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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
- 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

TERMINOLOGY

Abbreviations
- Cavum septi pellucidi (CSP)
- Cavum vergae (CV)
Definitions
- Cystic CSF cavity of septum pellucidum (CSP) ± posterior continuation (CV)

IMAGING

General Features

Best diagnostic clue

- Elongated finger-shaped CSF collection between lateral ventricles

Location

- CSP: Between frontal horns of lateral ventricles
- CV: Posterior extension between fornices

Size

- From slit-like to several mm, occasionally > 1 cm

Morphology
```
- Elongated, finger like
```

CT Findings

NECT
```
- CSF collection in septum pellucidum
```
CECT
```
- Does not enhance
```

MR Findings

T1WI

- Axial: Finger-like CSF space between lateral ventricles
- Sagittal: Extends posteriorly from rostrum to splenium of corpus callosum (CC) above, ICVs below

T2WI
```
- Isointense with CSF
```
FLAIR
```
- Suppresses completely
```
DWI
```
- Does not restrict
```

Ultrasonographic Findings

Grayscale ultrasound

- Septum pellucidum invariably present in normal fetus
        - Width of fetal CSP increases between 19-27 weeks
        - Plateaus, then gradually closes in rostral direction between 28 weeks and term
        - Inability to find CSP on fetal US requires search for CC

DIFFERENTIAL DIAGNOSIS

Asymmetric Lateral Ventricles
- Septum pellucidum bowed but intact
Cavum Velum Interpositum
- Triangular shaped; no extension anterior to foramen of Monro
Ependymal Cyst
- In body/atrium of lateral ventricle
Septooptic Dysplasia
- SP absent, "squared off" frontal horns

PATHOLOGY

General Features

Etiology

- CSP forms if fetal septum pellucidum fails to obliterate
- Precise etiology of fluid accumulation unknown
- CSP is not "5th ventricle," nor is CV "6th ventricle"

Associated abnormalities
```
- Rare: Hydrocephalus
```

Staging, Grading, & Classification
- Shaw and Ellsworth classification for CSP, CV - Asymptomatic, incidental cavum (communicating or not) - Symptomatic, pathological, noncommunicating cavum - Simple and uncomplicated - Complicated by other lesions

CLINICAL ISSUES

Presentation

Most common signs/symptoms

- Usually asymptomatic, incidental
        - May remain asymptomatic even if mass effect present
- Headache (relationship to cyst unclear)

Demographics

Age

- CSP
        - Present in 100% of premature, 85% of term infants
        - From 1% up to 15-20% of adults
- CV
        - 100% at fetal age of 6 months, 30% at term
        - < 1% of adults

Natural History & Prognosis
- Normally regresses - May persist as normal variant
- Rare: Enlarges, may cause mass effect
Treatment
- Usually none

DIAGNOSTIC CHECKLIST

Image Interpretation Pearls
- CV almost never occurs without CSP

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References

Selected References

Cases

{'cases': [{'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '66e58cd7-5239-4b71-8bd5-88312583a976', 'description': 'Axial (image 1) and sagittal (image 2) T1WIs show classic cavum septi pellucidi (CSP) and Vergae. The CSP lies in between the frontal horns of the lateral ventricles (open arrows) and the cavum Vergae (CV) (curved arrows) extends posteriorly in between the bodies of the lateral ventricles. The CSP + CV form a "cigar-shaped" CSF-containing structure that lies between the lateral ventricles. Note that on the sagittal view, the cavum occupies the entire space under the corpus callosum, flattening the fornix (arrows). This contrasts with cavum velum interpositum, which usually displaces the fornix anterosuperiorly.', 'history': 'Middle-aged patient with headaches, no neurologic findings.', 'imagePoolId': 'fbd519fb-6ab7-498c-8474-51dbaa25dd2b', 'name': 'With cavum vergae', 'teachingPoint': None}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '15afabe5-824c-46be-9f9b-58cded699493', 'description': 'Axial T1-weighted MR scans show the classic appearance of cavum septi pellucidi (arrows) with posterior extension into a cavum Vergae (open arrows), seen here as a CSF-signal collection that lies between the bodies of the lateral ventricles.', 'history': 'Asymptomatic patient, incidental finding.', 'imagePoolId': '8d51f828-9478-4e8d-945d-09d8496552d5', 'name': 'CSP, vergae', 'teachingPoint': None}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'c38954f4-6732-402d-ad20-5bf751eefb80', 'description': 'Sagittal T1-weighted MR scan (#1) shows the classic finding of a cavum septi pellucidi (CSP), seen here as a CSF-filled collection under the corpus callosum (open arrows) that flattens and displaces the thinned fornix (arrows). Axial image (#2) and coronal image (#3) T2WIs show the mass follows CSF in signal intensity. On the coronal scan, the thinned fornices (arrows) are barely visible. Coronal FLAIR scan (#4) shows the rounded contours of the CSP. Fluid in the CSP suppresses completely on FLAIR.', 'history': None, 'imagePoolId': 'ae79975a-0e41-4b33-ad5f-5a209538cd81', 'name': 'CSP cyst, fornix dysplasia', 'teachingPoint': None}], 'caseType': 'typical', 'name': 'TYPICAL'}
{'cases': [{'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'ce9dcc88-81a6-4e2b-b127-03d2d2cbefe8', 'description': 'Axial NECT scans (#1, 2) show a rounded CSF-density mass in the septum pellucidum that is contiguous with an elongated CSF mass lying in-between the bodies of the lateral ventricles (arrows). This is a cavum septi pellucidi with cavum Vergae. Contrast-enhanced scans (source images from the CTA performed in this patient) show no enhancement (#3-5). \n\nThis case is a slight variant on the typical CSP + Vergae as it is somewhat rounder than usually seen. This is considered a normal variant.', 'history': 'Incidental finding.', 'imagePoolId': 'b7937706-cf34-4252-a8e0-4e96b937e7c9', 'name': 'Very round', 'teachingPoint': None, 'demographics': '30 Years old male'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}, {'key': '789e84ce-9fde-4452-b27a-21d45423ac32', 'value': 'Anne Kennedy, MD, FSRU, FAIUM'}], 'caseVersionId': 'a5a4b3e1-aaa0-4d47-ae95-c458d17afb1f', 'description': 'Fetal MR (#1) and ultrasound (# 2) show absent septum pellucidum in corpus callosum agenesis. Note "Viking helmet" appearance on the coronal T2WI through the frontal and temporal horns (#1), with widely spaced parallel lateral ventricles and a high-riding third ventricle that is continuous superiorly with the interhemispheric fissure. Colpocephaly (enlarged occipital horns) is common in callosal agenesis and is seen on image #2 (arrow).', 'history': 'Routine prenatal imaging.', 'imagePoolId': '53203fa9-945d-44e0-8723-bab3d8cf207c', 'name': 'Absent CSP, CC agenesis', 'teachingPoint': None}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'b793cb29-03cb-45cd-a54d-1805f7544044', 'description': 'A classic cavum septi pellucidi (CSP) with cavum Vergae (CV) is seen (arrows). This case is unusual because the CSP and CV are very small.', 'history': 'Incidental finding. Patient being imaged for possible intracranial metastases.', 'imagePoolId': '77f1b3ce-a427-4b7e-b075-8278f3c4e3ce', 'name': 'Very small', 'teachingPoint': None}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'ede02258-1779-427d-9e2e-f9aeb96dfac9', 'description': 'An unusually large cavum septi pellucidi with cavum Vergae is present. Note mass effect with lateral bowing of the leaves of the septum pellucidum on the coronal scans (#3-4, arrows). Lateral/inferior displacement of the internal cerebral veins on the sagittal image (#1, open arrows) and coronal views (#3-4) (#3, open arrows) is seen. Axial scan (#2) shows lateral bowing of the fornices posteriorly (arrows). Image 4 also shows lateral displacement of the foramen of Monro (curved arrows). No obstructive hydrocephalus is present.', 'history': 'Asymptomatic patient, incidental finding.', 'imagePoolId': '80daa008-e840-43a4-82e4-b9d25b8696f1', 'name': 'Large with mass effect', 'teachingPoint': None, 'demographics': '20 Years old female'}], 'caseType': 'variant', 'name': 'VARIANT'}

Images

Selected Images

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

Coronal T1 C+ SPGR MR shows a classic large CSP between the frontal horns . There is lateral bowing of the leaves of the septum pellucidum .

Axial T2 MR shows cavum septi pellucidi 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 (TBI), such as boxers and American professional football players.

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 .

Additional Images

Axial NECT shows a variant of cavum septi pellucidi. Here, the CSP appears almost round .

Sagittal T1 C+ MR shows a large CSP/CV that extends from just behind the corpus callosum genu all the way posteriorly to the splenium. The fornices are not visible, and the internal cerebral vein is flattened .

Coronal T1 C+ MR in the same patient shows the large CSP bowing the leaves of the septum pellucidum laterally .

Axial T1 MR shows a small cavum septi pellucidi with cavum vergae . Note the finger-like appearance of the CSF collection that lies between the frontal horns and bodies of the lateral ventricle.

Axial T2 MR shows a variant of a cavum septi pellucidi with cavum vergae. Note the large CSF collection between leaves of septum pellucidum continuing directly posteriorly with the CSF collection, splaying the fornices laterally .

Axial T2 MR shows cavum septi pellucidi 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 TBI, such as boxers and American professional football players.

Coronal T1 MR shows a classic large CSP between the frontal horns , bowing the leaves of the septum pellucidum laterally .

21 KiB Raw Blame History

KEY FACTS

Terminology

Imaging

Top Differential Diagnoses

Pathology

Clinical Issues

Diagnostic Checklist

TERMINOLOGY

Abbreviations

Definitions

IMAGING

General Features

Best diagnostic clue

Location

Size

Morphology

CT Findings

NECT

CECT

MR Findings

T1WI

T2WI

FLAIR

DWI

Ultrasonographic Findings

Grayscale ultrasound

DIFFERENTIAL DIAGNOSIS

PATHOLOGY

General Features

Etiology

Associated abnormalities

Staging, Grading, & Classification

CLINICAL ISSUES

Presentation

Most common signs/symptoms

Demographics

Age

Natural History & Prognosis

Treatment

DIAGNOSTIC CHECKLIST

Image Interpretation Pearls

References

Selected References

Cases

Images

Selected Images

Additional Images

21 KiB

Raw Blame History