In Utero MR Imaging for Fetuses with Small Head Sizes without Intracranial Abnormalities Detected on Ultrasonography.

Background and purpose: Many studies have shown that in utero MR imaging (iuMRI) is a valuable adjunct to ultrasonography studies (USS) when a brain abnormality has been shown on USS. There is an increasing tendency, however, for fetal maternal experts to use iuMRI in fetuses with small heads but no evident brain abnormality on USS. The diagnostic and clinical value for that approach is not known at present, and the aim of this study is to close that gap in medical knowledge.

Materials and methods: We recruited 200 women whose fetuses had small head sizes but no brain abnormality on USS, to assess the rate and type of intracranial abnormalities found on iuMRI. A retrospective analysis was made of the change in prognosis brought about by iuMRI-derived abnormalities. The relationship between the fetal head circumference measured on USS and the rate of brain abnormalities shown on iuMRI was also assessed to perform sensitivity/specificity analyses.

Results: Intracranial abnormalities were present on iuMRI in 21/200 (10.5%; 95% CI, 7.0-15.5%) fetuses, and changes in prognosis were brought about (all worsened) following iuMRI in 16/21 (76.2%). There was an increased chance of an intracranial abnormality being present in fetuses with more severe reductions in head size.

Conclusions: There is a high detection rate of intracranial abnormalities on iuMRI of fetuses with small head sizes (10.5%). In most cases, the intracranial abnormalities shown on iuMRI brought about a change in prognosis. There was an increased risk of intracranial abnormalities in fetuses with more severe reductions in head size. These data make a strong case in favor of offering iuMRI to women whose fetuses haves a small head size but no intracranial abnormality on USS.