Pictorial review: Renal ultrasound.

Ultrasound (US) is the first-line imaging modality for evaluating azotemic patients for urinary obstruction and renal size. US is also valuable for distinguishing congenital variants and simple cystic lesions from renal masses. Doppler US is effective in detection of renal calculi and evaluation of vascular pathology. Unfortunately, renal US is limited in distinguishing causes of medical renal disease. The kidneys have a complex internal architecture with a highly variable appearance on US. This article illustrates non-neoplastic renal conditions, including normal and embryological variants, parenchymal, cystic, and vascular diseases. Renal infections, calcifications, and trauma and fluid collections are also discussed, with an emphasis on distinguishing US features and pathophysiology.