Evaluation of Posterior Fossa Biometric Measurements on Fetal MRI in the Evaluation of Dandy-Walker Continuum

Abstract

Background and purpose: Dandy-Walker malformation, vermian hypoplasia, and Blake pouch remnant represent a continuum of anomalies and are common reasons for referral for fetal MR imaging. This study aimed to determine biometric measurements that quantitatively delineate these 3 posterior fossa phenotypes.

Materials and methods: Our single-center institutional review board approved a retrospective analysis of all fetal MRIs for posterior fossa malformations, including Dandy-Walker malformation, vermian hypoplasia, and Blake pouch remnant. Measurements included the anterior-to-posterior pons, craniocaudal and anterior-to-posterior vermis, lateral ventricle size, and tegmentovermian and posterior fossa angles. Measurements were compared with normal biometry and also between each subgroup.

Results: Thirty-three fetuses met the criteria and were included in the study. Seven were designated as having Dandy-Walker malformation; 16, vermian hypoplasia; and 10, Blake pouch remnant. No significant group interactions with adjusted mean gestational age for tegmentovermian and posterior fossa angles were observed. The tegmentovermian angle was significantly higher in Dandy-Walker malformation (109.5° [SD, 20.2°]) compared with vermian hypoplasia (52.13° [SD, 18.8°]) and Blake pouch remnant (32.1° [SD, 17.9°]), regardless of gestational age. Lateral ventricle sizes were significantly higher in Dandy-Walker malformation at a mean of ≥23.1 weeks' gestational age compared with vermian hypoplasia and Blake pouch remnant. The anterior-to-posterior and craniocaudal vermes were significantly smaller in Dandy-Walker malformation compared with vermian hypoplasia and Blake pouch remnant at mean of ≥23.1 weeks' gestational age.

Conclusions: Dandy-Walker malformation can be described in relation to vermian hypoplasia and Blake pouch remnant by an increased tegmentovermian angle; however, other potential qualifying biometric measurements are more helpful at ≥23.1 weeks' gestational age. Because they fall along the same spectrum of abnormalities, the difficulty in distinguishing these entities from one another makes precise morphologic and biometric descriptions important.

FIG 1.

Examples from cohort of Dandy-Walker continuum with TVAs. Sagittal (A) and axial (D) T2 single-shot FSE images from fetal MR imaging at 30 weeks’ GA demonstrate a BP with elevated TVA at 24°; however, the vermis is normal in size and morphology. Sagittal (B) and axial (E) T2 single-shot FSE images from fetal MR imaging at 32 weeks’ GA with VH. There is a coexisting BP marked by an elevated TVA; however, the tentorium is not considered elevated. Sagittal (C) and axial (F) T2 single-shot FSE images from fetal MR imaging at 24 weeks’ GA with classic DWM. The vermis is very small and rotated, and the tentorium is elevated with upward displacement. There is also separation and flattening of the cerebellar hemispheres (F, arrows).

FIG 2.

Measurements of the patients included in this cohort for AP pons (A), AP vermis (B), CC vermis (C), and TCD (D) plotted in relation to the normal growth curves by GA.