Mediastinum

● Continuous with the cervical and lumbar sympathetic trunks ● Lie against the heads of the ribs in the superior part, the costovertebral joints in the middle, and sides of the vertebral bodies in the inferior part of the thorax ● Located prevertabrally, outside the posterior mediastinum ● Preganglionic fibers to the preaortic ganglia of abdomen

Thoracic symphathetic trunks

● Has greater, lesser, and least splanchnic nerves ● Part of the abdominopelvic splanchnic nerves because they supply viscera inferior to the diaphragm ● Sympathetic innervation to the viscera of the abdomen. ● Usually, the greater splanchnic nerve innervates the foregut. ● Carries sensory innervation to the pancreas -sometimes transected/electrocauterized in pancreatic cancer cases to alleviate pain.

Lower thoracic sphlanchnic nerve

→ Infection/inflammation → Abscess can follow the track of pleural space along posterior mediastinum ▪ Infection in neck can spread to the chest → Middle mediastinum issue → Inflammation of pericardium ▪ Pericardial sac contracts → Heart has no room for expansion ▪ Chest pain

Mediastinitis; Pericarditis

ARTERIAL SUPPLY: ● Mainly from the ___________________, a thin branch of the internal thoracic artery → Parallels the phrenic nerve to the diaphragm ● Smaller contributors: → Musculophrenic artery (terminal branch of internal thoracic) → Bronchial, esophageal, and superior phrenic arteries (from thoracic aorta) → Coronary arteries for the visceral layer of serous pericardium (first branches of aorta) VENOUS DRAINAGE: ● ___________________ (tributaries of brachiocephalic or internal thoracic) ● Tributaries of the azygos venous system

pericardiacophrenic artery; pericardiacophrenic veins

● A bag where the heart is located ● It has fluid, a potential space, just enough for the mobility of the heart ● If it has no fluid, very adherent, it lead to pericardial rub ● If it's filled with so much fluid, engorged veins are observed as well as compensatory tachycardia, faint heart sounds, and hypotension → _________________: Heart cannot expand because the pericardial sac is filled with fluid → __________________: happens when stabbed; blood in pericardial sac; may lead to cardiac tamponade

pericardial sac; cardiac tamponade; hemopericardium

● Arise from ventral rami C3, C4 and C5 of the cervical plexus ● Supply diaphragm with motor and sensory fibers (sensory is 1/3 of the nerve fibers) → Sensory to superior and inferior diaphragm ● Supply sensory fibers to pericardium and mediastinal pleura ● Enters mediastinum between subclavian artery and origin of the brachiocephalic vein, passing anterior to the roots of the lungs → Landmark ▪ Anterior scalene muscle ▪ Follow that plane and go behind/dorsal to the subclavian vein, it courses along the pericardium → Location ▪ Lateral to pericardium ▪ Outside the pericardial sac ● "Doc, masakit po leeg ko." → Cancer of the liver irritating the diaphragm, pneumonia irritating the pleura or pericarditis

phrenic nerve

● Both sensory and motor ● There are cases when there is a problem in the mediastinum but pain is felt in the neck ● Its sensory somatic fibers (passing between the heart and the lungs) sense pain of the parietal pericardium, which will be felt on the skin of the ipsilateral supraclavicular region (part of the dermatomes of C3-C5) ● Provides motor innervation to the diaphragm. ● Diaphragm flattens when it contracts. If phrenic nerve is injured, elevated diaphragm is seen.

phrenic nerve

● Posterior to pericardium, where they are related to esophagus and thoracic aorta ● Receive lymph from the esophagus, the posterior aspect of the pericardium and diaphragm, and the middle posterior intercostal spaces ● Drains to the right or left venous angles via the right lymphatic duct or thoracic duct ● On each side of vertebral column ● Communicates with abdominal Inferior Vena Cava ● Drains the back and thoracoabdominal walls and mediastinal viscera ● Unpaired, but its main tributary, the hemi-azygos veins arise from the IVC and/or renal vein, merging with the ascending lumbar veins

posterior mediastinal lymph nodes; azygos vein

____________________ ● Posterior part of inferior mediastinum ● Boundaries: → Superior: ______________ → Anterior:_______________ → Posterior: _______________ → Lateral: ____________ ● Contents? (6) ● Contents at the level of angle of Louis? → Right? (3) → Left? (3)

posterior mediastinum; transverse thoracic plane; pericardium and diaphragm; T5-T12 vertebrae; parietal pleura Contents of the Posterior Mediastinum: 1) Thoracic aorta 2) Thoracic duct and lymphatic trunks 3) Posterior mediastinal lymph nodes 4) Azygos and hemi-azygos veins 5) Esophagus 6) Esophageal nerve plexus 7) Sympathetic trunks right: arch of the azygos draining into the SVC, pulmonary a., v., right bronchus left: pulmonary a., v., impression of arch of the aorta, descending aorta

● _________________ → Passes along right side of brachiocephalic vein, SVC, and right atrium → Descends on right side of IVC to the diaphragm, where it pierces the caval opening ● __________________ → Descends between left subclavian and left common carotid arteries → Passes over the left superior intercostal vein → Runs along the fibrous pericardium, superficial to left atrium and ventricle → Pierces the diaphragm to the left of the pericardium, where it branches for distribution on the diaphragm's inferior or abdominal surface

right phrenic nerve; left phrenic nerve

_________________ → Gives rise to _________________, which hooks around the ______________ and ascends between trachea and esophagus to supply larynx → Passes posterior to right brachiocephalic vein, SVC, and root of right lung → Divides into the _________________, __________________ (right and left vagus), and nerves which contribute to the ___________________ ________________ → Enters mediastinum between the left common carotid and left subclavian artery → Separated laterally from the phrenic nerve by the left superior intercostal vein at the level of the arch of the aorta → Gives rise to _____________, which passes inferior to ___________, lateral to ligamentum arteriosum, and ascends to larynx in the tracheoesophageal groove → Passes posterior to root of left lung → Divides into the _____________, ________________ (right and left vagus nerve fibers) → Along the course of the esophagus, you have the anterior vagus, which was previously the left vagus nerve

right vagus nerve; right recurrent laryngeal nerve; right subclavian artery; right pulmonary plexus; esophageal nerve plexus; cardiac plexus; left vagus nerve; left recurrent laryngeal nerve; aortic arch; left pulmonary plexus; esophageal nerve plexus

_______________________ • Central compartment of the thoracic cavity, containing all the thoracic viscera (thymus, pericardial sac, heart, trachea, major arteries and veins) and structures except the ________ • Can accommodate movement and volume or pressure changes because of the loose connective tissue and elastic lungs and parietal pleura: - Respiration (movements of diaphragm, thoracic wall, tracheobronochial tree) - Contraction of the heart - Pulsations of great arteries - Passage of ingested substances through esophagus

mediastinum; lungs

________________________ Mainly the content of the pericardium or the pericardial sac Contents? (5) ● Coating of the heart ● Encloses the heart and roots of the ascending aorta, pulmonary trunk, and superior vena cava → Heart and roots of great vessels - within the pericardial sac posterior to sternum, costal cartilages, and anterior ends of the 3rd - 5th ribs on the left side → Heart and pericardial sac are situated obliquely, 2/3 to the left and 1/3 to the right → Ascending aorta - carries pericardium superiorly to level of sternal angle → The base of the heart is fixed posteriorly to the pericardial wall, opposite the bodies of vertebrae T5 to T8 (T6 to T9 when standing) ● Influenced by movements of the heart, great vessels, sternum, and diaphragm ● Layers: Epicardium, Endocardium, Pericardium

middle mediastinum; pulmonary veins; pulmonary artery and aorta; SVC and IVC; pericardium

● Exit the cranium and descend through the neck posterolateral to the common carotid arteries ● Enters the mediastinum posterior to the SC joint and brachiocephalic vein ● Pass posterior to the roots of the lungs ● Development of right and left vagus nerves → Direction of stomach is at the left side with the greater curvature lateral → Initially, the greater curvature is dorsally located. The stomach is rotated to the left, thus: ▪ the right vagus nerve became ______________ ▪ the left vagus nerve became _____________

vagus nerve; posterior; anterior

→ Collateral pathway between the SVC and IVC → Drains blood from the posterior walls of the thorax and abdomen → Passes close to the inferior 8 thoracic vertebrae → Arches over superior aspect of root of the right lung to join the SVC → Communicates with the vertebral venous plexus that drains the back, vertebrae, and structures in the vertebral canal, along with the posterior intercostal veins → Receives the mediastinal, esophageal, and bronchial veins → Connections: ▪ Abdominal IVC ▪ Hemiazygos vein → Counterpart is the thoracic duct - draining all the lymphatic system of the left side ▪ Azygos system of veins sort of drain the thoracic cavity into the right side → Relationship of the azygous with that of the right bronchus: ▪ Tumors of the right bronchus may manifest as azygos vein issue, thus, operation in this area may result to injury to the azygous

Azygos veins

● Formed by union of internal jugular veins and subclavian veins posterior to the sternoclavicular joints ● Unite to form the SVC at the level of the 1st right costal cartilage ● The left is twice as long as the right since it crosses over to the opposite side to unite for the SVC ● Shunt blood from the head, neck and upper limbs to the right atrium Begins at aortic orifice, around 2.5 cm in diameter ● Only branches are the coronary arteries from the aortic sinuses ● Intrapericardial and inferior to the transverse thoracic plane, and thus is considered a content of middle mediastinum

Branchiocephalic Veins; ascending aorta

→ Arises on left side of vertebral column by junction of left subcostal and ascending lumbar veins → Posterior to thoracic aorta until T9 vertebra, where it crosses to the right to join the azygos vein → Receives the inferior three posterior intercostal veins, the inferior esophageal veins, and several small mediastinal veins → May connect with left renal vein

Hemi-azygos veins

→ People who have this disease would sometimes have an enlarged thymus, known as ___________, which could obliterate the superior and anterior mediastinum by X-ray → A motor issue at the level of the motor neurons. → Common manifestation: Eyelids okay in the morning but cannot be opened anymore in the afternoon ● Corresponds to the aorta on the right side of the trachea, over the root of the right lung ● Drains thorax ● Superior to main bronchus ● Arch around right main bronchus

Myasthenia gravis; thymoma; azygos vein

● Returns blood from all structures superior to the diaphragm except lungs and heart → SVC drains the head, neck and upper anterior chest ● Ends and enters __________ at level of the 3rd costal cartilage ● Lies in the right side of the superior mediastinum, anterolateral to trachea and posterolateral to ascending aorta ● Lies beside the right phrenic nerve which is between the SVC and mediastinal pleura ● Its terminal half is in the middle mediastinum, where it forms the posterior boundary of the transverse pericardial sinus ● __________________ → If squeezed because of a tumor or because of a mediastinal structures compressing it, blood can go in but cannot go back 🡪 leads to an enlarged head and prominent veins in neck → Edematous arm and head

Superior Vena Cava; right atrium; SVC syndrome

● Found at the level of the 2nd ribs ● Corresponds to SVC before it enters the pericardium ● Above the plane of the angle of Louis is the arch of the aorta ● Transects arch of the aorta and the trachea ● Curved continuation of the ascending aorta ● Begins posterior to 2nd right sternoclavicular (SC) joint at level of sternal angle ● Ascends anterior to right pulmonary artery and bifurcation of trachea ● Apex at left side of trachea and esophagus, passing over the root of the left lung ● Ends by becoming the thoracic (descending) aorta posterior to 2nd left SC joint enumerate the three branches of the arch of the aorta

angle of louis; arch of the aorta; left subclavian a., left common carotid a., branchiocephalic trunk which branches into the right common carotid a. and right subclavian a.

_______________________ ● Potential space anterior to middle mediastinum ● Smallest subdivision of the mediastinum ● Boundaries: → Anterior: _______________ → Posterior: _______________ → Superior: ______________ → Inferior: ____________ ● In infants and children, this part contains the inferior part of the thymus ● Contents? → Could be present: ▪ Ectopic parathyroid tumors ▪ Thymoma (tumor from epithelial cells of thymus)

anterior mediastinum; body of sternum; pericardium; transverse thoracic plane/superior mediastinum at sternal angle; diaphragm; thymus

● The branches of the thoracic aorta arise and course within three vascular planes → _________________ - unpaired, serving visceral branches to the gut (what arteries) → _________________ - paired, serving viscera other than the gut (what arteries) The right bronchial arteries arise indirectly as branches of a right posterior intercostal artery while the left bronchial arteries arise directly from the aorta → _________________ - paired/segmental, serving parietal branches to the body wall (what arteries) Supply all but the upper two intercostal spaces and subcostal arteries ● Exceptions to the vascular planes? → _____________ - paired, parietal branches which anastomose with the musculophrenic and pericardiophrenic branches of internal thoracic → _____________- unpaired branches that send twigs to the pericardium

anterior, midline plane; esophageal arteries; lateral planes; bronchial arteries; posterolateral plane; posterior intercostal arteries; superior phrenic arteries; pericardial branches

● First and largest branch of the aortic arch ● Anterior to trachea, posterior to right brachiocephalic vein ● Divides into the right common carotid and right subclavian veins at the right SC joint ● Second branch of the aortic arch ● Anterior to the left subclavian artery ● Enters the neck by passing posterior to the left SC joint ● 3rd branch of aortic arch ● Arises from posterior part of the arch, posterior to the left common carotid artery ● Ascends lateral to the trachea and left common carotid artery through the superior mediastinum ● Enters the root of the neck without branching, passing behind the left SC joint

branchiocephalic trunk; left common carotid a.; left subclavian a.

● Fibromuscular tube that extends from pharynx to the stomach ● Enters superior mediastinum between the trachea and vertebral column (T1-T4 vertebrae) ● Flattened anteroposteriorly and compressed anteriorly (by root of left lung) ● Inclines to the ______ but is pushed back to the median plane by aortic arch ● Lies on the right side of the thoracic duct ● Three constrictions: 1. __________ esophagus taking off from the ______________ level (C6) ▪ Cricopharyngeus should close when you eat, but when food reaches the pharynx, it opens (upper esophageal sphincter) 2. Non-functional, anatomical _________________ constrictions because of the impression of the ____________ and the ___________ 3. The next constriction would be at the level of the _________, where the esophagus would go to the stomach. ▪ Foreign bodies get stuck in the constrictions _________________ - passageway into the diaphragm, terminates at ___

esophagus; left; cervical; cricopharyngeal; mid-esophageal; arch of the aorta; left main bronchus; hiatus; esophageal hiatus; T10

Fibroserous membrane* ● ________________ - tough external layer which protects the heart against sudden overfilling → Cone-shaped bag with attachments which retain the heart in its position and limit cardiac distention → Innervated by _____________ and supplied by ____________________ → Attachments: ▪ Superior: tunica adventitia (perivascular connective tissue) of vessels entering and leaving the heart, pretracheal layer of deep cervical fascia ▪ Inferior: pericardiacophrenic ligament (site of continuity to the central tendon of diaphragm) ▪ Anterior: sternopericardial ligament (attached to posterior surface of sternum) ▪ Posterior: loose connective tissue connecting to structures in posterior mediastinum

fibrous pericardium; phrenic nerves; pericardiocophrenic vessels

● _______________ - composed of mesothelium, a single layer of flattened cells lining the fibrous pericardium and external surface of the heart → _____________ - inner serous membrane, reflected onto the heart at the aorta, pulmonary trunk and veins, and superior and inferior venae cavae (SVC and IVC) → _____________ - forms the epicardium, the outermost layer of the heart ▪ Continuous with the parietal layer at the following: a. Superiorly, where the aorta and pulmonary trunk leave the heart b. Posteriorly, where the SVC, IVC, and pulmonary veins enter the heart → Pericardial cavity - narrow space between opposing layers of the parietal and visceral layers, containing a thin film of fluid that enables the heart to move and beat in a frictionless environment ▪ ___________________ - transversely running passage between the two groups of vessels (aorta, pulmonary trunk and SVC, IVC, pulmonary veins) and the reflections of serous pericardium around them a. Posterior to intrapericardial parts of pulmonary trunk and ascending aorta b. Anterior to SVC c. Superior to atria ▪ ___________________ - wide pocket-like recess formed by the left atrium; a blind sac (cul-de-sac) a. Posterior to base of heart b. Laterally bound by pericardial reflections surrounding pulmonary veins and IVC c. Posteriorly bound by pericardium overlying the anterior surface of the esophagus d. Obliqueness is due to impression of IVC & SVC to the right side of the mediastinum ▪ The sinuses form during development of the heart as a consequence of the folding of the primordial heart tube a. Venous end folds posterosuperiorly to lie adjacent to arterial end, separated by transverse pericardial sinus

serous pericardium; parietal layer; visceral layer; transverse pericardial sinus; oblique pericardial sinus

Divisions of the Mediastinum 1) ________________: Thoracic inlet to transverse thoracic plane (T1-T4) 2) _______________: Angle of Louis (sternal angle) anteriorly (where 2nd rib can be found) and junction of T4 and T5 posteriorly 3) _______________: Transverse thoracic plane to diaphragm 4) _______________: Bounded by pericardial sac 5) _______________: Anterior to pericardial sac and posterior to body of sternum 6) _______________: Anterior to thoracic spine (T5-T12) and posterior to pericardial sac and diaphragm

superior mediastinum; transverse thoracic plane (T1-T4); inferior mediastinum; middle mediastinum; anterior mediastinum; posterior mediastinum

● Continuation of arch of the aorta (descending) ● Begins on left side of inferior border of the body of T4 vertebra ● As it descends, it approaches the median plane and displaces the esophagus to the right → Unpaired visceral branches? (2) → Paired visceral branches? → Paired parietal branches? → Exception? ● Posterior to the root of the left lung, pericardium, and esophagus ● Terminates at the ____ vertebra and enters the abdomen through the __________ in the diaphragm (along with the thoracic duct and azygos vein) _______________ - supply lymph nodes and other tissues of posterior mediastinum _______________ - Autonomic nerve plexus which surrounds the thoracic aorta

thoracic aorta; esophageal, pericardial; bronchial arteries; intercostal; anterior pair of superior phrenic arteries; T12; aortic hiatus; mediastinal arteries; thoracic aortic plexus

● Largest lymphatic channel in the body ● Lies on the bodies of the inferior 7 thoracic vertebrae ● Ascends in the posterior mediastinum between the thoracic aorta and azygos vein ● Crosses to the left, posterior to esophagus at level of T4, T5 or T6 ● Conveys most lymph of the body to the venous system (from lower limbs, pelvic cavity, abdominal cavity, left upper limb, left side of thorax, head, and neck) except from the right superior quadrant → Empties into venous system near the union of the left internal jugular vein and subclavian veins ● Originates from the ______________ in the abdomen ● Ascends through the aortic hiatus in diaphragm ● Often beaded because of numerous valves → Receives branches from middle and superior intercostal spaces of both sides through several collecting trunks → Often receives jugular, subclavian, and bronchomediastinal lymphatic trunks near its termination

thoracic duct; cisterna chyli

Boundaries of the Mediastinum - Superior: ___________ - Inferior: _____________ - Anterior: ___________ - Posterior: _____________ - Lateral: _____________

thoracic inlet; diaphragm; sternum and costal cartilages; thoracic spine; right and left pleural cavities

● Primary lymphoid organ located in the inferior part of the neck and anterior part of superior mediastinum → Training ground for the T-lymphocytes → 2-lobed ● Flat gland with flask-shaped lobes ● Extends into the anterior mediastinum, anterior to fibrous pericardium ● Atrophies in adult; size to be perceived as fatty mass ● Supplied by anterior intercostal and anterior mediastinal branches of internal thoracic arteries ● Venous drainage by left brachiocephalic, internal thoracic, and inferior thyroid veins ● Lymphatic drainage by parasternal, brachiocephalic, and tracheobronchial lymph nodes

thymus

● Anterior to esophagus → C6 to T4 at sternal angle → Bifurcates into right and left bronchi at the carina, approximating the level of the angle of Louis and the level of T4 → The bifurcation is different when lying down and when standing up ● Enters superior mediastinum, inclining a little to the right of the median plane

trachea

● Borders of Superior Mediastinum → Inferior: ________________ → Superior: ______________________ ● Connects the neck and the chest What are the contents of the superior mediastinum? (6) ● Contents from anterior to posterior according to Moore: (6) ______________ (ectopic- in an abnormal place or position) − Embryologically, superior and inferior were derived from the 4th and 3rd branchial arches, respectively, along with the thymus. − When the thymus and the parathyroid went down embryologically, the parathyroid should still remain in the neck but occasionally, it may ectopically be found in the superior mediastinum.

transverse thoracic plane (imaginary plane from T4 and T5 vertebra to the sternal angle); thoracic inlet Contents of the Superior Mediastinum (anterior to posterior): 1) Thymus 2) Great vessels - branchiocephalic veins, SVC - arch of the aorta, branchiocephalic trunk, left common carotid a., left subclavian a. - phrenic n., vagus n. 3) Cervical viscera (trachea, esophagus, left recurrent laryngeal nerve) 4) Thoracic duct and lymphatic trunks 5) Level VII lymph nodes 6) Parathyroid Thymus -> Veins -> Arteries -> Airway -> Alimentary Tract -> Thoracic Duct and Lymphatic Trunks parathyroid