The Mediastinum

Question 1

Relations of the mediastinum

Answer 1

Surrounded by T1-12, sternum, costal margin, thoracic inlet, outlet, lungs

Mainly contains the heart

Question 2

What are the parts of the mediastinum and how are they separated?

Answer 2

Superior
Inferior

Inferior made up of anterior, middle and posterior

Superior and inferior separated by sternal angle at T4/5

Question 3

Describe the structure of the great veins at the superior mediastinum

Answer 3

L int jugular (from head and neck), L subclavian => L brachiocephalic => SVC => RA in inf mediastinum

R int jugular, R subclavian => R brachiocephalic => SVC => RA in inf mediastinum

Azygos joins SVC at sternal angle

Question 4

Describe the relative positions of the SVC to the sternum

Describe the relative lengths of the R brachiocephalic to the L

How does the pulmonary trunk relate to the sternal angle

Answer 4

R brachiocephalic and SVC on R of sternum

R brachiocephalic, more vertical and shorter than L

Stops at sternal angle to split into the pulmonary arteries

Question 5

Describe the structure of the great arteries at the superior mediastinum

Answer 5

Aortic arch at the level of the sternal angle
Aorta comes ant => sup => post => inf

R brachiocephalic => R subclavian and R common carotid

L common carotid (directly from the arch
L subclavian (directly from the arch)

Question 6

Describe the relative position of the aorta to the sternum

Describe the relative position of the arteries here to the veins

Answer 6

Arteries and the aorta is generally on the L

Arteries are behind the veins

Question 7

Describe the location of the thymus gland

Describe the composition of the thymus gland

Describe the arterial supply of the thymus
Describe the venous drainage supply of the thymus

Answer 7

Small asymmetrical bilobed gland
1% glandular tissue, 99% fat, infiltrated during puberty

Found in front of the SVC and behind the sternal angle

Arteries from internal thoracic
Drains via int thoracic vein, brachiocephalic vein

Question 8

Describe the thymus in adults and in children

Answer 8

In children, v large, covers large proportion of lungs, helps give rise to T cell population

Regress in puberty and role taken up by other glands

Question 9

Describe the contents of the anterior mediastinum in the inferior mediastinum

Answer 9

Space infront of the heart below the sternal angle
Sternal ligament found between pericardium and sternum
Int thoracic artery also found here

Question 10

Describe the relations of the oesophagus to the aorta, trachea and bronchi and pulmonary arteries

Answer 10

Oesophagus starts as the most posterior tube
Crossed by aortic arch, oesophagus comes post => ant
Compressed by L bronchus
Posterior to LA
Passes through the diaphragmatic hiatus in L hemidiaphragm w vagus

Question 11

Describe how the position of the aorta changes in the posterior mediastinum

Answer 11

Aortic arch T4/5

Goes from R=> L => central as it comes up, over and behind

Question 12

Describe the pathway of the L vagus

Answer 12

Comes between int jugular and common carotid , behind left lung root

Becomes the ant vagal trunk due to rotation of stomach

Question 13

Describe the pathway of the R vagus

Answer 13

Parallel to trachea, post to SVC and R bronchus

Becomes the post vagal trunk due to rotation of stomach

Question 14

Describe the route of the vagus around the oesophagus and the aorta

Answer 14

Esophageal plexus formed from R and L vagus
Both pass through diaphragm with oesophagus

L vagus => ant vagal trunk
R vagus => post vagal trunk

Both lead to the stomach

Question 15

Describe the pathway of the recurrent laryngeal nerves

What does it innervate?

Answer 15

L vagus => L recurrent laryngeal, passes infront, under, behind aortic arch

R vagus => R recurrent laryngeal, passes infront, under, behind subclavian artery

Innervate muscles in larynx minus cricothyroid

Sensory for mucosa below vocal folds

Question 16

Where is the oesophagus constricted

Answer 16

Cricoid cartilage (C6)
-Narrowest part of the oesophagus

Skeletal muscle oesophagus, innervated by somatic vagus

Aortic arch (T4)
-Where it arches around

L main bronchus (T5)

L atrium (T6-10)

Esophageal opening (T10)
-Passes through muscular part of diaphragm, can act as a sphincter

Oesophagus ultimately deviates => L => stomach

Question 17

What could dysphagia be due to?

Answer 17

May be due to compression from cancer, aneurysm

Question 18

Describe the venous and lymphatic drainage in the posterior mediastinum

Answer 18

Azygos on the R
Accessory hemiazygos and hemiazygos (T7)

Cisterna chyli => thoracic duct runs next to R of aorta => crosses over to the L at T4 =>arches at T2-3 to join L subclavian from behind the artery and vein

SVC on the R of the L thoracic duct

R lymphatic duct drains the upper right quadrant of the body

Question 19

Describe the arteries supply in the posterior mediastinum

Answer 19

Aortic arch wrapped around the L bronchus

Bronchial arteries supply the bronchi and areas without gas exchange

Posterior intercostal arteries, esophageal branches and mediastinal branches come off aorta

Aorta on the L of the oesophagus but goes more posterior as it descends

Question 20

Describe the branches of nerves that come off the inferior vagal ganglion and what they innervate

Answer 20

Sup laryngeal => ext and int laryngeal

Ext laryngeal, cricothyroid muscle and sensory
Int laryngeal, sensory innervation above vocal folds

Recurrent laryngeal, sensory innervation below vocal folds, efferents for all int muscles except cricothyroid

Cervical cardiac branches off vagus, heart

Vagus innervates oesophagus via heart and lungs

Question 21

Where is the vagus found entering the superior thoracic aperture

Where does it enter the lungs?

Answer 21

Between common carotid and int jugulars

Post to lung root and enters lung root

Question 22

Describe the innervations of the phrenic and its branches

How does it relate to the lung root

Answer 22

C3-5
Gives off the pericardiac branches

Passes between the subclavians

Supplies diaphragmatic and mediastinal pleura

Ant to lung root but doesnt supply them

R phrenic passes down caval opening
L phrenic passes diaphragm on its own

Question 23

Describe the location of the sympathetic chain

Answer 23

Found outside the pericardium, either side of the vertebral column behind medial arcuate ligament

Question 24

Describe the autonomic supply to the lungs

Answer 24

Sympathetics

• Mainly T2-4, sometimes T1-5
• Afferent pain across sternum and inner arm
• T3-4 => pulmonary plexus

Parasympathetic

• Vagus, afferent to visceral stretch of pleura
• Bronchoconstriction, bonchosecretion

Question 25

What are the 3 plexuses in the chest

Answer 25

Pulmonary
Cardiac
Oesophageal

Question 26

Describe the sympathetic and parasympathetic innervation of the pulmonary plexus

Answer 26

Sympathetic from T1-5
Parasympathetics from vagus

innervate bronchial tree and visceral pleura
Ant, infront
Post, behind

Question 27

Describe the sympathetic and parasympathetic innervation of the cardiac plexus

Answer 27

Sympathetics from T1-4 (pain afferents, +ve chronotropes, inotropes)
-descending tract onto T1-4 => enter symapthetic chain, some fibres extend into the sup/mid/inf cervical ganglion => onto heart as sympathetic cardiac nerves

Parasympathetics from vagus

Question 28

Describe the sympathetic and parasympathetic innervation of the esophageal plexus

Answer 28

Sympathetics from T2-6 (pain afferents, controls vascular tone)
Parasympathetic from vagus (motor supply of the skeletal and smooth muscle)