* State the relationship of the great arteries as they exit the heart in the adult and explain how they arrived at that position based on your knowledge of embryology. (6 pts)

Answer

• The great arteries/vessels are defined as the aorta and the pulmonary trunk. Both of these vessels are derived from the truncus arteriosus (TA) and bulbus cordis. The septation must take place to divide the TA. This septation must also occur in the correct spiraling fashion (180o) so that the pulmonary trunk connects the developing right ventricle and the left ventricle is continuous with the aorta.

• The formation of the aorta and pulmonary valves requires communication of multiple areas of the heart. Development of the conotruncal/aorticopulmonary (AP) septum is essential for separation of the TA into the aorta and pulomanary valves. The septum is composed of the right and left bulbar ridge and the endocardial cushions. The spiraling of this septum is required for correct “sidedness” in ventricle and great vessel association (as described above). In addition, the spiraling of the AP septum (as well as the folding of the heart) leads to the adult anatomy of the pulmonary trunk residing more anterior and to the left as it exits the right ventricle and the aorta being more posterior and to the right upon its exit from the left ventricle. Thus, the adult aorta contains a posterior semilunar cusp within the aortic valve, while the pulmonary trunk contains an anterior semilunar cusp within the pulmonary valve. Both of the great vessels posses a right and left semilunar valve.

• In addition to the AP septum, a fully developed atriventricular septum is required for continuity between the great vessels and their respective ventricles. Without the AV septum also being present, the aorta and pulmonary trunk may be divided into separate structures each vessel will be in communication with BOTH left and right ventricles. Therefore, in addition to the development of the great vessels, the final septation of the Bulbus Cordis results in the presence of the cous arteriosus in the right ventricle (giving origin to the pulmonary trunk) and the aortic vestibule in the left ventricle inferior to the aortic valve.

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 where you would perform this procedure without causing a pneumothorax, and what layers (from outside in) you will penetrate to gain access to the pericardial cavity. (6 pts) (sas630)

Where:

• Needle inserted at the 5th or 6th intercostal space at the left sternal border- cardiac notch of the left lung is located here leaving pericardium exposed
• Another option is the left costoxiphoid angle at a 45 degree angle to the skin then angling the needle posterosuperiorly

Layers from outside in:

• Skin
• Tela subcutanea
• Pectoralis Major (possibly fibers from pectoralis minor)
• External intercostal membrane
• Internal intercostal muscle
• Neurovascular plane- internal thoracic artery/vein
• Transversis thoracis
• Endothoracic fascia
• Fibrous coat of pericardium
• Parietal layer of serous pericardium
• Fluid contained between parietal layer of serous pericardium and visceral layer of serous pericardium (aka epicardium)

Interesting Note

• The pericardium is composed of a fibrous connective tissue that cannot stretch and fluids that collect in the pericardial cavity may compress the heart.

Discuss the relationships of structures (i.g., ligaments, tendons, vascular supply, nerves) to the sustentaculum tali, and the importance of these structures to gait and ankle stability. (6 pts).

• Sustentaculum tali is a horizontal, bony eminence on the medial/anterior/superior calcaneus

• Dorsal sustentaculum tali is part of the talocalcaneonavicular joint; plantar articular surface of the head of talus bone rests on ST

*Discussion of the “keystone” arrangement of the talus, calcaneus and navicular bones can supplement addressing the ST as a component of the TCN joint

• The tendon of the flexor hallucis longus muscle grooves the plantar surface of the ST.

• The margins of the groove give attachment to deep part of flexor retinaculum

• The posterior tibial artery and its calcaneal branches are in close apposition to the sustentaculum tali

• The calcaneus bone, including the ST, is innervated by branches of the tibial, sural and deep fibular nerves

Sustentaculum Tali Attachments:

The plantar calcaneonavicular ligament (spring ligament) is attached distally to the medial margin of ST, medial margin is narrow, rough and convex.

• “A slip” from the tendon of tibialis posterior muscle attached proximally

• Superficial fibers of the deltoid ligament (tibiocalcaneal contribution) attached proximally

• Fibers from medial talocalcaneal ligaments attached proximally

• Distal to attachment of deltoid ligament, the tendon of the flexor digitorum longus muscle is related to the margin of the sustentaculum and may groove it

Discuss the location, course, and relationships of the thoracic duct in the posterior mediastinum. (6 pts). (amk397)

• Thoracic duct begins around L2 commencing at the confluence of lymph trunks/cisterna chili
• Extends from L2 to the base of the neck, traversing the posterior mediastinum
• The thoracic duct enters the posterior mediastinum by traversing the retrocurual space of the diaphragm with the aorta, azygos and hemiazygos veins.
• Thoracic duct ascends in the posterior mediastinum, on the right of the midline, between the descending thoracic aorta (on L) and azygos vein (on R). *Posterior relationships: vertebral column, right posterior intercostal arteries, terminal segments of hemiazygos and accessory hemiazygos veins, sympathetic trunks, splanchnic nerves (posterior-lateral).
• Anterior relationships: esophagus, esophageal plexus, right and left vagus nerves, diaphragm, middle mediastinum contents
• At T5, thoracic duct inclines to the left, enters superior mediastinum, then arches laterally at C7 and ultimately ends by opening into the junction of the left subclavian and left internal jugular veins.
• Drains 75% of total body lymph (all except upper right quadrant)

*Discuss the contents, boundaries (i.e., superior, inferior, medial, lateral, anterior, posterior), and relationships of the saphenous opening. (6 pts) *

Definition/Relationships:

• A natural opening/gap/hiatus in the fascia lata, the deep fascia of the thigh, allowing the Great Saphenous Vein to drain into the Femoral Vein
• Inferior to the Inguinal Ligament and about 3-4cm inferiolateral to the Pubic Tubercle
• Great Saphenous Vein enters through the anterior surface of the Femoral Vein, which lies medial to the Femoral Artery in the Femoral Triangle
• This will help you gain access to the Femoral Artery for the procedure described above

Contents:

• Cribriform Fascia fills the opening
• Great Saphenous Vein (also known as the Long Saphenous Vein)
• Tributaries of the Great Saphenous Vein
• Superficial Epigastric Vein
• Superficial Circumflex Iliac Vein
• Superficial External Pudendal Vein

Boundaries:

• Superior: Superior Cornu of the Falciform Margin
• Inferior: Inferior Cornu of the Falciform Margin
• Medial: Smooth blending of Cribriform Fascia
• Lateral: Falciform Margin
• Anterior: Cribriform Fascia forms the roof over the opening
• Posterior: Anterior layer of Femoral Sheath