The sonographic distinction between neonatal multicystic kidney and hydronephrosis.

Distinction between multicystic kidney and hydronephrosis, the two most common causes of neonatal abdominal masses, is important because of differences in management; however, these two entities may have a similar ultrasonographic appearance. Sonograms of 22 cases of multicystic kidney and hydronephrosis were retrospectively reviewed without knowledge of the pathologic findings to determine if the sonographic patterns were sufficiently distinct to be usable in clinical diagnosis. Nine of the 22 cases were correctly diagnosed with ultrasound as multicystic kidney, 6 cases were correctly diagnosed as hydronephrosis, and 7 cases of pathologically proved multicystic kidney were incorrectly diagnosed as hydronephrosis. Four of these incorrect diagnoses occurred in cases of the hydronephrotic type of multicystic kidney. An additional 9 cases were reviewed with knowledge of the pathologic results. It is concluded that sonography is accurate at differentiating classic multicystic kidney disease from moderate hydronephrosis; however, there is often considerable difficulty in distinguishing severe hydronephrosis from the hydronephrotic form of multicystic kidney disease.