Perirenal fat stranding is not a powerful diagnostic tool for acute pyelonephritis

Abstract

Purpose: Pyelonephritis, an upper urinary tract infection, is a serious infection that often requires hospitalization. However, the accurate diagnosis of acute pyelonephritis can be difficult, especially among older individuals who can present with unusual symptoms. Imaging with computed tomography (CT) is not unusual in the diagnosis of pyelonephritis, with some clinicians regarding perirenal fat stranding (PFS) as a characteristic finding. However, the sensitivity and specificity of PFS in diagnosing pyelonephritis are currently unknown. We therefore sought to clarify the relevance of PFS in diagnosing acute pyelonephritis.

Patients and methods: We conducted a case-controlled retrospective analysis of medical records. The pyelonephritis group included 89 patients who had been diagnosed with acute pyelonephritis, while the control group included 319 patients who had undergone percutaneous renal biopsy. CT findings were available for both groups. The frequency of PFS and its sensitivity and specificity for the diagnosis of acute pyelonephritis were investigated.

Results: The mean ages of the pyelonephritis and control groups were 74±15 years and 63±16 years, respectively. A total of 28% of men were in the pyelonephritis group vs 61% of men in the control group. The frequency of PFS was 72% in the pyelonephritis group vs 39% in the control group. Age and renal dysfunction were associated with an increased frequency of PFS. After adjusting for age, sex, and renal function using a propensity score analysis, the sensitivity, specificity, and positive likelihood ratio of PFS for diagnosing acute pyelonephritis were 72%, 58%, and 1.7, respectively.

Conclusion: The presence of PFS was not useful in diagnosing acute pyelonephritis.

Keywords: CT; acute pyelonephritis; perirenal fat stranding; sensitivity; specificity; urinary tract infection.

Figure 1

Representative image of PFS (open arrow heads). Abbreviation: PFS, perirenal fat stranding.

Figure 2

Flowchart showing participant screening for this study. Abbreviations: ICD-10, 10th revision of the International Statistical Classification of Diseases and Related Health Problems; CT, computed tomography; PRB, percutaneous renal biopsy; UTI, urinary tract infection.

Figure 3

Frequency of PFS by age group. Abbreviations: PFS, perirenal fat stranding; NS, not significant.

Figure 4

Frequency of PFS by sex. Abbreviations: PFS, perirenal fat stranding; NS, not significant.

Figure 5

Frequency of PFS by eGFR. Abbreviations: PFS, perirenal fat stranding; eGFR, estimated glomerular filtration rate; NS, not significant.