intervertebral disc at T4/T5 Inferior Boundary: Diaphragm Lateral Boundary: Pleural cavities on either side Anterior boundary – Anterior margin of pericardium Posterior boundary – Posterior margin of pericardium Posterior Mediastinum  Posterior Mediastinum Superior Boundary: Transverse plane between sternal angle and intervertebral disc at T4/T5 Inferior Boundary: Diaphragm Lateral Boundary: Pleural cavities on either side Anterior boundary – Pericardial sac Posterior boundary – Bodies of T5-T12 Vertebrae CONTENTS: o Oesophagus and oesophageal nerve plexus o Descending aorta and its branches o Azygos system of veins o Thoracic duct and lymph nodes o Sympathetic trunk and thoracic splanchnic nerves Structures of Posterior Mediastinum  Oesophagus Muscular tube Begins: Inferior border of cricoid cartilage at C6 Ends: Cardiac opening of stomach at T11 Descends on anterior aspect of vertebral bodies, in midline Moves slightly to left inferiorly to lie anterior to descending aorta Right side is covered with parietal pleura, left side in contact with aorta Thoracic duct lies posterior to oesophagus Right pulmonary artery lies anterior to oesophagus below bifurcation of trachea  Oesophageal Plexus Right and left vagus nerves pass behind root of lung Both nerves divide into several branches which spread over oesophagus to create oesophageal plexus Fibres of right and left vagus nerves mix and converge to form two trunks: 1. Anterior vagal trunk – mainly left vagus nerve fibres 2. Posterior vagal trunk – mainly right vagus nerve fibres  Thoracic Aorta Thoracic portion of descending aorta Begins: Lower edge of T4 vertebrae Ends: Lower edge of T12 vertebrae Passes through aortic hiatus to enter abdomen BRANCHES: o Pericardial o Bronchial o Oesophageal o Mediastinal o Posterior intercostal o Superior phrenic  Azygos System of Veins Series of longitudinal vessels on either side of body draining blood into superior vena cava Important anastomotic pathway o Can return blood to heart if SVC is blocked  Azygos System of Veins AZYGOS VEIN: Arises opposite L1/L2 by union of right ascending lumbar vein and right subcostal vein (May arise as direct tributary of IVC) Enters thorax by ascending through aortic hiatus, lies on right side of thoracic duct At T4 it arches over root of right lung o Joins SVC before entering pericardial sac Tributaries: Right superior intercostal vein, 5th-11th posterior intercostal veins.  Azygos System of Veins HEMIAZYGOS VEIN: Arises at junction between left ascending lumbar and left subcostal vein Enters thorax by ascending through left crus Tributaries: Lower 4-5 Posterior intercostal veins, oesophageal and mediastinal veins ACCESSORY HEMI-AZYGOS VEIN: Descends from left side of posterior mediastinum till T8 Crosses vertebral column to join azygos or ends in hemi-azygos Has a connection to left superior intercostal vein  Thoracic Duct Principal channel of lymph being returned to venous system Begins: Confluence of lymph trunks in abdomen – dilation o CISTERNA CHYLI - L2 o Drains abdominal viscera, pelvis and perineum and lower limbs Enters thorax posterior to aorta as it ascends through aortic hiatus Runs on right side of midline between thoracic aorta and azygos vein  Thoracic Duct At T5: Thoracic duct moves to left of midline and enters superior mediastinum where it continues into neck Drains into junction between left subclavian and left jugular veins Sympathetic Trunks  Sympathetic Trunks Important component of autonomic nervous system Consists of two cords with 11-12 ganglia each Ganglia connected to adjacent thoracic spinal nerves by white and gray rami communicantes o Numbered based on thoracic spinal nerve Ends when both trunks fuse anterior to coccyx to form Ganglion impar Two Types: 1. Type 1: o Branches from upper 5 ganglia, has postganglionic sympathetic fibres o Contain visceral afferent fibres, supply thoracic viscera 2. Type 2: o Branches from lower 7 ganglia, has preganglionic sympathetic fibres o Has visceral afferent fibres, supply abdominal and pelvic viscera  Sympathetic Trunks GREATER SPLANCHNIC NERVE: o T5-T9 Ganglia o Descends across vertebral bodies medially o Ends in coeliac ganglion o Some fibres go straight to medulla of adrenal gland LESSER SPLANCHNIC NERVE: o T10-T11 Ganglia o Ends in aorticorenal ganglion LEAST SPLANCHNIC NERVE: o T12 Ganglion o Ends in renal plexus Vagus and Phrenic Nerves in the Mediastinum  Vagus Nerves RIGHT VAGUS NERVE Lies between brachiocephalic trunk and right brachiocephalic vein Descends posteriorly towards trachea and crosses lateral surface of trachea passing posterior to oesophagus Gives branches to: o Cardiac plexus o Pulmonary plexus o Oesophageal plexus  Vagus Nerves LEFT VAGUS NERVE Lies posterior to left brachiocephalic vein, between left common carotid and left subclavian arteries Lies deep to parietal pleura, crosses left side of arch of aorta, passing posterior to root of left lung Gives branches to: o Cardiac plexus o Pulmonary plexus o Oesophageal plexus  Vagus Nerves Left recurrent laryngeal nerve Branch of left vagus nerve Arises at inferior margin of arch of aorta Lies lateral to ligamentum arteriosum Passes inferior to arch of aorta, entering groove between trachea and oesophagus  Phrenic Nerves RIGHT PHRENIC NERVE Enters mediastinum lateral to vagus nerve Lies posterolateral to right brachiocephalic vein and continues along right side of SVC Descends along right side of pericardial sac within fibrous pericardium, anterior to root of right lung Passes through diaphragm at caval opening  Phrenic Nerves LEFT PHRENIC NERVE Enters mediastinum lateral to left vagus nerve Lies posterolateral to left brachiocephalic vein Passes superficially to left vagus nerve and left superior intercostal vein Follows left side of pericardial sac and lies anterior to root of left lung Pierces diaphragm near apex of heart Superficial Anatomy of the Heart Pericardium  Pericardium Fibro-serous sac surrounding heart and root of great vessels Serous Pericardium Fibrous Pericardium Visceral Pericardium Parietal Pericardium  Fibrous Pericardium Tough connective tissue outer layer Cone-shaped bag, apex is continuous with adventitia of great vessels Base is attached to central tendon of diaphragm Anteriorly attached to sternum via sternopericardial ligaments Attachments help retain position, and sac limits cardiac distention Phrenic nerves pass through and innervate fibrous pericardium, with pericardiophrenic vessels  Serous Pericardium Thin, consists of two parts: Parietal and Visceral layers Between two layers is pericardial cavity – filled with fluid, potential space allows for relatively uninhibited movement of heart Parietal layer continuous with visceral layer around roots of great vessels Parietal layer lines fibrous pericardium Visceral layer is adherent to the heart  Serous Pericardium REFLECTIONS OF SEROUS PERICARDIUM 1. Superiorly – surrounds aorta and pulmonary trunk 2. Posteriorly – surrounding veins (IVC and Pulmonary veins) Zone of reflections around veins is J-shaped (cul-de-sac) o The cul-de-sac is termed: OBLIQUE PERICARDIAL SINUS Passage between two sites of reflections is TRANSVERSE PERICARDIAL SINUS o Lies posterior to ascending aorta and pulmonary trunk o Anterior to superior vena cava o Superior to left atrium  Vessels and Nerves ARTERIAL: o Internal thoracic artery o Pericardiophrenic, Musculophrenic and Inferior phrenic arteries o Thoracic aorta VENOUS: o Azygos system of veins o Superior phrenic vein o Internal thoracic vein NERVOUS: o Vagus and Phrenic nerves o Sympathetic trunks External Sulci  Coronary Sulcus Encircles heart Separates atria from ventricles Contains: o Right coronary artery o Small cardiac vein o Coronary sinus o Circumflex branch of left coronary artery  Interventricular Sulci ANTERIOR INTERVENTRICULAR SULCUS On anterior surface of heart Contains anterior interventricular artery and great cardiac vein POSTERIOR INTERVENTRICULAR SULCUS On diaphragmatic surface of heart Contains posterior interventricular artery and middle cardiac vein Great Vessels  Pulmonary Trunk Contained within pericardial sac, covered by visceral layer of serous pericardium – associated with ascending aorta in same sheath Arises from conus arteriosus of right ventricle at opening of pulmonary trunk, slightly anterior to aortic orifice. Ascends, moving posteriorly Initially anterior and then to left of aorta At intervertebral disc between T5/T6 pulmonary trunk divides: o Right Pulmonary artery – Posterior to ascending aorta and SVC o Left Pulmonary artery – Anterior to descending aorta, inferior to arch of aorta  Aorta ASCENDING AORTA Originates at aortic orifice at base of left ventricle, level of lower edge of 3rd costal cartilage Continues to level of 2nd costal cartilage where it enters superior mediastinum to become arch of aorta ARCH OF AORTA Begins as ascending aorta emerges from pericardial sac Courses superiorly, posteriorly and to the left Ends at T4/T5 vertebral level Extends as high as manubrium of sternum Initially anterior and then lateral to trachea  Aorta BRANCHES OF ARCH OF AORTA: First Branch – Brachiocephalic Trunk Most anterior branch At level of sternoclavicular joint it divides: 1. Right Common Carotid artery – head and neck 2. Right Subclavian artery – right upper limb Second Branch – Left Common Carotid Artery Ascends on left of trachea Left side of head and neck Third Branch – Left Subclavian Artery Ascends on left of trachea Left upper limb  Ligamentum arteriosum Important in embryonic circulation – ductus arteriosus Ductus arteriosus connected pulmonary trunk and arch of aorta and allowed blood to bypass lungs during development Closes soon after birth and forms the ligamentum arteriosum  Superior Vena Cava Lower half is encased in pericardial sac Passes through fibrous pericardium at 2nd costal cartilage Begins by union of right and left brachiocephalic veins and drains into right atrium Receives azygos vein immediately before entering pericardial sac  Inferior Vena Cava Enters fibrous pericardium at T8. Formed at L5 by the union of the right and left common iliac veins. Ascends anterior to the vertebral column, on the right side of the abdominal aorta. Clinical Relevance  Aortopulmonary Window Left recurrent laryngeal nerve passes between pulmonary artery and aorta – through a region known as aortopulmonary window May get compressed by any mass in this region; compression leads to left vocal cord paralysis and hoarseness of voice https://doi.org/10.1053/j.jvca.2016.08.002  Pericardial Effusion Normally only a tiny amount of fluid exists in pericardial cavity In case of excess fluid it is known as pericardial effusion Since fibrous pericardium is “fixed” it cannot expand easily Therefore, an increase in fluid within pericardial sac would compress heart – resulting in cardiac tamponade This results in biventricular failure Fluid removed with needle to relieve symptoms  Aortic Arch Anomalies Normal aortic arch courses to left of trachea and passes over left main bronchus A right-sided aortic arch occurs when vessel courses to right of trachea and passes over right main bronchus This is sometimes associated with: o Dextocardia (Right-sided heart) o Situs inversus (left-to-right inversion of body’s organs). https://www.ncbi.nlm.nih.gov/books/NBK556074/ That’s All Folks! For any queries or questions please feel free to contact me: [email protected]  RESOURCES Grays Anatomy for Students, 6th Edition Chapter 3 – Thorax Mediastinum https://www.clinicalkey.com/student/content/book/3-s2.0- B9780323934237000034#hl0002550