Septum pellucidum

1. Connective tissue structure formed from paired laminae that separates the anterior horns of the lateral ventricles of the cerebral hemispheres; there may be a cavity, the cavum septum pellucidum, in the midline between the laminae of the septum pellucidum
   1. persistent cavum septum pellucidum is found in 80% of normal neonates with most shrinking – only 4% of adults have one
      1. thickened septum pellucidum more than 3 mm is suspicisous for infiltrating neoplasm
      2. most common septal neoplasm is astrocytoma but lymphomas and germinomas also occur; thickening can also be seen in NF-1; other tumors with a predilection for the septum pellucidum include central neurocytoma, subependymoma, and giant cell astrocytoma
   2. cavum vergae, a posterior extension of cavum septum pellucidum, is seen in 30% of term infants
      1. cavum vergae never occurs without cavum septum pellucidum
      2. appears as a fingerlike CSF collection that lies in the midline below the corpus callosum between the fornices
2. The septal nuclei are located in the rostral forebrain adjacent to the septum pellucidum; a portion of the septal nuclei climb up the septum pellucidum