Overview

Each lung invaginates its own closed pleural sac, like a fist pushed into a balloon. The inner layer, the visceral pleura, is firmly adherent to the lung and dips into its fissures; the outer layer, the parietal pleura, lines the thoracic wall, diaphragm and mediastinum and rises above the first rib as the cervical pleura (cupula). The two layers are continuous around the lung root and pulmonary ligament. Between them lies the pleural cavity, a potential space containing only a few millilitres of serous fluid.

The fluid lubricates the surfaces and, through surface tension, couples the lung to the chest wall, so expansion of the thorax expands the lung. The pleural sacs are separate, so a pneumothorax or infection on one side is normally confined to that side.

Where parietal pleura folds from one wall to another it forms recesses that the lungs enter only in deep inspiration: the costodiaphragmatic recesses (between costal and diaphragmatic pleura, deepest in the mid-axillary line) and the costomediastinal recesses (behind the sternum, larger on the left at the cardiac notch).

Location: Lining the pulmonary cavities of the thorax and the surfaces of the lungs.

Parts & subdivisions

Visceral pleura
Covers the lung surface, including fissures.
Parietal pleura
Costal, mediastinal, diaphragmatic and cervical parts.
Pleural cavity
Potential space containing pleural fluid.
Costodiaphragmatic recess
Lowest part of the pleural cavity; site of fluid collection and of diagnostic aspiration.
Costomediastinal recess
Anterior recess behind the sternum and costal cartilages.

Anatomy

Histology: Simple squamous mesothelium with microvilli on a thin layer of loose connective tissue containing elastic and collagen fibres, blood vessels and lymphatics.

Function

Reduces friction between lung and chest wall.
Couples lung movement to chest-wall movement through pleural fluid and negative intrapleural pressure.
Compartmentalises each lung, limiting spread of infection and air leaks.

Clinical significance

Pleurisy

Inflammation of the parietal pleura (viral, pneumonia, PE, autoimmune) causes sharp pain worse on inspiration and coughing, and a pleural friction rub.

Surface markings

Inferior pleural reflection: 8th rib (midclavicular), 10th rib (mid-axillary), 12th rib posteriorly (crossing below the medial 12th rib at the costovertebral angle). Upper abdominal and renal surgery or biopsy near the 12th rib can breach the pleura and cause a pneumothorax.

Mnemonics

Pleura vs lung borders

Lungs: 6–8–10. Pleura: 8–10–12 (midclavicular, mid-axillary, paravertebral lines).

Test yourself

Irritation of the pleura over the central part of the diaphragm typically produces pain referred to the:

Epigastrium
Tip of the shoulder
Lower intercostal spaces
Umbilicus

Answer: Tip of the shoulder

Mediastinal and central diaphragmatic parietal pleura are supplied by the phrenic nerve (C3–C5), so pain is referred to the C4 dermatome over the shoulder. Costal and peripheral diaphragmatic pleura are supplied by intercostal nerves, giving localised chest-wall or abdominal-wall pain.

In the erect patient, where does a small pleural effusion first collect?

Cardiac notch
Costomediastinal recess
Pleural cupula
Costodiaphragmatic recess

Answer: Costodiaphragmatic recess

The costodiaphragmatic recess is the most dependent part of the pleural cavity, lying between the inferior border of the lung (6–8–10) and the pleural reflection (8–10–12). Fluid there blunts the costophrenic angle on an erect radiograph; it is also the site for diagnostic aspiration.

When a needle or chest drain is passed through an intercostal space into the pleural cavity, it should run:

Just below the lower border of the rib above
Through the exact middle of the space, regardless of rib position
Along the costal groove
Just above the upper border of the rib below

Answer: Just above the upper border of the rib below

The intercostal vein, artery and nerve (VAN, from above down) run in the costal groove along the inferior border of each rib. Passing just above the upper border of the rib below avoids the main neurovascular bundle.