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Mediastinum SCRUBS AnatomyRevisionLearningOutcomes • Identify and describe the locations, boundaries and contents of the anterior, middle, posterior and superior mediastinum • Describe the orientation of the heart • Describe the location of the pericardial cavity • Identify the surface projections of the heart • Identify features of the adult heart related to foetal anatomyMediastinum • Central Compartment of the thoracic cavity • Contains all the thoracic viscera (except the lungs) Boundaries Anteriorly: Sternum Posteriorly: Vertebral Column (thoracic) Superiorly: Thoracic Inlet Inferiorly: Diaphragm Laterally: Mediastinal PleuraSuperiorMediastinum Anteriorly: manubrium Posteriorly: upper 4 thoracic vertebrae Superiorly: plane of the thoracic inlet Inferiorly: imaginary plane passing through sternal angle and T4 On each side: mediastinal pleuraContentsofthesuperiormediastinum 1- Trachea and oesophagus 2- Arteries: a- Arch of aorta b- brachiocephalic artery c- left commoncarotid artery d- Left subclavianartery 3- Veins : a- Upper half of superior vena cava b- Rightand left brachiocephalic veins c- Left superior intercostalveins 4- Nerves: vagus,phrenic nerves,leftrecurrentlaryngealnerve 5- Thymusgland 6- Thoracic duct 7- Lymph nodes: paratracheal, brachiocephalic, tracheobronchialAnterior Mediastinum Boundaries: Anteriorly: body of sternum Posteriorly: pericardium Superiorly: imaginary plane Inferiorly: superior surfaceof diaphragm On each side: mediastinalpleura Contents: 1. Sternopericardialligaments 2. Lymphnodes withlymphatics 3. Lowestpart of the thymusMiddle Mediastinum Contents: 1. Heartenclosedin pericardium 2. Arteries a.Ascending aorta b. Pulmonarytrunk and its2 branches Veins: a. upper part of IVC b. Lower half of superior vena cava c. Terminal part of the azygosvein 4. Nerves=phrenic 5. Lymph nodes 6. Bifurcationoftrachea into Right and left principal bronchi Posterior Mediastinum Boundaries: Posteriortoheartandpericardium,anteriortovertebraeT5－T12 On each side : mediastinalpleura Contents: 1- Oesophagus 2- Arteries:Descendingaortaanditsbranches 3- Veins:(i)Azygosvein (ii) Hemiazygosveins (iii)Accessoryhemiazygosvein 4- Nerves:(i)vagi (ii)splanchnic nerves 5- Lymph nodes i)Posteriormediastinalgroup ii)Thethoracicduct Locatedin the middle mediastinum (along with the heart and root ofgreat vessels) Fibroserousmembrane: external fibrouspericardiumand internal serouspericardium which reflects ontothe heart at the great vessels becoming the visceral pericardium Pericardium Continuouswith the central tendon ofthe diaphragm Fibrouspericardium is continuouswith the tunicaadventitia and pretracheal layer of deep cervicalfascia and forms the sternopericardialligaments and boundposteriorlyby loose connectivetissue.Thymus • Primary lymphoid organ • Superior mediastinum (passing into anterior mediastinum) • Atrophies with age & replaced by fat after puberty • Maturation of T cellsAorta • Ascendingaorta:Aortic orifice to sternal angle(middlemediastinum) Branches= CoronaryArteries • Arch of Aorta:sternalangleto T4 (superiormediastinum) Branches= Brachiocephalic,leftcommon carotidandleft subclavian arteries Main branches: • Parietal branches • Nine pairs posterior intercostal arteries • One pair subcostal artery • Visceral branches • Bronchial branches: one or two for each lung • Oesophageal & Pericardial br. • Mediastinal • Superior phrenic Azygos Venous System The Azygosveinreceives the right posterior intercostalveinsand originatesfrom the junction ofthe right ascendinglumbarand subcoastal veins. The accessory andhemi accessory azygosveins receive the left posteriorintercostalveinsand drainintothe azygosvein DrainsintosuperiorvenacavaBrachiocephalicVeins • Internal jugular + subclavian = brachiocephalic veins • Brachiocephalic veins join behind the lower border of the first right costal cartilage to form the superior vena cava. Right& leftrecurrent laryngeal nerveSympathetic Trunk • Innervates visceral structures of thorax and abdomen • T1– T4 supplies the Thoracic viscera • T5– T9/ T10 - Greatersplanchnic nerve • T9/ T10 – T11 - Lessersplanchnic nerve • T12 - Least splanchnic nerveWhich nerves are labelled?Recurrentlaryngealnerves RightRLNhooksaroundrightsubclavianartery LeftRLNhooksaroundtheaorticarch •Both ascend in tracheo-oesophagealgroove •Innervation: laryngeal mucosa below fissure of glottis, all laryngeal muscles (exceptcricothyroid)Nerves • Phrenic: -C3C4 C5 keeps thediaphragm alive! -Supplies thediaphragm, mediastinalpleura and pericardium -Runs anterior tothe lung roots • Vagus: -Right vagus forms the posterior oesophageal plexus -Leftvagus forms the anterioroesophageal plexus -CNX -Exits from theoesophageal hiatus T10Oesophagus • Compressionsites:Pharynx,aortic arch, left main bronchus,oesophageal hiatus! Lymphatics • The thoracicduct isa contentofthe posteriormediastinum. • Originatesat L1 from the cisterna chyli. • Passes betweenoesophagusandvertebral column. • Receiveslymphatictrunks • Terminatesat the left venousangle • Vslymphaticduct drainsright upper quadrantFoetal Remnants DuctusArteriosus ---Ligamentum ForamenOvale--- Fossa Arteriosum Ovalis Shuntsbloodawayfrom Shuntsbloodfrom the right pulmonaryartery to the aortic atriumto the left atrium, arch, awayfrom the lungs awayfrom the lungs MCQ Which of the following structures passes through the oesophageal hiatus • A) Thoracic duct • B) Vagus nerve • C) Accessory hemiazygos vein • D) Phrenic Nerve• Which of the following structures passes through the oesophageal hiatus • A) Thoracic duct • B) Vagus nerve • C) Accessory hemiazygos vein • D) Phrenic Nerve Anterior and posterior vagal plexuses!MCQ What forms the posterior border of the superior mediastinum? • A) Parietal pleura • B) Pericardium • C) Vertebral bodies T5-T12 • D) Vertebral Bodies T1-T4• What forms the posterior border of the superior mediastinum? • A) Parietal pleura • B) Pericardium • C) Vertebral bodies T5-T12 • D) Vertebral Bodies T1-T4Thanksforlistening! amccalmont04@qub.ac.uk