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Septo-optic dysplasia (SOD), also known as de Morsier syndrome, is a condition characterized by optic nerve hypoplasia and absence of the septum pellucidum and, in two-thirds of patients hypothalamic-pituitary dysfunction. It is best thought of as being part of the holoprosencephaly spectrum (see classification system for midline malformations).
Septo-optic dysplasia has an estimated prevalence of ~1:50,000. There is no recognized gender predilection.
A number of risk factors have been identified 8,9:
- maternal diabetes
- quinidine ingestion
- drug and alcohol abuse
- cytomegalovirus infection
Clinical presentation of septo-optic dysplasia is varied and mostly dependent on whether or not it is associated with schizencephaly (~50% of cases). This association is used to define two forms of the condition 1,8:
- not associated with schizencephaly
- visual apparatus more severely affected
- hypothalamic-pituitary dysfunction present in 60-80% of patients 6,8
- may present as hypoglycemia in the neonatal period 6
- small pituitary gland with hypoplastic or absent infundibulum and ectopic posterior pituitary seen as a focus of T1 high signal intensity in the median eminence of hypothalamus
- olfactory bulbs may be absent (Kallmann syndrome) 8
- associated with schizencephaly
In addition, a number of other associations are recognized including:
The abnormality develops during 4th-6th weeks of gestation, during early forebrain development. The exact etiology is unknown, with an underlying genetic defect currently accounting for <1% of cases 9.
All imaging modalities that can visualize the septum pellucidum (ultrasound, CT and MRI) will detect its absence in septo-optic dysplasia. Some additional modality dependent features may also be visible.
In addition to enlarged lateral ventricles with an absent septum pellucidum, CT may demonstrate small optic apparatus (best seen with volumetric scanning and coronal reformats) and associated small bony optic foramina.
MRI is the modality of choice for assessing septo-optic dysplasia.
- may show a "point down" appearance of the lateral ventricular frontal horns on coronal images
- absent septum pellucidum
- hypoplastic pituitary stalk
- hypoplastic optic chiasm/optic nerves and globes
Treatment and prognosis
The management of septo-optic dysplasia requires a multidisciplinary team to assess and treat for hormonal imbalance, loss of vision, autism and obesity 9.
History and etymology
Septo-optic dysplasia was first described by George de Morsier (1894-1982), Swiss neurologist in 1956 6,7.
- may not be able to be differentiated 8
- cerebral anterior artery will have its course shifted anteriorly in lobar holoprosencephaly (sign described on prenatal ultrasound also, midline sagittal view with color Doppler)
- optic chiasma is not expected to be hypoplastic
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