CV Lea Thoracic Cavity and Mediastinum Flashcards
Describe the vertebral components of the thorax
12 thoracic vertebrae
a. costal facets on bodies of articulation w/rib head
1. superior and inferior demifacets
2. atypical: TV1 and TV10-12 have single facet
b. costal facets on transverse processes for articulation w/right tubercle (TV1-100
Describe the ribs of the thoracic wall
True ribs 1-7: attach directly to sternum
False ribs 8-10: attach to costal cartilage of rib above and form the infracostal margin
Floating ribs 11-12: not attached to sternum, anteriorly end in muscle
Describe anatomical features of typical ribs
ribs 3-9
Head - proximal end; articulates w/adjacent vertebral bodies
Neck - between head and tubercle
Tubercle - at jxn of neck and body, articulates w/transverse process
Angle - anterolateral angulation of body just lateral to tubercle
Shaft - mid and distal portion of rib; inferior portion has a concave internal surface, the costal groove, which provides protection for intercostal VAN
Costal cartilage - provides increased elasticity for thoracic wall
Describe anatomical features of atypical ribs
1st rib is broad, horizontal shaft with pronounced curvature. Head has single facet for TV1. Shaft contains 3 grooves for subclavian a and v and, scalene tubercle
2nd rib has serratus ant tuberosity superiorly
10th rib has single articular facet for TV10 body
11th and 12th ribs have single facet on head and absence of neck/tubercle
What are clinical correlations of the rib
Rib fractures occur near angle where rib is weakest.
Middle ribs are most often broken.
Flail chest: results from multi broken ribs in 2 or more places and causes a loose segment of thoracic wall which moves paradoxically during resp
Describe landmarks of the manubrium
Suprasternal notch (jugular) - anterior to TV2/3 intervertebral disc
Clavicular notch - for articulation w/clavicle
Lateral facets for articulation w/costal cartilage of ribs 1 & 2
Articulates w/body of sternum via manubriosternal joint/symphysis
Sternal angle or Angle of Louis is located at manubriosternal joint
Describe the body of the sternum
Articulates w/ costal cartilages of ribs 2-7
Describe the Xiphoid process
Cartilaginous but ossifies w/ age.
Lateral demi-facets for articulation w/costal cartilage of rib 7.
Articulates w/ body of sternum via xiphosternal joint/synchondrosis
Note the infrasternal angle
What are the clinical correlations of the sternum
Sternal angle demarcates articulation of rib 2. A horizontal plane passed from sternal angle to disc between T4-T5 marks the boundary between superior and inferior mediastinum - THE TRANSVERSE THORACIC PLANE
What are pectus excavatum and carinatum
anterior thoracic wall sunken-in and anterior wall protrusion “pigeon breast”, respectively.
These are congenital malformations of the sternum and ribs
What are the borders of the Superior Thoracic Aperture
Ant: jugular notch
Lat: 1st rib
Post: 1st thoracic vertebra
What is the clinical relevance of the Superior Thoracic Aperture
It extends obliquely from 1st thoracic vertebral anteroinferiorly to manubrium. The plural space extends superiorly into the neck.
Injury or surgery within this region may affect plural cavity and lungs i.e. pneumothorax
What are the borders of the Inferior Thoracic Aperture
Ant: Xiphisternal joint
Lat: costal margin
Post: 12th thoracic vertebrae and 11th&12th ribs
Why is the Inferior Thoracic Aperture clinically relevent
It extends obliquely from TV12 anterosuperiorly to xiphisternal joint. The plural space extends inferiorly to lie posterior to the abdominal region.
Injury or surgery to this region may affect plural cavity and lungs i.e. pneumothorax
Describe the sternocostal joint
Articulates costal cartilages and sternum (7 pair)
Joint capsule supported by ant and post radiate ligaments.
1st sternocostal joint is a synchondrosis, permitting no movement (imptn in mechanics of respiration)
2nd-7th sternocostal joints are synovial plane
Describe costochondral joints
Articulation between rib and costal cartilage.
Synchondroses - very little movement, frequently dislocated in minor trauma
Describe the interchondral 8th-10th joints
Articulations between costal cartilages of ribs 8-10 w/costal cartilage above
Describe costovertebral joints
Articulation between rib head w/vertebral bodies, intervertebral disc, and is synovial plane.
Ribs 2-9 artic w/adjacent vert bodies and intervertebral discs; an intra-articular lig extends from crest of the head to intervertebral disc limiting movement of this joint.
Ribs 1,10-12 artic only w/body of same # vertebrae
Radiate ligs support joint capsule
Describe costotransverse joint
Articu between rib tubercle and vert transverse proc.
Synovial.
Ribs 11 & 12 do not have costotransverse joints
Support lig include: lateral, superior costotransverse lig, constotransverse lig
What are the muscles of the thoracic wall
EXTERNAL INTERCOSTALS - fibers pass infero-medially.
1. Anteriorly, at costochondral joint, muscle replaced by external intercostal membrane.
INTERNAL INTERCOSTALS - fibers pass inferio-laterally
1. Posteriorly, at angel of rib, muscle replaced by internal intercostal membrane.
INNERMOST INTERCOSTALS -
1. discontinuous sheet of of muscle - transversus thoracis (sternocostalis) anteriorly, innermost intercostal laterally and subcostalis posteriorly.
Neurovascular bundle runs between 2nd and 3rd layers (internal and innermost intercostals)
Describe the deep Thoracic Fascia
The Endothoracic Fascia is the CT lining entire surface of internal thoracic wall and superior diaphram.
It adheres parietal pleura to thoracic wall.
Why is Endothoracic Fascia clinically relevent
Provides a cleavage plane between thoracic wall and pleura; important for surgeries requiring access to thoracic cavity
Describe the “pump handle motion” of thoracic wall
Rotational movement at costotransverse joint causes elevation & depression of most distal (ant) portion of upper ribs.
Bc of inferior slope of distal portions of ribs, ant elevation causes increase in A-P diameter of thoracic wall.
Importance of 1sr rib fixation in mediating this motion.
Describe “bucket handle motion” motion of thoracic wall
Gliding movement at post (costovertebral & costotransverse) joints causes elevation & depression of lateralmost portions of ribs.
Bc inferior slope of lateral portion of ribs, lateral elevation also causes an increase in transverse diameter of thoracic wall.
What increases the vertical diameter of the thoracic wall
Caused by contraction of the DIAPHRAGM
Inn by phrenic n (C3,4,5 keeps diaphragm alive).
Musculotendinous septum separating thoracic and abdominal cavities.
Primary muscle of respiration, especially quiet resp.
Flattens during contraction and increases intrathoracic volume.
During deep expiration the sup surface extends to 4th intercostal space
During forced inspiration diaphragm can move down 10 cm (2 vert bodies).
What are the additional muscles of resp that are located in the thoracic wall
Serratus post sup and inf (inspiration) Levator costarum (insp) external intercostal muscles (insp) internal intercostal muscles (exp) transverse thoracic muscles (exp)
What are other muscles that are included in forced resp
Sternocleidomastoid (insp) scalene (insp) serratus ant (insp) pectoralis major and minor (insp) quadratus lumborum (insp) anterolateral abd wall muscles (exp)
Describe innervation of the thoracic wall by intercostal (11pair) and subcostal (1 pair) nerves
Ventral rami of 12 pair of thoracic spinal nn form 11 intercostal nn and 1 subcostal n which travel in costal groove along inferior margin of rib.
Provide inn to muscles of thoracic wall (except levator costarum) & skin of anterolateral thoracic and abd wall.
Provide preganglionic symp n cell processes from spinal cord to symp chain via 14 pair of white rami.
Provide postganglionic symp nerve cell processes to sweat glands, smm in arrector pili, and smm in blood vessels of thoracic & abd wall.
Describe the course of intercostal nerves
1st, travel w/in endothoracic fascia.
Near rib angle, nerve pass between 2nd and 3rd muscle layers
What are the branches of intercostal nerves
Rami communicantes, muscular branches, collateral branches given off near angle of rib, course along sup border of rib.
Lateral perforating branch given off near midaxillary line, pierce lateral body wall and divide into ant & post cutaneous branches.
Ant perforating branches - given off near lateral border of sternum, pierce ant body wall and divide into medial and lateral cutaneous branches supplying sensory innervation to thoracic and abd walls
Describe atypical intercostal nerves
Ventral ramus T1 divides into large superior trunk which goes to brachial plexus and small inferior trunk (1st intercostal nerve). Intercostal nerve 1 typically has no cutaneous branch, and therefore, T1 dermatome is not represented on thoracic wall.
Lateral cutaneous branch of intercostal n 2 (often 3) forms intercostobrachial cut n, supplying skin & subcutaneous tissue of axilla & medial brachium.
Intercostal nerves 7-11 subcostal n continue anterolaterally as thoracoabdominal nn to supply skin & musculature of abd wall
What is the dermatome pattern of the thoracic wall
Nipple - T4 (males)
Xiphoid - T6
Umbilicus - T10 (key dermatome)
Note the C4 dermatome abuts the T2 dermatome anteriorly
Describe the vasculature of the thoracic wall via Anterior intercostal arteries (9 pair)
Originate from:
a. Internal thoracic artery (aka internal mammary a.)
1. Branch of subclavian artery.
2. Descends along internal surface of anterior thoracic wall, lateral to sternum.
3. Near 6th or 7th costal cartilage, divides into two terminal branches: musculophrenic and superior epigastric arteries.
4. Directly provides ant intercostals arteries 1-6.
b. Musculophrenic artery - Follows costal arch and provides anterior intercostal arteries to lower intercostal spaces.
Describe the courses and branches of anterior intercostal arteries
a. Typically, two anterior intercostal arteries supply each intercostal space.
b. Anastomose with the posterior intercostal arteries.
c. Perforating and muscular branches follow same pattern as nerves.
Describe vasculature of thoracic wall via Posterior intercostal aa (11 pair) and subcostal a (1 pair)
Originate from
a. Thoracic (descending) aorta – segmentally provides posterior intercostal arteries 3-11 and subcostal artery.
b. Costocervical trunk (branch of subclavian artery) – provides supreme (superior or highest) intercostal artery which supplies the posterior 1st and 2nd intercostal spaces.
Describe courses and branches of post intercostal arteries and subcostal a
a. Travel with and follow the same course and distribution of intercostal nerves.
b. Posterior branch (ramus) – given off near vertebral column; supplies skin, subcutaneous tissue, and intrinsic muscles of back, as well as the spinal cord and vertebral column. (same course and distribution as the doral ramus of a spinal nerve)
c. Collateral branch – given off near angle of the rib.
d. Lateral perforating (cutaneous) branch – given off near the MAL.
e. Anterior perforating (cutaneous) branch – given off in parasternal area.
Describe the intercostal veins
- The 1st–3rd posterior intercostal veins unite to form the superior intercostal vein; drains directly into the azygos (right) or brachiocephalic vein (left).
- Anterior intercostal veins drain to internal thoracic veins.
- Posterior intercostal veins drain to the azygos system of veins
Describe the neurovascular bundle of intercostal space
“VAN” – orientation of neurovascular bundle within the intercostal space
-Collateral branches travel along superior border of lower rib
Why is the neurovascular bundle clinically important
a needle or chest tube inserted into the intercostal space needs to be inserted along the superior border of the rib in order to avoid the main neurovascular bundle.
Describe the parasternal nodes
- Along the lateral border of the sternum.
- Afferents: anterior thoracic wall, superior portion of the abdominal wall, superior surface of the liver, and the medial portions of the mammary gland.
- Efferents: bronchomediastinal trunk.
Describe intercostal nodes
- Located near the heads and necks of the ribs.
- Afferents: posterolateral thoracic wall.
- Efferents: thoracic duct or right lymphatic duct (1st – 6th spaces); also spread to abdomen and enter cisterna chyli directly (7th – 11th spaces).
Describe lateral diaphragmatic (phrenic) nodes
a. Located where phrenic nerves pierce diaphragm.
b. Afferents: central diaphragm, superior surface of liver.
c. Efferents: to parasternal and posterior mediastinal lymph nodes
Describe anterior diaphragmatic nodes
a. Located near the xiphoid process on the superior surface of diaphragm.
b. Afferents: anterior diaphragm; superior surface of the liver.
c. Efferents: drain to parasternal nodes.
Describe posterior diaphragmatic nodes
a. Located near the aortic hiatus.
b. Afferents: posterior portion of diaphragm.
c. Efferents: posterior mediastinal nodes
What are the divisions of the mediastinum
- Superior Mediastinum
- Inferior Mediastinum
a. Anterior mediastinum
b. Middle mediastinum
c. Posterior mediastinum
What are the boundaries of the Superior Mediastinum
- Superior: superior thoracic aperture
- Inferior: transverse plane passing from sternal angle to the disk between TV4-TV5, (transverse thoracic plane).
- Anterior: manubrium
- Posterior: anterior surface of vertebral bodies of TV1-TV4
Describe the thymus in the superior mediastinum
a. Located directly posterior to manubrium.
b. Primary lymphatic organ in infants, in adults mostly replaced with fatty tissue.
c. Vascular supply – internal thoracic and inferior thyroid vessels.
d. Lymphatic drainage – parasternal and tracheobronchial nodes.
e. Innervation is mainly from the vagus nerve and sympathetic trunk (vasomotor).
Describe the brachiocephalic veins in the superior mediastinum
a. Formed posterior to sternoclavicular joint from union of subclavian and internal jugular veins (called venous angle or jugulovenous angle).
b. Left brachiocephalic v. is longer than right and travels transversely across superior mediastinum; right brachiocephalic v. descends just right of manubrium.
Describe the superior vena cava in the superior mediastinum
a. Formed from the union of the left and right brachiocephalic veins.
b. Descends to the right of the sternum from the level of the first costal cartilage to the third costal cartilage (where it then enters the right atrium).
Describe the aortic arch and its main branches in the superior mediastinum
a. Begins at TV4/TV5 intervertebral space as a continuation of ascending aorta.
b. Arches posteriorly and to the left over the root of the left lung.
c. Ends posteriorly and to the left of midline at the TV4/TV5 intervertebral disc, becoming the descending (thoracic) aorta.
d. 3 main branches (65% of population)
1. Brachiocephalic trunk (artery)
2. Left common carotid artery
3. Left subclavian artery
e. Ligamentum arteriosum passes from the origin of the left pulmonary artery to the arch of the aorta; represents remnant of the fetal ductus arteriosus which shunted blood from the pulmonary trunk to aorta in order to bypass the fetal lungs.
What additional structures are located w/in the superior mediastinum
Trachea (see lung lecture for details).
Esophagus (see posterior mediastinum for details).
Thoracic duct (see posterior mediastinum for details).
Sympathetic trunk / sympathetic chain ganglia (see posterior mediastinum for details)
Describe the phrenic nerve w/in the superior mediastinum
a. Derived from spinal segments C3, C4, C5
b. Motor innervation to the thoracic diaphragm.
c. Sensory innervation to the diaphragm, mediastinal pleura, and pericardium.
d. Enters thorax from neck by passing anterior to the subclavian artery.
e. Pass anterior to the root of the lungs
Describe the Vagus N (CN X) w/in superior mediastinum
a. Enter the superior mediastinum along lateral border of common carotid arteries.
b. Pass posterior to the root of the lung.
c. Carry preganglionic parasympathetic nerve cell processes to thoracic autonomic plexuses.
d. Within superior mediastinum, the left vagus nerve gives off a left recurrent laryngeal nerve which loops underneath the arch of the aorta just lateral to the ligamentum arteriosum, then courses superiorly in the tracheo-esophageal groove to supply laryngeal muscles.
e. As the right and left vagus nerves approach the esophagus in the posterior mediastinum, the left vagus becomes the anterior vagal trunk and the right vagus becomes the posterior vagal trunk.
Discuss the clinical relevance of vagus nerve in the superior mediastinum
Due to its position in the superior mediastinum, aortic aneurysm, bronchogenic or esophageal cancer, and/or enlargement of mediastinal lymph nodes can impinge on the recurrent laryngeal nerve and cause hoarseness (due to loss of innervation to laryngeal muscles).
What are the boundaries of the anterior mediastinum
a. Superior: transverse thoracic plane
b. Inferior: diaphragm
c. Lateral: mediastinal parietal pleura
d. Anterior: sternum
e. Posterior: anterior surface of pericardium
What structures are associated w/anterior mediastinum
thymus, sternopericardial ligaments, fat, lymphatics, connective tissue.
What are the borders of the posterior mediastinum
- Superior: transverse thoracic plane
- Inferior: diaphragm
- Lateral: mediastinal parietal pleura
- Anterior: posterior surface of pericardium
- Posterior: bodies of thoracic vertebrae TV5-TV12
Describe the esophagus w/in posterior mediastinum
a. Originates at the CV6 level as a continuation of the pharynx.
b. Travels through superior mediastinum posterior and slightly left of trachea.
c. Travels right along midline through the posterior mediastinum.
d. Exits thorax through the esophageal hiatus of the diaphragm at TV10.
e. Cervical, Thoracic and Diaphragmatic Constrictions – CV6 pharyngoesophageal, TV4-5 broncho-aortic, TV10 diaphragmatic.
f. Vascular supply – esophageal and bronchial arteries and veins.
g. Lymphatic drainage – posterior mediastinal lymph nodes
Describe the Esophageal autonomic plexus sympathetic innervation
i. Preganglionic nerve cell bodies at T2-T6 and processes enter sympathetic chain.
ii. Postganglionic nerve cell bodies in sympathetic chain ganglia.
Many of these nerve cell processes travel with the cardiopulmonary splanchnic nerves ; thus esophageal pain and pain from myocardial infact can present very similarly.
1. Functions: vasoconstriction; decreased gland secretion.
Describe the Esophageal autonomic plexus parasympathetic innervation
a. Preganglionic nerve cell bodies in brainstem, processes travel with vagus nerve.
b. Vagus nerve provides numerous esophageal branches.
c. Postganglionic cell bodies in the wall of esophagus.
d. Functions: vasodilation; increased gland secretion; increased peristalsis
Describe the descending aorta w/in the posterior mediastinum
a. Continuation of the aortic arch at TV4/TV5 level.
b. Travels through the posterior mediastinum to the left of midline.
c. Exits thorax at TV12 through aortic hiatus of thoracic diaphragm.
What are the branches of the descending aorta w/in the posterior mediastinum
- Posterior intercostal (9 pair) and subcostal arteries
- Bronchial artery (usually 2 on left and 1 on right)
- Esophageal artery (3-5 unpaired branches)
- Pericardial and mediastinal arteries (unpaired)
- Superior phrenic arteries (1 pair)
Describe the azygous system
a. Provides collateral circulation for venous blood between the IVC and SVC.
b. Azygos vein
1. Formed by union of right ascending lumbar and right subcostal veins.
2. Tributaries: right posterior intercostal veins, right esophageal, bronchial, mediastinal, pericardial, hemiazygos, and accessory hemiazygos veins.
3. Travels superiorly on the right side of the vertebral bodies, at TV4 it arches anteriorly over the root of right lung to enter the SVC.
4. Receives tributaries from the IVC.
Describe the Hemiazygos
- Forms from union of left ascending lumbar and left subcostal veins.
- Receives blood from the inferior 3 left posterior intercostal veins.
- Travels superiorly through the posterior mediastinum to the left of midline; at TV9 crosses the midline and joins the azygos vein.
Describe the Accessory Hemiazygos
- Begins at medial end of the 4th or 5th intercostal space and descends to TV8 where it cross the midline and joins the azygos vein.
- Drains left posterior intercostal veins (4 - 8).
