Guidelines for management of asthma

papillary necrosis. Such patients will not present with renal failure if the contralateral kidney functions normally, and under these circumstances the diagnosis of an obstructed pyonephrosis can easily be delayed, with potentially serious consequences for renal function. If acute obstruction is suspected in the presence of infection a negative ultrasonogram is of no clinical value (and, as Dr Webb implies, a dilated collecting system will require further evaluation by other means). Such patients deserve urography, and if this shows a "non-functioning" kidney antegrade pyelography should be carried out, which can be followed by percutaneous drainage if obstruction is present. STEPHEN J AUSTIN