Normal Developmental Globe Morphology on Fetal MR Imaging

Age-dependent structural changes of the globes occur during gestation. The posterolateral globe margins bulge outward, and the eyes are conical in early gestation. Later, the globes are ellipsoid. The purpose of this study was to establish normal developmental fetal globe morphology.

The fetal MR imaging data base at an academic children's hospital was queried for all brain MRIs performed during 8 years. Motion artifacts, brain/craniofacial/globe malformations, and chromosomal defects were exclusion criteria. Two board-certified neuroradiologists evaluated each examination for globe shape (elliptic/nonelliptic) and hyaloid visibility. Logistic regression was used to evaluate correlations among variables. Age-specific cut-points for globe shape and hyaloid visibility were chosen to optimize specificity.

We identified 1243 examinations from 1177 patients. Six hundred eighty-two examinations met the inclusion criteria (17-39 weeks). Receiver operating characteristic analysis showed that age was highly predictive of globe shape (area under the curve = 0.99) and fetal vasculature visibility (area under the curve = 0.94). Nonelliptic globes were universal up to 22 weeks. Thereafter, globes gradually assumed an elliptic shape, present in nearly all patients 29 weeks and older (sensitivity, 81%; 95% CI, 76%-85%; specificity, 99%; 95% CI, 98%-100%). The hyaloid vasculature was visible in most patients up to 19 weeks and occasionally in those at 20-24 weeks, but never in those 25 weeks and older (sensitivity, 69%; 95% CI, 65%-72%; specificity, 100%; 95% CI, 95%-100%).

Physiologic nonspheric globe shapes are normal up to 29 weeks' gestation and should not be misinterpreted as pathologic. Thereafter, globes are generally elliptic. The timing of this process coincides with the resolution of the primary vitreous and may be related.