====== Absence of the septum pellucidum ====== Absence of the [[septum pellucidum]] occurs in septo-optic dysplasia, a rare developmental disorder also 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.