MEDIASTINUM & PLEURAE

DR A. O. AJELETI

OUTLINE

• THORACIC CAVITY

• MEDIASTINUM & CONTENTS

• PLEURAL TYPES, REFLECTION & RECESSES

• ASSOCIATED ANATOMICAL RELATIONS

Learning objective

• By the end of this lecture, students should be able to:

• Know the types of mediastinum and their anatomical relationship

• Know the pleural types and their anatomical relationship

• Have the knowledge of pleural reflection and their clinical importance

• Have the knowledge of pleural recesses and their clinical importance

• Understanding the anatomical correlates.

THORACIC CAVITY

• Thoracic cavity is divided into

• Rt & Lt pleural cavities

• Mediastinum

THORACIC CAVITY

MEDIASTINUM

• The mediastinum is the region between the two pleural sacs (pulmonary cavities).

• It is bounded on each side by the pleura, in front by the sternum, and behind by the bodies of the thoracic vertebrae and the intervertebral discs.

• It is divided into: superior, anterior, middle and posterior mediastina.

• The middle is occupied by the pericardium, others are according to the relationship they present to the pericardium.

MEDIASTINUM

CONTENTS OF THE MEDIASTINUM

• Contents of the mediastinum are:

• The heart within the pericardium

• Vessels proceeding to and from the heart

• The trachea

• Structures in transit from neck to abdomen: esophagus, the vagus nerves, phrenic nerves, and thoracic duct.

THE PLEURAE

• Each pleura has main 3 parts

• Parietal

• Visceral

• Connecting / root – connect the pulmonary pleura to the mediastinal layer of parietal pleura.

• (Cervical)

THE PLEURAE

• Parietal layer lines each pleural cavity. Parts are:

• Costal pleura

• Mediastinal pleura

• Diaphragmatic pleura

• Cervical pleura (cupola)

THE STERNAL COSTAL (PLEURAL)

REFLECTION

• The lines of pleural reflection are those along which the costal pleura becomes continuous with the mediastinal pleura in front and behind, and with the diaphragmatic pleura below.

THE STERNAL COSTAL (PLEURAL)

REFLECTION

PLEURAL REFLECTION

• The anterior shows a difference on the two sides.

• Right side it is indicated by a line from the sterno-clavicular joint to the centre of the sternal angle.

• Passes downwards a little to the left of the middle line as far as the base of the xiphoid process.

• Left side it corresponds to the right line of reflection as far as the level of the fourth coastal cartilage.

• At this point the line suddenly deviates to the left, and then turns downwards along the side of the sternum to reach the level of the seventh rib.

PLEURAL REFLECTION

• The inferior reflection curves downwards and laterally.

• It crosses the eighth rib in the midclavicular line, the tenth interspace in the midaxillary line, and the eleventh space in the scapular line (the last line being drawn vertically through the inferior angle of the scapula).

• The inferior reflection ends half an inch below the twelfth rib.

PLEURAL REFLECTION

• The posterior reflection lies just lateral to the vertebral spines, and extends as high as the seventh cervical spine.

• The cervical pleura may be indicated by a curved line convex upwards, from the sterno-clavicular joint to the junction of the middle and medial thirds of the clavicle, its highest point being one inch above the clavicle.

PLEURAL RECESSES

• Right costodiaphragmatic recess

• Left costodiaphragmatic recess

• (Left) costomediastinal recess.

PLEURAL RECESSES

MEDIASTINUM

• It is occupied by the mass of tissue between the two pulmonary cavities.

• The central structure within the mediastinum is the heart. It is covered on each side by mediastinal pleura and contains all the thoracic viscera and structures except the lungs.

• It extends from the superior thoracic aperture to the diaphragm inferiorly, and from the sternum and costal cartilages anteriorly to the bodies of the thoracic vertebrae posteriorly.

MEDIASTINUM

MEDIASTINUM

• It is divided into:

• Superior

• Anterior

• Posterior

• Middle – area within the pericardium.

SUPERIOR MEDIASTINUM • Region above the critical plane joining the sternal angle to

the intervertebral disc between the 4th and 5th thoracic vertebrae.

CONTENTS

• The aortic arch and the 3 great vessels that arise from it

• Brachiocephalic (innominate) veins, the upper part of the superior vena cava, and the arch of the azygos vein

• The trachea and esophagus

• The vagus, phrenic, left recurrent laryngeal, and cardiac nerves

• The thoracic and the right lymphatic ducts

• The remains of the thymus gland and certain lymph glands.

ANTERIOR MEDIASTINUM

• It’s an area where the sternal reflexion of the left pleural fails to meet the right pleura.

• It’s an insignificant area in front of the pericardium.

POSTERIOR MEDIASTINUM

• It lies behind the pericardium. It extends downward between the diaphragm to Th 12.

CONTENTS :

• The descending thoracic aorta and its branches

• The esophagus

• The azygos and hemiazygos veins

• The thoracic duct and lymph glands

• The vagi nerves

• The splanchnic nerves

MIDDLE MEDIASTINUM

• It contains the heart and the roots of 8 great vessels.

• Lateral to the pericardium on each side runs the Phrenic Nerves and their companion vessels.

RIGHT MEDIASTINUM ASPECT • The following are displayed: • Pericardiac sac. • The 2 sites devoid of content: where the right and left layers of

mediastinal pleura come into apposition. Between the sternum and pericardium : Level of 2nd to the 4th costal cartilages.Between the lower part of esophagus and the aorta. Here the 2 layers form a dorsal mesophagus.

• Great Veins: – Inferior vena cava – Superior vena cava – Right brachiocephalic (innominate) vein – Right jugular vein – Right subclavian vein

• Esophagus, trachea, and right vagus nerve • Root of lung and pulmonary ligament: bronchus, pulmonary artery,

pulmonary veins, Nerve plexus (ant. & post. pulmonary), bronchial vessels, lymph vessels.

• Arch of the azygos vein.

RIGHT PHRENIC NERVE

• Enters the thorax behind the junction of subclavian and Internal Jugular Vein.

• Descends subpleurally in the line of the great veins: brachiocephalic V; SV Cava, pericardium, IV Cava.

• It then pierces the diaphragm and spread out on its abdominal surface.

• It is accompanied by the pericardiacophrenic artery, a branch of the Int. thoracic artery.

LEFT MEDIASTINUM ASPECT

• The structures covered with left mediastinal pleura are:

• Pericardial sac • Root of left lung and pulmonary ligarment • Aortic arch and descending aorta • Esophagus, trachea, left recurrent nerve, and thoracic

duct • Left common carotid and left subclavian arteries • Left phrenic and vagus nerve and left superior

intercostal vein

THE AORTIC ARCH • It is the portion of the aorta lying in the superior

mediastinum.

• It begins at the level of the sternal angle where the ascending aorta leaves the pericardium.

• It arches backward and to the left above the root of the left lung, rising half the height of the manubrium sterni and reaching the vertebral column at the 5th thoracic vertebra.

• Continued as the descending aorta, it traverses the posterior mediastinum in contact with the bodies of the lower 8 vertebrae.

• Finally, at the disc between the last thoracic and the first lumbar vertebra, it passes behind the median arcuate ligament of the diaphragm to become the abdominal aorta.

ESOPHAGUS & TRACHEA

• In the angle between them runs the left recurrent laryngeal nerve.

• On the side of the esophagus, the thin-walled thoracic duct ascends embedded in a film of fat.

• The aortic arch crosses these 4 structures as a unit.

THORACIC CROSS SECTION

LEFT COMMON CAROTID AND LEFT SUBCLAVIAN ARTERIES

• The Left Common Carotid and Left Subclavian Arteries arise from the convexity of the aortic arch where it crosses the trachea, and pass obliquely upward and backward in semispiral fashion round “unit of 4”, crossing in turn the trachea, recurrent nerve, esophagus, and thoracic duct.

LEFT PHRENIC NERVE

• It enters the thorax between the subclavian artery and vein (at the beginning of the brachiocephalic) and runs a subpleural course, being covered throughout with mediastinal pleura.

• After crossing the subclavian artery, it at once crosses the internal thoracic artery and from it acquires a companion, the pericardiacophrenic artery. In its course it runs just in front of the root of the lung.

LEFT VAGUS NERVE

• The Left Vagus Nerve, after traversing the neck within the carotid sheath on the lateral side of the common carotid artery.

• It continues through the superior mediastinum on the lateral side of the same artery, and, therefore, between it and the subclavian artery.

• These 2 arteries conduct it to the aortic arch, which it crosses to gain the back of the root of the lung.

• Thereafter, it passes to the esophagus and behaves like the right vagus.

LEFT RECURRENT LARYNGEAL NERVE

• The Left Recurrent Laryngeal Nerve springs from the vagus where the latter crosses the left side of the aortic arch.

• It then passes below the arch and up on its right side to gain the angle between the trachea and the esophagus.

THE SYMPATHETIC TRUNK

• At the superior aperture of the thorax, the trunk lies on the neck of the 1st rib.

• In the thorax, it crosses the head of the 2nd to 9th ribs, the 10th costovertebral joint, and the bodies of the 11th and 12th vertebrae.

• It continues into the abdomen along the anterior border of the psoas muscle.

• The intercoastal arteries and veins cross the trunk posteriorly.

THE SPLANCHNIC NERVES

• They are preganalionic fibers coming from white rami communicantes and making “nonstop journeys” through symphathetic ganglia.

• They end in the celiac and renal ganglia, where they relay as unmyelinated postganglionic fibers.

THE SPLANCHNIC NERVES

• There are 3 (paired) splanchnic nerves in the thorax – greater, lesser, and lowest.

THE SPLANCHNIC NERVES

• The greater splanchnic nerve, larger than the sympathetic trunk itself, springs from the (4th), (5th), (6th), (7th), 8th, 9th, and 10th ganglia, runs caudally just lateral to the azygos (or hemiazygos) vein, pierces the crus of the diaphragm, and ends in the celiac ganglion.

• The lesser splanchnic nerve springs from the (9th), 10th, 11th, and (12th) ganglia, runs caudally – lateral to the greater nerve – pierces the crus, and ends in the lower part of the celiac ganglion (specifically, the aorticorenal ganglion).

• The lowest splanchnic nerve, when present, springs from either the 11th or 12th ganglion or from both ganglia, takes a similar course, and ends in the renal plexus.

Text & Image Sources: Acknowledgement

• Drake, Vagi & Mitchell. 2015. Gray’s Anatomy for Students 3rd Ed; Churchill Livingstone Elsevier Inc. Philadelphia

• Agur & Dalley II. 2013. Grant’s Atlas of Anatomy, 13th Ed; Lippincott Williams & Wilkins. Philadelphia.

• Sinnatamby C.S. 2011. Last’s Anatomy Regional & Applied Anatomy, 12th Ed; Churchill Livingstone Elsevier Inc. Philadelphia

• Moore, Dally II & Agur. 2014. Lippincott Williams & Wilkins. Philadelphia.

• Chung & Chung. 2012. BRS Gross Anatomy, 7th Ed; Lippincott Williams & Wilkins. Philadelphia.

• Basmajian J.V. Grant’s Method of Anatomy. Williams & Wilkins

THANKS FOR KEEPING YOUR PLEURAL & MEDIASTINUM

INTACT FOR SURVIVAL.