Serous membrane forming 2 closed sacs flanking mediastinum; allows smooth lung movement.

Definition

• Mesothelium-lined; 2 layers: visceral + parietal
• Continuous at root of lung
• Between them: pleural cavity (potential space, thin serous fluid film)

Visceral Pleura

• = pulmonary pleura; covers lung surface + fissures; firmly adherent
• Absent at hilum + along pulmonary ligament
• Insensitive to pain; autonomic supply

Parietal Pleura

• Lines thoracic cavity; thicker; loosely attached via endothoracic fascia
• Pain-sensitive; somatic supply (intercostal + phrenic nerves)

Comparison

Pleural Cavity

• ~5–10 ml serous fluid; lubricates, reduces friction, surface tension helps lung follow chest wall
• Negative pressure keeps lung expanded

Parietal Pleura Subdivisions

Costal — ribs, cartilages, intercostal spaces; separated by endothoracic fascia; intercostal nerve supply

Diaphragmatic — peripheral = intercostal nerves; central = phrenic nerve

Mediastinal — reflected around lung root; continues with visceral pleura at hilum; forms pulmonary ligament below root

Cervical — dome above 1st rib; ~2.5 cm above medial 1/3 clavicle; ~5 cm above 1st costal cartilage; covered by suprapleural membrane (Sibson’s fascia) (C7 transverse process → 1st rib inner border)

Risk: subclavian cannulation, supraclavicular procedures, brachial plexus block → pneumothorax

Pulmonary Ligament

• Double pleural fold below lung root; loose areolar tissue + lymphatics
• Allows inferior pulmonary vein expansion + lung root descent on inspiration
• Divided during pneumonectomy

Nerve Supply

Parietal:

Visceral: sympathetic T2–T5; parasympathetic vagus; insensitive to pain

Blood Supply

Lymphatics

Surface Markings

Cervical pleura — curved line, SC joint to junction of medial+middle clavicle thirds; summit 2.5 cm above clavicle

Anterior pleural reflection:

• Right: SC joint → sternal angle midpoint → vertically to xiphisternal joint
• Left: same to 4th costal cartilage → deviates laterally (cardiac notch) → 6th costal cartilage, ~3 cm from midline

Inferior pleural reflection:

Pleura 2 ribs lower than lung at these landmarks → costodiaphragmatic recess

Applied Anatomy

Pleuritic pain — parietal pleura pain-sensitive; costal = thoracic wall pain; central diaphragmatic/mediastinal = shoulder tip (phrenic)

Pneumothorax — air abolishes negative pressure → lung collapse; causes: trauma, bleb rupture, iatrogenic injury

Pleural effusion — collects first in costodiaphragmatic recess

• Signs: stony dullness, ↓breath sounds, ↓chest expansion, blunted costophrenic angle on CXR

The pleura is a serous membrane forming two closed pleural sacs, one on each side of the mediastinum. It allows smooth movement of the lungs during respiration and is clinically important because pleural pain, pleural effusion, pneumothorax, and thoracocentesis depend on its anatomy.

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Definition

The pleura is a serous membrane lined by mesothelium. Each pleural sac has two layers:

1. Visceral pleura
2. Parietal pleura

The two layers are continuous with each other at the root of the lung.

Between them lies the pleural cavity, a potential space containing a thin film of serous fluid.

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Visceral Pleura

The visceral pleura is also called pulmonary pleura.

Features:

• Covers the lung surface.
• Extends into the fissures.
• Firmly adherent to lung tissue.
• Absent at the hilum and along the pulmonary ligament.
• Insensitive to pain.
• Supplied by autonomic nerves.

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Parietal Pleura

The parietal pleura lines the thoracic cavity.

Features:

• Thicker than visceral pleura.
• Loosely attached to thoracic wall by endothoracic fascia.
• Sensitive to pain.
• Supplied by somatic nerves: intercostal and phrenic nerves.

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Parietal vs Visceral Pleura

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Pleural Cavity

The pleural cavity is a slit-like potential space containing about 5-10 ml of serous fluid.

Functions of pleural fluid:

• Lubricates pleural surfaces
• Reduces friction during respiration
• Helps lung follow thoracic wall movement through surface tension

Normal pleural pressure is negative, helping keep the lung expanded.

Pathological Contents

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Subdivisions of Parietal Pleura

The parietal pleura has four parts.

Costal Pleura

• Lines ribs, costal cartilages, intercostal spaces, and sides of vertebral bodies.
• Separated from thoracic wall by endothoracic fascia.
• Supplied by intercostal nerves.

Diaphragmatic Pleura

• Covers superior surface of diaphragm.
• Peripheral part supplied by intercostal nerves.
• Central part supplied by phrenic nerve.

Mediastinal Pleura

• Lines lateral surface of mediastinum.
• Reflected around root of lung.
• Continues with visceral pleura at hilum.
• Forms pulmonary ligament below lung root.

Cervical Pleura

The cervical pleura forms the dome of pleura above the first rib.

Extent:

• About 2.5 cm above medial one-third of clavicle
• About 5 cm above first costal cartilage

It is covered by the suprapleural membrane / Sibson’s fascia, a thickening of endothoracic fascia attached from the transverse process of C7 to the inner border of the first rib.

Clinical importance:

• It may be injured in subclavian venous cannulation, supraclavicular procedures, and brachial plexus blocks, causing pneumothorax.

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Pulmonary Ligament

The pulmonary ligament is a double fold of pleura below the root of the lung.

Formation:

• At the root, pleura surrounds structures entering and leaving the lung.
• Below the root, the two layers hang down as a loose fold.

Features:

• Extends from the root of lung towards diaphragm.
• Contains loose areolar tissue and lymphatics.
• Allows expansion of inferior pulmonary vein.
• Allows descent of lung root during inspiration.
• Is divided during pneumonectomy.

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Nerve Supply

Parietal Pleura

Visceral Pleura

Visceral pleura is insensitive to pain.

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Blood Supply

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Lymphatic Drainage

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Surface Markings of Pleura

Cervical Pleura

A curved line from the sternoclavicular joint to the junction of medial and middle thirds of clavicle, with summit 2.5 cm above the clavicle.

Anterior Pleural Reflection

Right side:

• Sternoclavicular joint
• Midpoint of sternal angle
• Down vertically to xiphisternal joint

Left side:

• Same as right up to the 4th costal cartilage
• Then deviates laterally because of cardiac notch
• Reaches 6th costal cartilage about 3 cm from midline

Inferior Pleural Reflection

The pleura is two ribs lower than the lung at these landmarks, forming the costodiaphragmatic recess.

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Applied Anatomy

Pleuritic Pain

Parietal pleura is pain-sensitive.

• Costal pleura pain is felt in the thoracic wall.
• Central diaphragmatic and mediastinal pleural pain is referred to the shoulder tip through the phrenic nerve.

Pneumothorax

Air in the pleural cavity abolishes negative pressure and causes lung collapse.

Common causes:

• Trauma
• Rupture of lung bleb
• Iatrogenic injury during procedures

Pleural Effusion

Fluid collects first in the costodiaphragmatic recess.

Clinical signs:

• Stony dullness to percussion
• Decreased breath sounds
• Reduced chest expansion
• Blunting of costophrenic angle on chest X-ray

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