---

Surface Markings of the Lung

---

Apex

---

Anterior Border

• Right lung: Passes from the apex downward to the sternoclavicular joint, then descends vertically close to the midline, behind the sternum, reaching the level of the 6th costal cartilage.
• Left lung: Follows a similar course down to the 4th costal cartilage, where it deviates laterally to form the cardiac notch (because the heart bulges into the left pleural cavity). It then curves back medially and reaches the 6th costal cartilage. This creates the costomediastinal recess on the left.

---

Inferior Border (Lung Margin)

Note: The parietal pleura (costodiaphragmatic recess) lies two rib spaces below the lung margin at each reference line (VIII, X, XII), forming a potential space for fluid collection.

---

Posterior Border

---

Fissures and Lobes

Oblique Fissure (Both Lungs)

• Posteriorly: Begins at the spinous process of T4 (TIV) in the midline
• Courses inferolaterally, crossing the 4th and 5th intercostal spaces
• Laterally: Crosses rib V at the midaxillary line
• Anteriorly: Follows the contour of rib VI and its costal cartilage

Horizontal Fissure (Right Lung Only)

• Follows the 4th intercostal space from the sternum anteriorly
• Meets the oblique fissure where it crosses rib V laterally
• In the anterior view, it follows the contour of rib IV and its costal cartilage

---

Summary Table

---

Anterior and Posterior Views

---

Lateral and Posterior Views with Arm Abducted

---

Clinical Relevance

• The costodiaphragmatic recess (between lung margin and pleural reflection) is the lowest potential space - pleural effusions collect here first and can be detected by dullness on percussion below the lung's inferior margin.
• The costomediastinal recess is present anteriorly on the left due to the cardiac notch.
• Because the posterior surface is largely lower lobe, auscultation over the back mainly samples the lower lobe (both sides). The upper lobes are best heard anteriorly and apically.
• The middle lobe of the right lung lies mainly adjacent to the lower anterior chest wall and is heard best in the right axilla and right lower anterior chest.

Surface Markings of the Lung

---

Lungs - Basic Structure

---

1. Apex

• Projects 2.5 cm above the medial third of the clavicle into the root of the neck
• Corresponds to the level of the neck of the 1st rib
• The parietal pleura (cervical pleura) also projects superiorly above the first costal cartilage at this point

---

2. Anterior Border

• Descends from the apex to the sternoclavicular joint
• Runs vertically downward close to the midline, posterior to the sternum
• Reaches the 6th costal cartilage where it turns to become the inferior border

• Follows the same course as the right down to the 4th costal cartilage
• Then deviates laterally to form the cardiac notch (due to the heart bulging into the left pleural cavity)
• Curves back medially as the lingula and meets the inferior border at the 6th costal cartilage
• This deviation creates the costomediastinal recess anteriorly on the left

---

3. Inferior Border (Lung Margin)

---

4. Posterior Border

• Runs vertically close to the vertebral column on each side
• Extends from the apex down to the level of vertebra TX posteriorly

---

5. Pleural Reflection (vs. Lung Margin)

---

6. Fissures and Lobes

Oblique Fissure - Both Lungs

• Posteriorly: Begins at the spinous process of T4 (TIV) in the midline
• Laterally: Descends, crossing the 4th and 5th intercostal spaces, reaching rib V at the midaxillary line
• Anteriorly: Follows the contour of rib VI and its costal cartilage

The left oblique fissure starts slightly higher - between the spinous processes of TIII and TIV - and is slightly more oblique than the right.

Horizontal Fissure - Right Lung Only

• Anteriorly: Follows the 4th intercostal space from the sternum to the midaxillary line
• Laterally: Crosses rib V at the midaxillary line, where it meets the oblique fissure
• In the anterior view, follows the contour of rib IV and its costal cartilage

---

Anterior and Posterior Views

---

Posterior and Lateral Views

---

Quick Reference Summary Table

---

Clinical Relevance

• Auscultation: The posterior chest wall overlies mainly the lower lobes of both lungs. The upper lobes are best heard anteriorly and at the apices. The right middle lobe is best heard at the right lower anterior chest and right axilla.
• Pleural effusion: Fluid collects first in the costodiaphragmatic recess. Dullness to percussion below the lung margin (between rib VI and rib VIII at MCL) suggests an effusion.
• Pleural tap (thoracocentesis): Performed above the rib margin between the lung's inferior border and the pleural reflection (typically around the 8th-9th rib space at the posterior chest wall) to avoid the lung and neurovascular bundle.
• Pneumothorax: Air rises to the apex; absent breath sounds and hyper-resonance over the upper chest anteriorly.