Urolitiasis (Batu Saluran Kemih)

01Pathophysiology

Urolithiasis develops when urinary solutes exceed their solubility threshold, leading to supersaturation, crystallization, and aggregation into stones. The balance between promoters (calcium, oxalate, phosphate, uric acid, sodium) and inhibitors (citrate, magnesium) of crystallization governs stone formation. Low urine volume is the single most important modifiable risk factor across all stone types because it concentrates every solute simultaneously.

The colicky pain pattern reflects ureteral obstruction. As a stone migrates down the ureter, peristaltic contractions intensify against the obstruction, triggering wave-like pain that radiates along dermatomes T10 to L1. The pain pattern follows the stone's location: a stone at the ureteropelvic junction causes flank pain, mid-ureteral stones radiate to the lower abdomen and lateral flank, and ureterovesical junction (UVJ) stones cause groin/genital pain plus urinary urgency, frequency, and dysuria from bladder irritation. The three anatomic narrowings (UPJ, where the ureter crosses the iliac vessels, and UVJ) are the most common sites of impaction.

The classic restless presentation distinguishes renal colic from peritonitis. In peritonitis the patient lies perfectly still because movement worsens parietal peritoneal irritation, whereas a patient with renal colic paces, writhes, and shifts position trying to find relief. This single behavioral observation is a high-yield exam clue.

Stone composition reflects underlying metabolic or environmental drivers. Calcium oxalate stones form in normal to acidic urine and dominate overall epidemiology. Calcium phosphate stones favor alkaline urine and are linked to distal (type 1) renal tubular acidosis and primary hyperparathyroidism. Uric acid stones precipitate in acidic urine (pH less than 5.5), classically in patients with gout, tumor lysis syndrome, chronic diarrhea, and metabolic syndrome. Struvite (magnesium ammonium phosphate) stones form in alkaline urine generated by urease-producing organisms (Proteus mirabilis, Klebsiella, Staphylococcus saprophyticus, Pseudomonas), and these bacteria split urea into ammonia, raising pH and precipitating magnesium ammonium phosphate. Struvite stones grow rapidly into staghorn configurations filling the renal pelvis and calyces. Cystine stones occur in autosomal recessive cystinuria from defective tubular reabsorption of dibasic amino acids (cystine, ornithine, lysine, arginine; mnemonic COLA).

Hematuria results from mucosal abrasion as the stone traverses the urothelium. Its absence does not exclude stones because complete obstruction can prevent blood from reaching the bladder.

02Classification

BASED ON LOCATION

BASED ON STONE TYPE

03Diagnostic Workup

The diagnostic sequence begins with urinalysis and a focused history. A patient with sudden colicky flank pain radiating to the groin, hematuria, and a restless presentation is highly suggestive of urolithiasis. Pregnancy must be excluded in women of reproductive age before imaging.

The best initial imaging test depends on the patient. In nonpregnant adults, noncontrast helical CT of the abdomen and pelvis is both the initial test of choice and the gold standard because it detects stones of all compositions (including radiolucent uric acid stones), measures size, identifies location, and reveals secondary signs such as hydronephrosis, perinephric stranding, and "tissue rim sign" around the stone. CT also evaluates alternative diagnoses (appendicitis, diverticulitis, abdominal aortic aneurysm).

In pregnant patients and children, ultrasound is the preferred initial study to avoid ionizing radiation. Ultrasound shows hydronephrosis and large stones at the UPJ or UVJ but has lower sensitivity for small mid-ureteral stones. If ultrasound is nondiagnostic in pregnancy and clinical suspicion remains high, MR urography is the next step.

KUB plain radiography has limited use because it misses radiolucent uric acid and indinavir stones and small stones overall. It is useful for following known radiopaque stones over time.

Urinalysis findings give compositional clues.

• Alkaline urine (pH greater than 7) with positive nitrites and leukocyte esterase points to a struvite stone with infection.

• Acidic urine (pH less than 5.5) without infection suggests uric acid

• Hexagonal crystals are pathognomonic for cystine, and a positive sodium nitroprusside (cyanide-nitroprusside) test confirms cystinuria

• Envelope-shaped (calcium oxalate dihydrate) or dumbbell-shaped (monohydrate) crystals point to calcium oxalate.

Indications for hospital admission and urgent urologic consultation include obstructing stone with fever or pyuria (urosepsis risk), acute kidney injury, intractable pain or vomiting, solitary or transplanted kidney, bilateral obstruction, and stones larger than 10 mm. Obstruction plus infection is a urologic emergency requiring immediate decompression.

For recurrent stone formers, a 24-hour urine collection (typically two collections off therapy) measures volume, calcium, oxalate, citrate, uric acid, sodium, potassium, magnesium, phosphate, creatinine, and pH. Combined with stone analysis, this guides targeted prevention.

04Management & Treatment

Acute Stabilization

The first priority in acute renal colic is pain control with NSAIDs, which work by reducing prostaglandin-mediated ureteral spasm and inflammation around the stone. Ketorolac 30 mg IV or IM is standard. NSAIDs outperform opioids for renal colic pain in head-to-head trials and avoid respiratory depression and nausea. Opioids remain useful adjuncts or alternatives when NSAIDs are contraindicated (renal failure, active GI bleed, third-trimester pregnancy). IV fluids restore euvolemia in vomiting patients but forced diuresis does not accelerate stone passage and may worsen pain. Antiemetics treat associated nausea.

The next best step in management logic after analgesia is risk stratification. Determine size, location, and presence of complications. Stones smaller than 5 mm in the distal ureter pass spontaneously in about 90% of cases, so outpatient management with oral analgesics, hydration, and urine straining (to capture the stone for analysis) is appropriate. Stones 5 to 10 mm benefit from medical expulsive therapy with tamsulosin 0.4 mg orally once daily, an alpha-1 blocker that relaxes ureteral smooth muscle and improves passage rates, particularly for distal ureteral stones. Treat for up to 4 weeks; if the stone has not passed, refer for urologic intervention.

Indications for Urgent Intervention

Refer for emergent urologic decompression in any of the following: urosepsis with obstructing stone, acute kidney injury, intractable pain or vomiting, solitary or transplanted kidney with obstruction, bilateral obstruction, or complete obstruction lasting more than a few days. Obstructed pyonephrosis is a true emergency: place a ureteral stent or percutaneous nephrostomy tube to decompress, start broad-spectrum IV antibiotics (such as piperacillin-tazobactam or a third-generation cephalosporin plus an aminoglycoside), and defer definitive stone removal until infection clears.

Definitive Stone Removal

Procedure choice depends on stone size, location, and composition:

Shock wave lithotripsy (SWL) uses focused acoustic waves to fragment stones for spontaneous passage. It is ideal for stones smaller than 2 cm in the kidney or proximal ureter. Contraindications include pregnancy, uncorrected coagulopathy, abdominal aortic aneurysm, and obstruction distal to the stone. SWL is less effective for hard stones (cystine, calcium oxalate monohydrate, brushite) and obese patients.

Ureteroscopy with holmium laser lithotripsy allows direct stone visualization and fragmentation. It has the highest success rate for distal ureteral stones and is the preferred procedure during pregnancy because it avoids ionizing radiation and shock waves.

Percutaneous nephrolithotomy (PCNL) is the procedure of choice for stones larger than 2 cm, staghorn calculi, and complex lower-pole stones. Access is gained through a flank puncture into the renal collecting system.

Long-Term Prevention by Stone Type

Universal advice for all stone formers: fluid intake to produce at least 2.5 liters of urine per day, reduce dietary sodium (less than 2,300 mg/day), maintain normal calcium intake (1,000 to 1,200 mg/day; calcium restriction worsens calcium oxalate stones by increasing oxalate absorption), and limit animal protein.

Contraindications and Special Populations

In pregnancy, NSAIDs are contraindicated in the third trimester (premature ductus arteriosus closure) and best avoided throughout. Use acetaminophen and opioids for pain. Imaging starts with ultrasound. Tamsulosin is generally avoided. Ureteroscopy is the preferred intervention if needed.

In chronic kidney disease and elderly patients, NSAIDs can precipitate acute kidney injury and should be used with caution or avoided. Adjust opioid dosing.

05Differential Diagnosis & Distractors

06Traps & High-Yield Pearls

The classic exam trap in urolithiasis is failing to recognize "renal colic" as a ruptured abdominal aortic aneurysm in an older man. Any patient over 60, especially with hypertension or known vascular disease, presenting with new "first-time kidney stone" and flank or back pain should prompt immediate consideration of ruptured AAA. Test writers love this scenario because the cognitive shortcut to "stone" can kill the patient. Always check the abdomen for a pulsatile mass and pay attention to age and hemodynamics.

A second high-yield trap is missing obstruction with infection. A febrile patient with an obstructing stone has urosepsis until proven otherwise. The correct next step is urgent decompression (stent or percutaneous nephrostomy) plus IV antibiotics, not definitive stone removal. Choosing "ureteroscopy with stone extraction" instead of "decompression" is a classic distractor.

A third pitfall is counseling calcium restriction for calcium oxalate stones. Restricting dietary calcium increases free intestinal oxalate, raising urinary oxalate and worsening stone formation. The correct advice is normal calcium intake with reduced sodium and oxalate.

Other high-yield pearls:

The restless patient distinguishes renal colic from peritonitis. If the vignette says the patient is "writhing" or "cannot get comfortable," think stone; if the patient "lies perfectly still," think peritonitis.

Pregnancy changes imaging: ultrasound first, MRI if needed, avoid CT.

Tamsulosin works best for distal ureteral stones 5 to 10 mm; not indicated for stones smaller than 5 mm (which usually pass on their own) or larger than 10 mm (which usually need intervention).

Stone composition clues from urine pH: alkaline points to struvite or calcium phosphate; acidic points to uric acid or cystine. Crystal shapes are buzzwords: hexagonal equals cystine, coffin-lid equals struvite, envelope or dumbbell equals calcium oxalate, rhomboid equals uric acid.

Staghorn calculi are struvite until proven otherwise, and complete surgical removal is required because residual fragments harbor bacteria and cause recurrent infection. Treat the infection but understand that antibiotics alone will not clear the stone.

Uric acid stones are radiolucent on KUB but visible on noncontrast CT. Treatment with urinary alkalinization (potassium citrate) can dissolve them, the only stone type that can be medically dissolved without surgery.

Cystinuria presents in childhood or young adulthood with recurrent stones, autosomal recessive inheritance, and hexagonal crystals. The sodium nitroprusside (cyanide-nitroprusside) test is the screening test.

The core competencies tested in urolithiasis questions are: recognizing the classic vignette, sequencing imaging correctly (CT in adults, ultrasound in pregnancy), choosing the right initial pharmacologic management (NSAIDs, then tamsulosin for eligible stones), identifying emergencies (obstruction with infection, ruptured AAA mimic), and matching stone type to urine pH, crystal shape, and prevention strategy.