A toddler with failure to thrive and impaired vision
Diagnosis: Septo-optic dysplasia
Septo-optic dysplasia is a form of optic nerve hypoplasia, the most common congenital optic nerve anomaly, which results from a decreased number of ganglion cell axons.1,2 By definition the syndrome also includes the absence or dysplasia of the septum pellucidum. In many cases, there are other central nervous system abnormalities, such as thinning of the corpus callosum, pituitary malformation, and schizencephaly.3 Most cases of septo-optic dysplasia are diagnosed in infancy and childhood, and there is an equal gender distribution. While rare (6.3 cases per 100,000), septo-optic dysplasia is potentially fatal.1,4
The exact cause of septo-optic dysplasia is unknown; however, both genetic and environmental factors appear to play a role. It has been linked with a defect in the HESX1 gene, young maternal age, maternal insulin-dependent diabetes mellitus, and a variety of toxins.1,5
Poor vision and the “double ring” sign
Most patients present with visual disturbance secondary to optic nerve hypoplasia. Visual acuity may range from 20/20 to no light perception; however, the majority of patients have vision worse than 20/200.1,3 Severe congenital vision loss often leads to sensory nystagmus and strabismus, as well as absent fixation, visual inattentiveness, and an afferent pupillary defect.1,2,6
On examination of the fundus, you may see a “double ring” sign, the appearance of 2 borders around the optic nerve. This outer ring shows a visible sclera at the outer border of a normal-sized nerve and the inner represents the junction between the retinal pigment epithelium and the actual nerve border.1,2,3,7
From CNS abnormalities to pituitary and adrenal problems
While the absence of a septum pellucidum alone has been shown to be clinically insignificant, the presence of other central nervous system abnormalities—such as schizencephaly, cortical heterotopias, or periventricular leukomalacia—can lead to a variety of deficits.8,9 Three-fourths of patients present with seizures, mental retardation, focal neurological deficits, cerebral palsy, or cortical visual loss.1,9
In addition, 15% of patients have some level of pituitary hormone deficiency. Decreased growth hormone is most common, followed by lack of thyroid-stimulating hormone, corticotropic hormone, and vasopressin. Common presentations include failure to thrive, hypoglycemia, prolonged jaundice, thermoregulatory dysfunction, developmental delay, growth retardation, hypotension, recurrent infection, polydipsia, polyuria, and hyper-natremia.1,4,10
Sudden death has been reported in septo-optic dysplasia patients who exhibit hypocortisolism (adrenal insufficiency), diabetes insipidus, and thermo-regulatory dysfunction. Viral illness and other forms of stress are particularly problematic for these patients, as they are unable to mount an appropriate response and are overwhelmed by hypoglycemia, dehydration, shock, and high fevers.4 As a result, clinicians need to be watch for those infants and neonates who are vulnerable to this stress. Extra care should be taken if they require surgery.4,6
