Urinary tract infection (UTI) is one of the most common infections in female patients. Approximately 40% to 50% of women will have at least one UTI in their lifetime
11). Ascending infection, probably due to reflux, is the most common route of infection, and hematogenous seeding is rare in acute pyelonephritis. Uncomplicated acute pyelonephritis usually responds well to appropriate antibiotics. Detection of renal abscess and other severe renal parenchymal infection is an important problem for clinicians who have to distinguish patients requiring more extensive medical therapy or surgical intervention from the vast majority of patients with uncomplicated acute pyelonephritis. Hill and Clark
12) described the pathophysiology of acute pyelonephritis and its sequelae in the rabbit model. Profound cortical vasoconstriction was found in areas of acute inflammation with inflammatory cells clogging the peritubular capillary. After one week, these areas progressed to necrosis (abscess) and then to scarring. Contrast enhanced CT scan demonstrated various findings in the evolving stages of acute pyelonephritis. In the 1970’s, radiologists began to describe a subset of patients with acute renal infection who had very severe regional or generalized renal parenchymal abnormalities without apparent abscess, a severe protracted clinical course and eventual atrophy of the affected renal parenchyma
3, 4). They use the term acute (focal) bacterial nephritis (acute lobar nephronia) in the subset of this category. The clinical feature of acute focal bacterial nephritis is similar to that of acute pyelonephritis and it is not possible to distinguish acute focal bacterial nephritis from acute pyelonephritis on clinical grounds. The spectrum of CT findings in acute renal infection depends on clinical severity. Huang et al. showed that renal bacterial infection may manifest the continuum of severity from uncomplicated acute pyelonephritis to acute bacterial nephritis and, finally, to frank abscess formation
13). Talner et al
10), in their outstanding review on terminology of acute pyelonephritis, suggested that the terms acute (focal) bacterial nephritis, acute lobar nephronia (nephritis), preabscess, renal cellulitis, renal phlegmon and renal carbuncle should not be used in orden to avoid confusion in terminology. In their review, patients with clinically mild and uncomplicated pyelonephritis appear normal on both pre- and post-contrast CT scan. With more severe infection, there is often renal enlargement or focal swelling with normal attenuation on precontrast scans. After contrast enhancement, findings are one or more wedge-shaped or streaky zones of low attenuation extending from papilla to kidney capsule. Zones of low attenuation on post contrast scans are almost certainly caused by focal ischemia, obstructed tubules and interstitial inflammation. Therefore, an accurate and precise description of the spectrum of imaging manifestations of this disease has now become important in order to ensure distinction from other focal renal diseases such as tumor, renal infarct and renal abscess
8). We performed contrast enhanced CT examination on those who had symptoms and signs of clinically acute pyelonephritis at the time of visit to our emergency room to find out the frequency of focal inflammatory process and its clinical outcome. Perfusion defects on contrast enhanced CT scans are very frequently encountered in clinically uncomplicated acute pyelonephritis as shown in our cases. High fever, chill, flank pain, CVA tenderness and leukocytosis were almost universally present in our patients. Negative urine cultures present in 38.1% of group 1 and 64.3% of group 2 patients, which are very high in our cases, have been reported in up to 20% of patients with acute focal bacterial nephritis and renal abscess
3–7,14). Low yield of urine cultures are probably due to the administration of antibiotics prior to our emergency room visit. The most common organism cultured is Escherichia coli which is present in about 80% of our cases and is similar to other reports
11). Large proportions of our patients (57.1%) in group 1 had predisposing factors and these figures were similar to cited frequencies of up to 60% in previously reported series of patients with acute focal bacterial nephritis or renal abscess
15). There were no differences between group 1 and group 2 in the rate of predisposing factors. Patients with perfusion defects (group 1) treated with antibiotics (cefazolin + tobramycin) became afebrile in about 7 days (mean duration of defeverscence, 7.0±4.6 days) which was longer than group 2. Clinical responses to antibiotics were very good and it was not necessary to use antibiotics for a prolonged period. Some patients had severe clinical courses such as septic shock and DIC which were resolved by early antibiotic treatment. Extent of perfusion defects, which was classified by CT pattern, did not influence the duration of defeverscence after admission. Pitfalls in CT diagnosis include failure to detect focal perfusion defects in studies performed without contrast enhancement and the overlap between the CT appearance of inflammatory, cystic and neoplastic disease in the kidney. As many as 5% of renal masses detected on CT scans are of indeterminate nature and require further evaluation
16). There is disagreement in the literature about the best imaging modality for evaluating suspected renal infection
17). Intravenous pyelogram is an insensitive test for acute pyelonephritis. Ultrasound examination is frequently chosen initially because of easy availability and relatively lower cost, but the majority of kidneys with uncomplicated acute pyelonephritis appear normal despite the frequent presence of perfusion defects on contrast enhanced CT scans
10). In summary, those patients who had perfusion defects on contrast enhanced CT showed relatively severe clinical courses but responses to early antibiotics were very good. Contrast enhanced CT scans may be very sensitive for the detection of acute renal parenchymal inflammatory disease and for defining the extent of disease, but it is clinically not essential to perform in the early uncomplicated acute pyelonephritis because CT diagnosis does not change management. Clinical use of contrast enhanced CT scan may be appropriate in the case of persistence of fever and leukocytosis for more than seven days despite antibiotic treatment.