The function of the thorax is dependent on blood supply. Discuss the collateral circulation (arteries/veins, relationships to surrounding structures, parent arteries/veins) of the thoracic wall. (8 pts)

General Comments

• The vasculature supply to the thoracic wall travels within the neurovascular plane defined superficially by the internal intercostal muscles and membrane (posterior) and deeply by the subcostal (posterior), innermost intercostal (intermediate), and transversus thoracis (anterior) muscles. The intercostal veins, arteries, and nerves are located inferior to the costal groove of the superior rib defining an intercostal space. From superior to inferior is vein, artery, nerve. Posterior, lateral, and anterior branches of the intercostal vessels leave the neurovascular plane to supply superficial regions of the thoracic wall. The lateral branches further divide into posterior and anterior branches whereas the anterior branches further divide into medial and lateral branches.
• The bulk of the anterior vasculature has the subclavian arteries and brachiocephalic veins as the parent vessels whereas the bulk of the posterior vasculature has the descending aorta (first two intercostal spaces qualified) and azygous system as the parent vessels. The anterior and posterior vasculatures anastomose within the thoracic wall. Thus, the aortic arch can deliver blood directly to the descending aorta or indirectly to the descending aorta by way of the anterior vasculature (subclavian to internal thoracic to anterior intercostals to posterior intercostals to descending). See below for refining considerations.

Arteries

• Anterior intercostal spaces
  • 1-6 - Internal thoracic artery from subclavian artery
  • 7-9 - Musculophrenic artery from internal thoracic artery
  • 10-11 - Superior epigastric from internal thoracic artery
• Posterior intercostal spaces
  • 1-2 Supereme (highest) thoracic artery from costocervical trunk of subclavian artery
  • 3-11 Posterior intercostal arteries from the descending aorta

• Internal thoracic artery-
  • Arises inferiorly from the first part of the subclavian artery sternal clavicle
  • Descends behind the first 6 costal cartilages
  • Divides at the level of the 6th intercostal space into musculophrenic and superior epigastric branches.
  • Separated from pleura by endothoracic fascia, and below the 3rd costal cartilage by transversus thoracis.
  • Artery is accompanied by lymph nodes and venae comitantes that unite at the 3 costal cartilage to become medial to the artery.

• Anterior Intercostal branches-
  • Supplies upper 6 ICS
  • Pass laterally along the space to anastomose with the posterior intercostals aa and collateral branches
  • Usually arise as single branches and immediately divide into two branches to supply upper and lower spaces
  • Lie between pleura and internal intercostals at first then between the innermost and internal intercostals

• Musculophrenic Artery-
  • Passes inferolaterally behind the 7-9th costal cartilages, traverses the diaphragm near the 10th and ends near the last ICS
  • Anastomoses with the inferior phrenic and lower two posterior intercostal aa and ascending branches of the deep circumflex iliac aa.
  • Supplies 7-9th ICS

• Superior Intercostal Artery
  • Arises from costocervical trunk
  • Anastomoses with the 3rd posterior intercostal a
  • Gives off 1st IC artery and becomes the 2nd IC artery
  • Not constant and more common on the right

• Posterior Intercostal Arteries
  • Usually 9 pairs distributed to the lower 9 ICS
  • Arise from the posterior aspect of the descending aorta
  • Right posterior intercostals aa are longer because aorta deviates to the left crossing the vertebral bodies
  • Lower two arteries anastomose with subcostal, superior epigastric, and lumbar arteries

Veins

• Anterior intercostal spaces
  • 1-6 - Internal thoracic vein
  • 7-9 - Musculophrenic vein
  • 10-11 - Superior epigastric vein
• Right posterior intercostal spaces
  • 1 - Supreme (highest) intercostal vein from brachiocephalic vein
  • 2-4 - superior intercostal vein from azygous vein
  • 5-11 - Posterior intercostal veins from azygous vein
• Left posterior intercostal spaces
  • 1 - Supreme (highest) intercostal vein to brachiocephalic vein
  • 2-4 - superior intercostal vein from accessory hemiazygous vein, or brachiocephalic vein, or coronary sinus
  • 5-11 - Posterior intercostal veins from hemiazygous vein
• Internal Thoracic Veins-
  • Venae comitantes of inferior half of the internal thoracic artery
  • Near 3rd costal cartilage the veins unite and ascend medial to the artery ending in the brachiocephalic vein
• Left Superior Intercostal vein-
  • Drains the 2nd and 3rd (sometimes 4th) left posterior intercostals vv into left brachiocephalic v
• Posterior Intercostal Veins-
  • Accompany arteries in 11 pairs
  • 1st intercostal vein on both sides in the ipsilateral brachiocephalic or vertebral vein
  • On the right side- 2, 3, and sometimes 4 form a right superior intercostal vein that joins directly to azygos
  • On the left side- 2, 3, and sometimes 4 form a left superior intercostal vein
  • Veins from 4 or 5th to 8th ICS end in accessory hemiazygos
  • Veins from 9-11th ICS end in hemiazygos vein
• Azygos Vein-
  • Begins at the posterior aspect of the IVC at or distal to the renal veins
  • Ascends anterior to the lumbar vertebrae
  • Ascends in the posterior mediastinum to the level of T4 ending in the SVC
• Hemiazygos Vein
  • Formed on the left side by from the lower 3 Posterior IC veins
  • Ascends anterior to the vertebral column to about T8 crossing the vertebral bodies posterior to the aorta, esophagus, and thoracic duct ending in the azgyos vein
• Accessory Hemiazygos Vein-
  • Descends on the left lateral to the vertebral column
  • Receives posterior IC vv from the 4 or 5th to 8th ICS
  • Crosses T7 to join azygos or may join the hemiazygos
  • The most variable

Acute pericarditis is an inflammatory process involving the pericardium that results in a clinical syndrome with the triad of chest pain, pericardial friction rub, and changes in the electrocardiogram (ECG). Discuss the structure of the pericardium/pericardial sac, including innervation, vascularization, lymphatics, and means of stabilization. (8 pts) (amk397)

Structure of pericardium/pericardial sac

• Content of the middle mediastinum
• Pericardium contains the heart and the juxtacardiac parts of the great vessels
• Fibrous layer of parietal pericardium - outermost
• Serous pericardium
  • Serous parietal pericardium - lining the inner surface of the fibrous parietal pericardium
  • Visceral pericardium (epicardium) - outer surface of myocardium
• Pericardial cavity
  • Collapsed serous cavity within the pericardial sac
  • The content of the pericardial cavity is, under nonpathological conditions, a small amount of serous fluid. This provides reduced friction to accommodate movement of the heart.
• Reflections
  • Arterial mesocardium – reflection around aorta and pulmonary trunk
  • Venous mesocardium – reflection around SVC, IVC, and pulmonary veins
  • Define transverse sinus and oblique sinus

Innervation

• Parietal pericardium - somatic (sharp pain) innervation by phrenic and intercostal nerves
• Visceral pericardium - visceral (dull pain) innervation by superficial and deep cardiac plexuses which, in turn, are formed by cardiac nerves derived from the vagus nerves and from the sympathetic trunks
• Anatomic pathways for pain sensation (visceral) from the visceral pericardium follow - cardiac plexuses, splanchnic nerves, rami communicantes, spinal nerve ventral ramus (intercostal nerve), dorsal root (dorsal root ganglion at T2), spinal cord at T2 (T1-4)

Vascularization

• Parietal pericardium - based on location, the pericardicophrenic, internal thoracic, anterior intercostal, musculophrenic, bronchial, esophageal, and superior phrenic vessels
• Visceral pericardium - based on location, the coronary arteries and branches
• Veins are tributaries of azygos system

Lymphatics

• mediastinal nodes - bronchopulmonary nodes - paratracheal nodes - bronchomediastinal lymph trunks
• parts of fibrous paracardium drain to parasternal nodes
• parasternal and paratracheal drainages combine to form the bronchomediastinal lymph trunks
• right - right lymph duct into brachiocephalic v.
• left - thoracic duct or independently into left brachiocephalic v.

Means of Stabilization

• Superiorly: fibrous pericardium blends with adventitia of great vessels
• Inferiorly: support by central tendon of diaphragm
• Anteriorly: superior and inferior pericardiosternal ligaments
• Posteriorly: support by contents of posterior mediastinum, SVC

Strain of the hamstring muscles is common in runners, and alteration of hamstrings is important in disease such as spastic cerebral palsy. Discuss the anatomy of the hamstring muscles including criteria for inclusion, innervation, vascularization, and function. (8 pts).

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