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THORACIC WALL AND CAVITY (PART B) - Coggle Diagram
THORACIC WALL AND CAVITY (PART B)
Mediastinum
Definition
: It is the central space of the thoracic cavity located behind the sternum and between the two lungs and their respective pleura.
Boundaries (General)
Anterior
: sternum and transversus thoracic muscles.
Posterior
: vertebral column.
Superior
: thoracic inlet.
inferior
: diaphragm.
Lateral
: pleura of the lung.
Etymology
: Medial, based on Latin "Medius" middle.
Boundaries (Specific)
Superior mediastinum
Boundaries
: Superior -> First rib; Inferior-> Transthoracic plane.
Organs
: Thymus (prepubertal), Right and Left brachiocephalic veins (joint to form SVC), Aortic arch and its 3 branches, Trachea, Esophagus.
Causes of mediastinal masses
: Lymphomas, Thymomas.
Vessels
Arteries
: Aortic arch, Brachiocephalic a., Left common carotid a., Left subclavian a.
Veins
: SVC, Brachiocephalic Veins.
Inferior mediastinum
Middle
Boundaries
: Anterior -> Anterior margin of pericardium; Posterior -->posterior pericardium.
Organs
: Heart and pericardium, Tracheal bifurcation.
Causes of mediastinal masses
: Bronchogenic cysts, Hiatal Hernia, Metastases, Bilateral hilar lymphadenopathy.
Vessels
Arteries
: Root of aorta, Pulmonary trunk, Pericardiophrenic artery.
Veins
: SVC, IVC, Arch of azygos vein, Pulmonary veins.
Posterior
Boundaries
: Anterior -> Fibrous pericardium, Posterior sloping surface of diaphragm; Posterior -> vertebral column T5 - T12.
Organs
: Esophagus.
Vessels
Veins
: Azygos vein, Hemiazygos vein.
Arteries
: Thoracic portion of aorta
Causes of mediastinal masses
: Esophageal cancer, Aneurysm, Neurogenic tumor, Multiple Myeloma.
Anterior
Boundaries
: Anterior -> Body of sternum, Transversus thoracic muscles; Posterior -> pericardium.
Organs
: Thymus remnants (postpubertal), Connective tissue, Fat.
Vessels
Arteries
: internal thoracic arteries.
Veins
: internal thoracic veins.
Causes
of mediastinal masses: 4Ts; Thymoma, Thyroid (substernal goiter), Teratoma, Terrible lymphoma.
Blood Supply
Aortic arch
Branches
: Brachiocephalic trunk, Left common carotid artery, Left subclavian artery.
Location
: Superior mediastinum.
Supplies:
Head, Upper extremities.
Thoracic aorta
Location
: Posterior mediastinum.
Supplies
: Lungs, Mediastinum, Esophagus, Pericardium, Diaphragm, Chest wall.
Branches
: Bronchial arteries. Mediastinal arteries. Esophageal arteries Pericardial arteries Superior phrenic arteries. Posterior intercostal arteries (9pairs). Subcostal arteries.
Ascending aorta
Branches
: Left Coronary artery, Right Coronary artery.
Supplies
: Heart.
Location
: Middle mediastinum (posterior to sternum).
Pleura
Function
Protects and cushions the lungs, and reduces friction of movements, allowing the lungs to move smoothly in the chest cavity.
Layers & Innervation
Parietal pleura (4 layers)
Diaphragmatic peripheral part:
intercostal nerves.
Diaphragmatic central part:
Phrenic nerves.
Costal part
: Intercostal nerves.
Mediastinal part:
Phrenic nerves.
Visceral pleura
: Visceral sensory nerves that course with the autonomic nerves.
Definition: A thin double layer if tissue that surrounds the lungs and the thoracic wall.
Pleural Cavity
Definition
: The potential space between the parietal and visceral layers of the pleura.
Recesses
Content
: Costodiaphragmatic recesses, Costomediastinal recesses
Function
: Provides potential space for the lungs to expand during inspiration and movement of the diaphragm.
Potential space for:
Blood
: Hemothorax
Fluid
accumulation
: pleural effusion
Air
: pneumothorax
Content
: Pleural fluid (secreted by serous membranes in the pleura)
Pleura & Ribs
Visceral Pleura
Midaxillary line
: 8th Rib
Paravertebral line:
10th Rib
Midclavicular line:
6th Rib
Parietal Pleura
Midclavicular line
: 8th Rib
Midaxillary line
: 10th Rib
Paravertebral line
: 12th Rib
Clinical Relevance:
Open pneumothorax:
Occurs when air enters the pleural cavity following a penetrating wound of the chest cavity.
Tension pneumothorax
: Occurs when a piece of tissue covers and forms a flap over the wound.
Management & Procedure
Chest decompression
Method: Needle thoracostomy
Procedure
Adults -> 2nd ICS at MCL or 4th-5th ICS between the anterior and midaxillary line.
Children: 2nd ICS at MCL.
Diaphragm
Function: Main muscle of inspiration, and separates the thoracic cavity from the abdominal cavity.
NOTE
: The right hemidiaphragm is higher than the lest due to the liver below it.
Definition: C-shaped musculotendinous structure that separates the thoracic cavity from the abdominal cavity.
Respiration
Inspiration
Core muscles
: External intercostal, Diaphragm.
Accessory muscles
: Sternocleidomastoid muscle, Pectoralis minor.
Expiration
Core muscles
: Internal muscles Diaphragm.
Accessory muscles:
Abdominals, Quadratus lumborum.
Clinical Relevance
: Injuries to diaphragm or phrenic nerve palsies result in respiratory abnormalities because the diaphragm is the primary muscle of respiration.
Structure
Central tendon
: Forms the central part of the diaphragm where the muscle fibers converged.
Peripheral muscular parts
sternal part
: From the posterior surface of the sternum.
Lumbar part
: L1-L3 vertebrae (Right crus -->broader and longer; Left crus)
Costal part
: from inner surface of the sternum.
Hiatus (3 openings)
Esophageal hiatus (T10)
Location
: Located on the left of the midline within the muscle of the right crus.
Structures: Esophagus, Vagus nerve (CNX)
Aortic hiatus (T12)
Location
: Located in the midline behind the two crura.
Structures: Aorta, Azygos vein, Thoracic duct.
Caval hiatis (T8)
Location
: Located on the right of the midline within the central tendon
Structures: IVC and right phrenic nerve.
Clinical Relevance
Hiatal Hernia
: The protrusion of an abdominal structure\Organ into the thorax through a lax\abnormally large diaphragmatic esophageal hiatus is referred to as a hiatal hernia.
Innervation
Nerves
: Phrenic nerve (C3 - C5) C3,C4,C5 keep the diaphragm alive.
Clinical Relevance
: Referred pain -> Because of innervation to the diaphragm (motor and sensory) is primarily from C3 to C5 spinal nerves, pain arising from the diaphragm (e.g. subphrenic abscess) is referred to these dermatomes in the shoulder region.