Forebrain development in fetal MRI: evaluation of anatomical landmarks before gestational week 27

Forebrain malformations include some of the most severe developmental anomalies and require early diagnosis. The proof of normal or abnormal prosencephalic development may have an influence on further management in the event of a suspected fetal malformation. The purpose of this retrospective study was to evaluate the detectability of anatomical landmarks of forebrain development using in vivo fetal magnetic resonance imaging (MRI) before gestational week (gw) 27.

MRI studies of 83 singleton fetuses (gw 16-26, average +/- sd: gw 22 +/- 2) performed at 1.5 Tesla were assessed. T2-weighted (w) fast spin echo, T1w gradient-echo and diffusion-weighted sequences were screened for the detectability of anatomical landmarks as listed below.

The interhemispheric fissure, ocular bulbs, corpus callosum, infundibulum, chiasm, septum pellucidum (SP), profile, and palate were detectable in 95%, 95%, 89%, 87%, 82%, 81%, 78%, 78% of cases. Olfactory tracts were more easily delineated than bulbs and sulci (37% versus 18% and 8%), with significantly higher detection rates in the coronal plane. The pituitary gland could be detected on T1w images in 60% with an increasing diameter with gestational age (p = 0.041). The delineation of olfactory tracts (coronal plane), chiasm, SP and pituitary gland were significantly increased after week 21 (p < 0.05). Pathologies were found in 28% of cases.

This study provides detection rates for anatomical landmarks of forebrain development with fetal MRI before gw 27. Several anatomical structures are readily detectable with routine fetal MRI sequences; thus, if these landmarks are not delineable, it should raise the suspicion of a pathology. Recommendations regarding favorable sequences/planes are provided.