✅ Model Answer:
• Radiopaque density overlying the renal shadow (left kidney).
• Oval or round shape with well-defined margins.
• Located within the renal pelvis or calyx (overlaps psoas shadow).
• Appears ~6-8 mm in size.
• No contrast needed – stone is visible on plain film.
• Diagnosis: Renal calculus (nephrolithiasis) – likely calcium oxalate stone.

✅ Model Answer:
• Calcium oxalate (60-90% of pediatric stones) – radiopaque.
• Calcium phosphate – radiopaque (often associated with alkaline urine, RTA).
• Struvite (magnesium ammonium phosphate) – radiopaque (infection stones, Proteus).
• Cystine – faintly radiopaque (hexagonal crystals, family history).
• Uric acid – radiolucent (not visible on KUB; associated with acidic urine, gout).
• Xanthine – radiolucent (rare).
• Indinavir – radiolucent (drug-induced).
• Key: Most radiopaque stones are calcium-based or struvite; uric acid stones are radiolucent.

✅ Model Answer:
• Renal colic – sudden onset severe flank pain radiating to the groin (loin-to-groin).
• Nausea and vomiting – due to autonomic stimulation.
• Gross or microscopic hematuria – due to mucosal irritation.
• Dysuria, urgency, frequency – if stone is in the distal ureter.
• Fever and chills – if associated with infection (pyelonephritis).
• Abdominal pain – may be the only symptom in younger children.
• Failure to thrive – in chronic cases with recurrent stones.

✅ Model Answer:
• Ultrasound (USG) of the kidney and bladder – first-line imaging.
• Reasons:
- No ionizing radiation (particularly important in children).
- Can detect hydronephrosis, renal stones (≥3 mm), and ureteral dilation.
- Can assess for complications (pyonephrosis, abscess).
- Limited sensitivity for small stones and ureteral stones.
• Gold standard: Low-dose non-contrast CT (for definitive diagnosis, especially if USG is negative and clinical suspicion is high).

✅ Model Answer:
• KUB (Kidney, Ureter, Bladder) radiograph is a plain abdominal X-ray.
• Role:
- Detects radiopaque stones (calcium oxalate, calcium phosphate, struvite).
- Useful for follow-up – to monitor stone size and position.
- Can be used to assess stone radiopacity (helps predict composition).
- Limited: Cannot detect radiolucent stones (uric acid, xanthine).
- May miss small stones (<3 mm) or stones obscured by bowel gas.
• Recommendation: KUB is often performed as an initial screening test, especially if a radiopaque stone is suspected.

✅ Model Answer:
• Pain management:
- NSAIDs (ibuprofen, ketorolac) – first-line for renal colic.
- Opioids (morphine, fentanyl) – for severe pain if NSAIDs are contraindicated.
- Antiemetics (ondansetron) – for nausea and vomiting.
• Hydration: IV fluids if the child is vomiting or unable to tolerate oral intake.
• Medical expulsive therapy (MET):
- Tamsulosin (0.4 mg/day) – for distal ureteral stones <5 mm.
- Nifedipine (alternative) – less commonly used.
• Strain urine: To collect the stone for analysis.
• Antibiotics: If there is evidence of infection (fever, pyuria).
• Surgical intervention: Ureteroscopy, ESWL, or PCNL if stone >10 mm or failed MET.

✅ Model Answer:
• MET uses medications to facilitate spontaneous passage of ureteral stones.
• Indications: Distal ureteral stones <5 mm in diameter.
• Medications:
- Tamsulosin (α-blocker) – relaxes ureteral smooth muscle, reduces peristalsis.
- Nifedipine (calcium channel blocker) – alternative.
• Benefits: Reduces time to stone passage, decreases need for surgical intervention.
• Duration: Usually 2-4 weeks with follow-up imaging.
• Contraindications: Hypotension, renal impairment.

✅ Model Answer:
• Most common: Calcium oxalate stones (60-90% of pediatric stones).
• Risk factors:
- Low fluid intake (most important).
- High dietary oxalate (spinach, nuts, chocolate, tea).
- High dietary sodium (increases calcium excretion).
- Hypercalciuria (idiopathic or genetic).
- Hyperoxaluria (primary or enteric).
- Hypocitraturia (decreased stone inhibitors).
- Urinary tract infections (struvite stones).
- Anatomic abnormalities (UPJ obstruction, horseshoe kidney).
- Family history of nephrolithiasis.

✅ Model Answer:
• Staghorn calculus: A large stone that fills the renal pelvis and extends into the calyces (branched, "deer antler" shape).
• Composition: Usually struvite (infection stone) – associated with urease-producing bacteria (Proteus, Klebsiella, Pseudomonas).
• Significance:
- Can cause chronic pyelonephritis, renal damage, and renal failure.
- Often requires surgical intervention (PCNL) for complete removal.
- Risk of urosepsis.
• Management: Treat underlying infection, complete stone removal (PCNL ± ESWL).

✅ Model Answer:
• This is a distal ureteral stone <5 mm with mild hydronephrosis.
• Management:
1. Medical expulsive therapy (MET): Tamsulosin 0.4 mg/day.
2. Pain management: NSAIDs (ibuprofen) as needed.
3. Hydration: Encourage oral fluids (2-3 L/day).
4. Strain urine: Collect stone for analysis.
5. Follow-up imaging: KUB or ultrasound in 2-4 weeks to confirm stone passage.
6. If stone does not pass: Consider ureteroscopy or ESWL.
• Note: Stones <5 mm have a 90% chance of spontaneous passage with MET.

✅ Model Answer:
• Extracorporeal shock wave lithotripsy (ESWL):
- Non-invasive, uses shock waves to fragment stones.
- Indicated for stones <20 mm in the renal pelvis or upper ureter.
- Contraindicated in pregnancy, coagulopathy, or urinary obstruction.
• Ureteroscopy (URS) with laser lithotripsy:
- Indicated for ureteral stones or small renal stones.
- High success rate, minimal invasiveness.
• Percutaneous nephrolithotomy (PCNL):
- For large (>20 mm), complex, or staghorn stones.
- Minimally invasive with a nephroscope through a small incision.
• Open surgery: Rarely performed now (reserved for failed endoscopic procedures).

✅ Model Answer:
• Metabolic evaluation (24-hour urine collection):
- Volume, calcium, oxalate, citrate, uric acid, creatinine, pH.
- Serum calcium, phosphorus, PTH, vitamin D, electrolytes.
• Medical management for hypercalciuria:
1. Increase fluid intake: Target urine output >1.5 L/m²/day.
2. Dietary modifications: Reduce sodium, moderate calcium (not restriction), reduce oxalate.
3. Thiazide diuretics: Hydrochlorothiazide 1-2 mg/kg/day – reduces urinary calcium excretion.
4. Potassium citrate: Increases citrate, binds calcium, inhibits stone formation.
5. Citrate supplementation: For hypocitraturia.