Frequently Asked Questions in Urology: Urinary Stone Disease

Selected by Pietro Cazzola

 

Urinary stonesQuestion: Besides the well-established dietary recommendations to minimize stone disease, what else do you tell your patients about dietary changes they can make?

Answer: I often find that it is challenging for patients to follow dietary recommendations that are excessively complex. This problem is compounded when patients undertake Internet searches for dietary recommendations on their own, prior to seeking counseling from me. In many cases, the patients find recommendations that are all but impossible to adopt and maintain, and, often, the information can be contradictory from website to website. The cornerstone of my dietary recommendations is to maximize fluid intake; 2 liters per day should be a minimum, and patients should strive to exceed that each day.
Once they master fluid intake, which can take several months, I tell them to begin to focus on strict sodium restriction. There is strong epidemiological evidence that a low-sodium diet can reduce stone risk. With regard to oxalate-containing foods—a commonly asked question—I recommend that patients moderate their consumption. If they do have an oxalate-rich meal, I recommend that they also increase fluid consumption at that meal. Finally, I instruct them just to maintain normal calcium intake, and not consume excessive animal protein.

Question: How do you minimize the use of ionizing radiation in the surveillance of stone patients over time? 

Answer: We routinely rely on renal sonography for surveillance imaging studies; it provides stone-specific information without subjecting patients to ionizing radiation. Recognizing that stones are a recurrent disease, and that patients will likely undergo multiple CT scans in their lifetime, we make every effort to order a CT scan only if it is absolutely necessary. Fortunately, that rarely happens in surveillance; most of our CT imaging is performed for preoperative planning. 

Question: When do you choose SWL over ureteroscopy for treatment of ureteral stones? 

Answer: More often than not, ureteroscopy is the therapy we undertake for patients harboring ureteral stones. There is good evidence that success rates in patients with distal ureteral stones are superior with ureteroscopy compared with SWL; the success rates are comparable in patients with proximal ureteral stones. And ureteroscopy is a reasonable alternative in both situations. In the majority of cases, the bias of the patient directs our therapeutic choice—some prefer the definitive nature of ureteroscopy, whereas others prefer the noninvasive nature of SWL. 

Question: What is your preferred antibiotic prophylaxis in high-risk patients prior to PCNL? 

Answer: Postoperative sepsis is not a rare event following PNL, and it can be a life-threatening complication. We perform preoperative urine cultures in all of our patients, which we use to direct preoperative antibiotic therapy. In many cases, though, given the infected nature of the stone burden, it is not possible to eradicate bacteriuria—in those cases, we maintain patients on antibiotic therapy for 1 week prior to the surgery. It is known that up to one-third of patients with negative urine cultures may still harbor bacteria in the stone itself. Therefore, we place those patients on a broad-spectrum antibiotic for the week prior to the surgery. 

Question: How do you use prior stone analysis in a patient to guide future management? 

Answer: Prior stone analysis may help guide decision-making for future surgical therapies. For example, if the patient with a history of uric acid stone formation develops a recurrent stone, we may initially pursue a strategy of pH manipulation before we undertake a stone removal procedure. Patients with cystine stones, on the other hand, can exhibit very rapid rates of stone growth. Given, too, that cystinuria may be associated with diminished renal function, we make every effort to avoid subjecting these patients to PNL procedures; therefore, we will often have a very low threshold for performing ureteroscopy in patients with smaller stone burdens. If the patient has a history of struvite stone formation and presents with a new stone and bacteriuria with an urea-splitting organism, we may consider PNL more closely as it provides for the most complete stone clearance. 

Question: How do you manage obstructing renal stones in patients with urinary diversions? 

Answer: The surgical management of stone disease in patients with urinary diversions can be particularly challenging. If the stone is obstructing and the patient is acutely ill from it, we will generally decompress the renal unit with a percutaneous nephrostomy, as the placement of such a drain can be accomplished more reliably than retrograde stent placement. In my experience, retrograde access in patients with an orthotopic neobladder reconstruction or continent catheterizable urinary diversion is difficult, and, in some cases, may not even be possible. Retrograde access is more easily accomplished in patients with an ileal conduit diversion, although such procedures have to be performed with a flexible ureteroscope. It is important to recognize that maneuvers such as intravenous administration of indigo carmine to define the ureterointestinal anastomosis and employing angled-tip and hydrophilic guidewires are often required. 

Question: How do you manage incidentally found non-obstructing renal stones? 

Answer: As one of my mentors used to tell me, “It is hard to make the asymptomatic patient feel any better.” With that thought in mind, we generally follow such stones expectantly, unless the patient has a relative indication for removal. I consider the following to be among those indications: a solitary kidney, where an obstructing stone event would constitute a medical emergency; frequent travel to areas where appropriate medical care is not reliably available; military service with battlefield deployment; vocational reasons such as a commercial airline pilot. 

Question: How do you use CT stone characteristics and patient factors to impact surgical planning? 

Answer: CT imaging can provide a great deal of information that can affect surgical planning. When selecting the most appropriate treatment options, we examine not just stone size and location, but also CT-detected parameters such as stone density (Hounsfield units) and skin-to-stone distance. We are looking for a density of < 1000 and a skin-to-stone distance of < 10 cm in patients who are undergoing SWL. I view CT imaging as mandatory for pretreatment planning in patients undergoing PNL. Not only will it guide you to the most appropriate point of access to the renal unit, but it also will inform you as to perinephric structures that should be avoided in the course of the procedure, such as a retrorenal colon, spleno- or hepatomegaly, or a particularly low pleural reflection. 

Question: How do you manage problematic cystinuric patients with frequently recurrent stones? 

Answer: That can be a very challenging cohort of patients to manage. The medications that we use in the treatment of cystinuria can have cumbersome prescription regimens and can be accompanied by significant side effects. Therefore, it can be difficult to maintain patient compliance. If patients are unable to tolerate ideal medical therapy, we will generally perform frequent surveillance renal sonography, and, when small stones are identified, we will proceed with ureteroscopy. Treating a 5-mm cystine stone with flexible ureteroscopy and laser lithotripsy is a far more desirable endeavor than performing a PNL on a 3-cm staghorn cystine stone.

Question: When do you use medical dissolution therapy in treating uric acid stones? 

Answer: If the stone is not causing acute difficulties, such as obstruction or pain, we will begin a course of pH manipulation with the goal of dissolving the stone. In my experience, the timecourse to complete dissolution can be a long one, lasting up to several months. It is often successful for small stones; however, my success is more limited using oral dissolution therapy for staghorn-type stones.

Brian R Matlaga