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The Human Phenotype Ontology (HPO) is downloaded weekly from The file downloaded is considered the "last stable build" available for the ontology. For more about the HPO, view their website at

Term:Absent septum pellucidum
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Accession:HP:0001331 term browser browse the term
Definition:Absence of the septum pellucidum (meaning translucent wall in Latin - SP), also known as the ventricle of Sylvius. The septum pellucidum is a thin, triangular double membrane separating the frontal horns of the right and left lateral ventricles of the brain. It extends between the anterior portion of the corpus callosum, and the body of the fornix and its width varies from 1.5 to 3.0 mm.
Comment:In contrast to the septum pellucidum, the cavum septum pellucidum (CSP) is a potential cavity between the membranous leaves of the septum pellucidum, separated by at least 1 mm, and is considered a normal anatomical variation.
Synonyms:exact_synonym: Absence of septum pellucidum;   Absence of the septum pellucidum;   Agenesis of the septum pellucidum;   Missing septum pellucidum
 alt_id: HP:0006969
 xref: MESH:C535562;   SNOMEDCT_US:253143001;   UMLS:C0431371

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  Human phenotype 0
    Phenotypic abnormality 0
      Abnormality of the nervous system 0
        Abnormal nervous system morphology 0
          Morphological central nervous system abnormality 0
            Abnormal brain morphology 0
              Abnormal forebrain morphology 0
                Abnormal cerebral morphology 0
                  Abnormal septum pellucidum morphology 0
                    Absent septum pellucidum 0
                      Septo-optic dysplasia 0
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