Kidney stones in children: Clinical features and diagnosis

INTRODUCTION — Nephrolithiasis is increasingly recognized in children. Its presentation varies, and often patients, especially young children, do not present with the classic acute onset of flank pain commonly seen in adults. As a result, children are frequently evaluated for other conditions before the diagnosis of nephrolithiasis is made. The clinical features and diagnosis of childhood nephrolithiasis will be reviewed here. The epidemiology, risk factors, acute management, and prevention of recurrent nephrolithiasis in children are discussed separately. (See "Kidney stones in children: Epidemiology and risk factors" and "Kidney stones in children: Acute management" and "Kidney stones in children: Prevention of recurrent stones".)

CLINICAL PRESENTATION — Most children with nephrolithiasis present symptomatically, usually with flank or abdominal pain. Approximately 15 to 20 percent are asymptomatic, primarily young children who are diagnosed because of stone detection when abdominal imaging is performed for other purposes [1-4].

In those with symptomatic presentation, the most common symptom is pain [1-3,5]. Other potential manifestations include gross hematuria, dysuria and urgency, and nausea/vomiting.

Pain — Pain can be located either as abdominal, back, or flank pain (referred to as renal colic). In several case series, pain was the presenting complaint in 50 to 75 percent of patients [1-3,5,6].

Pain frequency varies with age. In one report, for example, pain was present in 60, 40, and 20 percent of adolescents, school-aged children, and children below five years of age, respectively [2]. The age-related difference in pain may be related to stone location at presentation. Younger children (ie, less than five years of age) are much less likely to have ureteral stones than school-aged children and adolescents (32 versus 64 and 82 percent, respectively) [7]. Ureteral stones are generally painful, since they cause ureteral obstruction, whereas nonobstructing kidney stones are often asymptomatic and may be diagnosed as an incidental finding on abdominal imaging.

Similar to adults with nephrolithiasis, the intensity of pain can vary from a mild ache to severe debilitating pain. In children below five years of age, the pain, if present, appears to be milder and is nonspecific. In addition, young children often are unable to articulate the location and severity of the pain. As a result, young children are frequently evaluated for other causes of abdominal pain before the diagnosis of nephrolithiasis is made.

In addition, nephrolithiasis may be the cause of recurrent abdominal pain in children, as illustrated by a retrospective study that included patients that required hospitalization or underwent appendectomy for abdominal pain [8].

Hematuria — Hematuria can present as the sole symptom of kidney stones or concomitantly with abdominal pain. In pediatric case series, gross hematuria as a presenting symptom for nephrolithiasis varied from 30 to 55 percent [1-3,5].

Dysuria and urgency — Approximately 10 percent of children with nephrolithiasis present with symptoms of dysuria and urgency suggestive of a urinary tract infection (UTI) [1,5,6,9]. In some cases, urinary tract infection is present and is a contributing factor to stone formation, especially in young children [1,2,6]. In other cases, dysuria and urgency can be seen when the stone is present in the bladder or urethra without an associated UTI. (See "Kidney stones in children: Epidemiology and risk factors", section on 'Infection'.)

In addition to these symptoms, nausea and vomiting are common, reported in up to 56 percent of pediatric patients [1,10].

Young children — As noted above, young children with nephrolithiasis are less likely to display the classical presentation of abdominal/flank pain commonly seen in older children and adults [2,7,11]. Younger children are also more likely than older children to have a renal rather than a ureteral stone [7,11]. In one of the largest case series, abdominal pain and gross hematuria were the presenting symptoms in approximately one-half of the children below six years of age [2]. The other half of patients presented with a urinary tract infection and/or incidental finding of stones on abdominal imaging [4].

INITIAL EVALUATION — Because renal stones can cause urinary obstruction, and are often associated with urinary tract infection, children who present with symptoms suggestive of nephrolithiasis should be evaluated promptly.

History — The evaluation begins with a history that identifies any of the following factors that are associated with an increased likelihood for nephrolithiasis:

●History of previous renal stone.

●Family history of nephrolithiasis. In one case series, 16 percent of children had a first-degree relative and 17 percent had a second-degree relative with renal stones [3]. (See "Kidney stones in children: Epidemiology and risk factors".)

●History of underlying renal and urinary tract structural abnormalities. (See "Kidney stones in children: Epidemiology and risk factors", section on 'Congenital/structural abnormalities'.)

●History of underlying metabolic conditions associated with nephrolithiasis, such as malabsorption leading to enhanced enteric absorption of oxalate and hyperoxaluria, or the use of a ketogenic diet to treat epilepsy. (See "Kidney stones in children: Epidemiology and risk factors".)

●History of medications associated with stone formation (ie, furosemide, topiramate, zonisamide, acetazolamide, sulfadiazine), or a history of conditions associated with such medications (ie, prematurity, cardiac disease, seizure disorder) [12]. (See "Kidney stones in children: Epidemiology and risk factors", section on 'Other metabolic causes'.)

●History of recurrent urinary tract infection, especially with a urease-producing organism, such as Proteus or Klebsiella. (See "Kidney stones in children: Epidemiology and risk factors", section on 'Infection'.)

Physical examination — The physical examination in the child with suspected nephrolithiasis should include:

●An abdominal examination for tenderness or mass (eg, evidence of urinary obstruction or another cause of abdominal pain, such as appendicitis).

●Growth measurements, as poor weight gain and/or failure to thrive may be an indication of a congenital or chronic condition that may be associated with nephrolithiasis, such as renal tubular acidosis or Dent's syndrome. (See "Kidney stones in children: Epidemiology and risk factors".)

●Blood pressure measurement and assessment for edema. The presence of hypertension and/or edema in a child with hematuria suggests an alternative diagnosis to nephrolithiasis, such as glomerular disease. (See 'Differential diagnosis' below.)

●Documentation of temperature. The presence of fever may represent a urinary tract infection, which warrants immediate attention. (See "Kidney stones in children: Acute management", section on 'Management of urinary tract infection'.)

Laboratory evaluation — The initial laboratory evaluation for the child with suspected nephrolithiasis includes:

●Urinalysis – Examination of the urine sediment may be useful if crystals are present. As an example, cystine crystals, which are colorless, flat, and hexagonal, are diagnostic of cystinuria (picture 1). Other crystals that can be seen in the sediment include calcium oxalate (picture 2A-B), calcium phosphate, uric acid (picture 3A-B), and phosphate (picture 4). Drugs, such as sulfadiazine, can also crystallize in the urine (picture 5).

●Urine culture – A urine culture should be obtained because urinary tract infection (UTI) can be present in a child with nephrolithiasis. A UTI is also the most common condition in the differential diagnosis of pediatric nephrolithiasis. (See 'Differential diagnosis' below.)

●Serum creatinine and/or cystatin c – Measuring serum creatinine and/or cystatin c to estimate glomerular filtration rate.

Further evaluation for metabolic risk factors (ie, hypercalciuria and hyperuricosuria) with blood and urine testing, is important, but should be performed once the acute episode is over, while the patient is at home, fully ambulatory, consuming a regular diet, and free of infection. (See "Kidney stones in children: Prevention of recurrent stones".)

DIAGNOSIS — The diagnosis of nephrolithiasis is initially suspected by the presentation and initial clinical evaluation [10]. It is confirmed by the detection of a stone on imaging studies or retrieval of a passed stone. As previously mentioned, the diagnosis is made as an incidental finding in approximately 15 to 20 percent of pediatric cases when abdominal imaging is performed for other purposes [1-3].

Imaging — The three imaging modalities currently used to diagnosis nephrolithiasis in children are non-contrast helical computed tomography (CT), ultrasonography, and plain abdominal radiography. Non-contrast CT is the most sensitive for the detection of renal stones, followed by ultrasonography and plain radiography [13,14]. However, ultrasonography is the recommended initial imaging modality because of concerns about radiation exposure from CT [15,16].

Ultrasonography — Ultrasonography is the recommended primary imaging modality for suspected nephrolithiasis, as it is effective in detection of renal and ureteral stones while avoiding radiation [16,17]. Ultrasonography can detect radiolucent stones, such as uric acid stones, and urinary obstruction [18]. However, it is limited in its ability to uncover small stones (eg, less than 5 mm), papillary or calyceal stones, or ureteral stones [17,19].

The experience and expertise of the ultrasonographer is an important factor in the sensitivity of the study, especially in the accurate detection of small stones or ureteral stones.

Non-contrast helical CT — Similar to in adults, non-contrast helical CT is the most sensitive modality to detect renal or ureteral stones in children (image 1A-B) [10,13,20]. CT is helpful if there is a strong clinical suspicion for a stone, but no stone is seen on ultrasound. CT can detect stones in the following conditions, which may not be detected by the other modalities:

●Ureteral stones, which may not be detected by ultrasonography

●Radiolucent stones (eg, pure uric acid stones), which are not detected by plain radiography

●Small (ie, 1 mm in diameter) stones, which are not detected by ultrasonography or plain radiography

CT also provides more detailed anatomic information including detection of obstruction or a structural abnormality [21].

CT is a rapid procedure requiring less than two minutes to be performed. Patients who undergo CT generally do not require anesthesia. If necessary, contrast can be given after non-contrast images have been obtained to provide additional anatomic detail, such as subtle signs of urinary obstruction or increased detail of an anatomic abnormality.

While CT scan is the most sensitive imaging modality, the exposure to radiation raises concerns about its use as the initial imaging modality. The radiation exposure during CT varies with different equipment and institutional protocols. Concerns have been raised that small children can be exposed to excessive radiation if conventional adult radiation doses are used during the procedure [15,22]. However, radiation doses can be significantly reduced through adjusting scanning parameters to the size and weight of the child while still maintaining adequate imaging quality [23,24]. In institutions that provide care for children, protocols to ensure effective and safe radiation doses for CT should be implemented as outlined by guidelines from the National Cancer Institute [22,25].

Abdominal plain radiography — A plain abdominal radiograph will detect radiopaque stones (eg, calcium, struvite, and cystine stones) (image 2), but will miss radiolucent stones (eg, uric acid stones), may miss small stones or those that overlay bony structures, and will not detect urinary obstruction. It is also sometimes challenging to distinguish between kidney stones and fecaliths in the overlying bowel on plain radiography. In settings where renal ultrasonography and CT are not available in children, plain abdominal radiography remains a reasonable alternative, recognizing that the reported sensitivity of this study is approximately 60 percent [13].

Our approach — We recommend ultrasound in the initial diagnostic evaluation of pediatric nephrolithiasis. Ultrasonography is preferred to plain film since it is a more sensitive test and can also detect radiolucent stones and urinary tract obstruction. If CT is used as part of subsequent evaluations, radiation doses are adjusted to the size and weight of the child to reduce the radiation exposure.

DIFFERENTIAL DIAGNOSIS — The differential diagnosis in a child with suspected nephrolithiasis depends upon the presenting symptoms. Nephrolithiasis is differentiated from the other conditions by demonstration by imaging of a stone within the kidney or urinary tract.

Abdominal or flank pain — Abdominal pain is one of the most common complaints in children and the differential is extensive. Constipation, as well as infections, such as gastroenteritis, urinary tract infections (UTI), appendicitis, and pneumonia, are the most common cause of abdominal or flank pain. Other signs and symptoms, most commonly fever, usually distinguish them from nephrolithiasis. (See "Causes of acute abdominal pain in children and adolescents" and "Emergency evaluation of the child with acute abdominal pain".)

Gross hematuria — In children, the most commonly identified causes for gross hematuria include UTI, irritation of the meatus or perineum, and trauma. These are differentiated from nephrolithiasis by the history and physical examination. Glomerular disease, such as postinfectious glomerulonephritis, is a less common cause of gross hematuria that is distinguished from nephrolithiasis by cola-colored urine instead of red urine, examination of the urinary sediment, and the possible presence of hypertension and/or edema. (See "Evaluation of gross hematuria in children".)

Urinary tract infection — Many of the symptoms associated with nephrolithiasis (eg, abdominal/flank pain, gross hematuria, dysuria, and urgency) can also be seen in children with UTI. In addition, the two conditions can present concomitantly with the UTI contributing to the process of stone formation.

Children with UTI diagnosed by urine culture usually begin to show clinical improvement within 24 to 48 hours of initiation of appropriate antibiotic therapy. If the clinical condition worsens or fails to improve as expected within 24 to 48 hours of the start of antimicrobial therapy, imaging should be performed to determine if the failed or slow response to therapy is due to the presence of renal stone, renal abscess, or underlying anatomic abnormalities or obstruction. (See "Urinary tract infections in infants older than one month and children less than two years: Acute management, imaging, and prognosis", section on 'Imaging'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Kidney stones" and "Society guideline links: Pediatric nephrolithiasis".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Kidney stones in children (The Basics)")

●Beyond the Basics topics (see "Patient education: Kidney stones in children (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Clinical presentation – Childhood nephrolithiasis usually presents with symptoms that most commonly include abdominal, back, or flank pain, nausea/vomiting, and/or gross hematuria. However, 15 to 20 percent of children are asymptomatic and are diagnosed because of stone detection when abdominal imaging is performed for other purposes. (See 'Clinical presentation' above.)

•Pain – Abdominal or flank pain as a presenting symptom varies in intensity from a mild ache to severe debilitating pain. Pain is a common feature in adolescents and school-aged children with nephrolithiasis, but is only present in approximately half of the children below six years of age.

•Young children – Urinary tract infection and/or an incidental finding of a stone on imaging are the presenting findings in almost half of the children below six years of age. (See 'Clinical presentation' above.)

●Initial evaluation – The initial evaluation of a child with suspected nephrolithiasis includes the following:

•History focusing on underlying risk factors for stone formation (eg, family history, renal and urinary tract structural abnormalities, metabolic disorders, or recurrent urinary tract infection). (See "Kidney stones in children: Epidemiology and risk factors".)

•Physical examination that includes measurement of blood pressure and growth parameters, and abdominal examination for signs of urinary obstruction or another cause of abdominal pain.

•Laboratory tests, including urinalysis, urine culture, and measurement of serum creatinine. (See 'Initial evaluation' above.)

●Diagnosis – The diagnosis of nephrolithiasis is made by the detection of a renal stone by imaging studies or retrieval of a passed stone.

●Imaging – We recommend abdominal imaging for any child suspected to have nephrolithiasis. In most patients, we recommend ultrasound as the first line of imaging.

•Ultrasonography – Ultrasonography detects radiolucent stones and urinary obstruction and remains the overall imaging choice for when radiation should be avoided, such as in pregnant adolescents. (See 'Imaging' above.)

•Computed tomography (CT) – CT does provide the greatest sensitivity of the available imaging modalities, but consideration of radiation exposure is important. If CT is needed, it is important that radiation doses be adjusted to the size and weight of the child to reduce radiation exposure.