What imaging findings may help distinguish ADPCKD from ARPCKD in an infant or young child?
The renal US appearance of ADPCKD and ARPCKD can be quite similar. The kidneys are often large and echogenic with each syndrome. Careful inspection with US can occasionally detect tubular ectasia in echogenic renal pyramids, which is typical of ARPCKD. Sonographically resolvable cysts are more suggestive of autosomal dominant disease. Additionally, the liver should be examined for abnormal echotexture caused by hepatic fibrosis and biliary ectasia, which is often associated with autosomal recessive disease ( Figure 88-11 ). In adolescents with ARPCKD, the renal involvement is less marked than the liver disease, the latter of which causes portal hypertension and splenomegaly. IVU or CTU can occasionally be helpful to distinguish the recessive from the dominant disease. In ARPCKD, there is delay and prolongation of the nephrogram; contrast material is taken up by dilated tubules and has a spoke-wheel appearance. These findings are typically absent in ADPCKD, in which contrast excretion is prompt.