A 12 year old girl arrives at the emergency department cradling her side and complaining of left flank and abdominal pain. Her pain is severe and started one hour ago. Her other symptoms include nausea, vomiting, and hematuria. There is no history of trauma, fever, diarrhea, constipation, dysuria, urgency, or bloody stools. She reports no previous similar episodes. She is premenarchal. Her past medical and family histories are not significant. A dietary history reveals her diet mostly consists of processed foods and carbonated soft drinks.
Exam: T 37, HR 100, RR 20, BP 130/75. She is obese (BMI 26, >95th percentile). She is in severe pain. Heart and lung exams are negative. Auscultation of the abdomen reveals normoactive bowel sounds. There is no tenderness, guarding, rebound, or palpable masses. Examination of the back is positive for left CVA tenderness. Genitourinary examination reveals no abnormalities.
She is given intranasal fentanyl for pain control. An IV is started and she is given IV ketorolac, ondansetron, and IV fluid hydration. An ultrasound of her kidneys shows a 12 mm stone at the left ureteropelvic junction with associated calyceal dilation (i.e., grade II hydronephrosis). Ultrasound of her abdomen is otherwise negative. A transabdominal ultrasound of her ovaries shows normal blood flow. A urine dipstick is positive for moderate blood and a urine hCG is negative. Subsequently, the patient undergoes ureteroscopy with shock wave lithotripsy to remove the large, obstructing calculus. Microscopic analysis reveals the stone to be composed of calcium oxalate. Serum electrolytes, calcium, phosphorus, magnesium, uric acid, and a 24-hour urine collection are obtained which reveals a diagnosis of normocalcemic hypercalciuria. The patient and family are counseled on lifestyle modifications, such as increasing water intake and decreasing sodium intake, to prevent stone recurrence.
Despite making the necessary changes, the patient experiences another episode of renal colic one year later. A new 5 mm stone is in the distal right ureter without signs of obstruction or infection. Oral tamsulosin is prescribed to ease stone transit and the stone is successfully passed within two weeks. Microscopic analysis confirms calcium oxalate stones. The patient is prescribed a thiazide diuretic and her urinary calculi do not recur.
Urolithiasis is defined as the formation of urinary calculi (stones), which may deposit anywhere along the urinary tract. Pediatric urolithiasis was once considered a rare phenomenon in the United States. This has changed in recent decades as the incidence of urinary stone disease in children has increased steadily at a rate of 5% to 10% per year (1). In the pediatric population, most cases occur in adolescent females (1). Although the reasons for gender differences remain unclear, it is hypothesized that increasing rates of obesity and changing dietary habits (e.g., decreased water consumption and increased salt and fructose intake) are responsible for the growing number of pediatric stone disease cases (2).
The formation of urinary tract stones is a complex process, which ultimately results in the precipitation and crystallization of urinary solutes. Factors favoring stone formation include low urine volume, urine pH abnormalities, supersaturation of the urine with crystallizable solutes (e.g., calcium, sodium, oxalate, and urate), and urinary stasis (usually the result of anatomic abnormalities or foreign bodies) (3). Urinary calculi are classified based on their composition: calcium (calcium oxalate and/or calcium phosphate), struvite (ammonium magnesium phosphate), uric acid, or cystine. Stones formed during childhood show a similar distribution to that of adults, with calcium oxalate being the most common (45% to 65%), followed by struvite (3% to 30%), and uric acid and cystine stones (5% to 10%). Often, pediatric urinary stones are the result of underlying metabolic disorders, the most common being normocalcemic hypercalciuria (idiopathic). Struvite stones are an exception to the rule in that they are frequently attributed to genitourinary tract abnormalities which predispose to urinary tract infections with urea splitting organisms such as proteus (1,3) and sometimes present as large staghorn calculi that occupy the renal pelvis.
The pediatric patient with urinary stone disease most often presents with abdominal and/or flank pain that radiates to the scrotum or labia. Intermittent pain occurs when the calculus obstructs a narrowing of the urinary tract, increasing pressure in the collecting system (2). Other possible symptoms include dysuria, gross hematuria, urgency, nausea, and vomiting. In infants, it can be easy to misinterpret symptomatic stones as gastrointestinal colic (3).
To establish a diagnosis of urolithiasis in children, special attention should be given to the past medical, family, and dietary histories to unravel potential underlying genetic or metabolic factors. Clinicians should identify children with a history of prematurity, urinary tract abnormalities, urinary tract infections (UTIs), gastrointestinal malabsorption, and immobility, as they are at an increased risk of stone disease (1). A dietary history should be obtained from every patient, with an emphasis on fluid and salt intake, vitamin and mineral supplementation, and special diets. Additionally, inquiring about a family history of nephrolithiasis, hematuria, and chronic kidney disease can help identify those with an underlying metabolic or genetic condition (1). Because pediatric stone disease is still relatively uncommon, the physical examination should aim to exclude the long list of potential differential diagnoses. Important conditions to consider include UTI, glomerular disease, gastrointestinal disease, cholecystitis, intestinal or urinary obstruction, musculoskeletal inflammation or spasm, inguinal hernia, and testicular or ovarian torsion (4). The presence of dysmorphic facies, rickets, tetany, or gout can also help to narrow metabolic and genetic etiologies (1).
The pain from urolithiasis is very severe and is known as renal colic. Opiate narcotic medications are often used for analgesia initially; however, NSAIDs (non-steroidal anti-inflammatory drugs) are preferred, since they have been proven to be more effective than opiates and are associated with fewer adverse events (5). Ketorolac is a commonly administered IM/IV NSAID.
The next steps in evaluating suspected renal colic include obtaining imaging of the urinary tract, urinalysis with microscopic examination, and a urine culture if clinically indicated. Although CT scans (known as CT KUB) are the most accurate imaging modality for the detection of renal stones, ultrasonography plus a plain radiographs of the abdomen/pelvis are the preferred initial imaging studies in children because of the risks of increased radiation exposure from CT scans (3). Unfortunately, renal ultrasonography has some significant drawbacks: calculi are only visualized when adjacent to the bladder or in the renal pelvis; and stones smaller than 3 mm are not usually seen. The use of low-dose non-contrast CT in children becomes necessary when signs of secondary obstruction (e.g., hydronephrosis, hydroureter) are seen in the absence of stone visualization on ultrasound (2).
Once the diagnosis of urinary stones is established with imaging, all patients should be managed with adequate hydration and analgesics. Additional diagnostic labs include a basic metabolic panel (includes BUN and creatinine to determine renal function), as well as calcium, phosphorus, magnesium, and uric acid levels. In the case of calcium or phosphorus abnormalities, 25-hydroxyvitamin D and parathyroid hormone levels should also be obtained (1,2,3). If a urinary stone is retrieved (either by surgery or urination), the stone should be sent to the laboratory for microscopic evaluation to determine the exact type of stone. Once the stone has passed, all pediatric patients should undergo a more comprehensive urinary metabolic evaluation (i.e., 24-hour urine collection). The reason for this is two-fold: 1) Underlying metabolic disorders are identified in about half of pediatric urolithiasis patients. 2) These patients experience a much higher rate of stone recurrence (3 to 5 times) compared to children without metabolic derangements (3).
After pain control, the acute treatment of symptomatic urolithiasis is dependent on several factors, including stone size, location, composition, and whether there is associated obstruction or infection. Generally, smaller stones (<5 mm) tend to pass spontaneously, while larger stones may require medical expulsive therapy (MET) or surgical removal (1).
In medical expulsive therapy, alpha-adrenergic antagonists (e.g., tamsulosin) inhibit ureteral smooth muscle contraction, which results in dilation of the urinary tract and promotes stone passage. The current 2016 American Urological Association (AUA) guidelines for surgical management of kidney stones recommend medical expulsive therapy or observation alone for children with uncomplicated urinary stones less than 10 mm in size (6). This recommendation is supported by several meta-analyses, which have shown that pediatric patients treated with tamsulosin experience a greater stone expulsion rate compared to those treated with analgesics alone (5).
Surgical intervention for the removal of urinary calculi becomes necessary when the patient fails to pass the stone on their own (with or without MET), the stone is >10 mm, or when there is an associated urinary tract infection or obstruction (6). In children, operative management of pediatric urolithiasis is not uncommon, with approximately 25% to 50% of cases requiring surgical removal (3). The three main surgical options include shockwave lithotripsy (SWL), ureteroscopy (URS), and percutaneous nephrolithotomy (PCNL). Shockwave lithotripsy uses extracorporeal sound waves to fragment the stone and is typically reserved for smaller stones in the upper urinary tract. In ureteroscopy, a ureteroscope is passed upwards from the urethra to the bladder and ureter, where laser, ultrasound, or pneumatic lithotripsy techniques are then used to disrupt the calculi. Larger stones are treated similarly with percutaneous nephrolithotomy, which differs by creating a percutaneous working tract to fragment and remove the stone. Open nephrolithotomy is rarely indicated in the modern era, except in very young children with large stones or in the case of a large stone that would require multiple endoscopic procedures (7).
Current evidence for the comparison of each surgical modality’s effectiveness in children is lacking, although recent trends suggest a preference for ureteroscopy (7,8). The 2016 AUA guidelines recommend shock wave lithotripsy or ureteroscopy for a stone burden of less than 20 mm, and percutaneous nephrolithotomy or shock wave lithotripsy for a stone burden of greater than 20 mm (6).
Preventative measures to reduce the recurrence of kidney stones include addressing the child’s underlying metabolic disorder (if any), fluid and dietary intake, as well as medication. Increased fluid intake remains the mainstay of urinary stone prevention, regardless of stone composition or the underlying cause. For this reason, children are advised to drink more than 30 ml/kg of neutral pH fluid daily (1). Diet modification also plays a key role in the secondary prevention of calcium, uric acid, and cystine stones. An overall balanced diet with limited sodium, oxalate, and animal protein intake, and increased consumption of foods rich in potassium and citrate (e.g., fruits and vegetables) is ideal (9). Pharmacotherapy may be initiated if fluid and dietary therapy are insufficient to prevent stone recurrence. This can include thiazide diuretics (reduces urinary calcium excretion) such as hydrochlorothiazide or chlorthalidone, and/or potassium citrate for the prevention of calcium stone formation; sodium bicarbonate or allopurinol for uric acid stones; and penicillamine or sodium bicarbonate for cystine stones (1,2,4). Current practice guidelines support a repeat 24-hour urine specimen and follow-up within six months of treatment initiation to assess for response to lifestyle modifications and/or treatment (9).
Although once considered rare, pediatric urolithiasis is an increasingly common issue presenting to emergency physicians, nephrologists, and urologists. In contrast to adults, children with urolithiasis are more likely to have underlying metabolic derangements, neurologic abnormalities, and urinary tract anomalies, which contribute to increased rates of recurrence and infection. Evaluation and treatment should be pediatric-focused, prioritizing ruling out metabolic and genetic conditions, minimizing radiation exposure, and decreasing the risk of stone recurrence.
Questions
1. What are the four main types of urinary calculi and which is the most common?
2. How does pediatric stone disease typically differ from that of adults?
3. What is the preferred modality for visualizing urinary stones in pediatric patients?
4. How does the management change for a 5 mm stone versus a 15 mm stone?
5. Explain the importance of lifestyle modifications for the prevention of recurrent urolithiasis.
References
1. Tasian GE, Copelovitch LA. Management of Pediatric Kidney Stone Disease. In: Partin AW, Dmochowski RR, Kavoussi LR, Peters CA (eds). Campbell-Walsh-Wein Urology, 12th ed. 2021. Philadelphia, PA: Elsevier. pp: 853-870.
2. Elder JS. Urinary Lithiasis. In: Kliegman RM, St. Geme JW, Blum NJ, et al (eds). Nelson Textbook of Pediatrics, 21st edition. 2020, Elsevier, Philadelphia, PA. pp. 2835-2840.
3. Panzarino V. Urolithiasis in Children. Adv Pediatr. 2020;67:105-112. doi:10.1016/j.yapd.2020.03.004
4. Fontenelle LF, Sarti TD. Kidney Stones: Treatment and Prevention. American Family Physician. https://www.aafp.org/pubs/afp/issues/2019/0415/p490.html. Published April 15, 2019. Accessed June 15, 2022.
5. Skolarikos A. Medical treatment of urinary stones. Curr Opin Urol. 2018;28(5):403-407. doi:10.1097/MOU.0000000000000523
6. Assimos D, Krambeck A, Miller NL et al. Surgical Management of Stones: American Urological Association/Endourological Society Guideline, part II. J Urol. 2016; 196: 1161. https://www.auanet.org/guidelines/guidelines/kidney-stones-surgical-management-guideline#x3164. Accessed June 15, 2022.
7. Barreto L, Jung JH, Abdelrahim A, Ahmed M, Dawkins GPC, Kazmierski M. Medical and surgical interventions for the treatment of urinary stones in children. Cochrane Database Syst Rev. 2019;10(10):CD010784. doi:10.1002/14651858.CD010784.pub3
8. Bowen DK, Tasian GE. Pediatric Stone Disease. Urol Clin North Am. 2018;45(4):539-550. doi:10.1016/j.ucl.2018.06.002
9. Pearle MS, Goldfarbe DS, Assimos DG, et al. Medical Management of Kidney Stones: AUA Guideline. J Urol. 2014; 192:316. https://www.auanet.org/guidelines/guidelines/kidney-stones-medical-mangement-guideline#x2868. Accessed June 15, 2022.
Answers to questions
1. The main types of urinary stones are composed of calcium, struvite (ammonium magnesium phosphate), uric acid, and cystine. Calcium oxalate stones are by far the most common and account for 45% to 65% of all pediatric urolithiasis cases.
2. In contrast to adults, children with urolithiasis are more likely to have underlying metabolic, neurologic, and urinary tract abnormalities, which contribute to increased rates of stone recurrence and infection.
3. The preferred imaging modalities in children include a combination of kidney, ureter, and bladder (KUB) ultrasonography plus plain pelvic/abdominal radiography.
4. Due to their small size, 5 mm stones may pass spontaneously. Management options include simple observation or observation with medical expulsive therapy (MET). Stones larger than 10 mm, or those causing obstruction or infection are treated with more urgent surgical options. The three main surgical options include shockwave lithotripsy (SWL), ureteroscopy (URS), and percutaneous nephrolithotomy (PCNL).
5. Low urine volume and the supersaturation of urinary solutes are important risk factors for the formation of urinary calculi. Lifestyle modifications are useful because they can target several of these factors and are not limited to a specific type of urinary stone. For example, increasing fluid intake has the benefit of increasing the volume of urine and diluting the concentration of all urinary solutes. Similarly, reducing dietary sodium helps to reduce the total amount of ions in the filtrate, reducing the risk of precipitation.