Septum pellucidum


The septum pellucidum is a thin, triangular, vertical double membrane separating the anterior horns of the left and right lateral ventricles of the brain. It runs as a sheet from the corpus callosum down to the fornix.
The septum is not present in the syndrome septo-optic dysplasia.

Structure

The septum pellucidum is located in the midline of the brain, between the two cerebral hemispheres. It is attached to the lower part of the corpus callosum, the large collection of nerve fibers that connect the two cerebral hemispheres. It is attached to the front forward part of the fornix. The lateral ventricles sit on either side of the septum.
The septum pellucidum consists of two layers or laminae of both white and gray matter. During fetal development there is a space between the two laminae called the cave of septum pellucidum which, in ninety per cent of cases, disappears during infancy.

Confusion over the term

The septum pellucidum is often confused with the septal nuclei. Logically, the septum pellucidum is a septum in the medial plane and could therefore be termed 'medial septum', but this is incorrect. The term medial septum is reserved for a small group of nuclei which are closely associated with the septum pellucidum.
The cavum was occasionally referred to as the fifth ventricle but this is no longer used as the space is usually not continuous with the ventricular system. The fifth ventricle is recognised as the terminal enlargement of the spinal cord.

Clinical significance

Absence of the septum pellucidum occurs in septo-optic dysplasia, a rare developmental disorder usually characterized by abnormal development of the optic disk and pituitary deficiencies. Symptoms of septo-optic dysplasia are highly variable and may include vision difficulties, low muscle tone, hormonal problems, seizures, intellectual problems, and jaundice at birth. Management is directed at the symptoms a person is affected with.

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