Part 7: Posterior Mediastinum

Question 1

What are the boundaries of the posterior mediastinum

Answer 1

Space posterior to pericardium and diaphragm, continuous with the superior mediastinum and the space between pre-tracheal and pre-vertebral facia. Bound posteriorly by T4-12, anteriorly by pericardium and diaphragm

Question 2

Where does the descending thoracic aorta commence?

What are the branches of descending thoracic aorta?

Answer 2

T4, just to left of midline
9 posterior intercostals
subcostal
bronchial 
small oesophageal

Question 3

Where does oesophagus commence?

Answer 3

From cricoid cartilage at C6 in midline

Question 4

What are levels of diaphragmatic openings for aorta, oesophagus, and IVC?

Answer 4

T8 - IVC
T10 - Oesophagus
T12 - Aorta

Question 5

What structures cross the oesophagus?

Answer 5

Arch of aorta
Aygous vein on right
Left main bronchus
Right pulmonary artery
Thoracic duct inclines from R-L posteriorly

Question 6

What are the constrictions of the oesophagus?

Answer 6

Narrowest part at cricopharyngeal sphincter (15cm from incisors)
Constriction where crossed by aortic arch (22cm from incisors), Left main bronchus (27cm) and on passing through diaphragm (38cm)

Question 7

What is the blood supply to the oesophagus?

Answer 7

Upper 1/3 - Inferior thyroid
Middle 1/3 - oesophageal branches of aorta
Lower 1/3 - L gastric artery

Question 8

What is the venous drainage of oesophagus?

Answer 8

upper 1/3 - inferior thyroid veins
middle 1/3 - azygous
lower 1/3 - L gastric vein (empty’s to portal vein thus anastomosis between portal and systemic systems, anastomosis at T8)

Question 9

What is the lymph drainage of the oesophagus?

Answer 9

Follows arteries to deep cervical, tracheobronchial group and pre-aortic nodes

Question 10

What is the nerve supply to oesophagus?

Answer 10

Upper - Recurrent laryngeal nerve and sympathetic fibres from cervical ganglion
Lower - greater splanchnic nerves
Parasympathetic supply is from vagus nerves

Question 11

What is the structure of oesophageal muscle?

Answer 11

Inner circular and outer longitudinal layer of muscle. Upper 1/3 is skeletal muscle and lower 2/3 is visceral (this allows for rapid passing of bolus into oesophagus.
inner layer is directly continuous with cricopharyngeus muscle.
Lower 5cm acts as physiological sphincter but has no anatomical thickening

Question 12

What is the structure of oesophageal mucosa?

Answer 12

Thick mucous membrane which in collapsed state thrown into longitudinal folds. Stratified squamous epithelium, sparse mucous glands in sub mucosa

Question 13

Describe the major groups of lymph nodes in the thorax

Answer 13

Pre-aortic nodes - in front of aorta, drain mid oesophagus
Para-aortic - alongside aorta, drain intercostal spaces
Parasternal - alongside internal thoracic artery, drains anterior IC spaces
Anterior, middle and posterior diaphragmatic groups drain associated spaces

Question 14

Where does the thoracic duct commence and what is its path?

Answer 14

Cisterna chyli (T12). Passes upwards to R of aorta, inclines L behind oesophagus to reach L mediastinum. Lies anterior to aortic IC branches. Enters point of confluence of L IJV and SCV entering as 2-3 valveless branches

Question 15

Thoracic duct receives lymph from where?

Answer 15

Lower 1/2 body
L posterior IC nodes
L jugular and subclavian nodes (ie L head and neck)
Thus drains all lymph apart from R thorax, R arm and R head and neck

Question 16

What drains into R lymphatic duct and where does it enter venous system?

Answer 16

R arm
R head and neck
R thorax
Enters into venous system at R BCV or as seperate branches into jugular and subclavian veins

Question 17

Describe the overall layout of azygous and hemiazygous veins?

Answer 17

Posterior intercostal and lumbar veins drain posterior wall into azygous veins which form longitudinal trunks.
R - single vein: azygous vein
L - divided veins: hemiazygous veins

Question 18

What embryologic veins do the azygous veins represent?

Answer 18

Posterior cardinal veins

Question 19

Describe the course of the azygous vein

Answer 19

Functionally commences with union of subcostal and ascending lumbar veins.
Goes through aortic opening, post to oesophagus. Arches over R main bronchus.. Enters SVC at T4.

Question 20

Where does azygous vein receive from?

Answer 20

Lower 8 posterior IC veins

R superior intercostal, R bronchial veins, veins middle of oesophagus

Question 21

Describe the hemiazygous and accessory vein?

Answer 21

Hemiazygous - lower half
Accessory - upper half
Sometime join with each other but usually enter azygous vein separately

Question 22

Where do hemiazygous veins receive from?

Answer 22

Lower (Hemiazygous) - lower 4 posterior IC veins

Upper (accessory) - middle 4 PIC, L bronchial, veins from middle oesophagus

Question 23

The thoracic sympathetic trunk consists of how many ganglia?

Answer 23

12, but typically fewer

Question 24

Where do the ganglia receive from?

Answer 24

white ramus from corresponding spinal nerve, and a postganglionic grey ramus given to each thoracic nerve

Question 25

Where do the splanchnic nerves arise?

Answer 25

Lower 8 ganglion of thoracic sympathetic trunk

Question 26

Where does the thoracic sympathetic trunk lie?

Answer 26

Necks of ribs just lateral to heads and anterior to IC vessels and nerves