The right lung is split into 3 lobes: superior, middle, and inferior by 2 fissures–(a) an oblique fissure and (b) a horizontal fissure
The left lung is split into 2 lobes: (a) superior and (b) inferior by an oblique fissure.
Oblique Fissure: A Long Oblique Fissure Runs Obliquely Downwards And Forwards Crossing The Posterior Border About 6 Cm (2 Inches) Below The Apex And Inferior Border About 7.5 Cm (3 Inches) Lateral To The Midline. It Divides The Superior And Middle Lobes From The Inferior Lobe.
Horizontal Fissure: A Short Horizontal Fissure Is Present Only In The Right Lung. It Begins With Oblique Fissure At The Midaxillary Line And Runs Horizontally Forwards To The Anterior Border Of The Lung. It Splits The Superior And Middle Lobes.
The oblique fissure in left lung runs obliquely downwards and forwards crossing the posterior border about 6 cm below the apex and inferior border nearly at its apex. It divides the superior lobe from the inferior lobe.
Points to notice
A. The oblique fissure functions as a plane of cleavage so that during inspiration, the upper part of lung enlarges forwards and laterally, on the other hand the lower part of the lung expands downwards and backwards.
B. In X ray chest PA view, the horizontal fissure is observable in 60% of the cases. The oblique fissure is normally observable in X ray chest sidelong view.
C. Oblique fissure of left lung is more vertical than the oblique fissure of the right lung.
Identification Of The Completeness Of The Fissure.
It isimportant before performing lobectomy (i.e., removal of the lobe of the lung because people with incomplete fissures are more prone to develop postoperative air leakage than those with whole fissures).
Accessory Lobes And Fissures
A. Lobe of azygos vein: Occasionally the medial part of the superior lobe is partly divided by a fissure of varying length, which includes the terminal part of the azygos vein, enclosed in the free margin of a mesentery originated from the mediastinal pleura. This is called lobe of azygos vein. It changes in size and occasionally consists of the apex of the lung.
B. A left horizontal fissure is a normal form seen in 10% of the people.