Clinical impact of perinephric fat stranding detected on computed tomography in patients with acute pyelonephritis: a retrospective observational study

Perinephric fat stranding (PFS) is often detected on computed tomography (CT) in patients with acute pyelonephritis (APN). However, its clinical impact remains unclear. This study aimed to evaluate the clinical impact of PFS detected on CT in patients with APN. This retrospective observational study included patients with APN who underwent CT (median age, 79.5 years). Patients were classified into PFS (patients with PFS observed on CT) and non-PFS (patients without PFS observed on CT) groups, which were further classified into bacteraemia and non-bacteraemia groups. Clinical findings between the groups were compared. Among 194 patients who underwent CT, 111 (57.2%) patients demonstrated PFS. The rate of bacteraemia was significantly higher in the PFS group than in the non-PFS group (55.2 vs. 23.1%, p < 0.001). CT findings other than PFS were not associated with bacteraemia. The median peak body temperature was significantly higher in the PFS group than in the non-PFS group (38.8 vs. 38.5 °C, p < 0.001); however, the duration of fever and in-hospital mortality rates were not significantly different between the groups. Concordance between blood and urine culture results was observed in 75.0% of the patients; the presence of PFS was not different between patients with concordant and discordant results, regardless of the pre-treatment antibiotic used. Our findings suggest that the presence of PFS in patients with APN predicts bacteraemia; thus, clinicians should consider obtaining blood cultures if PFS is found on CT in patients with APN, even if the patients had received antibiotics prior to admission.