Calculus Disease of the Urinary Tract: Endourinary Procedures
Renal calculi have plagued humankind throughout the ages. Before the advent of antibiotics, the surgical treatments and the ensuing infections were frequently more damaging than the initial problems themselves, as alluded to in the Hippocratic Oath’s, “I will not cut for stone.” With the introduction of antibiotics, open surgical procedures such as ureterolithotomy/pyelotomy and anatrophic nephrolithotomy became effective treatments for obstructing stones, which previously had been reserved for only uroseptic patients. In this century, the invention and refinement of fiber-optic/endoscopic equipment and extracorporeal shock wave lithotripsy (ESWL) has revolutionized the treatment of stone disease. Today, indications for open or laparoscopic surgical management are limited to the few cases with concurrent stones and either a ureteral stricture or a ureteropelvic junction (UPJ) obstruction.
Stones are formed when concentrations of minerals become supersaturated and precipitate out as crystals and then aggregate together as calculi. Urine contains inhibitors of crystal formation such as citrate and magnesium, and inhibitors of aggregation such as Tamm-Horsfall protein and nephrocalcin.
Calcium phosphate together with calcium oxalate in either a dihydrate (softer) or monohydrate (harder) form is responsible for 75% of renal calculi. Hypercalciuria is the underlying reason in most cases and can be due to increased intestinal absorption, decreased renal absorption, and increased bone resorption. Hyperoxaluria has a 10 times greater effect on stone formation than calcium and is often seen in patients with small-bowel resections or inflammatory bowel disease who have increased oxalate absorption. Increased calcium oxalate/phosphate crystallization can often be seen in patients with renal tubular acidosis, high-animal protein diets, and strenuous exercise regimes. Citrate, which binds calcium, is an inhibitor of stone formation.
Struvite or magnesium ammonium phosphate (infection) stones make up 15% of stones and are the result of urea-splitting organisms such as Klebsiella, Proteus, and Pseudomonas, which create a high pH with resulting ammonia production and formation of staghorn calculi. These underlying infections can only be cleared by stone removal, long-term antibiotics, hydration, and the reduction of urinary phosphate.
Uric acid stones account for 5% and may precipitate in acidic urine to form radiolucent stones not visible on plain abdominal X-ray. Hyperuricosuria with hyperuricemia is often due to neoplastic processes, gout, inborn errors of metabolism, or other situations where there is significant breakdown of purines. Hyperuricosuria without hyperuricemia often suffer from chronic diarrhea, have high-protein diets, or are on uricosuric drugs such as thiazide diuretics. Patients with uric acid stone formation benefit from allopurinol 300 mg/day and can be managed by increasing their urinary output to 2 L/day along with raising their urinary pH to between 6.5 and 7.0 with potassium citrate.
Cystine stones account for 1% of stones and are due to an autosomal recessive defect in the renal tubular absorption of four amino acids: cysteine, ornithine, lysine, and arginine (COLA). A diagnosis of cystine stones can be made by finding hexagonal cystine crystals or a positive nitroprusside test in the urine. Treatment includes alkalinizing the urine above a pH of 7.0, increasing urinary volume to 3 to 4 L/day and the use of D-penicillamine or a-mercaptopropionyl-glycine to increase the solubility of cystine in the urine.
The classic presentation of renal calculi is with flank pain and hematuria but may vary with the size and location of the obstructing stone. As the stone moves down the ureter, the location of discomfort migrates from the costovertebral angle around the patients’ side down toward the groin. Pain from obstruction at the ureterovesical junction is often referred to the testicle/labia. The degree of pain can range from excruciating to completely asymptomatic. Acutely, pain is the result of obstruction and immediate dilation of the urinary tract and is frequently associated with nausea and vomiting. Pressure may be relieved by migration of the stone, forniceal rupture or decompression with a stent, which allows urine to flow. Mild fever and leukocytosis can also be seen. Urgent surgical intervention is warranted for fever over 101ºF and signs of infection, with a lower threshold for intervention for diabetic or immunocompromised patients.
Red blood cells (RBC) will be present on urinalysis in 90% of patients with renal calculi. Pyuria or significant bacteriuria, along with fever and leukocytosis, is a sign of infection and often indicates the need for urgent surgical intervention. Historically, the intravenous pyelogram (IVP) was first-line imaging for obstructing stones, but has been replaced in most settings by noncontrast abdominal and pelvic CT scans, which provide immediate determination of stone size and location, in addition to delineation of the patients’ anatomy. Kidney, ureter, bladder (KUB) plain abdominal X-rays allow visualization of 90% of stones and can be helpful in planning and following up treatment with significantly less radiation exposure to the patient.
Expectant Management/Medical Expulsive Therapies for Obstructing Renal Calculi
Obstructing renal calculi without infection can be managed expectantly and on an outpatient basis, as long as pain and nausea can be controlled. Over a 4- to 6-week time period, stones <10 mm have a 47% chance and stones 5 mm or less have a 68% chance of passing out. Alpha-blockers may increase the chance of stone passage by up to 25%. Stones >1 cm are unlikely to pass and should be treated on an elective outpatient basis without a trial of passage. If patients develop fever, intractable pain, or persistent nausea and vomiting, urgent surgical intervention is indicated. Many emergency departments have standard treatment algorithms (see below) by which acute renal colic is managed.
Emergency Department Kidney Stone Guideline
Basic Emergency Interventions For Patients With Renal Colic Pain Control
Toradol 15 to 30 mg IV q6 prn
Morphine 4 to 6 mg IV if needed
Basic labs: u/a, creatinine
Send urine cultures +++
Noncontrast abdominal ct scan if needed
Flomax 0.4 mg PO once the patient tolerates oral fluids
The Following Patients May Be Discharged Home Without Consulting Urology:
Obstructing stone/s <8 mm in size or nonobstructing stone of any size
No evidence of infection
Creatine less than 1.8 with two normally functioning kidneys
Pain controlled with oral analgesics
Able to tolerate POs
Filter urine to collect stone
Oral analgesics prn
Hydrate 2 to 3 l uop/day
Flomax 0.4 mg PO qd
Have patient contact urology for outpatient follow-up appointment
If Any Of Below Criteria Met May Need A Urology Consult And/Or Urology Admission:
One functioning kidney
Temp > 101.0°F
Creatine > 1.8
Immunocompromised — (DM, HIV, steroid tx, chemotherapy, etc.)
Pain not controlled with oral analgesics
Obstructing stone >8 mm
Unable to tolerate POs
Indications for Nonobstructing Stone Management
Nonobstructing stones <5 mm can be managed expectantly in the absence of infection given their high likelihood of passage. Nonobstructing stones 6 mm to 1.5 cm are usually treated first-line by ESWL in the absence of contraindications such as ESWL-resistant stones (cystine or calcium monohydrate), coagulopathies, or uric acid ureteral stones (radiolucent). Stones 1.5 to 2.5 cm require a ureteral stent to be placed prior to treatment with ESWL given a larger stone burden and the propensity of stone fragments to obstruct the ureter on passage, that is, Steinstrasse (Stone Street). Stone burdens >2.5 cm, which often are struvite (infectious) are best managed by percutaneous nephrolithotomy (PCNL), though often ESWL can be required subsequently to break remaining fragments to 5 mm or smaller.
Extra Corporeal Shock Wave Lithotripsy
ESWL first became commercially available when the Dornier HM3 Lithotripter was brought to America in 1984. This original electrohydraulic type machine uses a high-voltage current generated across an underwater spark gap electrode resulting in a high-energy pressure wave that is focused at a distant point. More recently, piezoelectric machines generate a shockwave across a grid of ceramic or piezoelectric crystals, which are stimulated with a coordinated high-energy electrical pulse. A third mechanism uses an electromagnetic coil to produce shock waves through a metallic membrane focused using an acoustic lens. Originally, patients were immersed in a water bath to allow the shockwave to be transmitted from water through the skin and soft tissues and focused on the stone. Today, water-filled cushions accomplish this in a much easier and safer fashion and allow ESWL to be performed under sedation rather than general anesthesia. Localization of the stone occurs by fluoroscopy, ultrasound or a combination of both. Fluoroscopy is able to visualize all radiopaque stones in both the kidney and the ureter with limitations caused by the bony pelvis, bowel contents, or confusion with pelvic phleboliths. Ultrasound can identify both radiopaque and radiolucent stones in the kidney but is poor at visualizing stones in the ureter.
Both renal and ureteral stones can be treated by ESWL with an overall single treatment success rate of 77%, but typically ESWL is indicated for renal stones <2 cm in diameter and ureteral stones <1 cm. The hardest stones (calcium oxalate monohydrate or cystine) are usually ESWL resistant and better treated by other modalities. Overall ESWL success rates for stones <2 cm are 80% to 90%. Impacted stones have a 60% to 70% chance of fragmentation and lower pole stones have a lower probability of passage. Stents are often placed before ESWL when stones are obstructing or the stone burden is >1.5 cm and the likelihood of post ESWL obstruction greater. Treatments typically take 20 to 30 minutes in time as only 2,500 shocks can safely be given in the kidney and 3,000 in the ureter. Multiple treatments can be required with KUB and CT reimaging between treatments for reassessment. ESWL remains the primary treatment for uncomplicated urinary tract stones with a stone-free rate of 83% in the proximal ureter requiring on average 1.4 treatments, and a stone-free rate of 85% in the distal ureter with an average of 1.29 treatments.