What broader group of conditions is septo-optic dysplasia related to, and which of these is the closest differential diagnosis?
Holoprosencephaly spectrum ranges from septo-optic dysplasia to alobar holoprosencephaly. Lobar holoprosencephaly is the closest differential.
What features are helpful in distinguishing lobar holoprosencephaly from septo-optic dysplasia?
An important finding in helping distinguish septo-optic dysplasia from lobar holoprosencephaly is unfused fornices in the former.
What associated abnormality is frequently present (not in this case) and how does it impact presentation?
Schizencephaly. When not associated with schizencephaly the visual apparatus more severely affected and hypothalamic-pituitary dysfunction present in 60-80% of patients.
Selected images from the MRI of a child demonstrates absence of the septum pellucidum and an optic chiasm that is markedly reduced in size. Also note the azygous anterior cerebral artery.