Thorax 3 - Mediastinum & Contents Flashcards
what is the mediastinum?
part of the thoracic cavity - consists of all thoracic viscera except the lungs & associated pleural cavities
anterior border of the mediastinum?
sternum & 1-5th costal cartilages
posterior border of the mediastinum?
thoracic vertebral bodies of T5-12
superior border of the mediastinum?
superior thoracic aperture - formed by the jugular notch, clavicles, 1st rib & T1 vertebral body
inferior border of the mediastinum?
diaphragm
lateral border of the mediastinum?
mediastinal parietal pleura
what are the anterior, posterior, superior, inferior & lateral borders of the mediastinum?
ANTERIOR - sternum & 1st-5th costal cartilages
POSTERIOR - T5-12 vertebral bodies
SUPERIOR - superior thoracic aperture (jugular notch, clavicles, 1st rib, T1 vertebral body)
INFERIOR - diaphragm
LATERAL - mediastinal parietal pleura
what divides the mediastinum into its superior & inferior subdivisions?
transverse thoracic plane - imaginary horizontal line at the level of the sternal angle (from 2nd rib to T4/5 IVD)
what are the divisions of the inferior mediastinum relative to WHAT structure?
anterior, middle, posterior - relative to the pericardial sac enclosing the heart
contents of the superior mediastinum?
trachea
oesophagus
arch of aorta
SVC
what part of the mediastinum holds the heart?
(inferior) middle mediastinum
structures within the (inferior) middle mediastinum? (5)
- heart & pericardial sac
- origins of the great vessels (ascending aorta, SVC, IVC, pulmonary vessels)
- phrenic nerve
- pericardiophrenic vessels
- main bronchi (left & right)
relationship of the middle mediastinum to the anterior mediastinum?
middle mediastinum is POSTERIOR to the anterior mediastinum
contents of the posterior mediastinum?
oesophagus (supplied by vagus nerve)
descending aorta
(vagus nerve)
what is the pericardium?
double-walled, fibro-serous sac that encloses the heart and the roots of the great vessels
what are the two layers of the pericardium?
fibrous (outer) pericardium
serous (inner) pericardium
what are the two layers of the serous pericardium?
visceral (inner) layer/ epicardium = adheres to heart’s surface
parietal (outer) layer = lines fibrous pericardium
function of the fibrous pericardium?
prevents overdistension and excessive movement of the heart (as a tough dense connective layer)
how is the fibrous pericardium attached to surrounding structures?
INFERIOR = attached to diaphragm’s central tendon via the pericardiophrenic ligament
SUPERIOR = fuses with tunica adventitia of the great vessels
ANTERIOR = connects to sternum via sternopericardial ligaments
LATERAL = in contact with the mediastinal pleura and phrenic nerves
inferior attachment of the pericardium to what surface? what ligament aids with this?
centrla tendon of diaphragm - via pericardiophrenic ligament
what layer of the great vessels is the pericardium superiorly attached to?
tunica adventitia of the great vessels
how does the pericardium have attachments anteriorly?
attaches to sternum via sternopericardial ligaments
what is the pericardial cavity?
potential space between the parietal and visceral layers of the serous pericardium
contains serous pericardial fluid (produced by mesothelial cells of serous PC)
functions/purpose of the pericardial fluid?
lubricates heart & reduces friction between heart and pericardium
has a cushioning effect against external shocks
what nerve runs in close relation to the pericardium?
phrenic nerve - runs laterally along fibrous pericardium (provides sensory innervation)
what nerve provides sensory innervation to the fibrous pericardium?
phrenic nerve
describe the layers of the serous pericarium
two layers - visceral layer & parietal layer
visceral layer adheres to the heart’s surface & reflects on itself at the roots of the great vessels to become the parietal layer, which is close to the fibrous pericardium
pericardial cavity in between the visceral & parietal layers, filled with 15-20ml of pericardial fluid
what is the clinical significance of the pericardial cavity in a pericardial effusion?
accumulation of excess fluid in the pericardial cavity = pericardial effusion
can be caused by: inflammation, infection, trauma
how is cardiac tamponade related to pericardial effusion?
accumulation of excess fluid in the pericardial cavity can compress the heart - leads to cardiac tamponade
cardiac tamponade restricts heart expansion, reduces cardiac output & leads to Beck’s triad presentation
what 3 symptoms are commonly associated with a pericardial effusion? what triad are they part of?
Beck’s triad:
1. hypotension
2. bulging neck veins
3. muffled heart sounds
what 3 symptoms are commonly associated with a pericardial effusion? explain how.
(Beck’s triad)
1. hypotension = build-up of fluid within the pericardial cavity can compress the heart, leads to cardiac tamponade & affects heart’s ability to fill properly, leading to reduced cardiac output and hypotension
- bulging neck veins = compression of the heart/ cardiac tamponade means blood can’t accept blood from the SVC - causes a backflow of blood into the internal jugular veins in the neck
- muffled heart sounds = fluid build-up in pericardial cavity muffles heart sounds
what sign/shape is commonly observed on a chest x-ray in patients with a large pericardial effusion?
‘water-bottle’ sign
what is the emergency treatment for a cardiac tamponade?
thoracotomy/ surgery - needle aspiration to release fluid
what is pericarditis? cause?
inflammation of the pericardium - caused by infection, trauma…
pericarditis is an inflammation of the pericardium that usually causes chest pain & sometimes is referred on the same side of the shoulder area - why?
the phrenic nerve (C3-5) provides sensory innervation to the fibrous and parietal layers of the pericardium - shares a dermatome with the shoulder
means that inflammation of the pericardium leads to referred pain in the shoulder due to shared dermatomes
three layers of the heart wall (from outermost to innermost)?
- epicardium/ visceral layer of serous pericardium
- myocardium (cardiac muscle)
- endocardium
what are the two pericardial sinuses formed by the reflection of the serous pericardium?
transverse sinus
oblique sinus
where is the transverse pericardial sinus located?
posteiror to the ascending aorta & pulmonary trunk
anterior to the SVC & pulmonary veins
(posterior to heart’s arterial system; anterior to venous system - separates them)
surgical significance of the transverse pericardial sinus?
surgeons can identify the transverse sinus by passing a finger through it - will know the arterial system is posterior & venous system anterior
isolating the great vessels during the cardiac surgery allows them to clamp them if needed
what structures does the transverse pericardial sinus separate?
separates the arterial system (aorta and pulmonary trunk) from the venous system (SVC, IVC, and pulmonary veins)
what is the oblique pericardial sinus?
blind-ended pouch posterior/behind the base of the heart - formed by the reflection of the serous pericardium around the pulmonary veins and IVC
if you put your hands through the oblique sinus, what blood vessel will you encounter?
pulmonary veins
function of the oblique pericardial sinus?
provides space for the heart to expand during filling
which pericardial sinus has greater surgical significance?
transverse sinus is more surgically significant - allows for isolation great vessels during cardiac procedures
