Absent septum pellucidum

Last revised by Jeremy Jones on 18 Dec 2019

An absent septum pellucidum may rarely be an isolated finding, or more commonly be seen in association with a variety of conditions.

The septum pellucidum is partly or entirely absent in 2 or 3 individuals per 100,000 in the general population. 

An absent septum pellucidum may be developmental or acquired secondary to another pathological process 1,2

Cavum septum pellucidum is always visualized between 18 and 37 weeks and within a biparietal diameter of 44 to 88 mm. Failure to detect the cavum septum pellucidum within this time interval requires further investigation. However, the absence of cavum septum pellucidum on the ultrasound exam prior to 18 weeks or later than 37 weeks is considered a normal finding.

Non-visualization of the septum pellucidum with direct communication of the frontal horns. Additionally, the following characteristics may be seen 3:

  • boxing/squaring off of the frontal horns
  • inferior pointing frontal horns
  • abnormally inferiorly positioned fornix (coronal views)

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Cases and figures

  • Case 1: semilobar holoprosencephaly
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  • Case 2: septo-optic dysplasia
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  • Case 3: schizencephaly (open lip type)
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  • Case 4: associated with open lip schizencephaly
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  • Case 5: apparently isolated
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  • Case 6: with polymicrogyria
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