Aaron G. Boonjindasup, MD, MPH
Raju Thomas, MD, MHA, FACS
BASICS
DESCRIPTION
• Renal urolithiasis refers to kidney stones within the kidney itself (parenchyma, calyces or renal pelvis. The majority of stones inthe urinary tract have their origin in the kidney.
• Renal urolithiasis is a significant cause of patient renal morbidity and a major source of medical costs in the UnitedStates.
• Calcium oxalate stones most common; also uric acid, struvite (magnesium ammonium phosphate), calcium phosphate, cystine, etc.
EPIDEMIOLOGY
Incidence
• Estimated to be 10–15% in the United States
• Males are affected 2–3× more than females
• Peak incidence: 4th–6th decades
• More common in Southeast, Southwest, and Northwest United States.
• Increasing incidence with increased obesity
• Accounts for 7–10 of every 1000 hospital visits
Prevalence
Highest prevalence in Caucasians
RISK FACTORS
• Calcium stone formation
– Dietary excess
– Hyperparathyroidism
– inappropriate loss of calcium in urine through renal tubules
– Excessive intestinal absorption
– Inadequate levels of stone inhibitors in urine
– Sarcoidosis
– Multiple myeloma
– Leukemia
• Uric acid stone formation
– Purine excess
– Gout
– Myeloproliferative disorders
– Chronic dehydration
– Lesch–Nyhan syndrome
– Ingestion of uricosuric drugs
• Struvite stones
– UTI with urease-splitting organisms (Proteus, Klebsiella, etc.)
Alkalinizes urine and magnesium ammonium phosphate crystallization
• Cystine stones
– Inherited disorder of renal tubular reabsorption of cysteine (See Urolithiasis, Cystine)
Genetics
• In general, urolithiasis associated with polygenic defect and partial penetrance
– Cystinuria: Homozygous recessive
• Renal tubular acidosis (RTA): Inherited
PATHOPHYSIOLOGY
• Supersaturation: Urine oversaturated with certain types of crystal, which then is precipitated out of solution.
– Saturation level is variably pH dependent based on crystal type
• Inhibitor deficiency: Inhibitors may limit crystal growth and aggregation
– Urinary citrate and magnesium are inhibitors
• Non-infection stones: Calcium oxalate, calcium phosphate (brushite, carbonate apatite), uric acid
• Infection stones: Magnesium ammonium phosphate (struvite), carbonate apatite, ammonium urate
• Genetic defects: Cystine, xanthine, 2,8-dihydroxyadenine (DHA)
• Drug stones: Indivavir, triamterene, others
ASSOCIATED CONDITIONS
• Congenital malformations or anatomic variations of kidney, collecting system, ureter, or bladder may predispose patient to urolithiasis due to stasis and/or impaired urine drainage
• Crohn disease
• Dehydration
• Gout
• Inflammatory bowel disease
• Intestinal bypass
• Medullary sponge kidney
• Renal tubular acidosis
GENERAL PREVENTION
• Decreased sodium intake
• Diuretics
• Encourage fluid intake; avoid dehydration
• Increase urinary citrate
• Reduce dietary protein (purine) if at-risk
• Restrict oxalate consumption
DIAGNOSIS
HISTORY
• Acute onset of severe pain
– Partially obstructive stones have more chronic, mild to moderate pain
– Pain radiates to groin or lower abdomen
• Gross hematuria
• Previous history of kidney stones or UTIs
• Family history of urolithiasis
• Changes in urination patterns
PHYSICAL EXAM
• CVA tenderness
– Moderate, deep tenderness in flank radiating to groin
– Great tenderness suggests pyelonephritis
• Fever present if associated infection
DIAGNOSTIC TESTS & INTERPRETATION
Lab
• Urinalysis
– Microscopic hematuria
Unless complete obstruction
Crystalluria may provide important information regarding the type of calculus.
– Pyuria
May suggest concomitant UTI
• Urine gram-stain and culture
– Authors opinion: Catheterized urine specimen should be collected for urinalysis, gram-stain, and culture in all female patients under consideration for surgical intervention
• CBC
– Leukocytosis: Suggests secondary infection
• Basic metabolic profile
– Elevated creatinine
May be present if bilateral obstruction present
– Calcium level
– Glucose: Impaired glycemic control in patients with diabetes especially in setting of infection
Imaging
• Non-contrast low-dose helical computed tomography (CT)
– Rapid study
– 1st-line test with acute renal colic
– Can determine degree of hydronephrosis, size, and location of stones
• Intravenous pyelogram (IVP)
– Requires IV contrast
– Delayed x-rays needed if high-grade obstruction present
– Some stones radiolucent—not visible on IVP
– Can provide some assessment of renal function
• Ultrasound
– Non-invasive, 1st-line evaluation for in patients at risk for X-ray exposure
Children, pregnant females
Operator-dependent
– Difficult to visualize ureter in adult
Resistive index (>0.7) suggestive of obstruction in the setting of acute obstruction
Ureteral Jets—Presence does not rule out partial obstruction
Diagnostic Procedures/Surgery
• Retrograde pyelography
– Invasive
– Can assist concomitant surgical management
Pathologic Findings
• Hydronephrosis
– Note degree and anatomic location of obstruction
– Perinephric stranding on CT
DIFFERENTIAL DIAGNOSIS
• Abdominal aortic aneurysm
• Appendicitis
• Bowel obstruction
• Gastritis, pancreatitis, peptic ulcer
• Mesenteric ischemia
• Musculoskelet al back pain
• Pyelonephritis, urinary tract infection
• Cholecystitis or biliary colic
• UPJ obstruction
• Sloughed renal papilla
TREATMENT
ALERT
The presence of pyuria, fever, leukocytosis, or bacteriuria suggests the possibility of a urinary infection and the potential for an infected obstructed renal unit or pyonephrosis. Such a condition is potentially life-threatening and should be treated as a surgical emergency.
GENERAL MEASURES
• Hydration and adequate pain control
• Patients with likelihood of spontaneously passing a stone (<4–5 mm in size) in the absence of indication for surgical intervention may be sent home with analgesics and a trial of medical expulsive therapy (MET); (hydration, analgesia, symptomatic relief)
– Should be instructed to return if pain worsens, or severe vomiting or fever
– Likelihood of spontaneous stone passage is related to location and size of stone
– Stones 2–3 mm: 80% probability of passing
– Stones 4–5 mm: 50% probability of passing
– Stones 7–8 mm: 20% probability of passing
– Stones >1 cm: unlikely to pass spontaneously
• Controversy exists regarding maximum period of observation for partially obstructing stone without development of significant irreversible renal dysfunction; generally, within 4–6 wk.
• Indications for intervention:
– Fever and/or infection
– Intractable pain
– Unable to tolerate oral fluid and at risk for dehydration
– Progressive renal deterioration; obstruction of solitary functioning kidney
• All urinary tract infections should be treated with culture-sensitive antibiotics prior to surgical treatment
MEDICATION
First Line (1,2)
• Patients with evidence of active UTI should be treated with broad-spectrum antibiotics (eg, ampicillin and gentamicin, 3rd-generation cephalosporin).
• Antiemetic if acute colic is associated with nausea and vomiting.
• Medical expulsive therapy (MET):
– α-Blockers (ie, terazosin, tamsulosin) or calcium-channel blockers (eg, nifedipine) can relax musculature of the ureter and lower urinary tract and can reduce pain associated with stone passage (tamsulosin 0.4 mg PO QD).
• Uric acid stones and cystine stones can be dissolved with medical therapy; calcium stones and struvite stones cannot be dissolved:
• Uric acid stones: Alkalinize urine with potassium citrate or bicarbonate, to maintain urinary pH between 6.5 and 7.0:
– Urinary pH >7.5 can precipitate calcium phosphate with resulting stone formation.
– May dissolve up to 1 cm per month
• Cystine stones: see Urolithiasis, Cystine
Second Line
N/A
SURGERY/OTHER PROCEDURES (3)
• Primary goal is to achieve maximal stone clearance with minimal morbidity.
• Patients with active UTI/sepsis: Obstructed kidney is drained by placement of ureteral stent or percutaneous nephrostomy tube.
• Preoperative urine culture should document no infection before stone removal:
• Calculi in kidney: Ureteroscopy vs. ESWL with or without stent placement (>1 cm)
• >2 cm: Percutaneous nephrolithotomy or if >1.5 cm in lower pole.
• Shock-wave lithotripsy (SWL)
– Intrarenal calculus <2 cm
– Relative contraindications
Stone > 2 cm
Within dependent or obstructed portions of collecting system
Body habitus/obesity that inhibits imaging and targeting of the stone
Lower pole stone
Uncorrected coagulopathy or recent anticoagulant use
• Ureteroscopy
– Used for lower pole stones or stones resistant to SWL
– Effective for treatment of cystine, calcium oxalate monohydrate, and brushite stones
• Percutaneous nephrolithotomy (PCNL)
– Stones >2 cm; no bleeding diathesis or obesity
– Staghorn calculi
• Laparoscopic and robotic stone surgery for large non-branching calculi
• “Sandwich technique”
– SWL in combination with other modality
ADDITIONAL TREATMENT
Radiation Therapy
N/A
Additional Therapies
NA
Complementary & Alternative Therapies
NA
ONGOING CARE
PROGNOSIS
• The most important measure to avoid future stone episodes is increased fluid intake.
• Once patient has initial incident, 50% chance that in 5 yr will have recurrent calculus.
• Produce >2 L of urine/day
• 24-hr urine collection for metabolic analysis
• Stone fragment chemical analysis should be performed when possible
• Metabolic workup after 2nd episode
COMPLICATIONS
• Pyelonephritis
• Renal deterioration
• renal abscess formation
• Surgery carries standard risks of bleeding, infection, ureteral stricture.
• Pneumothorax with nephrostomy access
FOLLOW-UP
Patient Monitoring
• Oral hydration to make 2–2.5 L of urine/day
• Diet low in protein and sodium intake
• Dietary modification and medical intervention tailored to underlying metabolic abnormality can prevent recurrence of stones in 75% patients and significantly reduce new stone formation in up to 98% of patients.
• Restriction of oxalate-rich foods such as chocolate, nuts, soybeans, rhubarb, spinach, sweet potatoes, beets.
• Maintenance of adequate intake of dietary calcium
Patient Resources
Urology care foundation: http://www.urologyhealth.org/urology/index.cfm?article=148
REFERENCES
1. Fink HA, Wilt TJ, Eidman KE, et al. Medical management to prevent recurrent nephrolithiasis in adults: Asystematic review for an American College of Physicians Clinical Guideline. Ann InternMed. 2013;158:535.
2. Sarkissian C, Noble M, Li J, et al. Decision making for asymptomatic renal calculi: Balancing benefit and risk. Urology. 2013;81:236.
3. Bandi G, Best SL, Nakada SY. Current practice patterns in the management of upper urinary tract calculi in the north central US. J Endourol. 2008;22(4):631–636.
ADDITIONAL READING
EAU Guidelines on Urolithiasis. http://www.uroweb.org/gls/pdf/21_Urolithiasis_LR.pdf
See Also (Topic, Algorithm, Media)
• Metabolic Stone Evaluation (24 Hour Urine Studies)
• Ureter, Stone Passage Statistics
• Urolithiasis, Adult, General
• Urolithiasis, Calcium Oxalate/Phosphate
• Urolithiasis, Cystine and Cystinuria (Hypercystinuria)
• Urolithiasis Image 
• Urolithiasis, Pediatric, General
• Urolithiasis, Staghorn
• Urolithiasis, Ureteral Calculi Algorithm
• Urolithiasis, Uric Acid
CODES
ICD9
• 274.11 Uric acid nephrolithiasis
• 275.49 Other disorders of calcium metabolism
• 592.0 Calculus of kidney
ICD10
• E79.8 Other disorders of purine and pyrimidine metabolism
• E83.52 Hypercalcemia
• N20.0 Calculus of kidney
CLINICAL/SURGICAL PEARLS
Renal stones >1 cm are unlikely to pass spontaneously.