In what position was this patient scanned? Why?
Prone. This is done in some centers to facilitate distinguishing a stone impacted at the vesico-ureteric juntion (VUJ) from a stone lying dependently in the bladder. The latter, when scanned prone, would fall to the front (dependent) part of the bladder. Note that the image has been flipped so that the anatomy is presented in the same way as a routine supine scan.
Non-contrast CT obtained with the patient prone, demonstrates a 4mm calculus in the right ureter at the level of the L3/4 disc. It is associated with mild hydronephrosis and extensive peri-ureteric and peri-renal stranding.
At the upper pole of the right kidney is what presumably represents a simple cyst.
The left kidney has a number of small calculi.