Diagnosis and Initial Management of Kidney Stones

Author: Andrew J. Portis, Chandru P. Sundaram
Date: April 1, 2001

The diagnosis and initial management of urolithiasis have undergone considerable evolution in recent years. The application of noncontrast helical computed tomography (CT) in patients with suspected renal colic is one major advance. The superior sensitivity and specificity of helical CT allow urolithiasis to be diagnosed or excluded definitively and expeditiously without the potential harmful effects of contrast media. Initial management is based on three key concepts: (1) the recognition of urgent and emergency requirements for urologic consultation, (2) the provision of effective pain control using a combination of narcotics and nonsteroidal anti-inflammatory drugs in appropriate patients and (3) an understanding of the impact of stone location and size on natural history and definitive urologic management. These concepts are discussed with reference to contemporary literature, with the goal of providing tools that family physicians can use in the emergency department or clinic. (Am Fam Physician 2001;63:1329-38.)

Urolithiasis is a problem that has confronted clinicians since the time of Hippocrates, and many family physicians have extensive experience in its clinical management. In recent years, technological advancements have greatly facilitated the diagnosis of stone disease. Physicians can now conclusively identify and, perhaps more importantly, exclude stone disease within minutes of considering the diagnosis. The management of urolithiasis is also becoming increasingly well defined. Clear indications for urologic referral are based on a recognition of the few urgent situations and a solid understanding of the natural history of stone progression.

Epidemiology

The prevalence of urolithiasis is approximately 2 to 3 percent in the general population, and the estimated lifetime risk of developing a kidney stone is about 12 percent for white males.(1) Approximately 50 percent of patients with previous urinary calculi have a recurrence within 10 years.(2)

Stone disease is two to three times more common in males than in females. It occurs more often in adults than in elderly persons, and more often in elderly persons than in children. Whites are affected more often than persons of Asian ethnicity, who are affected more often than blacks. In addition, urolithiasis occurs more frequently in hot, arid areas than in temperate regions.

Decreased fluid intake and consequent urine concentration are among the most important factors influencing stone formation. Certain medications, such as triamterene (Dyrenium), indinavir (Crixivan) and acetazolamide (Diamox), are also associated with urolithiasis. Dietary oxalate is another possible cause, but the role of dietary calcium is less clear, and calcium restriction is no longer universally recommended.(3)

Presentation and Differential Diagnosis

Urolithiasis should always be considered in the differential diagnosis of abdominal pain. The classic presentation of renal colic is excruciating unilateral flank or lower abdominal pain of sudden onset that is not related to any precipitating event and is not relieved by postural changes or nonnarcotic medications. With the exception of nausea and vomiting secondary to stimulation of the celiac plexus, gastrointestinal symptoms are usually absent. The pain of renal colic often begins as vague flank pain. Patients frequently dismiss this pain until it evolves into waves of severe pain. It is generally believed that a stone must at least partially obstruct the ureter to cause pain.

The pain is commonly referred to the lower abdomen and to the ipsilateral groin. As the stone progresses down the ureter, the pain tends to migrate caudally and medially (Table 1).

Distal ureteral stones may be manifested by bladder instability, urinary frequency, dysuria and/or pain radiating to the tip of the penis, or the labia or vulva. Increasingly, however, calculi are encountered in asymptomatic patients and are found incidentally on imaging studies or during the evaluation of microhematuria.

Symptoms similar to those of renal colic can be caused by noncalculus conditions. In women, gynecologic processes that must be considered include ovarian torsion, ovarian cyst and ectopic pregnancy. In men, symptoms of testicular processes, such as a tumor, epididymitis or prostatitis, may mimic the symptoms of distal ureteral stones.

Other general causes of abdominal pain, such as appendicitis, cholecystitis, diverticulitis, colitis, constipation, hernias or even arterial aneurysms, may elicit similar discomfort. Symptoms mimicking those of urolithiasis also occur with urologic lesions such as congenital ureteropelvic junction obstruction, renal or ureteral tumors, and other causes of ureteral obstruction.

Many family physicians have had experience with patients whom they suspect of having factitious colic. Frequently, these patients claim to be "allergic" to intravenous contrast media.(4) Noncontrast helical computed tomography (CT) is a relatively new modality with the capability to exclude calculi in such problem patients.

Confirmation of the Diagnosis

The diagnosis of urinary tract calculi begins with a focused history. Key elements include past or family history of calculi, duration and evolution of symptoms, and signs or symptoms of sepsis. The physical examination is often more valuable for ruling out nonurologic disease.

Urinalysis should be performed in all patients with suspected calculi. Aside from the typical microhematuria, important findings to note are the urine pH and the presence of crystals, which may help to identify the stone composition. Patients with uric acid stones usually present with an acidic urine, and those with stone formation resulting from infection have an alkaline urine. Identification of bacteria is important in planning therapy, and a urine culture should be routinely performed. Limited pyuria is a fairly common response to irritation caused by a stone and, in absence of bacteriuria, is not generally indicative of coexistent urinary tract infection.

Because of the various presentations of renal colic and its broad differential diagnosis, an organized diagnostic approach is useful (Figure 1). Symptomatic stones essentially present as abdominal pain. Renal colic may be suspected based on the history and physical examination, but diagnostic imaging is essential to confirm or exclude the presence of urinary calculi. Several imaging modalities are available, and each has advantages and limitations (Table 2).

ABDOMINAL ULTRASONOGRAPHY

Abdominal ultrasonography has limited use in the diagnosis and management of urolithiasis. Although ultrasonography is readily available, quickly performed and sensitive to renal calculi, it is virtually blind to ureteral stones (sensitivity: 19 percent), which are far more likely to be symptomatic than renal calculi.5 However, if a ureteral stone is visualized by ultrasound, the finding is reliable (specificity: 97 percent).

The ultrasound examination is highly sensitive to hydronephrosis, which may be a manifestation of ureteral obstruction, but it is frequently limited in defining the level or nature of obstruction. It is also useful in assessing renal parenchymal processes, which may mimic renal colic. Abdominal ultrasonography is the preferred imaging modality for the evaluation of gynecologic pain, which is more common than urolithiasis in women of childbearing age.

PLAIN-FILM RADIOGRAPHY

Plain-film radiography of the kidneys, ureters and bladder (KUB) may be sufficient to document the size and location of radiopaque urinary calculi. Stones that contain calcium, such as calcium oxalate and calcium phosphate stones, are easiest to detect by radiography. Less radiopaque calculi, such as pure uric acid stones and stones composed mainly of cystine or magnesium ammonium phosphate, may be difficult, if not impossible, to detect on plain-film radiographs.

Unfortunately, even radiopaque calculi are frequently obscured by stool or bowel gas, and ureteral stones overlying the bony pelvis or transverse processes of vertebrae are particularly difficult to identify. Furthermore, nonurologic radiopacities, such as calcified mesenteric lymph nodes, gallstones, stool and phleboliths (calcified pelvic veins), may be misinterpreted as stones.

Although 90 percent of urinary calculi have historically been considered to be radiopaque, the sensitivity and specificity of KUB radiography alone remain poor (sensitivity: 45 to 59 percent; specificity: 71 to 77 percent).(6) KUB radiographs are useful in the initial evaluation of patients with known stone disease and in following the course of patients with known radiopaque stones.

INTRAVENOUS PYELOGRAPHY

CHANDRU P. SUNDARAM, M.D., is assistant professor of urology at Washington University School of Medicine. He completed a residency in urology at the University of Minnesota Medical School-Minneapolis and a fellowship in endourology at Beth Israel Deaconess Medical Center/Harvard University, Boston.

Address correspondence to Chandru P. Sundaram, M.D., Division of Urologic Surgery, Washington University School of Medicine, 4960 Children's Place, Box 8242, St. Louis, MO 63110. Reprints are not available from the authors.

TABLE 1Relationship of Stone Location to SymptomsStone location Common symptomsKidney Vague flank pain, hematuriaProximal ureter Renal colic, flank pain, upper abdominal painMiddle section Renal colic, anterior abdominalof ureter pain, flank painDistal ureter Renal colic, dysuria, urinary frequency, anterior abdominal pain, flank painTABLE 2Imaging Modalities in the Diagnosis of Ureteral CalculiImaging modality Sensitivity (%) Specificity (%)Ultrasonography 19 97Plain radiography 45 to 59 71 to 77Intravenous 64 to 87 92 to 94 pyelographyNoncontrast helical 95 to 100 94 to 96 computed tomographyImaging modality AdvantagesUltrasonography Accessible Good for diagnosing hydronephrosis and renal stones Requires no ionizing radiationPlain radiography Accessible and inexpensiveIntravenous Accessible pyelography Provides information on anatomy and functioning of both kidneysNoncontrast helical Most sensitive and specific radiologic computed test (i.e., facilitates fast, definitive tomography diagnosis) Indirect signs of the degree of obstruction Provides information on nongenitourinary conditionsImaging modality LimitationsUltrasonography Poor visualization of ureteral stonesPlain radiography Stones in middle section of ureter, phleboliths, radiolucent calculi, extraurinary calcifications and nongenitourinary conditionsIntravenous pyelography Variable-quality imaging Requires bowel preparation and use of contrast media Poor visualization of nongenitourinary conditions Delayed images required in high-grade obstructionNoncontrast helical Less accessible and relatively expensive computed No direct measure of renal function tomographyTABLE 3Complications of UrolithiasisRenal failureUreteral strictureInfection, sepsisUrine extravasationPerinephric abscessXanthogranulomatous pyelonephritisTABLE 4Probability of Stone Passage[*] Probability ofStone location and size passage (%)Proximal ureter[greater than] 5 mm 05 mm 57[less than] 5 mm 53Middle section of ureter[greater than] 5 mm 05 mm 20[less than] 5 mm 38Distal ureter[greater than] 5 mm 255 mm 45[less than] 5 mm 74[*]--Approximately 50 percent of asymptomatic renal calculi becomesymptomatic within five years.Information from Morse RM, Resnick MI. Ureteral calculi: naturalhistory and treatment in the era of advanced technology.J Urol 1991;145:263-5, and Glowacki LS, Beecroft ML, Cook RJ,Pahl D, Churchill DN. The natural history of asymptomatic urolithiasis.J Urol 1992;147:319-21.TABLE 5Treatment Modalities for Renal and Ureteral CalculiTreatment IndicationsExtracorporeal Radiolucent calculi shock wave Renal stones [less than] 2 cm lithotripsy Ureteral stones [less than] 1 cmUreteroscopy Ureteral stonesUreterorenoscopy Renal stones [less than] 2 cmPercutaneous nephrolithotomy Renal stones [greater than] 2 cm Proximal ureteral stones [greater than] 1 cmTreatment Advantages LimitationsExtracorporeal Minimally invasive Requires spontaneous shock wave Outpatient passage of fragments lithotripsy procedure Less effective in patients with morbid obesity or hard stonesUreteroscopy Definitive Invasive Outpatient Commonly requires procedure postoperative ureteral stentUreterorenoscopy Definitive May be difficult to clear Outpatient fragments procedure Commonly requires postoperative ureteral stentPercutaneous nephrolithotomy Definitive InvasiveTreatment ComplicationsExtracorporeal Ureteral obstruction by shock wave stone fragments lithotripsy Perinephric hematomaUreteroscopy Ureteral stricture or injuryUreterorenoscopy Ureteral stricture or injuryPercutaneous Bleeding nephrolithotomy Injury to collecting system Injury to adjacent structures

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