Acute pyelonephritis and emphysematous pyonephrosis
Left flank pain and fever, 2/52 post insertion of a double J stent for ureteric obstruction by calculus
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A double J stent is in situ. It has fallen into the upper ureter (as seen on the coronal MIP delayed contrast) but is not associated with ureteric obstruction (i.e. contrast is being normally excreted albeit the proximal ureter is a little dilated). The stone has been pushed back into the lower pole calyx.
The renal pelvis contains gas and the upper ureter is thick-walled indicating inflammation/infection. Emphysematous pyonephrosis is a concern in this setting. The renal parenchyma on the cortical phase shows areas of both cortical and medullary swelling with reduced enhancement indicative of edema due to inflammation/infection (pyleonephritis). Note swelling in the perinephric fat.
Acute pyleonephritis is usually a clinical diagnosis but can sometimes be detected on corticomedullary or nephrographic phase CT of the kidneys. In this case it is a complication of stent insertion for ureteric obstruction by stone. The gas is thought to be due to infection rather than post-operative as there has been a delay of 2 weeks.