Absence of the septum pellucidum is a rare neurological condition that involves the thin membrane located at the midline of the brain between the two cerebral hemispheres, or halves of the brain. It is connected to the corpus callosum—a collection of nerve fibers that connect the cerebral hemispheres.

Absence of the septum pellucidum alone is not a disorder but is instead a characteristic noted in children with septo-optic dysplasia (an abnormality of the optic disc, with pituitary deficiencies and absence of the septum pellucidum) or other developmental anomalies. This rare abnormality has no cure but by itself, absence of the septum pellucidum is not life-threatening and some symptoms of the disorder can be treated. 

Symptoms of the disorder may include: 

• Learning difficulties 
• Abnormal development of the optic disk 
• Rapid involuntary movement of the eyes 
• Low muscle tone 
• Behavior issues 
• Seizures 
• Jaundice 
• Pituitary deficiencies/hormonal imbalance

Unfortunately, absence of the septum pellucidum is a rare condition and most cases happen without a known cause. This means there if often not much information known about the disorder. Doctors and researchers do not se enough patients with absence of the septum pellucidum. This makes hard from them to learn through observations or large studies.