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Horizontal fissure of right lung

The horizontal fissure of the right lung, also called the minor fissure, is an anatomical division that separates the right upper lobe from the right middle lobe. It runs horizontally from the oblique fissure near the midaxillary line and extends forward to meet the anterior border of the right lung, near the 4th costal cartilage. This fissure allows lobar separation and independent movement of lung segments during respiration. It is less constant than the oblique fissure and may be incomplete in some individuals, which is important in surgical planning and imaging interpretation.

Synonyms

  • Minor fissure

  • Right transverse fissure

  • Horizontal interlobar fissure

Function

  • Separates the right upper lobe from the right middle lobe

  • Allows independent expansion and contraction of lobes during breathing

  • Serves as an important surgical and radiological landmark

  • Aids in the spread assessment of infections, effusions, and tumors by defining lobar boundaries

CT Appearance

Lung Window:

  • Appears as a thin, curvilinear line of soft tissue density or a thin avascular plane between aerated lobes

  • Best seen on HRCT, running from the oblique fissure to the anterior chest wall

  • In incomplete fissures, the line may be absent or discontinuous

  • Pathology: fluid, thickening, or nodularity along the fissure may indicate pleural effusion, fibrosis, or tumor spread

Mediastinal Window:

  • Appears as a thin linear soft tissue density between lobes

  • Better demonstrates pleural thickening, nodularity, or tumor involvement

  • Useful for staging lung cancer and evaluating pleural-based disease

Contrast-enhanced CT (CECT):

  • Enhances detection of pleural or fissural nodules, especially for metastatic disease

  • Defines fissural anatomy for surgical planning (lobectomy/segmentectomy)

MRI Appearance

T1-weighted images:

  • The fissure itself appears as a low signal intensity line (due to pleura and adjacent air)

  • Surrounding fat planes may provide contrast

  • In pathological thickening, fissure becomes more conspicuous

T2-weighted images:

  • Normal fissure is usually not well seen, as air in adjacent lobes creates signal voids

  • Fluid or pleural thickening along the fissure appears as hyperintense lines or collections

  • Useful for detecting loculated effusions or pleural disease

T1 Post-Contrast (Gadolinium-enhanced):

  • Fissural pleura normally shows minimal or no enhancement

  • Pathology (inflammation, tumor, fibrosis) results in linear or nodular enhancement

  • MRI can highlight fissural involvement in pleural tumors or metastatic spread

CT images

Horizontal fissure of right lung anatomy CT coronal image -img-00000-00000

CT images

Horizontal fissure of right lung anatomy CT coronal image -img-00000-00000_00001