Dr.Naresh Kumar Junior Resident

Dept. of Pulmonary Medicine

Anatomy of pleura…Definition and layers of PleuraEmbryology HistologySurface markingRecesses of pleuraBlood supplyLymphatic drainageNerve supply

Definition and layers of Pleura

• Pleura :• Serous membrane that covers the lung parenchyma, mediastinum, diaphragm and the rib cage.• It comprise visceral and parietal layer.

Visceral pleura– Covers the lung parenchyma, not only at its point of contact with

chest wall, diaphragm and the mediastinum but also in the interlobar fissures.

– It apposed to lungs and cannot be dissected from the surface.• Endo pleura :

Most superficial layerComposed of a continuos layer of mesothelial cells

External elastic layer (chief layer)Consist of thin layer of dense collagen and elastic tissueResponsible for pleural mechanical stability

Vascular layer (interstitial layer)Consist of connective tissue containing lymphatic and blood vessels.Continuos with the interstitial tissue of the interlobular septa and

directly overlies the lobular-limiting membrane.

Parietal pleura– It lines the thoracic wall.– Covers the inner surface of rib cage,

mediastinum and diaphragm.– It extends into the root of neck to line the

undersurface of suprapleural membrane at thoracic outlet

According to intrathoracic surface it lines :-- Cervical pleura Costal pleura Diaphragmatic pleura Mediastinal pleura

• Cervical pleura :– “pleural capula” or dome of pleura.– It extends from the superior thoracic aperture

into the root of neck, forming a cup shaped pleural dome over the apex of lung.

– The cervical pleura at higher levels in infants and young children because of the shortness of their necks, thus more prone to injury.

– The small areas of pleura exposed in the costo vertebral angles inferiomedial to the 12th ribs are posterior to the superior poles of kidneys. More prone to injure during surgical procedure in posterior abdominal wall.

• Costal pleura :– It covers the internal surface of :

• Ribs Costal cartilages• Intercostal spaces Sides of vertebral bodies• Back of sternum

• Mediastinal pleura :– It covers the lateral aspects of the mediastinum.– It is attached to blood vessels and bronchi that

constitute the lung root.

• Diaphragmatic pleura :– Covers the superior or thoracic surface of

diaphragm on each side of mediastium. – In quite respiration the costal and the

diaphragmatic pleura are in apposition to each other.

– They separate in deep inspiration.

Pleural cuffThe two layers, parietal and visceral,

continuous with one another by means of a cuff of pleura.

This cuff surrounds the structures entering and leaving the lung at the hilum of each lung.

Pleural cuff hangs down as loose fold called the pulmonary ligament.

Fold contains a thin layer of loose areolar tissue with a few lymphatics.

It provides a dead space into which the pulmonary veins can expand during increased venous return.

Embryology of pleura• Pleural cavity :

– Derived from the coelomic cavity (body cavity)– Coelomic cavity divided into pericardium, pleural

cavities and the peritoneal cavity through the development of three sets of portions :• Septum transversum : serves as an early partial diaphragm.• Pleuro pericardial membranes : divide pericardial and

pleural cavities.• Pleuro peritoneal membranes : unite with the septum

transversum to complete the partition between each pleural and peritoneal cavity.

– Pleural cavity is fully lined by mesothelial membrane, the pleura.

Visceral pleura :Primordial lung buds grows and bulge into

right and left pleural cavities, carry along lining mesothelium which becomes visceral pleura.

Parietal pleura :Lining mesothelial of pleural cavity becomes

parietal pleura.

Histology • Grossly, normal pleura is a smooth, glistening,

semitransparent membrane.• Light microscopy, pleural consist of five layers :

– Mesothalial layer– Connective tissue layer– Superficial elastic layer– Loose subpleural connective tissue layer (rich in

vessels, nerves and lymphatics) In pleural fibrosis connective tissue is arranged in a coarse,

basket weave pattern and contains only a few capillaries.

– Deep fibroelastic layer (in continuity with the parenchymal structures of lung, diaphragm or the thorax)

Mesothelial layer• Single cell layer• Different shaped cells – flattend or cuboidal or

columnar• 6-12m thickness• Microvillae present to decrease friction• Stomata present between the mesothelial cells

that communicate directly with lymphatic lucanes.• Capable of transformation into macrophages.• In a rheumatoid pleuritis, normal mesothelial cell

covering absent, instead there is pseudostratified layer of epitheloid cells that focally forms multinucleated giant cells .

Surface marking

Recesses of pleuraThere are two folds or recesses of parietal

pleura which acts as reserve space for the lung to expand during deep inspiration.Costomediastinal recessesCostodiaphragmatic recesses

Costomediastinal recessesAre situated along the anterior margins of

pleura.They are slit like spaces between the costal

and the mediastinal parietal pleura.Seperated by a capillary layer of pleural fluid.During inspiration and expiration, the

anterior borders of the lungs slide in and out of the recesses.

Costodiaphragmatic recesses• Are slit like spaces between the costal and

diaphragmatic parietal pleura.• Separated only by a capillary layer of pleural fluid.• During inspiration, the lower margins of the lung

descend into the recesses.• During expiration, the lower margins of the lung

ascend so that the costal and the diaphragmatic pleura come together again.

• First part of pleural cavity to be filled up by pleural effusion.

• It has capacity upto 300 ml.

Blood supply• Arterial supply :

– Parietal pleura :• Costal pleura : small branches of intercostal arteries• Mediastinal pleura : supplied by pericardio phrenic

artery• Diaphragmatic pleura : supplied by superior phrenic

and musculophrenic artery.

– Visceral pleura :• Bronchial artery : supplies visceral pleura facing the

mediastinum, pleura covering the interlobular surface and part of the diaphragmatic surface.

• Pulmonary artery : supplies remaining portion.

Venous drainage :Parietal pleura

Through the intercostal veins which empty into inferior venacava or brachio-cephalic trunk.

Visceral pleura Through pulmonary veins.

Applied anatomy : Aspiration of any fluid from the pleural cavity is called parencentesis thoracis. It is usually done in the 6th intercostal space in the midaxillary line. The needle is passed through the lower part of the space to avoid injury to the neurovascular bundle.

Nerve supply• Parietal pleura :

– Sensitive to pain, temperature, touch and pressure. Costal pleura : innervated by segmental

intercostal nerves. Peripheral part of diaphragmatic pleura :

innervated by lower 6 intercostal nerves. pain is percieved in adjacent chest wall.

Central portion of diaphragmatic pleura and mediastinal pleura : innervated by phrenic nerve. Pain is percieved in ipsilateral shoulder.

• Visceral pleura :– Insensitive to common sensation such as pain

and touch.– Sensitive to stretch.– Innervated by autonomic nerves from the

spinal segments T4 and T5.

• Presence of pleuritic chest pain indicates inflammation or irritation of parietal pleura.

Applied anatomy :Intrapleural anaesthesia :it is infusion of small

volume of local anaesthetic agent into the intrapleural space through catheter. It diminish the pain sensation from the area by action on intercostal nerves, indicated in thoracotomy and insertion of chest drainage

Lymphatic drainage • Parietal pleura :

– Costal pleura : • Ventrally : towards nodes along the internal

thoracic artery.• Dorsally : towards the intercostal lymph nodes.

– Medistinal pleura :• Drain to tracheobronchial and mediastinal nodes.

– Diaphragmatic pleura : • Drain to parasternal, middle phrenic and posterior

mediastinal nodes.

• Lymphatic vessels in parietal pleura are in communication with the pleural space by means of stoma.

• Stoma : – 2-6 m in diameter– Round or slit like opening– Found mostly on the mediastinal pleura and on

the intercostal surfaces.– More stoma in the area where the mesothelial

cells are cuboidal rather then flat.

• Lacunas :– Lymphatic vessels in parietal pleura have many

branches, some submesothelial branches have dilated lymphatic space called lacunas.

• Stomas are found only over lacunas.• Significance : Stomas with their associated

lacunas and lymphatic vessels are main pathway for elimination of particulate matter from pleural space. This transport system may provide a mechanism for migration of malignant cell to distant organs in patients with positive pleural lavage cytology.

• Visceral pleura :– They have abundant lymphatic vessels.– Lymphatics form a plexus of inter

communicating vessels that run over the surface of lung towards the hilum.

– It also penetrate the lungs to join the bronchial lymph vessels.

– Lymphatic vessel in visceral pleura have one way valves, directing flow towards the hilum of lung.

– No stomas are seen in visceral pleura.

Physiology of pleuraPleural pressure Pleural fluid Pleural effusion Therapeutic application of pleural space Clinical condition associated with pleura

Pleural pressureIt is pressure within the pleural space.It is pressure at the outer surface of the lung

and heart, and inner surface of thoracic cavity. With the chest closed and the patient relaxed,

the respiratory system is at its functional residual capacity (FRC), which is approximately 35% of the total lung capacity. Thus, at FRC, the opposing elastic forces of the chest wall and lung produce a negative pressure between the visceral and the parietal pleura, which is called the pleural pressure.

Significance :Because the lung, the heart, and the thoracic

cavity are all distensible, and because the volume of a distensible object depends on the pressure difference between the inside and the outside of the object and its compliance, pleural pressure plays an important role in determining the volume of these structures.

Pleural liquid pressure pressure measured using fluid-filled catheters1.0 cm H2O/cm vertical height.It represents the pressure that influenced the

absorption of fluid. Pleural surface pressure

pressure measured using surface balloons or suction cups.

0.3 cm H2O/cm vertical height. It represents the balance between the outward

pull of the thoracic cavity and the inward pull of the lung.

MeasurementDirect methods

measured by inserting needles, trocars, catheters, or balloons into the pleural space.

Highly risk of producing a pneumothorax or of introducing infection into the pleural space.

Indirect methods measured by a balloon positioned in the esophagus. esophagus is a compliant structure situated

between the two pleural spaces, esophageal pressure measurements provide a close approximation of the pleural pressure.

Precaution to be taken – volume of air within the balloon must be small,

so that the balloon is not stretched and the esophageal walls are not displaced; balloon must be short and

balloon must be placed in the lower part of the esophagus.

GradientsPleural pressure is not uniform throughout

the pleural space.pleural pressure being lowest or most

negative in the superior portion and highest or least negative in the inferior portion.

factors responsible for gradientgravity, mismatching of the shapes of the chest wall

and lung, weight of the lungs

The magnitude of the pleural pressure gradient appears to be approximately 0.30 cm H2O/cm vertical distance.

Significance of gradient :alveolar pressure is constant throughout the

lungs, thus, higher pressure gradient at the apex of the lung is thought to be responsible for the formation of pleural blebs at the apex of the lung.

It also play a role in difference in ventilation at apex and base of lung.

Pleural fluidFluid present between the parietal and visceral

pleura, the pleural space is called pleural fluid.Fluid act as lubricant and allows the visceral

pleura covering the lung to slide along the parietal pleura lining the thoracic cavity during respiratory movements.

Volume :Mean amount of fluid in right pleural space in

normal individual is 8.4 +/- 4.3 ml.Normally the volume of fluid in right and left

pleural space is equal.

Thickness :Pleural space slightly more narrow near the

topm) than at bottom(20.3m). pleural space width in the most dependent recess

such as costodiaphragmatic recess reaches 1 to 2 mm.

Cells :Mean WBC count – 1,716 cells/mm3

Mean RBC count – 700 cells/mm3

Macrophages – 75 %Lymphocytes – 25 %Mesothilial, neutrophils, eosinophils ( < 2 % each )

Eosinophil > 10 % -- drug reaction, asbestosis, parasitic infection, churg-strauss syndrome.

Physiochemical factors :• Protein – pleural fluid is similar to that of serum

except that low molecular weight protien such as albumin present in relatively greater quantities in plural fluid.

• Ions : Bicarbonates : increase by 20-25% to that in plasma. Sodium : reduce by 3-5% to that in plasma Chloride : reduce by 6-9% to that in plasma Potassium : nearly identical to that in plasma

• Glucose : similar to that in plasma• Less than 60 mg/dl – parapneumonic effusion,

malignancy, TB, RA, parasitic infection, churg-strauss syndrome.

• Pco2 : same as the plasma Pco2

• pH : due to elevated pleural fluid bicarbonate the pleural fluid is alkaline with respect to plasma pH.

Appearance Underlying disaese

Pale yellow Transduates

Turbid Inflammatory exudates

Pus Empyema

Haemorrhagic Trauma, malignancy

Milky fluid Chylotorax

Brown Amoebic liver abcess

Black Fungal infection

Yellow to green Rheumatoid pleurisy

• Apperance : normally light yellow and clear

Pleural Fluid Formation

Sourcespleural capillaries,interstitial spaces of the lung,intrathoracic lymphatics,intrathoracic blood vessels,peritoneal cavity.

Pleural CapillariesThe movement of fluid between the pleural

capillaries and the pleural space governed by Starling's law of transcapillary exchange.

[Q]f - liquid movement

Lp - filtration coefficient/unit area or hydraulic water conductivity of the membrane

A - surface area of the membrane Pcap and cap - hydrostatic and oncotic pressures of

capillary Ppl and pl - hydrostatic and oncotic pressures of

pleural space d - solute reflection coefficient for protein,

Parietal Pleura

gradient for fluid formation is normally present.

Hydrostatic pressure hydrostatic pressure of capillaries in parietal

pleura is 30 cm of H2O

Pleural pressure is -5 cm of H2ONet hydrostatic pressure = 30 – (-5) = 35 cm of

H2O

Oncotic pressure :Oncotic pressure in plasma = 34 cm of H2OOncotic pressure in pleural space = 5 cm of

H2O

Net oncotic pressure = 34-5 = 29 cm of H2O

Net gradient = 35-29 = 6 cm of H2OThis gradient favours the movement of fluid

from capillaries in parietal pleura to the pleural space.

Visceral pleuraPressure in the visceral pleural capillaries is

approximately 6 cm of H2O less than that in the parietal pleural capillaries.

Filtration coefficient for the visceral pleura is less than that of parietal pleura, because the capillaries in the visceral pleura are much further from the pleural space than those in parietal pleura.

Thus, net gradient for fluid movements across the visceral pleura is close to zero.

InterstitialIt acts as a source of pleural fluid formation

in CHF Pulmonary edema Lung transplantation Pulmonary embolisation

Movement of fluid from interstitial to pleural space is closely related with pulmonary venous pressure than with the systemic venous pressure.

Peritoneal cavityAct as a source of pleural fluid formation in

Hepatic hydrothorax Meig’s syndrome Peritoneal dialysis

Pressure in the pleural cavity is less than that of peritoneal cavity

Thoracic duct/Blood vesselThoracic duct injury :

lymph will accumulate in pleural space producing chylothorax.

Rate of fluid accumulation can be more than 1000ml/day

Blood vessel injury :Trauma of the blood vessels leading to blood

accumulation in pleural space cause hemothorax.

Pleural fluid absorptionLymphatic clearance :

Pleural space is in communication with lymphatic vessels in the parietal pleura by stomas in parietal pleura.

Stomas are not present in visceral pleura Proteins, cells and all other particulate matter

are removed from the pleural space by this lymphatics in parietal pleura.

More fluid formation across the parietal pleura over the ribs compared with intercostal spaces.

Pleural fluid absorption more over intercostal spaces than over ribs.

More fluid formation over the caudal ribs than over the cranial ribs.

Increase in breathing frequency results in more fluid formation.

Pleural effusionPleural effusion is excess fluid that

accumulates between the two pleural layers, the fluid-filled space that surrounds the lungs.

It occurs when the rate of pleural fluid formation exceeds the rate of pleural fluid absorption.Normal rate of pleural fluid formation – 0.01

ml/kg/hrNormal rate of pleural fluid absorption – 0.01

ml/kg/hr but it can exceed upto 0.20 ml/kg/hr

Causes…Increased pleural fluid formation

Increased interstitial fluid in the lung (most common) Left ventricular failure, pneumonia, and pulmonary embolus

Increased intravascular pressure in pleura Right or left ventricular failure, superior vena caval syndrome

Increased permeability of the capillaries in the pleura Pleural inflammation Increased levels of vascular endothelial growth factor

Increased pleural fluid protein level Decreased pleural pressure

Lung atelectasis or increased elastic recoil of the lung Increased fluid in peritoneal cavity

Ascites or peritoneal dialysisDisruption of the thoracic duct Disruption of blood vessels in the thorax

Decreased pleural fluid absorption Obstruction of the lymphatics draining the

parietal pleura Elevation of systemic vascular pressures

Superior vena caval syndrome or right ventricular failure

Disruption of the aquaporin system in the pleura

Transudative vs exudativeTransudative –

CHF Cirrhosis Pulmonary embolism Nephrotic syndrome Peritoneal dialysis Myxedema SVC syndrome

Exudative : Infections Connective tissue

disease Cancer Pancreatitis Chylothorax Drug reaction

Exudative effusionLight’s criteria [satisfying anyone criterion

means it is exudative]Pleural total protein/serum total protein > 0.5Pleural LDH/serum LDH > 0.6Pleura LDH > 2/3 of the upper limits of normal

for serum LDH

For patients with high suspicion for transudative, but meets light’s criteria –

Serum albumin – pleural albumin < 1.2 gm/dl confirm the effusion is exudative.

Therapeutic uses of pleural spaceIntrapleural gene transfer :

Easy accessibilityLarge surface areaAbility to provide high concentration of

secreted gene products to chest structureLow risk of vector induced inflammation

Treatment of accidental hypothermia

Clinical conditions associated with pleura• Pleuritis or pleurisy : This is the inflammation of the

pleura. Acute pleuritis is marked by sharp, stabbing pain, especially on exertion.

• Pneumothorax : Presence of air in the pleural cavity. Entry of air into the pleural cavity, resulting from a penetrating wound of the parietal pleura or rupture of a lung results in partial collapse of the lung.

• Hemothorax : Presence of blood in the pleural cavity. It results more often from injury to a major intercostal vessel than laceration of lung.

• Hydropneumo thorax : prence of both fluid and air in the pleural cavity.

• Empyema : presence of pus in pleural cavity.