Editing AUA: Stone Surgery (2016) (section)

=== Imaging ===
* '''<span style="color:#ff0000">Non-contrast CT</span>'''
** CT protocols have been developed and evaluated utilizing radiation doses approximating those of plain film radiography.
** '''<span style="color:#ff0000">Should be obtained prior to performing PCNL</span>'''
*** Defines stone burden and distribution
*** Provides information regarding collecting system anatomy, position of peri-renal structures and relevant anatomic variants
*** May be used to predict stone composition
*** May be used to predict operative outcomes
** '''<span style="color:#ff0000">May be used to help select the best candidate for SWL vs. URS</span>'''
*** '''Ultrasound alone to select SWL vs. URS''' '''should be discouraged'''
**** '''Disadvantages of US:'''
***** '''Provides no information on stone density'''
***** '''Inaccurate in determination of stone size'''
****** US will correlate approximately 2/3 of the time with the stone size determined on CT scan.
******* '''<span style="color:#ff0000">US will overestimate the size of 1/3 of stones < 10 mm, and underestimate the size of 1/3 of stone, > 10 mm.</span>'''
******* '''<span style="color:#ff0000">KUB underestimates > 90% stones > 10 mm due in part to its inability to measure in three dimensions</span>'''
*** '''Factors associated worse SWL outcomes:'''
**** '''Renal stone attenuation >900-1000 Hounsfield units'''
**** '''Skin-to-stone distance >10cm'''
* '''<span style="color:#ff0000">Functional imaging study (DTPA or MAG‐3)</span>'''
** '''<span style="color:#ff0000">May be obtained if clinically significant loss of renal function in the involved kidney(s) is suspected</span>'''
* '''Additional contrast imaging may be obtained if further definition of the anatomy is needed'''
** '''Situations in which complex urinary tract anatomy may require further imaging include:'''
*** '''Ectopic kidneys''' (e.g., horseshoe kidney, pelvic kidney, cross-fused ectopia)
*** '''Other congenital kidney conditions''' (e.g., UPJ obstruction, duplicated collecting system, caliceal diverticulum, ureteral stricture, megaureter, ureterocele),
*** '''Renal transplant grafts'''
*** '''Kidneys with prior surgery'''
*** '''Complex stone anatomy/conditions''' (e.g., staghorn stones, nephrocalcinosis).
** Further imaging may be required in certain patients (e.g., neurologic disorders, including spinal dysraphism; unusual body habitus; presence of urinary diversion or prior kidney/ureteral surgery)
** '''<span style="color:#ff0000">CT and IVP are the most useful IV contrast studies</span>'''
*** '''MR urography can be useful in defining anatomy during pregnancy (without contrast) and in the setting of IV contrast allergy, although stones are typically not well visualized directly with MR imaging'''
*** Contrast imaging studies can also include retrograde or antegrade pyelography