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Septo-optic dysplasia

Septo-optic dysplasia (SOD) is a condition characterised by optic nerve hypoplasia and absence of 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).

Epidemiology

Septo-optic dysplasia has an estimated prevalence of ~ 1 : 50000. There is no recognised gender predilection. 

A number of risk factors have being identified, including 8:

  • maternal diabetes
  • drugs
    • quinidine ingestion
    • antiepileptics
    • illicit drugs
  • cytomegalovirus infection 

Clinical presentation

Clinical presentation of septo-optic dysplasia is varied, and largely dependent of whether or not it is associated with schizencephaly (approximately 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 hypoglycaemia in the neonatal period 6
    • ectopic posterior pituitary may be present
    • olfactory bulbs may be absent (Kallmann syndrome8
  • associated wtih schizencephaly
    • optic apparatus less severely affected
    • may be etiologically different 8
    • sometimes referred to as septo-optic dysplasia plus 8

In addition, a number of other associations are recognised including:

Radiographic features

All imaging modalities which can visualise the septum pellucidum (ultrasound, CT and MRI) will detect its absence in septo-optic dysplasia. Some additional modality dependent features may also be visible. 

CT

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

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

Etymology

Septo-optic dysplasia was first descrbed by De Morsier in 1956 6.

  • George de Morsier (1894 - 1982)  : Swiss neurologist 7

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