Oblique fissure of right lung

The oblique fissure of the right lung (Major fissure; Greater fissure) is a deep cleft in the visceral pleura that separates the right upper and middle lobes from the right lower lobe. It extends from the posterior aspect of the lung near the hilum, coursing obliquely downward and forward to the diaphragmatic surface.

Surface anatomy:

The right oblique fissure most commonly begins posteriorly at the level of the fifth rib, crosses the mid- axillary line at the sixth rib, and reaches the diaphragmatic surface in the anterior third of the hemidiaphragm. Its upper portion is typically concave and faces laterally, while its lower portion is usually convex and also tends to face laterally a key distinction from the left oblique fissure, whose lower portion typically faces medially.

Key anatomical features:

• The right oblique fissure begins at a slightly lower level than the left oblique fissure; a right oblique fissure positioned higher than the left almost always indicates a pathological process.

• The right horizontal (minor) fissure branches off from the right oblique fissure, typically at its middle third, and extends anteriorly to the lung surface this is unique to the right lung.

• The right oblique fissure configuration is more variable than the left, with S-shaped and linear configurations each occurring in about 28% of cases, compared to the predominantly linear left oblique fissure (78%).

Completeness and variations:

The right oblique fissure is frequently incomplete. Studies report completeness rates of approximately 64-77%, with incompleteness most commonly occurring in the parahilar region.

An incomplete fissure allows collateral ventilation and potential disease spread between lobes, which has important implications for thoracic surgery, endobronchial valve placement, and radiologic interpretation.