[Peroperative ultrasonics in excision of renal and ureteral calculi by the surgical approach. Apropos of 30 cases].

Ultrasound imaging was conducted in 30 patients during operation for removal of renal and ureteral stones, in most cases after contact radiography with small sterile films, and in all cases before opening the renal pelvis to avoid penetration of an air bubble into the intrarenal excretory tract. Each bubble may, because of its weak acoustic impedance, provoke total reflection of the waves simulating the image of a stone. Ultrasound provides data on cortical projection of calculi, the thickness of the parenchyma and the echoless avascular zones. All complex calculi (from Staghorn to caliceal types) should be investigated by ultrasound since it allows economy of time and reduced risks of excision of calculi. All stones greater than 1 mm give a hyperechogenic image with a cone shadow, the only differential diagnoses being air bubbles and intraparenchymatous calcification. Nonrecognition of calculi 1 mm in diameter is acceptable insofar as this type of caliceal or pyelic calculus may be excreted spontaneously. Ultrasound imaging during operation provides marked economy in time, of particular value during nephrotomy with pedicle clamping. Time is saved as a result of the three-dimensional detection of stones. Results in 30 cases showed a sensitivity of 97% for the method with excellent specificity, with only one false negative (residual microlithiasis) and one false positive (air bubble).