General

• Between manubrium and lateral aspect of upper 4 thoracic vertebrae
• Asymetry of arteries and viens in the superior mediastinum

Boundaries

• General - Wedge shaped
• Superior - Projection from jugular notch to T1 vertebra
• Inferior - Projeciton from sternal angle to T4 vertebra
• Anterior - Posterior surface of manubrium
• Posterior - Transverse processes of first four throacic vertebra
• Lateral left - reflection of mediastinal parietal pleura to costal pariental pleura - left lamina sternal pericardial ligament
• Lateral right - reflection of mediastinal parietal pleura to costal pariental pleura - right lamina sternal pericardial ligament

Relationships to external structures

• Superior - Cupula, thoracic inlet, and neck
• Inferior - Anterior, middle (pericardium), and posterior mediastinum
• Anterior - manubrium
• Posterior - Transverse processes of first four throacic vertebra
• Lateral left - pleural cavity and left lung
• Lateral right - pleural cavity and right lung

Contents and relations from anterior to posterior

• Internal thoracic arteries - short pathway within mediastinum
  • Superior - base of neck, subclavian artery
  • Inferior - anterior mediastinum (not considered content of anterior mediastinum
  • Anterior - most lateral aspect of manubrium
  • Posterior - ascending aorta
  • Lateral - sternal pericardial ligament, mediastinal pleura, pleural cavity, lungs
  • medial - sternal pericardial ligament, mediastinal pleura, pleural cavity, lungs
• Thymus - directly posterior to manubrium (largely replaced by fat and connective tissue in the adult)
  • Superior - base of neck
  • Inferior - may extend into anterior mediastinum
  • Anterior - manubrium
  • Posterior - ascending aorta
  • Lateral left - sternal pericardial ligament, mediastinal pleura, pleural cavity, lungs
  • Lateral right - sternal pericardial ligament, mediastinal pleura, pleural cavity, lungs
• Ascending aorta -
  • Superior - base of neck, brachiocephalic artery
  • Inferior - pericardium
  • Anterior - thymus
  • Posterior - descending aorta
  • Lateral left - mediastinal parietal pleura
  • Lateral right - superior vena cava and brachiocephalic vv
• Superior vena cava -
  • Superior - base of neck, brachiocephalic vv
  • Inferior - pericardium
  • Anterior - thymus
  • Posterior - trachea, right bronchus
  • Lateral left - ascending aorta
  • Lateral right - phrenic nerve, mediastinal parietal pleura, lung
• Right phrenic nerve and pericardiacophrenic vessels -
  • Superior - base of neck, brachiocephalic vv
  • Inferior - pericardium (anterior to hilum)
  • Anterior - mediastinal pleura
  • Posterior - trachea, right bronchus
  • Lateral left - superior vena cava
  • Lateral right - mediastinal parietal pleura, lung
• Left phrenic nerve and pericardiacophrenic vessels -
  • Superior - base of neck
  • Inferior - pericardium (anterior to hilum)
  • Anterior - mediastinal pleura
  • Posterior - left bronchus, vagus nerve
  • Lateral left - mediastinal parietal pleura, lung
  • Lateral right - anterior aspect aortic arch
• Aortic arch -
  • Superior - brachiocephalic artery, left common carotid artery, left subclavian artery, base of neck
  • Inferior - left recurrent laryngeal nerve, pericardium
  • Anterior - ascending aorta
  • Posterior - descending aorta
  • Lateral left - anterior: phrenic nerve and pericardiacophrenic vessels, posterior: left vagus nerve, superficial cardiac plexus
  • Lateral right - left recurrent laryngeal nerve, trachea and bifurcation,
• Trachea and bifurcation - centrally located with superior mediastinum
  • Superior - base of neck
  • Inferior - pericardium, posterior mediastinum
  • Anterior - ascending aorta, superior vena cava, deep cardiac plexus, paratracheal lymph nodes
  • Posterior - left: left recurrent laryngeal nerve, middle: esophagus, thoracic duct, right: right vagus nerve
  • Lateral left - aortic arch
  • Lateral right - arch of the azygos v
• Arch of the azygos vein
  • Superior - superior vena cava
  • Inferior - right main bronchus
  • Anterior - cupula, root of neck
  • Posterior - thoracic sympathetic trunk
  • Lateral left -trachea, right vagus (deep to arch), esophagus
  • Lateral right - mediastinal pleura, pleural cavity, lung
• Left Vagus
  • Superior - common carotid artery, cupula, root of neck
  • Inferior - hilum of lung (passes posterior to hilum)
  • Anterior - phrenic nerve, mediastinal pleura
  • Posterior - descending aorta, esophagus
  • Lateral left - mediastinal pleura
  • Lateral right - aortic arch
• Left recurrent laryngeal nerve
  • Superior - root of neck, cupula
  • Inferior - hilum of lung, posterior mediastinum
  • Anterior - aortic arch: ligamentum artiosum, tracheoesophageal groove: trachea
  • Posterior - aortic arch: descending aorta, tracheoesophageal groove: esophagus
  • Lateral left - aortic arch: superficial cardiac plexus, tracheoesophageal groove: aortic arch
  • Lateral right - aortic arch: trachea, tracheoesophageal groove: trachea, esophagus
• Right Vagus
  • Superior - brachiocephalic artery, cupula, root of neck
  • Inferior - hilum of lung (passes posterior to hilum)
  • Anterior - super vena cava
  • Posterior - azygos vein, esophagus
  • medial - trachea, right bronchus
  • Lateral - arch of the azygos vein
• Esophagus
  • Superior - root of neck, cupula
  • Inferior - posterior mediastinum
  • Anterior - middle: trachea, left: left recurrent laryngeal nerve, right: right vagus nerve, right main bronchus
  • Posterior - middle: thoracic duct, right posterior intercostal vein and artery, left: accessory hemiazygos vein, right: mediastinal pleura
  • Lateral left - descending aorta, left vagus nerve
  • Lateral right - arch of the azygos vein, mediastinal pleura
• Descending aorta
  • Superior - cupula, root of neck
  • Inferior - posterior mediastinum
  • Anterior - aortic arch
  • Posterior - accessory hemiazygos vein
  • Lateral left - mediastinal pleura
  • Lateral right - thoracic duct, esophagus
• Thoracic duct
  • Superior - root of neck
  • Inferior - posterior mediastinum
  • Anterior - left: descending aorta, right: esophagus
  • Posterior - right posterior intercostal artery and vein,
  • Lateral left - accessory hemiazygos vein
  • Lateral right - esophagus, mediastinal pleura
• hemiazygos vein (and/or accessory hemiazygos vein)
  • Superior - cupula, root of neck
  • Inferior - posterior mediastinum
  • Anterior - descending aorta
  • Posterior - left thoracic sympathetic trunk
  • Lateral left - mediastinal pleura
  • Lateral right - vertebral body, thoracic duct
• Right posterior intercostal arteries
  • Superior - cupula, root of neck
  • Inferior - posterior mediastinum
  • Anterior - right posterior intercostal veins, accessory hemiazygos vein, descending aorta, thoracic duct, esophagus
  • Posterior - vertebral bodies
  • Lateral left (medial) - vertebral bodies
  • Lateral right - thoracic sympathetic trunk, mediastinal pleura
• Thoracic Sympathetic trunk
  • Superior - cupula, root of neck
  • Inferior - posterior mediastinum
  • Anterior - right: arch of the azygos vein, left: accessory hemiazygos vein
  • Posterior - body of rib, intercostal nerves
  • Lateral - mediastinal pleura
  • medial - neck of ribs, vertebral bodies

General

• General comments here.

Fascial specializations

• crual fascia - investing fascia making up the lateral boundary of the lateral compartment
• Anterior intermuscular septum attaches to fibula - separates the lateral from the anterior compartment
• Posterior intermuscular septum attaches to fibula - separates the lateral from the posterior compartment

Boundaries

• Superior - crual fascia knee joint capsule
• Inferior - continuous with dorsum of foot
• Anterior - anterior intermuscular septum
• Posterior - posterior intermuscular septum
• Lateral - crual fascia between anterior and posterior intermuscular septa
• Medial - fibula

Contents and relationships

• Muscles
  • peroneus longus
  • peroneus brevis
• Nerves
  • Deep peroneal nerve - pierces posterior and anterior intermuscular septa (crual fascia)
    • crosses lateral aspect of the neck of the fibula prior to entering anterior compartment
    • supplies a twig to knee joint and, commonly, a motor branch to peroneus longus prior to entering anterior compartment
  • Superficial peroneal nerve - pierces posterior intermuscular to enter lateral compartment
    • crosses neck of fibula slightly inferior to deep peroneal nerve and more longitudinal
    • extends inferior between peroneus longus and brevis and provides motor innervation to peroneus brevis and peroneus longus
    • pierces the crual fascia to supply a cutaneous distribution on the dorsum of the foot
• Vasculature
  • fibular circumflex artery - superior in compartment
  • peroneal artery (posterior compartment) - branches pierce posterior intermuscular septum to supply middle of lateral compartment
  • branches of the malleolar anastomosis supply the inferior aspect of the lateral compartment

Actions at the foot

• Peroneus longus and brevis are primarily everters of the foot and secondary for plantar flexion

Support of the arches of the foot

• Peroneus longus and brevis support the lateral longitudinal arch as "suspension" elements
• Peroneus longus supports the transverse arch as a "tie-beam" element
• Peroneus longus supports the medial longitudinal arch as a staple - splays across plantar tarsal joints

Injury

• Damage to the lateral compartment would cause the foot to be inverted due to unopposed inverters (tibialis anterior/posterior). The lateral longitudinal arch would weaken due to reduced superior support. The transverse arch would weaken to do reduced transverse support (tie beam). The medial longitudinal arch would be minimally effected.

Anatomy of the superior gluteal nerve

• Leaves the pelvic cavity by way of the greater sciatic foramen to enter the gluteal region
• Enters the gluteal region superior to the piriformis muscle
• Extends laterally across gluteal region in a fascial plane deep (anterior) to gluteus medius and superficial (posterior) to gluteus minimus and supplies these two muscles
• Extends as far laterally as tensor fascia lata and supplies this muscle
• Vasculature supply is largely by the superior gluteal artery and vein

Intragluteal injection

• Accidental injection into the upper medial quadrant of the gluteal region puts the superior gluteal nerve at risk
• Upper lateral quadrant is preferred for injection because the super gluteal nerve has ramified prior the reaching this location

Origins and insertions based on proximal/distal

• Gluteus medius - origin: ala of ilium between anterior and posterior lines, insertion: superior greater trochanter
• Gluteus minimus - origin: ala of ilium between anterior and inferior gluteal lines, insertion: superior greater trochanter anterior to gluteus medius
• Tensor fascia lata - anterior superior iliac spine, insertion: head of fibula by way of joint capsule and iliotibial tract

Actions

• Gluteus medius - abduction of thigh, medial rotation
• Gluteus minimus - abduction of thigh, medial rotation
• Tensor fascia lata - abduction of thigh
• Functional reversal for all three muscles - abduction (stabilization) of pelvis when lower extremity is planted

Disruption of gate - both lower extremities are effected

• Paralysis of gluteus medius and minimus causes dropping of the pelvic girdle opposite to the side of injury. Normally, during walking, gluteus minimus and gluteus medius pull downward on the pelvic girdle opposite to the limb in swing phase. This action stabilizes the pelvic girdle. The gluteus minimus and medius mm are viewed as arising from the femur (greater trochanter) and inserting upon the ilium. This demonstrates a reversal of origin and insertion. When gluteus medius and minimus are paralyzed the pelvis drops to the side of swing phase. In order to restore the line of gravity, the patient leans to the side of the injury. The resulting gate is known as Trendelenberg's gate (gluteal waddle).

General

• Between the left atrium and ventricle is the bicuspid atrioventricular ( Mitral) valve
• Between the left ventricle and aorta is aortic semilunar valves
• Healthy valves permit little to no back flow
• Integrated with the skeleton of the heart
• Located in the ventricles (atrioventricular valves) and at the base of the arterial trunks (semilunar valves)
• The atrioventricular valves and the semilunar valves are closed by the pressure (they are not closed by muscular contraction applied to the cusps)
• Pulmonary veins to left atria to biscupid (mitral) valve to left ventricle to aortic valve to systemic circulation to coronary arteries during diastole
• Atrioventricular valves close (lub) during systole whereas the semilunar valves close (dub) during diastole

Structure

• Cone shaped having the aortic vestibule as the outflow path toward aortic valve
• Myocardial walls are thickest for the left ventricle
• Trabeculae carneae are fine and delicate relative to the right ventrical
• Interventricular septum - pars muscularis and pars membranacea
• Lymph drainage along coronary arteries toward tracheobronchial nodes and then bronchiomediastinal lymph trunks
• Branches of the AV bundle run through interventricular septum and outer wall

Atrioventricular valve - Biscuspid (Mitral Valve)

• Between the left atria and the left ventricle
• Two cusps open into the left ventricle
• Two papillary muscles - anterior and posterior
• Resists extreme pressure generated by left ventricular contraction
• Cusps are stabilized by chorda tendeneae - fibrous cords between cusps and papillary muscles
• Ventricular contraction raises pressure - blood pools on ventricular side of cusps causing the cusps to approximate each other and close the valve
• Adjustments by the papillary muscles and chorda tendeneae provide support and prevent eversion of the cusps into the atria
• Note - contraction of the papillary muscles, in the absence of ventricular contraction, open, not close, the atrioventricular valves

Semilunar valve - aortic valve

• Located at the base of the aortic trunk
• Prevents reverse flow from the aorta to the left ventricle during diastole
• Negative pressure of left ventricle and elastic recoil of systemic arteries move aortic blood toward the valve
• Opened by blood flow during systole - cusps move toward aortic wall and block coronary ostia
• Three cusps - no papillary muscles or chorda tendeneae
• Left and right coronary cusps (feed coronary arteries) and a non-coronary cusp
• Nodule - weighted fibrous thicking at the midline of the free edge of each cusp aids in approximating the cusps and closing the valve
• Aortic sinus - space between the wall of the aorta and each cusp
• Valve closed by pressure - blood pools in the aortic sinuses during diastole and aproximates the nodules

Referred pain to medial aspect of arm

• Anatomic pathways for pain sensation (visceral) from the heart (epicardium) 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)
• Anatomic pathways for pain sensation (somatic) from the medial arm follow - intercostobrachial nerve (T2), intercostal nerve, spinal nerve (ventral ramus), dorsal root (dorsal root ganglion at T2), spinal cord at T2.
• Cross talk is thought to occur within the dorsal ganglia or within the spinal cord (CNS).

Comment - Blood flow to the coronary vessels

• Coronary arteries are perfused during diastole when heart muscle is relaxed
• During systole the coronary ostia are blocked by the open cusps of the aortic valve
• During diastole blood pools in the aortic sinuses and closes the aortic valve.
• Blood driven into the left and right aortic sinuses enters into the ostia of the coronary arteries.
• Primary blood supply to the left ventricle and the interventricular septum is by the left coronary artery
• Right coronary artery supplies part of posterior wall of left ventricle on diaphragmatic surface