A 27-year-old woman, gravida 1, parity 0, was referred from an external center at a gestational age of 25 weeks with a preliminary prenatal ultrasound diagnosis of hydrocephalus. The patient underwent fetal magnetic resonance imaging (MRI). Sagittal T2-weighted (T2W) half-Fourier acquisition single-shot turbo spin-echo (HASTE) (a) image shows alobar holoprosencephaly (asterisk), along with a structure compatible with a proboscis (arrow) in the frontal region. Axial T2W HASTE (b) image shows cyclopia (arrows).

Alobar holoprosencephaly is an anomaly characterized by a monoventricular space, fused thalamus, and absence of midline structures. When holoprosencephaly is detected on prenatal imaging, the fetal face should be carefully evaluated.