Sacral agenesis

Last revised by Dr Derek Smith on 07 Feb 2022

Sacral agenesis (also considered as part of the caudal regression syndrome) is a rare and severe sacral developmental abnormality.

In normal pregnancy, the incidence is between 0.005 and 0.1%. However, in fetuses with diabetic mothers, the incidence rises to 0.2%. Of those with the condition, 16-20% have diabetic mothers.

Sacral agenesis can be categorized into four types 1:

  • type I: unilateral agenesis localized to sacrum or coccyx
  • type II: partial agenesis with bilateral defects; the iliac bone articulates with S1, but the distal sacral elements fail to develop
  • type III: total sacral agenesis; iliac bones articulate with the lowest lumbar element
  • type IV: total sacral agenesis; iliac bones fuse posteriorly

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Cases and figures

  • Case 1
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  • Case 2
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  • Case 3: type III in an adult
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  • Case 4
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