Surface marking of lung

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Surface Markings of the Lung

Surface markings describe how the lungs and their key features (apex, borders, fissures, lobes) project onto the body surface.

1. Apex of the Lung

The apex projects 2.5 cm above the medial one-third of the clavicle anteriorly.
Posteriorly, it is related to the neck of rib I and lies approximately 3.5 cm above the costal cartilage of rib I.
This is clinically significant: the apex is vulnerable in a Pancoast (superior sulcus) tumor, subclavian vessel injury, and during central line placement.

2. Anterior Border

Both lungs approach the midline behind the upper part of the sternum.
On the right, the anterior border runs vertically close to the midline from the sternoclavicular joint down to the 6th costal cartilage.
On the left, the anterior border diverges laterally from the level of the 4th costal cartilage (cardiac notch), creating the costomediastinal recess on the left.

3. Inferior Border (Lung Margin)

During quiet respiration, the inferior margin of the lung follows the contour:

Reference Line	Rib Level
Midclavicular line	Rib VI
Midaxillary line	Rib VIII
Posteriorly (paravertebral)	Vertebra TX (T10)

This is the "VI, VIII, X" rule for the lung margin.

4. Inferior Border of the Pleura (Costodiaphragmatic Recess)

The parietal pleura extends lower than the lung edge, creating the costodiaphragmatic recess:

Reference Line	Rib Level
Midclavicular line	Rib VIII
Midaxillary line	Rib X
Posteriorly	Vertebra TXII (T12)

This is the "VIII, X, XII" rule for the pleura.

The gap between the lung border (VI, VIII, X) and the pleural border (VIII, X, XII) represents the costodiaphragmatic recess - a potential space that fills with fluid in pleural effusion.

5. Fissures and Lobes

Oblique Fissure (both lungs)

Posteriorly: begins at the spine of vertebra TIV (T4), near the midline.
Runs laterally and downward, crossing the 4th and 5th intercostal spaces.
Reaches rib VI laterally and anteriorly, where it meets the costal cartilage of rib VI.
A practical landmark: with the arm raised, the medial border of the scapula parallels the oblique fissure.

Horizontal Fissure (right lung only)

Anteriorly: follows the line of rib IV and its costal cartilage, extending from the oblique fissure laterally to the anterior border of the lung.

Summary of Lobes (anterior view)

Right Lung	Left Lung
Superior, Middle, Inferior lobes	Superior, Inferior lobes
Superior and Middle divided by Horizontal Fissure (Rib IV)	No horizontal fissure
Middle and Inferior divided by Oblique Fissure (Rib VI)	Superior and Inferior divided by Oblique Fissure (Rib VI)

Diagrams

Anterior and Posterior views - Surface projections of lobes and fissures:

Surface projection of lung lobes - anterior and posterior

Posterior view and lateral view showing oblique fissure, horizontal fissure, and pleural borders:

Lung surface markings - posterior and lateral views with scapula landmark

Quick Memory Aid

Structure	Landmark
Apex	2.5 cm above medial clavicle
Lung inferior border	VI (MCL) - VIII (MAL) - X (posterior)
Pleura inferior border	VIII (MCL) - X (MAL) - XII (posterior)
Oblique fissure	TIV posteriorly → rib VI anteriorly
Horizontal fissure (R)	Along rib IV
Oblique fissure landmark	Medial border of raised scapula

Sources: Gray's Anatomy for Students, pp. 277-278; Color Atlas of Human Anatomy Vol. 2 (Thieme), pp. 209-210

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