Velum interpositum

Last revised by Naim Qaqish on 26 Feb 2021

The velum interpositum is a small membrane containing a potential space just above and anterior to the pineal gland which can become enlarged to form a cavum velum interpositum

Gross anatomy

The velum interpositum is formed by an invagination of pia mater forming a triangular membrane the apex of which points anteriorly.


It varies in shape from person to person, sometimes interposed between the internal cerebral veins and splenium, and depending on whether or not there is a cavum vergae (in which case the columns of the fornices are displaced inferiorly, narrowing the velum interpositum). 

When somewhat distended by fluid it forms a small triangular (in axial section) space and is referred to as a cavum velum interpositum. If larger and exterting mass effect it is known as a cavum velum interpositum cyst

The space between the two leaves of pia contains the posterior medial choroidal arteries 2

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Cases and figures

  • Case 1: cavum velum interpositum cyst
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  • Cavum veli interpositi
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