Pitfalls in the ultrasound diagnosis of upper urinary tract obstruction

Evaluation for possible obstruction of the upper urinary tract with ultrasound can be complicated by pitfalls. Representative examples of pitfalls are reviewed and illustrated in this essay. Since both overdiagnosis and underdiagnosis of urinary obstruction can lead to grave consequences, one must be aware of these pitfalls when performing and interpreting renal ultrasound studies.