5.1 Case Presentation

5.1.2 Imaging Findings and Impression

Coronal CT scan of the head without contrast (▶ Fig. 5.1a) and brain MR images without contrast including axial T2-weighted (▶ Fig. 5.1b), axial T1-weighted (▶ Fig. 5.1c), and coronal fluid-attenuated inversion recovery (FLAIR; ▶ Fig. 5.1d) images show persistence of a fluid-filled cavity (white arrows) in between leaflets of the septum pellucidum extending posteriorly to the foramina of Monro, consistent with a cavum septum pellucidum. There is an incidental curvilinear pericallosal lipoma (white arrowhead) along the splenium.

5.2 Differential Diagnosis

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  Cavum septum pellucidum (CSP):

  
  
  
  
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    It is a fluid-filled cavity within the leaflets of septum pellucidum, which follows the cerebrospinal fluid (CSF) signal intensity on all sequences located anterior to columns of fornix.

  
  
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  Cavum septum vergae (CSV):

  
  
  
  
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    Posterior extension of CSP beyond the columns of the fornix and foramen of Monro.

    
    
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    CSV is located posterior to the CSP and posterior and superior to the columns of fornix. ¹

    
    
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    It is hypodense with CSF density on head CT scans without contrast. It follows CSF signal intensity on MR images of the brain and will be suppressed on FLAIR sequences.

    
    
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    Although the CSP and CSV are believed to represent anatomic variations, investigators have shown an increased prevalence of them in traumatic brain injury patients. ^{2 , 3}

    
    
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    A large CSP in patients with schizophrenia can also be associated with more severe symptoms. ⁴

  
  
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  Cavum velum interpositum:

  
  
  
  
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    It is an enlarged potential space in between infolded layers of the velum interpositum.

    
    
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    Anatomically, it is triangle shaped and lies between the internal cerebral veins.

    
    
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    It is located below the column of the fornix and the splenium of corpus callosum and posterior to the foramen of Monro.

    
    
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    It has CSF-like density on head CT scans with a triangular configuration pointing forward and not extending anterior to the foramen of Monro. ⁵

    
    
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    Isointense to CSF on all MR sequences with a hypointense membrane surrounding it.