前脑无裂畸形，是一个较大正中线结构消失的脑室，包括丘脑。受影响的胎儿和新生儿存在典型的较重的面部缺陷，例如独眼畸胎。潜在的染色体异常,例如三倍体13，或母亲的糖尿病也是可能的原因。
This is holoprosencephaly in which there is a single large ventricle with fusion of midline structures, including thalami. The affected fetuses and neonates typically have severe facial defects, such as cyclopia, as well. Underlying chromosomal abnormalities, such as trisomy 13, or maternal diabetes mellitus are possible causes, but some cases are sporadic.