Right lung has three lobes and two fissures; left lung has two lobes and one fissure
Mnemonic
“Three on the right, two on the left, and the left has a lingula instead of a middle lobe”:
- Right - upper, middle, lower. Oblique and horizontal fissures
- Left - upper, lower. Oblique fissure only
Surface markings:
- Oblique fissure - follows the line of the sixth rib anteriorly, running from the spine of T3 posteriorly. Approximated by the medial border of the abducted scapula
- Horizontal fissure - runs along the fourth costal cartilage to meet the oblique in the mid-axillary line
“Everything you hear anteriorly on the right below the fourth rib is middle lobe; everything you hear posteriorly is lower lobe.” That is the single most useful consequence, and it is why posterior auscultation misses upper lobe pathology.
The lingula is the left equivalent of the middle lobe, part of the upper lobe, and losing the left heart border on a radiograph localises consolidation to it by the silhouette sign.
Expansion
Right lung - three lobes
- Oblique fissure and horizontal fissure
- Upper, middle and lower lobes
Left lung - two lobes
- Oblique fissure only
- Upper and lower lobes, with the lingula as part of the upper lobe
The left lung is smaller and carries the cardiac notch, because the heart projects to the left. A simple summary is right 3, left 2, and the same asymmetry recurs throughout the thorax, with the two-lobed left lung matching the two-cusped mitral valve.