42 J. REYNARD
A policy of arranging for a KUB x-ray and renal ultrasound in all patients with suspected renal infection is wise. The main clinical indicators that suggest you may be dealing with a more complex form of renal infection are length of symptoms prior to treatment and time taken to respond to treatment. Thorley and colleagues (1974) reviewed a series of 52 patients with per-inephric abscess. They noted that the majority of patients with uncomplicated acute pyelonephritis had been symptomatic for less than 5 days, whereas most of those with a perinephric abscess had been symptomatic for more than 5 days prior to hospitalisation. In addition, all patients with acute pyelonephritis became afebrile after 4 days of treatment with an appropriate antibiotic, whereas patients with perinephric abscesses remained pyrexial.
This is a severe renal infection usually (though not always) occurring in association with underlying renal calculi and renal obstruction. The severe infection results in destruction of renal tissue, and a nonfunctioning, enlarged kidney is the end result. E. coli and Proteus are common causative organisms. Macrophages full of fat become deposited around abscesses within the parenchyma of the kidney. The infection may be confined to the kidney or extend to the perinephric fat. The kidney becomes grossly enlarged and macroscopically contains yellowish nodules, pus, and areas of haemorrhagic necrosis. It can be very difficult to distinguish the radiological findings from a renal cancer on imaging studies such as CT (Fig. 3.14). Indeed, in most cases the diagnosis is made after nephrectomy for a presumed renal cell carcinoma.
Presentation and Imaging Studies
Patients present acutely with flank pain and fever, with a tender flank mass. Bacteria (E. coli, Proteus) may be found on culture urine. Renal ultrasonography shows an enlarged kidney containing echogenic material. On CT, renal calcification is usually seen, within the renal mass. Nonenhancing cavities are seen, containing pus and debris. On radioisotope scanning, there may be some or no function in the affected kidney.