CHAPTER 39 Renal/Ureteral Stone Surgery
What are the most common renal stones in North America and their percentages?
Calcium stones (calcium oxalate, calcium phosphate, mixed) account for approximately 70% of stones in the United States, while infection stones account for 15% to 20%. Uric acid stones make up 5% to 10% and cystine stones 1% to 5% of stones diagnosed in this country.
What are the ingredients of “triple phosphate” stones?
Triple phosphate stones are composed of calcium, magnesium, and ammonium phosphate.
Which stones are associated with laxative abuse?
Ammonium acid urate stones.
Which stones are most dense on plain radiograph?
Calcium hydrogen phosphate stones (brushite), followed by calcium oxalate monohydrate.
Which stones are radiolucent on plain radiography?
Uric acid, sodium urate, ammonium acid urate, xanthine stones, 2,8-dihydroxyadenine (rare), matrix, and indinavir stones are all radiolucent on plain radiography.
Which of these stones cannot be seen on CT scan without IV contrast?
Indinavir (Crixivan) is a protease inhibitor used for treatment in HIV patients, which cause stone formation. Indinavir can obstruct the ureter as a precipitate or as a pasty sludge. This type of stone is most commonly diagnosed endoscopically. If there is suspicion of a kidney stone and the patient is taking protease inhibitor drugs such as indinavir, an intravenous pyelogram (IVP) would be a better choice for a confirmatory imaging study.
Do all cystinuric patients produce kidney stones?
No. Cystinuria is an inherited disorder of renal tubular reabsorption of cystine, ornithine, lysine, and arginine. These 4 amino acids can be remembered by the mnemonic COLA. Of these 4, only cystine is relatively insoluble in urine and will precipitate to form stones. Patients with 24-hour urine cystine levels less than 400 mg/day rarely produce stones, while those with elevated levels over 1000 mg/day will produce large stone fragments unless treated medically.
What are the most common specific medications used as medical therapy for cystinuria and their most frequent complications?
Thiola and D-penicillamine are the 2 agents that are commonly used to treat cystinuria. Both agents act on the disulfide bond creating a more soluble compound. Patients on these agents require 24-hour urine protein collections to rule out nephrotic syndrome, which is often reversible when the medications are stopped. Goal of therapy is to titrate the medications until 24-hour cystine excretion is 250 mg or less. Nephrotic syndrome, dermatitis, and pancytopenia are more common with D-penicillamine, while asthenia, gastrointestinal (GI) distress, rashes, joint aches, and mental status changes are more common with Thiola.
What other treatments are available for cystinuria?
Initial therapy includes a high fluid intake sufficient to generate 3000 mL of urine per day or more. Cystine solubility rises when the urine pH increases so alkalinization therapy with potassium citrate is recommended although substantial alkalinization is difficult to maintain and overalkalinization can lead to calcium phosphate. Sodium intake restrictions are also helpful.
Which gas is produced by Holmium: YAG laser lithotripsy of cystine stones?
A malodorous sulfur dioxide gas is given off during laser lithotripsy of cystine stones.
What are the 4 common components of ESWL?
Energy source to produce shockwave, focusing device, coupling medium, and stone localization system.
Which geometric principle is the basis for most ESWL generators?
The first ESWL generator employed clinically was the Dornier HM3. This device employs a sparking electrode (electrohydraulic generator) to generate spherically shaped shock waves at the origin site (termed F1). The firing of this electrode creates shock waves that are focused by an ellipsoid focusing device to the site of the kidney stone (F2 position). Newer types of shock wave generators such as the piezoelectric and electromagnetic generators utilize nonspherically shaped shock waves with different coupling mediums and shapes.
What are the main clinical differences in newer generation lithotripters compared to the original nonmodified electrohydraulic lithotripter?
Newer second and third generation lithotripters sometimes employ wider apertures to spread the delivering energy over a greater surface area of the body, thereby limiting cutaneous pain. However, this increased aperture also narrows the focal treatment field leading to a lower stone-free rate in some of the newer models.
What are the factors that limit success with ESWL therapy?
Large stone burdens (size and number), stone composition, stone location, and clinical features such as body habitus and obesity are all factors that limit the stone clearance rate. A slower ESWL rate (60-90 shocks/min), pretreatment with 250 to 300 low energy shockwaves, good coupling, and general anesthesia also help improve the efficiency of the shock wave therapy. Using a single, large dollop of gel has been shown to leave fewer air gaps than other methods and is now the preferred way to place the coupling gel.
Which stones are most resistant to ESWL therapy?
Cystine stones are most resistant, followed by brushite stones, and then calcium oxalate monohydrate stones. Calcium oxalate dyhydrate are the most brittle.
Stones in which position are the most difficult to fragment with ESWL—proximal, mid, or distal ureteral stones?
Midureteral calculi, especially those located between the level of the inferior and superior margin of the sacroiliac joint are hardest to approach with ESWL. The patient is positioned prone and the stone may be difficult to visualize/localize against the background of the pelvic bones with current imaging. Only a few ESWL machines allow the treatment head to be rotated 180° so the patient can remain prone even with stones over the sacrum.
What are the 2 absolute contraindications to ESWL?
Pregnancy and uncorrected coagulopathy
What is “steinstrasse”?
Steinstrasse, meaning “stone street” in German, refers to a column of stone fragments that may line up in the ureter following ESWL. This may lead to symptoms of obstruction.
How is steinstrasse treated?
In mild cases, observation alone may be enough. Double pigtail catheters, ESWL, and ureteroscopy are other available options. In cases of sepsis secondary to steinstrasse, percutaneous nephrostomy should be considered first line therapy.
What is the most common clinically significant acute complication of ESWL therapy?
Subcapsular hematoma formation. Patients with uncontrolled hypertension (HTN) are believed to be at greatest risk.
What is the most common, serious long-term complication associated with ESWL?
Increased risk for HTN.
Which medications have been shown to help facilitate stone passage rates?
Tamsulosin (Flomax), nifedipine, and corticosteroids can improve stone passage from the distal ureter by approximately 30%. Other α-blockers also increase spontaneous passage. Such treatment is called “medical expulsive therapy.”
What is the most important factor in predicting spontaneous stone passage?
Stone size. If 4 mm or less, 90% will pass spontaneously.
A patient presents with flank pain. Laboratory work is normal. CT shows a 4-mm distal ureteral stone with hydronephrosis and forniceal extravasation. Is surgical intervention always indicated?
No. Given the small size, a trial of spontaneous passage is warranted. Forniceal extravasation is noted to occur more frequently in small, obstructing stones, and is not always an indication for surgery by itself.
What are the 3 areas of functional narrowing of the ureter?
The ureteropelvic junction (UPJ) is the proximal site of narrowing, followed by the level at which the ureter traverses the iliac vessels, and finally the ureterovesical junction.
Which of these areas is most often the narrowest point in the ureter?
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