The "lying down" adrenal sign: a sonographic indicator of renal agenesis or ectopia in fetuses and neonates.

An inability to image the kidneys, severe oligohydramnios, and an empty (nonvisualized) urinary bladder are the most common sonographic findings in fetuses with renal agenesis. The same features, except for the oligohydramnios, are seen in neonates with renal agenesis. Failure to visualize a kidney in the usual flank location with or without demonstration of the kidney in an ectopic location may also be a feature in fetuses or neonates with renal ectopia. The adrenal gland has an unusual but distinctive appearance on longitudinal sonograms in these patients. Sonograms of 23 fetuses and six neonates referred for presumed bilateral or unilateral renal agenesis or ectopia were reviewed retrospectively for the presence of a flattened ("lying down") adrenal gland. At the time of the examination, the adrenal gland was not actively sought as a part of the fetal survey or postnatal examination but was found retrospectively in 48% of these subjects. Although this finding has been described previously, the emphasis was on this observation as a potentially confusing sonographic feature. This manuscript emphasizes the characteristic appearance of the adrenal gland which instead serves as a simple means of confirming that the kidney did not develop in the flank. Detection of a flattened ("lying down") adrenal gland is an observation that should be actively sought in all fetuses and neonates with a presumed diagnosis of renal agenesis or ectopia.