The septum pellucidum: normal and abnormal.

The common embryologic origin of the septum pellucidum, of the corpus callosum, and of the limbic system explains the anatomic basis of a varying degree of concurrent involvement of these structures in disease processes, both developmental and acquired. Developmental absence of the septum pellucidum portends a more generalized dysplasia that encompasses the corpus callosum and the limbic system. When considered in this context, it is easy to understand the limbic system dysfunction that is engendered by this anomaly. It is rare for an acquired lesion to involve the septum pellucidum per se because of its small size. However, it is common for it to be secondarily involved in almost all types of acquired disease processes. With the exquisite anatomic morphology that MR now provides, one must carefully assess involvement of the septum pellucidum, of the corpus callosum, and of the limbic system in disease processes that occur in the vicinity of these structures, so that more incisive clinical insight into the functions that are subserved by these structures can be obtained.