[Diencephalic cyst--in relation to other midline dysraphism (author's transl)]

Area of Science:

• Developmental Neuroscience
• Pediatric Neurology
• Congenital Malformations

Background:

• The term "diencephalic cyst" was introduced in 1973 for midline cysts of diencephalic origin.
• Understanding of diencephalic cysts and their relationship to other midline dysraphisms remains limited.
• This study investigates four cases to clarify the nature of these cysts and their classification.

Observation:

• All cases presented an abnormal midline space communicating with the lateral ventricle.
• Two cases exhibited features consistent with alobar holoprosencephaly.
• Autopsy revealed olfactory tract absence, incomplete cerebral separation, and a monoventricle in one case.

Findings:

• Diencephalic cysts are proposed as a variant of holoprosencephaly, not a separate malformation.
• These malformations form before the 40 mm embryonic stage, distinct from agenesis of the corpus callosum (after 60 mm).
• Absence of the internal cerebral vein, straight sinus, and inferior sagittal sinus distinguishes these from simple agenesis of the corpus callosum.

Implications:

• Diencephalic cysts should be classified as holoprosencephaly variants, challenging previous classifications.
• Early embryonic timing differentiates these from agenesis of the corpus callosum.
• Severe hydrocephalus often accompanies these cysts, leading to poor intellectual outcomes despite surgical intervention.