Oblique Fissure

1. Overview

The oblique fissure is a major anatomical feature of both lungs that separates lobes and facilitates pulmonary expansion. It is present in both the right and left lungs, contributing to the division of lung parenchyma into functional lobes. The fissure is formed by an invagination of visceral pleura and plays an important role in lung mechanics, surgical orientation, and radiologic interpretation.

2. Location

The oblique fissure runs diagonally across the surface of both lungs. Its anatomical trajectory is as follows:

Right Lung

• Separates the superior and middle lobes (anteriorly) from the inferior lobe (posteriorly)

• Begins roughly at the level of the T2 vertebra posteriorly, descending obliquely and laterally to intersect the 6th rib anteriorly at the midclavicular line

Left Lung

• Separates the superior lobe from the inferior lobe

• Has a similar course as in the right lung, from the spine of T2 down to the 6th rib in the midclavicular line

3. Structure

The oblique fissure is composed of a double layer of visceral pleura, creating a potential space between adjacent lobes. Structurally, it:

• Is oriented diagonally in a posterosuperior to anteroinferior direction

• Varies in completeness—may be fully or partially formed depending on the individual

• Is associated with interlobar vessels and segmental bronchi deep within the lung tissue

On imaging, the fissure appears as a thin radiolucent line on CT scans and is variably visible on chest X-rays depending on positioning.

4. Function

Although not functional in the physiological sense like alveoli, the oblique fissure serves several structural and clinical roles:

• Divides lobes: Facilitates independent mechanical movement of lung lobes during respiration

• Compartmentalization: Limits the spread of infection or malignancy within the lung

• Surgical landmark: Used to guide resections such as lobectomies or segmentectomies

5. Physiological Role(s)

In respiratory physiology, the oblique fissure contributes to:

• Lobar motion: Allows more efficient expansion and recoil of lung lobes during inspiration and expiration

• Ventilation-perfusion matching: Enables regional ventilation distribution, especially in upright posture where lower lobes expand more

• Sinusoidal movement: The sliding of visceral pleura along fissures facilitates smooth lung motion

6. Clinical Significance

Lobar Pneumonia

The fissure acts as a boundary that can contain infections to specific lobes. On imaging, lobar consolidation may be clearly demarcated by the oblique fissure, helping radiologists determine which lobe is affected.

Pleural Effusion Tracking

Fluid in the pleural space may track along fissures and mimic pathology (e.g., pseudotumors). CT helps distinguish fluid from solid lesions.

Fissure Incompleteness

In some individuals, the fissure may be incomplete, allowing inter-lobar communication. This can:

• Alter disease spread

• Complicate surgical resections

Identified via high-resolution CT or during intraoperative exploration.

Surgical Relevance

The oblique fissure serves as a guide during lobectomies, where accurate identification ensures safe separation of lobes. Surgeons must take care not to injure interlobar vessels or airways lying within the fissure.

Radiological Significance

The fissure is variably visible on chest radiographs depending on patient positioning and beam angle. Lateral views may demonstrate the oblique fissure as a thin, curving line. Understanding its position is essential for accurate interpretation of:

• Consolidation

• Masses

• Atelectasis