Unit Ii Anatomy Lecture 9

Front 1

Describe the mediastinum

Back 1

Midline region between the lungs and the adjacent pleural cavities that houses a mass of tissue (except lungs) covered by mediostinal pleura
Forms a mobile midline septum that is loosely bound together by connective tissue
Extends from superior thoracic aperature to diaphragm, posterior to sternum and costal cartilages, and anterior to vertebral bodies of thoracic vertebrae

Front 2

Describe the divisions of the mediastinum

Back 2

Artificially divided into superior and inferior portions by an imaginary horizontal plane (transverse thoracic plane) through the sternal angle and the intervertebral disc of T4-T5
Highly mobile region
Generally houses mainly liquid or air-filled structures joined by loose connective tissue and lymphoid tissues, vessels, nerves, and fat
Has reduction of mobility with an increase in age because the CT becomes more fibrous

Front 3

Describe the superior division of the mediastinum

Back 3

Runs from superior thoracic aperature to horizontal plane
Contents include viscera, nerves, vessels, and lymphoid tissue

Front 4

Describe the viscera of the superior division of the mediastinum

Back 4

Include (from anterior to posterior) the thymus (main lyphoid organ) which occurs in lower neck and anterior part of mediastinum (replaced with fat as we age)

Front 5

Describe the thymus

Back 5

Consists of two loosely joined, assymetrical lobes
On each aspect are diverging borders of lungs and pleura that constitute the costomediastinal recess (where costal pleura reflects on diaphragm)
This recess is a fold of pleura that occupies superior part of the angle between the thoracic wall and the diaphragm
At birth, its superior extent reaches as high as the thyroid gland and is at its largest and most extensive size which is maintained until puberty
After puberty, it begins to gradually diminish in size
In adult, thymus is elongated, encapsulated, fatty, lymhpoid mass, lying in the loose tissue posterior to manubrium

Front 6

Describe the vessels of the thymus

Back 6

Posterior are two important vessels- brachiocephalic vein and aortic arch
May contain some inferior parathyroid tissue because thymus and inferior parathyroid both derived from tissue of third pharyngeal pouch of embryo
Inferior margin of thymus may extend through the superior mediastinum into the anterior mediastinum of inferior division and over superior part of pericardium
This area has rich supply of arterial blood including anterior intercostal arteries, anterior mediastinal arteries (via internal thoracic artery)
Its veins empty into the right and left brachiocephalic, internal thoracic, and inferior thyroid veins

Front 7

Describe the vessels of the mediastinum

Back 7

Include the great vessels (ascending aorta, pulmonary trunk, and superior vena cava)
Great veins (brachiocephalic) are formed by the union of the IJV and the subclavian vein, they join to form the SVC at the inferior border of the first right costal cartilage

Front 8

What are the two great veins and two great vessels of the mediastinum?

Back 8

Veins: left and right brachiocephalic veins
Vessels: superior vena cava and arch of aorta

Front 9

Describe the left brachiocephalic vein

Back 9

Lies posterior to sternoclavicular joint and descends obliquely posterior to superior half of manubrium to unite with right brachiocephalic vein
Halfway down right margin of manubrium, this union forms superior vena cava
Left brachiocephalic vein passes anterior and superior to three great branches of aortic arch
In children, it may extend above the superior border of manubrium and pose a surgical danger in neck operations
Two times longer then right
Shunts blood from left upper limb, neck, and head to right atrium
Thoracic duct joins at it left venous angle

Front 10

Describe the right brachiocephalic vein

Back 10

Lies posterior to right sternoclavicular joint and descends vertically to join left brachiocephalic vein to form the superior vena cava at level of first right intercostal space
In close association to phrenic and vagus nerves as they descend in superior mediastinum
Both nerves on right and left sides descend posterior to their respective brachiocephalic vein
Phrenic nerves will descend anterior to root of lungs and vagi will course posterior to root of lungs and exit thorax via diaphragm
Received lymph from right lymphatic duct at right venous angle

Front 11

Describe the superior vena cava

Back 11

Returns blood from all structures that are superior to diaphragm (except lungs and heart)
Descends to third right costal cartilage where it enters superior aspect of right atrium
Receives on its posterior surface the arch of the azygous system, which is draining posterior wall of thorax, and in part, abdominal wall
Occurs in right side of superior mediastinum
Phrenic nerve runs between it and mediastinal pleura
Accompanying it in its descent on posterior aspect of sternum is right phrenic nerve

Front 12

Describe the arch of the aorta

Back 12

Bowed continuation of ascending aorta, which begins posterior to second right sternocostal joint adjacent the sternal angle
Arch descends on the left side of the vertebral body of T4 and continues as thoracic aorta below the second left sternocostal joint

Front 13

`Describe the vagus nerve of the mediastinum

Back 13

Vagus (CN X) arises from medulla, exits the skull, descends the neck posterolateral to CCA, and enters superior mediastinum posterior to respective sternoclavicular joint and brachiocephalic vein

Front 14

Describe the phrenic nerve of the mediastinum

Back 14

Phrenics (C3-C5) supply the diaphragm of which 1/3 the fibers are sensory and each nerve enters the mediastinum between the origin of the brachicephalic vein and the subclavian artery
They pass anterior to roots of each lung (vagus passes posteriorly) and are the primary source of sensory fibers
Pain sensations conveyed by phrenic nerves are commonly referred to the skin of the ipsilateral supraclavicular region

Front 15

Describe the right vagus nerve of the mediastinum

Back 15

Enters thorax anterior to right subclavian artery where it gives rise to right recurrent laryngeal nerve
Right recurrent laryngeal loops around right subclavian artery and ascends between esophagus and trachea
Recurrent laryngeal supplies larynx (via inferior laryngeal branch), while right vagus supplies branches to many plexuses (e.g., pulmonary, esophageal, and cardiac) and superior laryngeal nerve and its branches (external and internal laryngeal)

Front 16

Describe the left vagus of the mediastinum

Back 16

Descends neck posterior to left common carotid artery and enters mediatinum between left common carotid artery and left subclavian artery
At left side of aortic arch, it diverges posteriorly from phrenic nerve and gives off left recurrent laryngeal nerve inferior to aortic arch
Left recurrent laryngeal nerve ascends in a groove between esophagus and trachea
Has superior laryngeal nerve as well

Front 17

Describe the vagus nerve plexuses

Back 17

Both form several plexuses including esophageal, cervical, thoracic, and cardiac plexuses
The last plexus is by cardian branches
Note right recurrent laryngeal does not enter mediastinum because it arises from right vagus in root of neck

Front 18

Describe the ansa cervicalis

Back 18

Includes branches from middle cervical ganglion (at level of transverse process of C6), which is connected to cervicothoracic ganglion by fibers both anterior and posterior to subclavian artery
Fibers on anterior aspect constitute ansa subclavia
A vertebral ganglion may lie anterior or anteromedial to vertebral artery at its origin
When this ganglion is present, it may receive ansa subclavia as well

Front 19

Describe the right phrenic nerve

Back 19

Runs along lateral aspect of right brachiocephalic vein, SVC, and pericardium over right atrium
Descends on lateral side of the IVC to diaphragm

Front 20

Describe the left phrenic nerve

Back 20

Descends betwee left subclavian artery and left CCA
It crosses left surface of aortic arch anterior to left vagus nerve and runs along pericardium, superficial to left atrium and ventricle

Front 21

What are some additional structures of the superior mediastinum?

Back 21

1) Trachea- ends at level of sternal angle and bifurcates
2) Esophagus- enters mediastinum between vertebrae and trachea
3) Thoracic duct- lies on left side of esophagus

Front 22

Describe the inferior division of the mediastinum

Back 22

Subdivided by pericardium into three regions which includes space between horizontal plane of sternal angle to thoracic aspect of diaphragm

Front 23

What are the three subdivisions of the inferior mediastinum?

Back 23

1) Anterior region
2) Middle region
3) Posterior region

Front 24

Describe the anterior region of the inferior mediastinum

Back 24

Smallest, narrow part of inferior mediastinum, which lies between the body of the sternum and the transverse thoracic muscles anteriorly and pericardium posteriorly
Consists of loose connective tissues (sternopericardial ligaments) and contains lymph nodes, costomediastinal recess, and is an area that may be involved in metastatic spread of tumors or a site of lymphoma

Front 25

Describe the middle region of the inferior mediastinum

Back 25

Largely filled by heart and roots of great vessels (ascending aorta, pulmonary trunk, SVC)
Medialmost part and contains pericardium, arteries, nerves, and nerve plexuses

Front 26

Describe the pericardium

Back 26

Serous membrane that has an outer fibrous layer that is attached at three points:
1) To diaphragm by central tendon and pericardiacophrenic ligament
2) To sternum by sternopericardial ligament
3) To structures of the posterior mediastinum by loose connective tissue
Composed of two parts: fibrous and serous pericardia

Front 27

Describe the fibrous pericardium

Back 27

Double-walled fibroserous sac that encloses the heart and roots of great vessels
Blends with connective tissue or tunica adventitia or great vessels, otherwise heart is free to move inside it

Front 28

Describe the serous pericardium

Back 28

Separates wall of heart from fibrous pericardium and is reflected onto heart at roots of great vessels as visceral layer (visceral pericardium)
Epithelium lines the internal surface of fibrous sac and external surface of heart
Bilayered with an outer parietal layer that lines inner surface of fibrous pericardium, while inner visceral layer covers heart
Carried up as a separate sleeve over SVC, aorta, and pulmonary trunk
Forms, in part, transverse pericardial sinus
Removal of heart and visceral pericardium displays the sleeve of the pericardium which encloses several structures (SVC, openings of IVC, and pulmonary veins) and the oblique pericardial sinus which is an irregular outline of the sleeve surrounding part of the pericardial cavity

Front 29

Describe the arterial portion of the middle region of the mediastinum

Back 29

Supplies pericardium and usually arises form percardiacophrenic arteries (branches of interal thoracic artery) which often accompanies or parallels the phrenic nerve to the diaphragm
Smaller arterial contributions arise via the musculophrenic artery (terminal branch of internal thoracic), bronchial, esophageal, and superior phrenic arteries (via thoracic aorta), and coronary arteries that serve the visceral layer of serous pericardium only
Venous drainage includes pericardiacophrenic veins (tributaries of brachiocephalic or internal thoracic veins) and variable tributaries of azygous system

Front 30

Describe the nerves of the middle region of the mediastinum

Back 30

Supplying pericardium are phrenic (sensory), vagus (unknown), and sympathetic trunk (vasomotor)

Front 31

Describe the cardiac nerves of the middle region of the mediastinum

Back 31

Occur on each side
Sympathetic fibers originate in a large part as cardiac nerves via cervical ganglia in neck
Some vagal branches may arise in neck, but most arise in inlet of thorax and near root of lung
Heart develops from cardiogenic cells posterior to mesoderm, destined, in part, to become diaphragmatic musculature (septum transversum)
Innervation of mesodermal derivatives of heart and diaphragm is from nerves in cervical region

Front 32

Describe the cardiac plexus of the middle region of the mediastinum

Back 32

Plexus of sympathetic and vagal fibers situated anterior to bifurcation of trachea, inferior to bifurcation of pulmonary trunk, and below arch of aorta
Subdivisions are artificial and should be disregarded, but extensions of it are right and left pulmonary plexus and plexus of thoracic aorta
Right and left pulmonary plexus are formed by cervical, cervicothoracic, and thoracic cardiac branches of both sides
At hilus of each lung, pulmonary plexus receive (both anteriorly and posteriorly) branches of vagus nerve and sympathetic trunk

Front 33

Describe the posterior region of the mediastinum

Back 33

Occurs anterior to T5-T12 and posterior to pericardium and diaphragm and between the parietal pleura of lungs
Contains aorta
Thoracic plexus surrounds descending aorta, which lies superior to root of left lung, pericardium, and esophagus
Thoracic aorta terminates at T12 within aortic hiatus
Thoracic duct and azygous ascend on right side of thoracic aorta

Front 34

What are the thoracic arteries of the posterior region of the mediastinum?

Back 34

Bronchial, pericardial, posterior intercostal, superior phrenic, esophageal, and mediastinal branches

Front 35

Describe the right bronchial artery

Back 35

Single vessel that may arise from superior posterior intercostal artery, thoracic aorta (via first aortic intercostal= 3rd posterior intercostal) or left superior bronchial artery

Front 36

Describe the left bronchial artery

Back 36

One or two branches
One branch may arise via arch of aorta, while second originates at subclavian
Supply trachea, bronchi, lung tissue, and lymph nodes

Front 37

Describe the pericardial arteries

Back 37

Send twigs to pericardium

Front 38

Describe the posterior intercostal arteries

Back 38

Pass through intercostal spaces 3-9

Front 39

Describe the superior phrenic artery

Back 39

Passes posterior surface of diaphragm and forms anastomosis with musculophrenic and pericardiophrenic (branches of internal thoracic artery) arteries

Front 40

Describe the esophageal arteries

Back 40

Usually include two branches that supply middle third of esophagus

Front 41

Describe the mediastinal arteries

Back 41

Small supply lymph nodes and other tissues (thymus) of posterior mediastinum

Front 42

Describe the esophagus

Back 42

Runs from superior to inferior mediastinum (via posterior division) and passes through esophageal hiatus at about level of T10 anterior to aorta
When full, three constrictions reveal several structures (aortic arch, left main bronchus, and diaphragm)

Front 43

Describe the lymph nodes and posterior mediastinum

Back 43

Occur posterior to pericardium and are related to esophagus and thoracic aorta
Several nodes occur posterior to inferior part of esophagus
Receives lymph from esophagus, posterior aspect of pericardium and diaphragm, and middle posterior intercostal space

Front 44

Describe the thoracic duct

Back 44

Largest lymphatic channel in body and conveys ost of the lymph of body to venous system at venous angle
May arise at chyle cistern in abdominal cavity and ascend through aortic hiatus to enter thoracic cavity
Thin walled, white, often beaded because of the presence of valves
In thorax, occurs between aorta on left and azygous on right

Front 45

Describe the nerves of the posterior region of the mediastinum

Back 45

Include thoracic part of sympathetic trunk and associated ganglia from major portions of autonomic nervous systems
Thoracic sympathetic trunks are continuous with cervical and lumbar trunks
Lower thoracic splanchnic nerves are part of abdominopelvic splanchnic nerves because they supply viscera below the diaphragm
Greater splanchnic- T5 or T6-T9 or T10
Lesser splanchnic- T10 or T11
Least splanchnic- T11 or T12

Front 46

Describe use of a medistinoscope

Back 46

Surgeons can see much of mediastinum and conduct minor surgeris using one
They insert this tubular, lighted instrument through a small incision at root of neck, superior to manubrium near jugular notch
During mediastinoscopy, surgeons can view or biopsy mediastinal lymph nodes to determine if cancer cells have metastasized to them from a bronchogenic carcinoma

Front 47

Describe widening of the mediastinum

Back 47

Often viewed by radiologist and emergency physicians on chest radiographs
Any structure may contribute to pathological widening
Often observed after trauma resulting from head on collision, which produces hemorrhage into mediastinum from lacerated great vessels
Malignant lymphoma (cancer of lymphatic tissue) produces massive enlargement of mediastinal nodes and widening of mediastinum
Enlargement of heart is common cause

Front 48

Describe aortic aneurysm

Back 48

Effects on vertebral bodes T5-T8 may be observed due to association of thoracic aorta in this region
Vertebrae often flattended on left sides
Bodies of T5-T8 may be partially eroded by pressure from aneurysm