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Cavum Septi Pellucidi (CSP)


KEY FACTS

Terminology

  • Cystic CSF cavity of septum pellucidum (SP)

    • Occurs ± cavum vergae (CV)

Imaging

  • Elongated finger-shaped CSF collection between lateral ventricles

    • Cavum septi pellucidi (CSP): Between frontal horns of lateral ventricles

    • CV: Posterior extension between fornices

    • CV is posterior extension of CSP

  • Size varies from slit-like to several mm, occasionally > 1 cm

  • SP invariably cystic in fetus

    • Width of fetal CSP increases between 19-27 weeks

    • Plateaus at 28 weeks

    • Gradually closes in rostral direction between 28 weeks and term

    • CSP present in 100% of premature, 85% of term infants

  • CSP seen in up to 15-20% of adults

Top Differential Diagnoses

  • Asymmetric lateral ventricles

  • Cavum velum interpositum

  • Ependymal cyst

  • Absent SP

Pathology

  • CSP forms if fetal SP fails to obliterate

  • Precise etiology of fluid accumulation unknown

  • CSP is not “5th ventricle”

  • CV is not “6th ventricle”

Clinical Issues

  • Usually asymptomatic, incidental

  • Headache (relationship to cyst unclear)

  • CSP frequent among athletes with history of repeated traumatic brain injury, such as boxers

Diagnostic Checklist

  • CV almost never occurs without CSP

Coronal graphic with axial insert shows classic cavum septi pellucidi (CSP) with cavum vergae (CV)
. Note the finger-like cerebrospinal fluid (CSF) collection between the lateral ventricles.

Axial T2WI MR shows CSP as a CSF collection between the leaves of the septum pellucidum
. Although seen incidentally, some studies have reported that CSP is frequent among athletes with a history of repeated traumatic brain injury, such as boxers and American professional football players.

Coronal T1WI MR shows a classic large CSP between the frontal horns
bowing the leaves of the septum pellucidum laterally
.

Axial FLAIR MR shows a large CSP with CV as a large CSF collection between the leaves of the septum pellucidum
, continuing directly posteriorly with the CSF collection, splaying the fornices laterally
.

TERMINOLOGY

Abbreviations

  • Cavum septi pellucidi (CSP)

  • Cavum vergae (CV)

Definitions

  • Cystic CSF cavity of septum pellucidum (CSP) ± posterior continuation (CV)

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