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 oedema due to inflammation/infection (pyleonephritis). Note swelling in the perinephric fat.