Parietal Pleura

1. Overview

The parietal pleura is the outer layer of the pleural membrane that lines the thoracic cavity. Together with the visceral pleura (which covers the lungs), it forms the pleural sac, a fluid-filled space essential for lung movement and protection. The parietal pleura is crucial in respiratory mechanics, lubrication, and compartmentalization of the thoracic organs.

2. Location

The parietal pleura lines the internal surface of the thoracic wall and is subdivided based on the area it covers:

• Costal pleura: Lines the inner surface of the ribs and intercostal spaces

• Diaphragmatic pleura: Covers the superior surface of the diaphragm

• Mediastinal pleura: Lines the lateral aspect of the mediastinum

• Cervical pleura (cupula): Extends into the root of the neck above the first rib

It is separated from the thoracic wall by the endothoracic fascia, and it meets the visceral pleura at the hilum of the lung, where structures enter and exit (bronchi, vessels, nerves).

3. Structure

The parietal pleura is composed of:

• Mesothelium: A single layer of flattened epithelial cells that secrete pleural fluid

• Submesothelial connective tissue: Supports blood vessels, lymphatics, and nerves

Unlike the visceral pleura, the parietal pleura is sensitive to pain, temperature, and touch due to its somatic innervation. It is richly supplied with lymphatic vessels and has different innervation in different regions:

• Costal and cervical pleura: Intercostal nerves

• Mediastinal pleura: Phrenic nerve

• Diaphragmatic pleura: Centrally by the phrenic nerve; peripherally by intercostal nerves

4. Function

The parietal pleura performs essential mechanical and protective functions:

• Provides a smooth surface: Facilitates frictionless lung expansion and recoil

• Encapsulates the pleural cavity: Helps maintain negative intrapleural pressure critical for ventilation

• Structural separation: Keeps lungs compartmentalized from the chest wall and other thoracic organs

• Immunological surveillance: Contains lymphatic drainage that helps remove debris and excess fluid

5. Physiological Role(s)

Within respiratory physiology, the parietal pleura plays a key role in:

• Respiratory mechanics: The pressure differential between the parietal and visceral pleurae helps keep the lungs inflated

• Pleural fluid regulation: Continuously produces and reabsorbs pleural fluid, which lubricates lung surfaces

• Sensory detection: Through somatic nerves, it detects pain and irritation—important in diagnosing pleural conditions

6. Clinical Significance

Pleuritis (Pleurisy)

Inflammation of the pleura, often involving the parietal pleura, causes sharp, localized chest pain that worsens with breathing. It may be associated with viral infections, autoimmune diseases, or pulmonary embolism.

Pleural Effusion

Abnormal accumulation of fluid in the pleural cavity. Causes include:

• Congestive heart failure

• Pneumonia (parapneumonic effusion)

• Malignancy

Symptoms: Dyspnea, chest heaviness, and reduced breath sounds. Diagnosed via ultrasound or chest X-ray; treated with thoracentesis or chest drainage.

Pneumothorax

Air entering the pleural cavity causes lung collapse. The parietal pleura is typically breached due to trauma, rupture, or iatrogenic causes (e.g., central line placement).

Mesothelioma

A rare but aggressive cancer of the pleural lining (often the parietal pleura), usually linked to asbestos exposure. Presents with:

• Chest pain

• Pleural effusion

• Weight loss

Treated with chemotherapy, surgery, or radiation.

Pleurodesis

A medical procedure that intentionally causes adhesion between the visceral and parietal pleura to prevent recurrent pleural effusion or pneumothorax. Agents like talc or doxycycline are introduced into the pleural space.

Sensory Relevance

Because of its somatic innervation, the parietal pleura is highly sensitive to pain—unlike the visceral pleura. Pain from pleural inflammation is well-localized and may radiate to the shoulder if the diaphragmatic pleura (innervated by the phrenic nerve) is involved.