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Question 6#

Which of the following is true regarding extracorporeal shockwave lithotripsy?

a. ESWL is more effective than ureteroscopy for an 8-mm distal ureteric stone
b. Anticoagulation with warfarin is not an absolute contraindication
c. Hounsfield Units (HU) of the stone is of limited use in predicting success
d. Fragmentation is more successful at a shock rate of 1 Hz compared to 2 Hz
e. Shockwaves converge on focal point F1 where stone fragmentation occurs

Correct Answer is D

Comment:

Answer D

ESWL relies on shockwave generation, a shockwave focussing, a coupling mechanism and a means of radiological imaging to localise the stone. Shockwaves may be generated at focal point F1 using electrohydraulic, piezoelectrical or electromagnetic lithotriptors. They are focussed, often by an ellipsoid dish, and converge on focal point F2, where stone fragmentation occurs. 

Anticoagulation with warfarin is an absolute contraindication to ESWL and aspirin therapy should be withheld. Pregnancy, evidence of urinary sepsis and the presence of a calcified arterial aneurysm in the vicinity of the stone are also contraindications to ESWL.

Stone hardness is an important factor in predicting the likelihood of success of ESWL and can be estimated according to Hounsfield Units on non-contrast CT. Stones with density >1,000 HU are less likely to fragment and it may be worth considering alternative treatment modalities in these cases. Cystine stones either respond well to ESWL or poorly which may reflect different stereoscopic crystalline structures.

According to a recent EAU/AUA meta-analysis, stone-free rates were significantly better for distal ureteric stones <10 mm and >10 mm and for proximal ureteric stones >10 mm treated with ureteroscopy (URS) compared to ESWL. Stone-free rates for mid-ureteric stones treated by URS and ESWL did not differ significantly.

A meta-analysis has shown that a shockwave rate of 1 Hz is optimal for stone fragmentation. Data regarding the risk of developing hypertension and diabetes are controversial and insufficient to allow specific recommendations.