The rim sign can be seen in association with chronic hydronephrosis.
In patients with chronic hydronephrosis, in all forms of contrast-enhanced imaging of the obstructed kidney, enhancement may occur in the residual, but markedly atrophic, renal parenchyma, surrounding the dilated calyces and renal pelvis 1,2.
The inner margin of this hydronephrotic rim is concave toward the renal hilum, and enhancement of the cortical columns between the dilated collecting system elements may be seen. The unopacified urine within the dilated system may act as a negative pyelogram.
See also
Other rim signs in radiology:
cortical rim sign: useful in distinguishing lobar nephronia from a segmental renal infarct
soft tissue rim sign: used to distinguish a ureteric calculus from a phlebolith
bright rim sign: described in DNETs