Superior Border of Mediastinum
thoracic inlet
Thoracic Inlet
T1, rib 1, suprasternal notch
Inferior Border of Mediastinum
thoracic outlet
thoracic outlet
T12, diaphragm, xiphoid process
Lateral Border of Mediastinum
mediastinal parietal pleura
Superior Mediastinum
above horizontal plane btwn sternal angle and T4-T% disc
A-P btwn manubrium and T1-T4
Inferior Mediastinum
btwn body and xyphoid process of sternum and T-5 through T-12
Anterior Mediastinum
(Inf subdiv)
smallest, btwn pericardium and sternum
Middle Mediastinum
(Inf Subdiv)
contains the heart
Posterior Mediastinum
(inf subdiv)
btwn heart and T5-T12; contains tubular structures (esophagus, aorta)
Thymus Gland
(Anterior M.)
bi-lobed lymphoid organ; mainly in Superior M.
fatty remnant in adults
Lymph Nodes
(Ant. M.)
potential site of tumor metastases
Middle Mediastinum Contents
Heart (w/in Pericardial Sac) Ascending Aorta Pulmonary Trunk Seven Veins (SVC, Azygos, IVC, 4 PVs) Phrenic Nerve Pericardiacophrenic Artery Mediastinal Lymph Nodes
Pericardium
membranous sac composed of outer fibrous membrane and inner serous membrane
Fibrous Pericardium
conical, inelastic, limits movement of heart
Apex of Fibrous Pericardium
pierced by Asc Aorta, SVC, Pulm Trunk; fused with their tunica adventitia
Base of Fibrous Pericardium
fused with central tendon of diaphragm; (respiratory movements affect it)
pierced by IVC
Posterior of Fibrous Pericardium
pierced by 4 Pulm Veins; fused with their tunica adventitia
Anterior of Fibrous Pericardium
tethered to sternum through sternopericardial ligaments
Cardiac tamponade
fluid in pericardial sac from torn heart or coronary vessel causes impaired beating due to external fluid pressure
pericardial paracentesis
tx for cardiac tamponade
1) insert needle parasternally into LT 5/6 ICS
2) immed to LT of Xiphoid and angled post. and superiorly at 45*
Rt superior border of fibrous pericardium
extends to level of 2 costal cartilage (sternal angle)
Rt superior border of heart
extends to level of 3 costal cartilage
embryology of fibrous pericardium
derived from body wall of somatic mesoderm of lateral plate
Serous pericardium
composed of two layers, pleural and visceral
forms coelomic lining of pericardial cavity
Parietal layer of serous pericardium
lines inner surface of fibrous pericardium, inseparable from it
visceral layer of serous pericardium
located on outer surface of heart, cont. with parietal layer of serous pericardium by reflecting onto great vessels
epicardium of heart
visceral layer of pericardium + subserous cT
Pericardial cavity
potential space btwn serious parietal/visceral pericardia
contains serous fluid
transverse pericardial sinus
(region of pericardial cavity)
portion btwn SVC (post), AA/PT (ant), SPVv (inf.)
formed by reflections of serous pericardium on above vessels
surgical landmark btwn SVC and PT/AA
transverse pericardial sinus
Oblique pericardial sinus
blind space of pericardial cavity btwn LA and post. wall of pericardial sac
reflection of serous pericardium from RA on SVC/IVC and LA on 4PVv
Division of Intraembryonic Coelom Step 1
continuous space in the lateral mesoderm
Division of Intraembryonic Coelom Step 2
end of wk 3, horseshoe shaped cavity in the trilaminar embryo prior to head/tail/lat folding
Division of Intraembryonic Coelom Step 3
lateral folding brings L and R sides of horseshoe together to form 1 coelom
Division of Intraembryonic Coelom Step 4
The pleuropericardial membrane septae and the thoracic diaphragm septae develop which divide coelom into pleural, pericardial, and peritoneal cavities
Pleuropericardial membrane
paired layers of somatic mesoderm that isolate the pleural cavities from the pericardial cavities
pleuropericardial membrane formation step 1
splitting off of inner layer of somatic mesoderm from the body wall due to rapid enlargement of developing lungs and future pleural cavities
pleuropericardial membrane formation step 2
fuse to each other to form the definitive fibrous pericardium, which surrounds newly partitioned pericardial cavity
pleuropericardial membrane innerv
phrenic nerves, lies btwn fibrous pericardium and mediastinal pleura
Thoracic diaphragm
separates the pleural and pericardial cavities from peritoneal cavities
What fuse together to form diaphragm?
septum transversum, paired pleuroperitoneal membranes, dorsal mesentery of the esophagus, myoblasts from somatic mesoderm of body wall
septum transversum
plate of mesoderm in ventral part of embryo that forms the central tendon of the diaphragm.
incompletely separates thoracic cavity from abdominal cavity
R and L pleuroperitoneal canals
(septum transversum)
spaces that link thoracic and ab coloemic cavities, loc. along foregut
pleuroperitoneal membranes
paired layers of somatic mesoderm located at caudal border of pleural cavities
pleuroperitoneal membrane formation
splitting of inner layer of somatic mesoderm from the body wall as the lungs enlarge (more caudal than pleuropericardial)
how are the pleuroperitoneal cavities closed?
pleuroperitoneal membrane fuses with septum transversum and dorsal mesentery of the esophagus
dorsal mesentery of the esophagus
forms the crura of the diaphragm
invaded by myoblasts
myoblasts from the somatic mesoderm of body wall
cont. to muscles of diaphragm
Diaphragm formation step 1
septum transversum lies at level of cervical somites and nerve fibers of C3-C5 grow into it
Diaphragm formation step 2
descent of diaphragm to L1 result of rapid growth of CNS in dorsal embryo pushing it
Diaphragm formation step 3
phrenic nerve dragged inferiorly with the ST
phrenic n. innerv.
diaphragm muscles
sensory to parietal pleura and parietal peritoneum of central diaphragm
intercostal n. innerv.
sensory to parietal pleura and parietal peritoneum of peripheral diaphragm
(pleuroperitoneal membrane derive)
hernia
protrusion of structure through tissues that normally contain it
Congenital Diaphragmatic Hernia (Foramen of Bochdalek)
hern. of ab organs into pleural cavity due to failure of pleuroperitoneal membrane (LT) to fuse with other contributors of the diaphragm.
Causes compression of lungs, high mortality rate
Esophageal Hiatal Hernia
hern. of stomach thru enlarged esophageal hiatus of diaphragm;
reflux due to esophageogastric sphincter being nonfunctional
vomiting when laid on back
Parasternal hernia (Foramen of Morgagni)
hern. of ab viscera thru enlarged sternocostal hiatus (surrounds superior epigastric artery)