I. Radiographic Evaluation of Stones:

A. Renal US does not require ionizing radiation exposure and can detect hydronephrosis, but has poor visualization of ureteral stones, limited sensitivity for stones <3mm

B. CT abd/pelvis non-contrast is preferred imaging modality before surgical stone treatments:

 - Collecting system and ureteral anatomy

 - Stone burden, size, location, Hounsfield units, skin-to stone distance

C. KUB can be used to follow progress of stone over time. If plan is trial of spontaneous passage KUB should be obtained 

MRI is not able to reliably identify urinary stones since it does not visualize calcium and are not visualized on T1 images. Stones can be seen as filling defects in urine on T2 images.

II. Medical Expulsive Therapy:

Use in patients with normal renal function, no signs of infection, and well controlled pain if there is reasonable likelihood of spontaneous stone passage.

% chance of stone passage = 100 - (stone size in mm X 10)

Flomax 0.4mg daily, increase PO fluid intake, urine strainer

III. ESWL (Extracorporeal shock wave lithotripsy):

Mechanism = cavitation action to fracture calculi

Primer setting used first (low energy first) followed by witholding shocks for 3-4 minutes, then increasing energy has been show to decrease renal injury

Steinstrasse = accumulation of obstruction stone fragments in ureter after ESWL (5-10%)

Factors associated with lower ESWL success:

 - Lower pole stone

 - acute infundibulopelvic angle

 - narrow infundibula

 - stone size >10mm

 - HU >1000

 - Skin to stone distance >9cm

 - cysteine or brushite stones

ESWL has lower complication rate compared to URS (bacteremia <15%, sepsis <1%, steinstrasse 5-10%). URS perforation rate 3%, ESWL ~0%.

But ESWL for ureteral stones has lower stone free rate (72% vs. 90% for URS).

IV. PCNL:

Usually reserved for larger stones >2cm, staghorn stones, or when ureteroscopy or ESWL not possible

Percutaneous access can be obtained via US, CT, or fluoroscopic guidance. 

Preferred location of access is posterior calyx (usually inferior posterior) to provide access to the largest stone burden. Pass through Brodel's avascular line to limit bleeding.

Upper pole access is best suited for complete staghorn stones, complex lower pole stones or large proximal ureteral stones. Upper pole access is associated with higher complication rate compared to lower pole (pleural injury/pneumothorax).

"Tubeless" PCNL = no postoperative nephrostomy tube. Indications for tubeless PCNL:

- no intraop hemorrhage, no collecting system injury, normal renal function, normal Plt and coags, stone free

Complications:

- Urosepsis (1%), Hemorrhage 1-10%, pseudoaneurysm, AV fistula, pleural injury (5%), bowel injury (0.5%)

- Management of bowel injury during percutaneous access:

   1. Nephrostogram shows contrast in bowel

   2. Abort procedure

   3. Retract nephrostomy tube into the bowel lumen to drain bowel for 7-10 days

   4. Place ureteral stent 

   5. Low residue diet, antibiotics

V. Ureteroscopy:

Semi rigid ureteroscopy for ureteral stones below level of iliac vessels, have large channels and improved visualization compared to flexible URS.

Felxible ureteroscopy for ureteral stones above iliac vessels, renal calculi, or staged ureteroscopy for larger renal stones instead of PCNL.

Steps for flexible ureteroscopy:

 1. Cystoscopy, cannulation of ureteral orifice with 5Fr open ended catheter

 2. Retrograde pyelogram can be performed to assess ureteral anatomy, stone location

 3. Guidewire passed up ureter to kidney under fluoroscopic guidance

 4. Dual lumen catheter used to pass up second wire (1 stiff working wire, 1 safety wire), then dual lumen withdrawn

 5. Ureteral access sheath is passed over the working wire under fluoroscopic guidance

 6. Flexible ureteroscope passed through access sheath

 7. Holmium laser lithotripsy, basket removal of stone fragments

 8. JJ ureteral stent placement

Flexible ureteroscopy can be passed directly over wire without using access sheath, but sheaths have been shown to improve stone free rates.

If URS procedure uncomplicated, no ureteral edema or injury, and no additional URS planned, then ureteral stent need not be placed.

VI. Optional Additional Reading:

1. Albala DM, Assimos DJ, Clayman RV, Denstedt JD, Grasso M, Gutierrez-Aceves J et al: Lower pole I: a prospective randomized trial of extracorporeal shock wave lithotripsy and percutaneous nephrostolithotomy for lower pole nephrolithiasis - initial results. J Urol 2001; 166: 2072-2080

2. Duffey B, Monga M. Principles of Urologic Endoscopy. Chapter 7, Vol 1. In: Wein AJ, Kavoussi LR, Partin AW and Peters CA, eds. Campbell Walsh-Urology, 11th Edition. Philadelphia, WB Saunders Elsevier; 2016