ARRS 2022 Abstracts

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E1051. An Undivided Mind: Practical Guide to Holoprosencephaly on Fetal MRI
Authors
  1. Lindsey Wells; Indiana University School of Medicine
  2. Brandon Brown; Division of Pediatric Radiology, Riley Hospital for Children, Indiana University School of Medicine
Background
Failure of ventral induction of the fetal brain results in a spectrum of malformations surrounding incomplete separation of the cerebral hemispheres, collectively referred to as holoprosencephaly. The traditional holoprosencephaly spectrum includes alobar, semilobar, and lobar. Increasing quality and availability of prenatal MRI allows radiologists to assess fetal cerebral anomalies and subtle variants of the spectrum more clearly than ever before, including syntelencephaly (middle interhemispheric variant) and septo-optic dysplasia. Recent large population studies have consistently demonstrated the diagnostic value added by fetal MRI as a complement to prenatal ultrasound, particularly for cases with positive or equivocal findings, and MRI in pregnancy is now more frequently utilized outside of large academic centers. The radiologist who encounters imaging in pregnant patients should be aware of the fetal MRI presentation of holoprosencephaly, not only to make accurate diagnoses, but also to improve prognostication and refine counseling for families during pregnancy.

Educational Goals / Teaching Points
This exhibit aims to highlight key prenatal imaging findings of the holoprosencephaly spectrum and outline a practical approach to diagnosing holoprosencephaly variants on fetal MRI; characterize milder forms of holoprosencephaly and differentiate these MRI findings from isolated agenesis of the septum pellucidum; differentiate severe holoprosencephaly and severe hydrocephalus on fetal MRI; and assess the prognostic factors associated with the spectrum of holoprosencephaly.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Anomalies in cerebral division have traditionally been assessed by antenatal ultrasound as early as 10 weeks gestation. Much of this assessment is based on facial malformations. These malformations are often associated with more severe forms of holoprosencephaly. Many features that would help distinguish details specific to the more mild forms of holoprosencephaly cannot be adequately visualized by ultrasound until 24 weeks or later, and ultrasound has limited accuracy in diagnosing the specific subtype of this malformation. Increasing evidence shows that fetal MRI be used for earlier detection of these anomalies and improve visualization of specific features. Fetal MRI can also help distinguish between holoprosencephaly and hydrocephalus, a common misdiagnosis. Although ultrasound has a strong negative predictive value, fetal MRI is useful to verify and classify holoprosencephaly in the case of a suspected malformation.

Conclusion
Fetal MRI is a valuable diagnostic technique for the prenatal diagnosis of holoprosencephaly that can allow earlier and more accurate assessment of the holoprosencephaly spectrum, to help guide family counseling.