Acute pyelonephritis (plural: acute pyelonephritides) is a bacterial infection of the renal pelvis and parenchyma most commonly seen in young women. It remains common and continues to have significant morbidity in certain groups of patients. Show On this page:The incidence of acute pyelonephritis parallels that of lower urinary tract infections: approximately five times more common in females with a sharp increase following puberty 6. Clinical presentation is fairly specific and classical in most cases, consisting of a rapid onset of high fever, flank pain and costovertebral angle tenderness (i.e. positive Murphy's kidney punch). In many instances, less specific symptoms such as nausea, vomiting, dysuria, urinary frequency, urgency and other non-specific signs may also be present 1,12. White cells and bacteria are usually present in the urine, and blood tests reveal the expected changes: leukocytosis and increased C-reactive protein (CRP) and/or erythrocyte sedimentation rate (ESR). In severe cases, sepsis may be present. The most commonly implicated organisms are from the gastrointestinal tract 5:
Infection gains access to the upper urinary tract by passing retrograde up the ureter from the bladder, facilitated by virulence factors that allow bacteria to adhere to the urothelium (e.g. adhesin P) and inhibit ureteric peristalsis (endotoxins) 1,5. The infection then passes into the collecting tubules and results in interstitial nephritis, with resulting alterations in renal filtration and blood flow in the affected region. Localized ischemia secondary to inflammatory changes results in altered imaging and may eventually lead to necrosis and scarring 2. In many instances, the clinical presentation suffices for making the diagnosis. Situations in which imaging is indicated include:
Plain radiographRadiography has a limited role, especially if patients are likely to go on to CT. Abdominal radiographs may demonstrate obstructing urinary tract calculi and occasionally may demonstrate gas within the collecting system (emphysematous pyelonephritis). UltrasoundUltrasound is insensitive to the changes of acute pyelonephritis, with most patients having 'normal' scans. Abnormalities are identified in only ~25% of cases 1. Possible features include:
Ultrasound is, however, useful in assessing for local complications such as hydronephrosis, renal abscess formation, renal infarction, perinephric collections, and thus may guide management. CTCT is a sensitive modality for evaluation of the renal tract, able to assess for renal calculi, gas, perfusion defects, collections and obstruction. Unfortunately, it does have a significant radiation burden and should be used sparingly, especially in young patients. There is usually no need for a three or four phase CT IVP (CT urography). A single 45-90 second post-contrast scan usually suffices, although clinical acumen may be necessary to choose the best contrast phase 1,3. For example, if renal colic is suspected then a non-contrast scan is often required to assess for renal calculi. If renal ischemia is suspected then an arterial scan (15-25 seconds) is ideal to assess perfusion 3. Non-contrast CT
If for some reason the kidney is imaged again within 3-6 hours, persistent enhancement of the affected regions may be evident due to slow flow of contrast through the involved tubules 1,3. MRIMRI is usually reserved for patients who are pregnant, and findings mirror those seen on CT. The kidney demonstrates wedge-shaped regions of altered signal:
A fast inversion recovery sequence obtained after contrast administration has been shown to be particularly effective in outlining affected regions which appear hyperintense compared to the low signal parenchyma. The contrast is thought to represent a combination of local edema and decreased T2 signal due to gadolinium in the perfused 'normal' portions 2. Nuclear medicineTechnetium-99m dimercaptosuccinic acid (DMSA) demonstrates a similar reduction in renal perfusion and function, which appears as one or more patchy scintigraphy defects in the outline of the kidneys 2. Treatment and prognosisMost patients respond rapidly to appropriate antibiotic therapy, and often no imaging whatsoever is required. Even when imaging has been performed, no follow-up imaging is usually required, unless patients do not respond clinically, and it should be stressed that imaging changes can take up to five months to resolve 1. The presence of an upper urinary tract infection in the presence of obstruction can threaten the viability of the kidney and a percutaneous nephrostomy is usually required on an emergency basis. ComplicationsComplications include 2:
General imaging differential considerations include:
Promoted articles (advertising)Which disorder includes the information of renal parenchyma in the collecting system?Emphysematous pyelonephritis (EPN) is a necrotizing infection which results in gas within the renal parenchyma, collecting system, or perinephric tissue. A majority of cases occur in patients with diabetes mellitus (DM).
Is described as an inflammation of the kidney parenchyma caused by microbial infection?Pyelonephritis is inflammation of the kidney, typically due to a bacterial infection.
Which disorder of the urinary system is caused by trichomonas?Trichomoniasis is caused by a parasite called Trichomonas vaginalis. In women, this parasite mainly infects the vagina and the urethra (the tube that carries urine out of the body).
|