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RENAL CALCULI

What causes renal calculi to fonn?
Many theories have been proposed to explain the cause of renal stone formation. Unfortunately, no one mechanism fully explains the cause in all stone formers. In one commonly accepted model of stone formation, a period of abnormal crystalluria is required. For crystals to form and grow, the urine must be supersaturated with the salt of the stone-forming crystal. Urinary substances which act as inhibitors to crystal formation must be reduced or absent from the urine, and certain proteins which act as the framework for crystal depositions must be present in the urine.
 
What risk factors enhance stone fonnation?
1. Metabolic state (influenced by patients genetic background)
2. Hormonal imbalances
3. Environmental factors
4. Dietary excesses
5. Anatomic abnormalities leading to chronic infection or stasis
 

Where do renal stones fonn?

Stones form in the collecting tubules and pass into the calyces, renal pelvis, and ureter.
 
List the four most common types of stones found in North America.
I. Calcium-containing stones (calcium ~xalate, calcium phosphate, mixed), 70%
2. Infection stones (struvite, magnesium ammonium phosphate), 15-20%
3. Uric acid stones, 5-10%
4. Cystine, 1-5%.
 
Name the most common stone found in American men.
Calcium.

 
Name the most common stone found in American women. Why?
Infection stones. Women are more prone to urinary tract infections than men.
 

What stone is inherited as an autosomal-recessive trait?
Cystine.
 
How does the typical patient present with a nonobstructing caliceal stone?
Nonobstruciing caliceal stones are usually discovered as incidental findings on radiographs . obtained forthe evaluation of other organ systems or during the evaluation of hematuria.
 

Describe the typical presentation of a patient with an obstructing renal pelvic stone?
Obstruction occurring at the level of the ureteropelvic junction causes sharp, intermittent, colicky pain typically localized to the flank or costovertebral angle. The pain is not related to activity and may be accompanied by nausea and vomiting.
 
 

What are the expected urinalysis findings in patients with renal colic?
Microscopic or gross hematuria is common. However, the absence does not exclude renal stone disease. Pyuria may be present without infection. Crystals may be seen.
 
 
Is urine pH important in determining the type of stone present?
Yes. An acid urine (pH 5.5) is suggestive of a uric acid stone, whereas a pH of 8 suggests an infectious stone.
 
Is a KUB film sufficient to diagnose a renal stone?
No, only 90% of stones are radiopaque. Pure uric acid stones are usually radiolucent and do not appear on a plain film of the abdomen.
 
What x-ray study should be performed?
An excretory urogram (IVP) is oQtained in all patients suspected of having a renal stone, unless they are allergic to the contrast.
 
List the indications for surgical stone removal.
. Persistent pain
. Recurrent, gross hematuria
. Obstruction with progressive renal damage
. Recurrent urinary tract infection
 
What type of stone can be dissolved?
Pure uric acid stones can almost always be dissolved by oral alkalinization therapy.
 
Is pyelolithotomy the treatment of choice in managing a l-cm obstructing calcium pelvic stone?
No. Extracorporeal shock-wave lithotripsy is the treatment of choice and is successful in > 90% of cases.
 
Can all renal stones be treated by extracorporeal shock-wave lithotripsy?
Stones larger than 2.5 cm in diam~ter are frequently associated with obstruction following this form of treatment. These patients may be best managed by either percutaneous or open surgical stone removal.

 
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