Diaphragmatic eventration

Last revised by Liz Silverstone on 26 May 2024

Diaphragmatic eventration refers to an abnormal contour of the diaphragmatic dome with no disruption to the diaphragmatic continuity. It typically affects only a segment of the hemidiaphragm, compared to paralysis/weakness where the entire hemidiaphragm is typically affected. 

Unilateral eventration 5

Bilateral eventration 5

In newborns, eventration of the diaphragm is a recognized cause of respiratory distress. However in adults, it is often asymptomatic 6

Diaphragmatic eventration is thought to be congenital in origin. It occurs due to incomplete muscularisation of the diaphragm with a thin membranous sheet replacing normal diaphragmatic muscle. Over time this region stretches and on inspiration does not contract normally. 

  • phrenic nerve agenesis

  • failure of myotomes to migrate to a localized area in the diaphragm leading to abnormal muscularisation

This should be differentiated from trauma/surgery/birth trauma leading to phrenic nerve paralysis

Congenital eventration is frequently seen in the anteromedial portion of the right hemidiaphragm, while acquired eventration is frequently seen in the left hemidiaphragm. Total eventration is most commonly seen in the left hemidiaphragm 6

Elevation of the affected portion of the diaphragm is usually seen as a smooth hump, while the remainder of the hemidiaphragm contour is normal. The frontal x-ray may show a 'double' diaphragmatic contour, which is easily confirmed on the lateral projection.

There is typically a ridge of muscle at the boundary with a mushroom-shaped bulge due to the eventration. The posterior diaphragm and costophrenic recess are normal in position and width and this helps to differentiate eventration from phrenic nerve palsy 4.

Possible considerations on plain film include:

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