7. Anatomy of Thoracic Wall.pdf

ANATOMY OF THORACIC WALL Thoracic wall is covered by: - Skin - Extrinsic muscles (muscles of the upper - Superficial fascia limb, muscles of abdomen, muscle...

ANATOMY OF THORACIC WALL Thoracic wall is covered by: - Skin - Extrinsic muscles (muscles of the upper - Superficial fascia limb, muscles of abdomen, muscles of the - Deep fascia back) The gap between the ribs are called intercostal spaces, which are filled up by the intercostal muscles, and contain intercostal nerves, vessels and lymphatics. STRUCTURE ASSOCIATED LAB/ LECTURE PHOTO INTERCOSTAL SPACES: - 11 intercostal spaces Classification of intercostal spaces: Typical intercostal space - 3rd to 6th space Atypical intercostal space - 1st, 2nd, 7th – 11th intercostal spaces INTERCOSTAL MUSCLES: - External intercostal muscle - Internal intercostal muscle - Transversus thoracis I. Intercostalis intimi II. Subcostalis III. Sternocostalis A. External Intercostal Muscle - 11 pairs - Extends from the tubercle of the rib behind to the costo-chondral membrane in front, where it is replaced by the anterior intercostal membrane - It arises from the lower border of the rib above, runs downwards forwards and medially in front (posteriorly however the fibres are running downwards and laterally) and inserts to the outer lip of the upper border of rib below - It is supplied by the intercostal nerve of the same space and functionally it elevates the ribs during inspiration. B. Internal Intercostal Muscle - 11 pairs - Extends from the side of the sternum to the angle of the rib behind, where it is replaced by the posterior intercostal membrane - It arises from the floor of the costal groove of the rib above, to run downwards forwards and laterally in  front (posteriorly however the fibres are running downwards and medially) and inserts into the inner lip of the upper border of the rib below. - Supplied by the intercostal nerve of the same space and functionally it elevates the ribs during expiration. C. Transversus thoracis muscle - Divided into I. Intercostalis intimus, II. Subcostalis, III. Sternocostalis I. Intercostalis intimus (11 pairs) - Occupies the middle two-fourth of the intercostal space - Arises from the inner surface of the rib above and inserts to the inner lip of the upper border of the rib below - Direction of the fibres same as internal intercostal - Supplied by the intercostal nerve of the same space and functionally it elevates the ribs during expiration II. Subcostalis - Lies in the same plane as Intercostalis intimus in the posterior part of the intercostal space - Arises from the inner surface of the rib near the angle and inserts on the inner surface of the 2nd or 3rd rib below. Direction of the fibres and nerve supply same as internal intercostal muscle - Functionally depressor of the ribs III. Sternocostalis - One on either side, and is situated behind the sternum and costal cartilages - Arises from the lower one-third of the posterior surface of the body of sternum and posterior surface of the xiphoid process; and posterior surface of the costal cartilages of lower 3 or 4 ribs - Fibres run upwards and laterally as slips and gets inserted into the lower border and inner surfaces of the costal cartilages of 2nd to 6th ribs - Supplied by the intercostal nerves and functionally draws down the costal cartilages to which it is inserted. IV. Levatores costarum - Placed on the back just lateral to the vertebral column - Arises from the tip of transverse processes of T7 to T11 vertebrae and gets inserted to the outer surface of rib between its tubercle and angle. - Functionally it elevates and rotates the neck of the rib in a forward direction; and also, rotators and lateral flexors of the vertebral column INTERCOSTAL NERVE: Ventral rami of thoracic spinal nerves Typical intercostal nerves (3rd, 4th, 5th, 6th): are those which remain confined to their own intercostal spaces. Atypical spinal nerves (1st, 2nd, 7th, 8th, 9th, 10th, 11th): extend beyond the thoracic wall and partly or entirely supply the other regions. Branches: - Rami communicantes, muscular branches, collateral branch (supplies intercostal muscles, parietal pleura and periosteum of ribs), lateral and anterior cutaneous branches - 7th – 11th nerves supply the muscles of the anterior abdominal wall, skin and parietal pleura. - Lateral cutaneous branch of 2nd intercostal nerve is called intercosto- brachial nerve INTERCOSTAL ARTERIES: Each space contains one posterior and two anterior intercostal arteries (upper & lower) present in the upper 9 spaces. Posterior Intercostal Arteries: - There are 11 pairs of intercostal arteries, one in each space Origin: I. The 1st and 2nd posterior intercostal arteries are the branches of superior intercostal artery—a branch of the costocervical trunk. II. The 3rd–11th posterior intercostal arteries arise directly from the descending thoracic aorta Posterior Intercostal Artery Branches: 1. Dorsal branch 2. Collateral branch 3. Muscular branches 4. Lateral cutaneous branch 5. Mammary branches (external mammary arteries) come from 2nd, 3rd, 4th posterior intercostal arteries to supply the mammary gland 6. Right bronchial artery – comes from right 3rd posterior intercostal artery NB: Coarctation of aorta: In coarctation of aorta (narrowing of arch of aorta), the posterior intercostal arteries are markedly enlarged and cause notching of the ribs, particularly in their posterior parts. Anterior Intercostal Arteries Origin: - In 1st – 6th spaces they arise from the internal thoracic artery (used to treat coronary heart disease). - In 7th and 9th spaces, they arise from musculophrenic artery. Termination The anterior intercostal arteries are short and end at the level of the costochonral junction as follows: - Upper anterior intercostal artery anastomoses with corresponding posterior intercostal artery. - Lower anterior intercostal artery anastomoses with collateral branch of the corresponding posterior intercostal artery. Branches: - pericardiophrenic branches - mediastinal branches - anterior intercostal branches - perforating branches - musculophrenic branches - superior epigastric branches. INTERCOSTAL VEINS: The number of intercostal veins corresponds to the number of intercostal arteries. Each intercostal space contains: - 2 anterior intercostal veins - 1 posterior intercostal vein Their tributaries correspond to the branches of the arteries Anterior Intercostal Veins - They are present only in the upper nine spaces. - Each space contains two veins that accompanies the anterior intercostal arteries Termination: - In upper six spaces, they end in the internal thoracic vein - In seventh, eighth, and ninth spaces, they end in the musculophrenic vein Posterior Intercostal Vein - They are present in all the spaces and one in each space - Each vein accompanies the posterior intercostal artery - Its tributaries correspond to the branches of posterior intercostal artery THORACIC OUTLET Boundaries: Anteriorly: Xiphoid process Posteriorly: Body of 12th thoracic vertebra. Laterally (on each side): Costal margin and 11th and 12th ribs. DIAPHRAM - Principle muscle of respiration - Consists of peripheral muscular part and central fibrous part called central tendon Origin: The origin consists of three parts: 1. Sternal part 2. Costal part 3. Vertebral part Sternal Part: It consists of two fleshy slips, which arise from the posterior surface of the xiphoid process Costal Part: On each side, it consists of six fleshy slips, which arise from the inner surface of lower six ribs near their costal cartilages. Vertebral Part: This part arises by means of: I. Right and left crura of diaphragm II. Five arcuate ligaments: a. Rt. & left Medial and lateral arcuate ligaments b. Median arcuate ligament Right crus: Originates from the anterior surface of the body of upper three lumbar vertebrae and intervertebral disc between them Left crus: Originates from the anterior surface of the body of upper two lumbar vertebrae and intervertebral disc between them - The medial tendinous margins of the crura pass forward and medial-ward, and meet in the mid- line to form an arch across the front of the aorta, the median arcuate ligament; which also serve for the origin of few fibres of diaphragm. Aorta passes deep to it - Medial Lumbocostal Arch - is the fascia covering the upper part of the Psoas major - medially, it is continuous with the lateral tendinous margin of the corresponding crus, and is attached to the side of the body of the L1 or L2 vertebra; laterally - it is fixed to the front of the transverse process of the L1 or may be L2. - Sympathetic trunk passes deep to it Lateral Lumbocostal Arch - arches across the upper part of the Quadratus lumborum - is attached, medially, to the front of the transverse process of the L1 - attached laterally, to the tip and lower margin of the twelfth rib. - Subcostal nerve and vessels pass deep to it - Arising from its convexity are fibres of origin of diaphragm Insertion of the diaphragm: From circumferential origin, the muscle fibres converge towards the central tendon and insert into its margins. The features of the central tendon are as follows: 1. It is trifoliate in shape, having a. an anterior (central) leaflet b. two tongue-shaped posterior leaflets. (b & c) 2. It is inseparably fused with the fibrous pericardium. 3. It is located nearer to the sternum than to the vertebral column. Major openings in the diaphragm and structures passing through them: Vena Caval Opening Transmits (T8) - Inferior vena cava - Right phrenic nerve Oesphageal opening transmits (T10): - Opening is present in right crus of the diaphragm - Oesophagus - Right and left vagal trunks - Oesophageal branches of left gastric artery Aortic opening transmits (T12) - it is an Osseo-aponeurotic opening - Azygos vein - Thoracic duct - Aorta Minor openings in the diaphragm and structures passing through them: - Superior epigastric vessels pass through the gap (space of Larry) between the muscular slips arising  from xiphoid process and 7th costal cartilage. - Musculophrenic artery passes through the gap between the slips of origin from 7th to 8th ribs. - Lower five intercostal nerves and vessels (i.e., 7th–11th) pass through gaps between the adjoining costal slips. - Subcostal nerves and vessels pass deep to the lateral arcuate ligament. - Sympathetic chain passes deep to the medial arcuate ligament. - Greater, lesser, and least splanchnic nerves pass by piercing the crus of diaphragm on the corresponding side. - Hemiazygos vein pierces the left crus of the diaphragm - Nerve supply to the diaphragm: Motor and sensory nerve supply I. Right and left phrenic nerves – sole motor to the diaphragm and sensory to the central part of the diaphragm II. Lower five intercostal and subcostal nerves – sensory to the peripheral part of the diaphragm - Sympathetic Supply from the coeliac plexus ARTERIAL SUPPLY: The diaphragm is supplied by the following arteries: 1. Superior phrenic arteries and Inferior phrenic arteries, from the abdominal aorta. 2. Pericardiophrenic arteries, from the internal thoracic arteries. 3. Musculophrenic arteries, the terminal branches of the internal thoracic arteries. 4. Superior epigastric arteries, the terminal branches of the internal thoracic arteries. 5. Lower five posterior intercostal and subcostal arteries from the aorta. NB: Corresponding veins accompanying the arteries drain into the systemic veins Action of Diaphragm: The diaphragm is the principal muscle of respiration. When it contracts, it descends and increases the vertical diameter of the thoracic cavity DEVELOPMENT OF DIAPHRAGM The diaphragm develops in the region of neck from the following four structures - Septum transversum, ventrally. - Pleuroperitoneal membranes at the sides. - Dorsal mesentery of esophagus, dorsally. - Body wall, peripherally. Most probably: - Central tendon of diaphragm develops from septum transversum. - Domes of diaphragm develop from pleuroperitoneal membrane. - Part of diaphragm around the oesophagus develops from the dorsal mesentery of oesophagus. - Peripheral part of diaphragm develops from the body wall. RESPIRATORY MOVEMENTS The anteroposterior diameter of the thoracic cavity is increased by: - Mainly by the elevation of the vertebrosternal ribs (2-6 ribs): Pump- handle movement - It is also partly increased by the elevation of vertebrochondral (7-10) ribs The transverse diameter of the thoracic cavity is increased by: - Mainly by the movements of the vertebrochondral (7-10) ribs: Bucket- handle movement - Partly by the elevation of the vertebrosternal ribs Vertical diameter is increased by the descent (contraction) of the diaphragm CLINICAL CORRELATION 1. Diaphragmatic Hernias a. Congenital diaphragmatic hernias: i. Posterolateral Hernia - commonest congenital diaphragmatic hernia - In this condition, there is herniation of abdominal contents into the thoracic cavity, which compress the lung and heart. - The herniation occurs through the gap (pleuroperitoneal hiatus) between the costal and vertebral origins of the diaphragm called foramen of Bochdalek. - The gap remains due to failure of closure of pleuroperitoneal canal. - It occurs commonly on the left. ii. Retrosternal Hernia: - It occurs through the gap between the muscular slips of origin from xiphisternum and 7th costal cartilage (space of Larry or foramen of Morgagni). - It is more common on the right side. - hernial sac usually lies between pericardium and right pleura. - Usually it causes no symptoms in the infants, but in later age, the patients complain of discomfort and dysphagia (difficulty in swallowing). iii. Paraesophageal or Rolling hernia: - there is defect in the diaphragm to the right and anterior to the oesophageal opening. - The anterior wall of the stomach rolls upwards in the hernial sac through this defect, until it becomes upside down in the thoracic cavity. b. Acquired diaphragmatic hernias: can be either traumatic or hiatal (sliding) i. Traumatic Hernia - may occur due to an open injury to the diaphragm by the penetrating wounds or closed injury to the diaphragm in road traffic accidents leading to sudden severe increase in the intra-abdominal pressure ii. Hiatal (sliding) hernia: - This is the commonest of all the internal hernias. - In sliding hernia, the gastroesophageal junction and cardiac end of stomach slides up into the thoracic cavity, but only anterolateral portion of the herniated stomach is covered by peritoneum, therefore the stomach itself is not within the hernial sac. - The hiatal hernia is caused by the weakness of the diaphragmatic muscle surrounding the oesophageal opening and increased intra-abdominal pressure. - This may cause regurgitation of acid contents of stomach into the esophagus leading to peptic esophagitis. - The patient complains of heart burn. The sliding hernia is usually associated with short oesophagus. 2. Paralysis of Diaphragm: - Unilateral damage of phrenic nerve leads to unilateral diaphragmatic paralysis - This condition is diagnosed during fluoroscopy when an elevated hemidiaphragm is seen on the side of lesion - Bilateral damage to of phrenic nerves leads to complete diaphragmatic paralysis and it may cause respiratory failure. 3. Hiccups - Occur due to involuntary spasmodic contraction of the diaphragm - Hiccups normally occur after eating or drinking as a result of gastric irritation - The pathological causes of hiccups include diaphragmatic irritation, phrenic nerve irritation, hysteria and uremia 4. Herpes Zoster: - In herpes zoster (shingles) involving the thoracic spinal ganglia, the cutaneous vesicles appear in the dermatomal area of distribution of intercostal nerve. It is an extremely painful condition. 5. Intercostal Nerve Block: - is given to produce local anaesthesia in one or more intercostal spaces by injecting the anaesthetic agent around the nerve trunk near its origin, i.e., just lateral to the vertebra. 6. Thoracotomy: The conventional thoracotomy (posterolateral) is performed along the 6th rib. The neurovascular bundle is protected from injury by lifting the periosteum of the rib. Considering the position of neurovascular bundle in the intercostal space, it is safe to insert the needle, a little above the upper border of the rib below