Part 7: Posterior Mediastinum Flashcards
What are the boundaries of the posterior mediastinum
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
Where does the descending thoracic aorta commence?
What are the branches of descending thoracic aorta?
T4, just to left of midline 9 posterior intercostals subcostal bronchial small oesophageal
Where does oesophagus commence?
From cricoid cartilage at C6 in midline
What are levels of diaphragmatic openings for aorta, oesophagus, and IVC?
T8 - IVC
T10 - Oesophagus
T12 - Aorta
What structures cross the oesophagus?
Arch of aorta Aygous vein on right Left main bronchus Right pulmonary artery Thoracic duct inclines from R-L posteriorly
What are the constrictions of the oesophagus?
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)
What is the blood supply to the oesophagus?
Upper 1/3 - Inferior thyroid
Middle 1/3 - oesophageal branches of aorta
Lower 1/3 - L gastric artery
What is the venous drainage of oesophagus?
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)
What is the lymph drainage of the oesophagus?
Follows arteries to deep cervical, tracheobronchial group and pre-aortic nodes
What is the nerve supply to oesophagus?
Upper - Recurrent laryngeal nerve and sympathetic fibres from cervical ganglion
Lower - greater splanchnic nerves
Parasympathetic supply is from vagus nerves
What is the structure of oesophageal muscle?
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
What is the structure of oesophageal mucosa?
Thick mucous membrane which in collapsed state thrown into longitudinal folds. Stratified squamous epithelium, sparse mucous glands in sub mucosa
Describe the major groups of lymph nodes in the thorax
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
Where does the thoracic duct commence and what is its path?
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
Thoracic duct receives lymph from where?
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
What drains into R lymphatic duct and where does it enter venous system?
R arm
R head and neck
R thorax
Enters into venous system at R BCV or as seperate branches into jugular and subclavian veins
Describe the overall layout of azygous and hemiazygous veins?
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
What embryologic veins do the azygous veins represent?
Posterior cardinal veins
Describe the course of the azygous vein
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.
Where does azygous vein receive from?
Lower 8 posterior IC veins
R superior intercostal, R bronchial veins, veins middle of oesophagus
Describe the hemiazygous and accessory vein?
Hemiazygous - lower half
Accessory - upper half
Sometime join with each other but usually enter azygous vein separately
Where do hemiazygous veins receive from?
Lower (Hemiazygous) - lower 4 posterior IC veins
Upper (accessory) - middle 4 PIC, L bronchial, veins from middle oesophagus
The thoracic sympathetic trunk consists of how many ganglia?
12, but typically fewer
Where do the ganglia receive from?
white ramus from corresponding spinal nerve, and a postganglionic grey ramus given to each thoracic nerve
