Incomplete Fissure Sign

• Clear crescentric, concave lucency seen adjacent to heart on frontal radiograph usually better demarcated when there is fluid in the pleural space laterally
• Called the “Incomplete Fissure Sign”
• The curvilinear edge is caused by a major fissure which does not completely separate the upper and lower lobes (middle on the right)]
• More common on the right side than the left
• Overall, quite common: over 60% are incomplete on the right and 50% on the left
• Incomplete fissures may allow for collateral air drift and the transmission of disease from one lobe to another



Incomplete Fissure. The black arrow points to a crescentric edge-like density that represents the medial border of an incomplete major fissure. The fissure is outlined by pleural fluid laterally.

Signs in Imaging: The Incomplete Fissure Sign. Meghan G. Lubner, MD. Radiology: 247, Issue 2.