Cavum septum pellucidum

Cavum septum pellucidum (CSP) is a normal variant CSF space between the leaflets of the septum pellucidum.

While the term "cavum septum pellucidum" is generally accepted, it is grammatically incorrect. Since it denotes a space (cavum meaning cave) of the septum pellucidum, the second part (septum pellucidum) should be a genitive, which would be inflected as cavum septi pellucidi. In its accepted misspelling as "cavum septum pellucidum" both "septum" and "pellucidum" are in fact used as adjectives of cavum. However, the term intends to refer to a space (cavum) that has persisted between the "septum pellucidum".

Historically it has also been called the fifth ventricle, but this use is now advised against as the cavum does not usually have any direct communication with the ventricular system.

A cavum septum pellucidum is present in the normal fetus, but over 85% of them fuse by 3-6 months of age meaning that a CSP persists in ~15% of the adult population. 

The cavum septum pellucidum commonly occurs, and is often confused with the cavum vergae, which is situated posterior to the anterior columns of the fornix. During development, these spaces obliterate posteroanteriorly - the cavum vergae followed by the cavum septum pellucidum - and it is not uncommon that both occur together. 

Cavum septum pellucidum is a Latin term deriving from, 'cavum' meaning 'space', 'septum' meaning 'fence', and therefore a dividing structure, and 'pellucidus' meaning 'transparent'. 

It has been loosely associated with 3-5:

  • schizophrenia
  • post-traumatic stress disorder (PTSD)
  • chronic brain trauma

However, an absent cavum septum pellucidum in antenatal imaging is a concerning feature and is associated with significant CNS anomalies 6

Anatomy: Brain
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Article information

rID: 1066
Section: Anatomy
Synonyms or Alternate Spellings:
  • Cavum septum pellucidum (CSP)
  • Cavum septum pellucidi
  • Fifth ventricle
  • Cavum septi pellucidi

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Cases and figures

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    Figure 1: lateral view
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    Case 1
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    Figure 2: anterior view
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    Case 2
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    Figure 3: CSP - gross pathology
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    Case 3: CSP and cavum vergae
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    Case 4: CSP and cavum vergae
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    Case 5
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    Case 6: CSP and cavum vergae
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    Case 7: cavum septum pellucidum - annotated
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