|Patient: 30 year old female|
|Findings: A midline cyst between the roof of the third ventricle and the fornices at the inferior margin of the lateral ventricle.|
|Diagnosis: Cavum velum interpositum.|
|Discussion: The third ventricle becomes bulbous and diamond-shaped as it merges with the quadrigeminal cistern. The lateral borders of the third ventricle are formed by thalami; the anterior border is the anterior commissure and the lamina terminalis; the posterior border is the posterior commissure. The inferior boundary of the third ventricle is the hypothalamus and the superior border is the velum interpositum and body of the fornix.|
The walls of the third ventricle diverge posteriorly to form a triangle. At this level the quadrigeminal cistern is also triangular; therefore, the junction of the third ventricle and the quadrigeminal cistern appears diamond-shaped. The telea choroidea may be seen as a thin band separating the third ventricle from the quadrigeminal cistern.
The retrothalamic cistern extends laterally from the quadrigeminal cistern, and the superior cerebellar cistern is posterior to the quadrigeminal cistern. The cavum velum interpositum represents anterior extension of the quadrigeminal cistern.
The velum interpositum is the normally narrow space between the roof of the third ventricle and the fornices at the inferior margin of the lateral ventricles.
Small developmental cysts within the velum interpositum (cavum velum interpositum, cavi veli interpositi or cyst of the velum interpositum) typically have the shape of an elongated triangle pointing anteriorly. Larger cysts of the velum interpositum become more rounded and mass-like. Such cysts may be arachnoidal or neuroepithelial in origin.
1. Weisberg,L. Nice,C. Cerebral Computed Tomography. 3rd ed. Philadelphia, PA: W. B. Saunders Company. 1989.
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Case Number: 29656245Last Updated: 08-08-2010 The reader is fully responsible for confirming the accuracy of this content.
The reader is fully responsible for confirming the accuracy of this content.