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Oblique fissure of left lung

The oblique fissure of the left lung is the major fissure that separates the upper lobe from the lower lobe. It begins posteriorly at the level of the T3–T4 vertebrae, courses obliquely downward and forward across the lung surface, and reaches the 6th costochondral junction anteriorly. The fissure provides anatomic division of lobes, allowing independent movement, expansion, and function of the lobes during respiration. It also acts as a surgical and radiological landmark for identifying lobar boundaries and guiding lobectomies, segmentectomies, and staging of lung disease.

Synonyms

  • Major fissure of the left lung

  • Left oblique fissure

  • Interlobar fissure (left lung)

Function

  • Separates the left upper lobe from the left lower lobe

  • Allows independent expansion and movement of lobes during respiration

  • Serves as a pathway for pleural reflections and compartmentalization of pleural fluid

  • Provides a landmark in imaging and thoracic surgery for identifying lobar anatomy

CT Appearance

Lung Window:

  • Appears as a thin, curvilinear line or cleft extending from the posterior chest wall (T3–T4 level) downward and anteriorly toward the diaphragm at the midclavicular line

  • Usually seen as a sharp avascular plane separating aerated lung of adjacent lobes

  • Incomplete fissures may appear as discontinuous or poorly formed clefts

Mediastinal Window:

  • The fissure is thinner and less conspicuous, sometimes only visualized when there is pleural thickening, effusion, or fibrosis

  • Provides better visualization of associated pleural disease, tumor spread, or fluid tracking

Contrast-enhanced CT (CECT):

  • Useful for identifying tumor or infection spread across lobes

  • The fissure acts as a barrier to disease, unless invaded or incomplete

MRI Appearance

T1-weighted images:

  • Normal fissure appears as a thin hypointense (dark) line between lobes

  • Surrounded by aerated lung (signal void), making direct visualization difficult without fluid or thickening

T2-weighted images:

  • Pleural fluid or thickening within the fissure appears hyperintense, highlighting the fissure margins

  • Normally, the fissure is faintly visible as a thin hypointense line

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal fissure shows no significant enhancement

  • Pathological thickening (pleural disease, tumor, infection) may show linear or nodular enhancement

CT images

Oblique fissure of left lung anatomy CT coronal image -img-00000-00000

CT images

Oblique fissure of left lung anatomy CT coronal image -img-00000-00000_00001