A renal ultrasound with screening images of the bladder is the best overall initial examination. The kidneys, bladder, and prostate gland can all be quickly evaluated. It is essential to distinguish between obstructive uropathy, which is an emergency potentially requiring immediate urological intervention, and medical renal disease. A plain film of the abdomen may be helpful if renal lithiasis is suspected. CT and IVP examinations may also be useful in order to assess the ureters and evaluate potential neoplastic causes of obstruction. Renal US is less sensitive for the detection of stones but quite effective in detecting hydronephrosis; US will not detect ureteral abnormalities. Detailed evaluation of the bladder can be attempted with cystography, but cystoscopy is required for a truly comprehensive evaluation.