has part has part characteristic of inheres in towards has modifier Cavum septum pellucidum Large cavum septi pellucidi Widened cavum septum pellucidum HP:0007091 Persistent cavum septum pellucidum HP:0006884 HP:0002389 HP:0007336 UMLS:C1840380 If the two laminae of the septum pellucidum are not fused then a fluid-filled space or cavum is present. The cavum septum pellucidum is present at birth but usually obliterates by the age of 3 to 6 months. It is up to 1cm in width and the walls are parallel. It is an enclosed space and is not part of the ventricular system or connected with the subarachnoid space. Abnormal septum pellucidum morphology abnormal unfused from lamina of septum pellucidum