Normal size of the fetal adrenal gland on prenatal magnetic resonance imaging.

Abstract

The adrenal gland plays a vital role in fetal growth. Many disease states such as congenital adrenal hyperplasia, hemorrhage and tumors can lead to morphological changes in the gland. Ultrasound measurements of normal adrenal sizes in the fetus reported in the literature have shown a trend of increasing size with gestational age. There is no literature available on standard fetal adrenal sizes or detailed appearance by fetal MRI. The purpose of this study was to provide MR data on the size and signal characteristics of the fetal adrenal gland throughout the second and third trimesters. In this retrospective review, we selected 185 prenatal MRIs obtained from Jan. 1, 2014, to May 31, 2017, with normal abdominal findings for inclusion. The adrenal glands were identified in coronal, sagittal or axial T2-W planes and coronal T1-W plane when available. We measured the length and thickness of the medial and lateral limbs of the right and left adrenal glands and recorded signal intensity on T1-W and T2-W sequences, gender and gestational age in each case. The gestational age (GA) ranged 18-37weeks. Visibility of the adrenal glands on T2-W images was high (90.3-97.2%) up to 30weeks of GA but declined afterward (47.5-62.2% at 31-37weeks). Visibility on T1-W images increased with GA, ranging from 21.4% visibility at 18-22weeks and increasing to 40% at 35-37weeks. Mean lengths of the adrenal gland limbs steadily increased from 8.2mm at 18-22weeks to 11.0mm at 35-37weeks. In the second trimester, adrenal glands were low in signal intensity on T2-W images and were surrounded by hyperintense perirenal fatty tissue. In the third trimester, the glands became less distinct, with increasing signal and obliteration of perirenal tissue. The glands were moderately hyperintense on T1-W images throughout pregnancy, with increasing visibility as pregnancy progressed. Normal sizes and signal intensities for adrenal glands are reported. Visibility of adrenal glands on T2-W images was 90.3-97.2% up to 30weeks but declined thereafter. Visibility on T1-W images increased in the third trimester. Adrenal gland sizes increased with gestational age.