FIGURE.

Dandy-Walker phenotype: MR imaging criteria. Balanced steady-state sequence (0.8-mm section thickness, 0.4-mm section spacing) in the sagittal (A), parasagittal (B), and axial (C) planes and coronal T2WI (1-mm section thickness, 0-mm section spacing, D) and axial T1WI (1-mm section thickness, 0-mm section spacing, E) from a neonate show inferior predominant VH, an enlarged tegmentovermian angle at 35° (thick-lined angle, A), an obtuse fastigial angle at 119° (thin-lined angle, A), an unpaired caudal lobe (ie, tail-sign; thin arrow, A), and inferolateral displacement of the taenia–tela choroidea complex and choroid plexus distant from the vermis (thick arrows, B–E). Similar findings are seen in the same patient on fetal MR imaging at 22 weeks’ gestational age in sagittal (F) and parasagittal single-shot T2WI (3-mm section thickness, 0-mm section spacing, G). Note a normal torcular position (stars); the torcular position is variable in all forms of posterior fossa abnormalities/anomalies and should not be considered in isolation as an interpretive criterion in the differential diagnosis.