Prenatal MR imaging of the normal pituitary stalk.

Background and Purpose: Prenatal imaging data of the normal pituitary gland and in vivo information on the development of the pituitary region are lacking; however, we noticed that the pituitary stalk (PS) is visible occasionally in utero on MR images. Our main purpose was to establish the detection rate of the PS in healthy fetuses at various gestational ages (GAs) by using single-shot fast spin-echo T2-weighted images.
Materials and Methods: We selected 73 fetal cases with normal findings on prenatal MR imaging and clinical postnatal follow-up. The GA ranged between 19 and 37 weeks. The 3 planes of MR imaging sections were 4 mm thick with 1.25 x 1.25 mm in-plane resolution. Two pediatric neuroradiologists evaluated in consensus whether the PS was present as a linear isointense structure connecting the hypothalamic region with the floor of sella turcica. In those cases in which the PS was visible on the sagittal section, the angle formed by the intersection of the PS and the sellar plane (SP) was measured (PS-SP angle).
Results: The PS was detectable on at least 1 coronal or sagittal section from 19 to 25 weeks' GA in 30/42 fetuses (71.4% sensitivity); from 26 to 37 weeks' GA, the PS was detected in all 31 fetuses (100% sensitivity). The PS-SP angle decreased significantly with GA, being <90 degrees in all fetuses after gestational week 25.
Conclusions: At the current spatial resolution of clinical prenatal MR imaging, PS can be reliably detected after 25 weeks' GA, so in case of a missing visualization, a strong suspicion of pituitary region anomaly could be raised.