Perirenal fat stranding on CT: Is there an association with bladder outlet obstruction?

Objective: To determine the association between perirenal fat stranding (PFS) on CT and bladder outlet obstruction (BOO). Methods: CT scans from 122 patients who had undergone urodynamic study for lower urinary tract symptoms (LUTS) were registered after exclusion of patients with renal or retroperitoneal disease. Images were independently reviewed by two radiologists and compared with those of 244 age- and sex-matched control patients without LUTS. The PFS severity was scored on a fourpoint scale, and the interobserver agreement was assessed with kappa statistics. The severity score and incidence was compared between the groups, and the association with baseline characteristics was analyzed. For the LUTS group, an association between PFS severity and urodynamic and laboratory data was evaluated. Results: PFS was more frequent and more severe in the LUTS group than in the control group (p-value<0.001); its presence was significantly associated with male gender and older age (p-value<0.001). PFS was predominantly bilateral in both groups (80.1-93.2%). In the LUTS group, PFS severity scores were significantly correlated with the maximum flow rate, maximum detrusor pressure and estimated glomerular filtration rate (p-value<0.001). Interobserver agreements were excellent for PFS presence (κ=0.883) and severity (κ=0.816). Conclusion: Severe PFS was observed in older, male patients with LUTS. PFS severity was associated with the degree of BOO and impaired renal function. Advances in knowledge: Recognition of PFS on the CT scan may warrant further evaluation of BOO and appropriate management to prevent renal impairment.