Lungs and pleura

Lobes and fissures

• Oblique fissure: from about the spine of T3 posteriorly, round the chest to the 6th costal cartilage anteriorly; it roughly follows the medial border of the scapula with the arm fully raised.
• Horizontal fissure (right only): along the 4th costal cartilage from the sternum to meet the oblique fissure in the midaxillary line at about the 5th rib.
• So the lower lobes are mostly posterior (listen at the back for lower lobe pneumonia) and the right middle lobe is anterior.
• Azygos lobe: in about 0.5–1% of people the azygos vein, during development, cuts down into the right upper lobe inside a pleural fold. The X-ray shows a thin curved line in the right upper zone ending in a tear-drop shadow (the vein). It is a normal variant and not a true lobe: it has no bronchus of its own.

Pleura and lung: surface lines

• The pleura lies two ribs lower than the lung at every line: 6–8–10 for lung, 8–10–12 for pleura.
• Cervical pleura (cupola) and lung apex rise 2–3 cm above the medial third of the clavicle. The cupola is covered and strengthened by the suprapleural membrane (Sibson fascia), a sheet from the transverse process of C7 to the inner border of the 1st rib, which stops the pleura bulging into the neck on coughing. Stab wounds, subclavian or internal jugular lines and supraclavicular blocks at the root of the neck can puncture the cupola and cause pneumothorax.
• Posteriorly the pleura passes below the medial end of the 12th rib, so a posterior approach to the kidney or adrenal through the bed of the 12th rib (or a supracostal renal puncture) risks pneumothorax.

Layers of the chest wall

From outside in at an intercostal space: skin, superficial fascia, external intercostal, internal intercostal, innermost intercostal, then endothoracic fascia, then parietal pleura. The intercostal vein, artery and nerve (VAN, top to bottom) run in the costal groove between the internal and innermost layers, under the lower border of the rib above. Needles therefore go just above the upper border of a rib.

Recesses, effusion and drainage

• Costodiaphragmatic recess: between lung and pleural lower limits (8th–10th ribs in the midaxillary line). It is the lowest part of the pleural cavity in the upright patient, so fluid collects there first (blunted costophrenic angle).
• Costomediastinal recess: anterior, behind the sternum and costal cartilages, larger on the left at the cardiac notch.
• Pleural tap: midaxillary or posterior line, one or two spaces below the top of the fluid, just above a rib, ideally ultrasound guided. Removing more than about 1.5 L quickly risks re-expansion pulmonary oedema (cough, frothy sputum, hypoxia, new shadowing in the same lung); stop if cough or chest tightness develops.
• Chest drain: in the safe triangle (anterior border of latissimus dorsi, lateral border of pectoralis major, line at the level of the nipple / 5th space, apex below the axilla).
• Haemothorax after trauma: urgent thoracotomy is indicated if more than 1500 mL drains immediately, or more than about 200 mL/hour continues for 2–4 hours. Clamping the drain only hides the bleeding.
• Tension pneumothorax (absent breath sounds, trachea pushed away, hypotension) is a clinical diagnosis: immediate needle decompression before any X-ray (in adults the 4th–5th space just anterior to the midaxillary line; 2nd space midclavicular in children), followed by a chest drain. A stable primary spontaneous pneumothorax with breathlessness is usually managed first by needle aspiration.

Pleura: nerves and pain

Roots and hila

• Right hilum: the eparterial bronchus (right upper lobe bronchus) lies above the pulmonary artery.
• Left hilum: the pulmonary artery is highest, bronchus below and behind.
• Pulmonary veins are the most anterior and inferior hilar structures on both sides.
• The azygos vein arches over the right root and the aortic arch over the left. The phrenic nerve passes in front of the root and the vagus behind.
• The pulmonary ligament is the double pleural fold hanging below the root.

Bronchial tree and aspiration

• The trachea divides at the carina at the level of the sternal angle (T4/T5). At bronchoscopy the first opening seen beyond the carina on the right is the right upper lobe bronchus, about 2.5 cm along the right main bronchus.
• The right main bronchus is wider, shorter and more vertical, so foreign bodies and aspirate usually enter the right lung.

• Middle lobe syndrome: the right middle lobe bronchus is long and narrow and is surrounded by lymph nodes, which can compress it (TB, malignancy), causing recurrent collapse or pneumonia of the same lobe. An endobronchial tumour must still be excluded.
• Airway order: trachea, main bronchi, lobar (secondary) bronchi, segmental (tertiary) bronchi, bronchioles, terminal bronchioles (last purely conducting, no cartilage), respiratory bronchioles, alveolar ducts and alveoli.
• Pores of Kohn between neighbouring alveoli (and bronchiole–alveolar channels) give collateral ventilation, so alveoli beyond a blocked bronchiole may stay aerated; they also let infection spread.

Bronchopulmonary segments

A segment is the lung tissue aerated by one segmental (tertiary) bronchus, with its own segmental branch of the pulmonary artery running centrally with the bronchus. The pulmonary veins run between segments (intersegmental) and drain adjacent segments. A surgeon divides the segmental bronchus and artery centrally and then follows the intersegmental veins to find the plane, which is why a segmentectomy is possible with little bleeding or air leak. Segments are not lobules (lobules are much smaller units).

Blood supply and lymph

• Pulmonary arteries: low-pressure, deoxygenated blood for gas exchange.
• Bronchial arteries: from the descending thoracic aorta (usually two left; one right, often from the 3rd posterior intercostal artery). They nourish the airways and are at systemic pressure, so they are the usual source of massive haemoptysis (treated by bronchial artery embolisation).
• Bronchial veins: superficial ones drain to the azygos vein on the right and the accessory hemiazygos or left superior intercostal vein on the left; deeper ones drain into pulmonary veins.
• Lymph: intrapulmonary nodes, then bronchopulmonary (hilar) nodes, then tracheobronchial (carinal) and paratracheal nodes, then bronchomediastinal trunks. Left lower lobe lymph often crosses to right-sided mediastinal nodes.

Remember Lung 6–8–10, pleura 8–10–12; the gap between them is the costodiaphragmatic recess.

Exam trap The neurovascular bundle lies between the internal and innermost intercostals, not deep to the innermost layer; deep to that is endothoracic fascia, then pleura.

Exam trap The azygos lobe is not a true lobe: it has no bronchus of its own.

How FCPS asks about this

• Lower border of lung and pleura posteriorly: lung T10, pleura T12; pleura crosses the 10th rib in the midaxillary line.
• Supine aspiration: superior segment of the right lower lobe.
• First bronchus seen beyond the carina on the right: right upper lobe (eparterial) bronchus.
• What defines a bronchopulmonary segment: a segmental (tertiary) bronchus with its own artery; veins are intersegmental.
• Structure strengthening the cervical pleura: suprapleural membrane (Sibson fascia).
• Pleural fluid site and tap: costodiaphragmatic recess; insert just above a rib.
• Recurrent same-lobe pneumonia with nodes compressing the bronchus: middle lobe syndrome.