Gross Anatomy of Pleurae (Prof. Akinlolu) PDF

TRUNK LECTURER’S NAME: Prof. AKINLOLU, A. A. Department of Anatomy, FUHSO LECTURE TOPIC: GROSS ANATOMY OF PLEURAE (3RD JULY, 2024). OUTLINE 1. Introduction 2. Sub-divisions, Reflections and Recesses o...

TRUNK LECTURER’S NAME: Prof. AKINLOLU, A. A. Department of Anatomy, FUHSO LECTURE TOPIC: GROSS ANATOMY OF PLEURAE (3RD JULY, 2024). OUTLINE 1. Introduction 2. Sub-divisions, Reflections and Recesses of Pleura 3. Applied anatomy 4. Class assignment The red dotted lines indicates the position of diaphragm, which separates thoracic & abdominal cavities. 1 Subdivisions and levels of mediastinum. Subdivisions of the mediastinum are demonstrated in the supine position. The level of the viscera relative to the subdivisions as defined by thoracic cage landmarks depends on the individual’s position bcuz the soft tissue of the mediastinum sags with the pull of gravity. Superior Trachea, brachiocephalic Posterior Esophagus with vagus nerves, mediastinum vein, thymus, aortic arch, mediastinum descending aorta, thoracic duct, esophagus, thoracic duct sympathetic trunks Middle portion Heart, ascending aorta, Anterior portion Smaller vessels and nerves, fat of mediastinum pulmonary trunk, pulmonary of mediastinum and connective tissue, thymus veins, phrenic nerves (only in the child) 2 Divisions of thoracic cavity and lining of pulmonary cavities. A. The CT scan and interpretive diagram above it are transverse cross-sectional views of the thoracic cavity demonstrating its kidney-like shape, resulting from the protruding vertebral bodies, and division into three compartments. The dimensional (B) and coronal cross-sectional (C) diagrams demonstrate the linings of the pleural cavities and lungs (pleurae). Each lung is invested by the inner layer of a closed sac that has been invaginated by the lung. Inset: A fist invaginating an underinflated balloon demonstrates the relationship of the lung (represented by the fist) to walls of the pleural sac (parietal and visceral layers of pleura). The visceral pleura extends into depths of fissures of lungs & covers all its surfaces except hilum & along the attachment of pulmonary ligt. It is firmly adherent to lung surfaces & cannot be separated from it. It provides the lung with a smooth slippery surface, enabling it to move freely on the parietal pleura. It also covers neurovascular structures of mediastinum & the bronchi. 3  PARIETAL PLEURA - It is thicker than visceral pleura & separable from the surfaces it covers. - It lines pulmonary cavities & separated from visceral pleura by pleura cavity containing a capillary layer of serous fluid. This cavity is filled with pus and fluid in clinical conditions. - The serous fluid lubricates pleural surfaces allowing its layers to slide smoothly over each other during respiration. Its surface tension provides the cohesion that keeps the lung surface in contact with the thoracic wall. This allows the lung to expand & fill with air when the thorax expands while still allowing sliding to occur, much like a film of water between two glass plates. - It is continuous with visceral pleura via a cuff of pleura fold, which surrounds lung root consisting of principal bronchi & pulmonary vessels passing in & out of hilum of lung. - Cuff of pleura is too large for lung root so it hangs down as loose triangular fold (pulmonary ligament – extending from lung root to diaphragm). It allows for expansion of pulmonary veins during increased venous return in exercises & also descent of lung roots (principal bronchi & pulmonary vessels) following descent of diaphragm in respiration. Same dead spaces appear near the root of SVC, and in femoral canal alongside femoral vein. - The pleural cuff fold contains loose areolar tissue & few lymphatics. 4  Right Lung (medial aspect) Left Lung (medial aspect) SUB-DIVISIONS OF PARIETAL PLEURA Cervical pleura: It covers the apex of lungs, & it is the superior continuation of costal & mediastinal pleura parts. It forms a cup-like dome (pleural cupula) over the apex that reaches its summit 2–3 cm superior to the level of the medial third of clavicle at the level of the neck of the 1st rib. It is strengthened by a fibrous extension of endothoracic fascia (suprapleural membrane or Sibson fascia), which attaches to the internal border of the 1st rib and the transverse process of C7 vertebra. Relations of cervical pleura: Anteriorly: Subclavian artery & scalenus anterior muscle Posteriorly: Neck of 1st rib & structures passing anterior to it Laterally: Sclanus medius muscle & Medially: Great vessels of the neck Costal pleura: It lines thoracic wall (sternum, ribs & costal cartilages, intercostal muscles & membranes, and sides of thoracic vertebrae) from which it is separated by endothoracic fascia to prevent infections of pleurae. The fascia attached to thoracic wall & diaphragm, & it is a thin, extrapleural layer of loose CT which forms a cleavage plane for surgical separation of costal pleura from thoracic wall. Mediastinal pleura: It lines lateral aspects of mediastinum i.e. tissues and organs separating pulmonary cavities and their pleural sacs. It is continuous with cervical pleura (superiorly); costal pleura (anteriorly & posteriorly) & diaphragmatic pleura (inferiorly). At the root of the lung, it forms the pleura cuff fold. Diaphragmatic pleura: It covers superior/thoracic surface of diaphragm on each side of mediastinum except along its costal attachment where it is fused with pericardium. Phrenicopleural fascia (a thin more elastic layer of endothoracic fascia) connects diaphragmatic pleura with muscular fibers of diaphragm. 5  PLEURAE REFLECTIONS AND RECESSES Anterior (costomediastinal) line of pleural reflection: It is assymetrical: (a) On the right side, it extends downwards and medially from the right sternoclavicular joint to the midpoint of the sternal angle, and then descends vertically up to the midpoint of the xiphisternal joint. (b) On the left side, it extends downwards and medially from the left sternoclavicular joint to the midpoint of the sternal angle, then descends vertically only up to the level of the 4th costal cartilage. It then arches outwards to reach the sternal margin of sternum and runs downwards a short distance lateral to this margin to reach the 6th costal cartilage, about 3 cm from the midline leaving a part of pericardium directly in contact with anterior chest wall (bare area of the heart). 3. Inferior (costodiaphragmatic) line of pleural reflection: It passes laterally around the chest wall from the lower limit of the anterior line of pleural reflection. It differs slightly on two sides: (a) On the right side, the line of reflection starts from the xiphisternal joint or behind the xiphoid process and crosses the 8th rib in the midclavicular line, 10th rib in the midaxillary line, and 12th rib at the lateral border of the erector spinae muscle, 2 cm lateral to the spine of T12 vertebra. (b) On the left side, the line of reflection starts at the level of the 6th costal cartilage, about 2 cm lateral to the midline. Thereafter it follows the same course as on the right side. 4. Posterior (costovertebral) line of pleural reflection: It ascends from the end of the inferior line, 2 cm lateral to the T12 spine along the vertebral column to the point, 2 cm lateral to the spine of C7 vertebra. The costal pleura becomes mediastinal pleura along this line. A. Vertical section of thoracic cavity. B. Transverse section of thoracic cavity. Costodiaphragmatic recesses: It lies inferiorly between costal & diaphragmatic pleurae. Vertically it measures about 5 cm & lies opposite 8th–10th ribs along midaxillary line. They are the most dependent parts of the pleural cavities, hence the fluid of pleural effusion first collect at these sites. Costomediastinal recess (CMR): It lies anteriorly between costal & mediastinal pleurae & lies between sternum & costal cartilages. The right CMR is possibly occupied by the anterior margin of the right lung even during quiet breathing. The left CMR is large due to the presence of cardiac notch in the left lung. Its location can be confirmed clinically during tapping from the area of underlying lung tissue to the area of left costomediastinal recess unoccupied by lung tissue, a change in tone, from resonant to dull, is noticed. This is called the area of superficial cardiac dullness. 6 Schematic diagram showing lines of pleural reflection. 7 8 Relationship of thoracic contents and linings of thoracic cage. A. The apices of the lungs and cervical pleura extend into the neck. The left sternal reflection of parietal pleura and anterior border of the left lung deviate from the median plane, circumventing the area where the heart is, lies adjacent to the anterior thoracic wall. In this “bare area” the pericardial sac is accessible for needle puncture with less risk of puncturing the pleural cavity or lung. B–D. The shapes of the lungs and the larger pleural sacs that surround them during quiet respiration are demonstrated. The costodiaphragmatic recesses, not occupied by lung, are where pleural exudate accumulates when the body is erect. The outline of the horizontal fissure of the right lung clearly parallels the 4th rib. The ribs are identified by number. Nerves & Blood Supply Parietal pleura is supplied by somatic nerves & sensitive to pain. Nerves accompany bronchial vessels. Costal and peripheral part of the diaphragmatic pleura is supplied by the intercostal nerves. Mediastinal and central part of the diaphragmatic pleura is supplied by the phrenic nerve. Visceral pleura is supplied by autonomic symp. nerves (T2-T5) & parasymp. nerves from vagus nerves. Blood supply: Parietal pleura is part of thoracic wall and is supplied by intercostal, internal thoracic & musculophrenic arteries. Venous drainage is to azygos and internal thoracic veins. Lymphatic drainage: Drain into internal mammary, posterior mediastinal and diaphragmatic nodes. Viseral pleura is supplied by bronchial arteries. Veins drain into bronchial and pulmonary veins. Lymphatic drainage is into bronchopulmonary lymph nodes. 9  Applied Anatomy Referred pain of pleura: The pain from central diaphragmatic pleura and mediastinal pleura is referred to the neck or shoulder through phrenic nerves (C3, C4, and C5) because skin at these sites has same segmental supply through the supraclavicular nerves (C3, C4, and C5). Pleurisy or pleuritis: It is the inflammation of the parietal pleura & commonly caused by pulmonary tuberculosis. Symptoms: Pain, which is aggravated by respiratory movements & radiates to thoracic & abdominal walls. The pleural surface becomes rough due to accumulation of inflammatory exudate causing surface friction between the two layers of pleura during respiratory movements. Thus pleural rub can be heard with stethoscope on the surface of the chest wall during inspiration and expiration. Pleural effusion: Normally the pleural cavity contains only 5–10 ml of clear fluid, which lubricates the pleural surfaces to allow their smooth movements without friction. The excessive accumulation of fluid in the pleural cavity is called pleural effusion. It usually occurs due to inflammation of pleura. It results in decreased expansion of lung on the side of effusion. Clinically it can be detected with decreased breath sounds and dullness on percussion on the site of effusion. Thoracocentesis/pleural tab: It is a procedure by which an excess fluid is aspirated from the pleural cavity. It is performed with the patient in sitting position. Usually the needle is inserted in the 6th intercostal space in the midaxillary line. The needle is inserted into the lower part of the intercostal space along the upper border of the rib to avoid injury to the intercostal nerve and vessels. The needle passes in succession through skin, superficial fascia, serratus anterior, intercostal muscles, endothoracic fascia, and parietal pleura to reach the pleural cavity. Pneumothorax: Accumulation of air in the pleural cavity is called pneumothorax. Open pneumothorax: Results from stab wounds on the thoracic wall piercing the pleurae, leading to the communication of air in the pleural cavity with the outside (atmospheric) air. Upon inspiration, the air is sucked into the pleural cavity. The clothing & layers of thoracic wall may combine to form a valve so that air enters through the wound during inspiration, but cannot exit through it. Air pressure builds up continuously in the pleural cavity on the wounded side which pushes mediastinum to the opposite (healthy) side (tension pneumothorax). Tension pneumothorax is characterized by (a) collapse of lung on the affected side, & Spontaneous pneumothorax: Common in (b) compression of lung on the healthy side. young male smokers. Due to presence of small blebs on superior surface of upper lobes. 10 References: for Contents and Diagrams. 1. Keith L. Moore, Arthur F. Dalley, and Anne M. R. Agur. Clinically Oriented Anatomy, 7th Edition, MD: Lippincott Williams & Wilkins, 2014. 2. B D Chaurasia's Human Anatomy. 7th Edition, Volume 1, 2017. Published by CBS Publishers. 3. Chummy Sinnatamby - Last's Anatomy, Regional and Applied. 12th Edition 2011. Published by Elsevier Health Sciences. 4. Vishram Singh. Textbook of Anatomy Upper Limb & Thorax. 2nd edition. 2014. ELSEVIER. Reed Elsevier India Private Limited. 5. Mahabadi N, Goizueta AA, Bordoni B. Anatomy, Thorax, Lung Pleura and Mediastinum. [Updated 2024 Mar 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519048/ Class Assignment: 1. With the aid of appropriate diagrams, describe pleurae, pleura reflections and recesses. Add a note on the applied anatomy of pleurae. 11