✅ Model Answer:
• Diagnosis: Nutcracker syndrome (left renal vein compression).
• Evidence: Thin adolescent, left flank pain, gross hematuria, orthostatic proteinuria, Doppler ultrasound showing left renal vein compression between the aorta and superior mesenteric artery (SMA).
• Next step: Conservative management – weight gain (increase BMI), hydration, avoid exercise. If severe hematuria/pain, consider surgical intervention (LRV transposition, renal autotransplantation, or stenting).

✅ Model Answer:
• Definition: Compression of the left renal vein (LRV) between the abdominal aorta (posteriorly) and the superior mesenteric artery (SMA) anteriorly.
• Mechanism: The SMA and aorta form a "nutcracker" that compresses the LRV → increased LRV pressure → venous congestion → rupture of thin-walled veins in the renal pelvis → hematuria.
• Risk factors: Thin body habitus (low BMI), rapid growth spurt, scoliosis, lordosis.
• Clinical significance: Most common cause of hematuria in adolescents (especially thin girls).
• Other causes: Retroaortic left renal vein, pelvic congestion syndrome (in females).

✅ Model Answer:
• Classic features:
- Gross hematuria: Intermittent, often after exercise or upright position.
- Left flank pain: Dull, aching pain (may radiate to the groin).
- Orthostatic proteinuria: Proteinuria that increases in the upright position.
- Pelvic congestion: In females – pelvic pain, dysmenorrhea, varicose veins.
- Fatigue, dizziness.
• Age: Most common in adolescents and young adults (thin body habitus).
• Gender: More common in females (due to lower BMI).
• Symptoms worse with: Exercise, upright posture, and dehydration.

✅ Model Answer:
• Imaging:
- Doppler ultrasound: First-line – shows LRV compression (peak velocity ratio >4.0 between the compressed and non-compressed segments).
- CT angiography: Shows the "nutcracker" anatomy (SMA angle <41°, LRV compression).
- Magnetic resonance venography (MRV): Alternative to CT.
- Intravenous pyelography (IVP): May show notching of the ureter (not specific).
• Laboratory:
- Urinalysis: Gross or microscopic hematuria, trace proteinuria.
- Orthostatic proteinuria: Check first morning urine vs. upright urine.
- Serum creatinine: Normal.
- Calcium studies: To rule out hypercalciuria (Ca:Cr >0.2).
• Endoscopy: Cystoscopy – may show blood coming from the left ureteral orifice (unilateral hematuria).

✅ Model Answer:
• Conservative management (first-line):
- Weight gain: Increase BMI (improves retroperitoneal fat, reduces compression).
- Hydration: Maintain adequate fluid intake.
- Avoid: Prolonged standing, exercise that worsens symptoms.
- No specific medication: Avoid NSAIDs (may worsen renal function).
• Interventional/Surgical (if severe symptoms):
- Left renal vein transposition: Surgical repositioning of the LRV.
- Renal autotransplantation: Rarely used.
- Endovascular stenting: Placement of a stent in the LRV (minimally invasive).
- Nephropexy: Not commonly performed.
• Indications for intervention: Severe pain, debilitating hematuria, renal vein thrombosis, or failure of conservative therapy.

✅ Model Answer:
• Renal:
- Persistent gross hematuria: Can cause anemia (chronic blood loss).
- Renal vein thrombosis: Rare, but possible.
- Proteinuria: Usually mild (orthostatic).
- Hypertension: Rare (if renal ischemia occurs).
• Other:
- Chronic pain: Left flank pain may be debilitating.
- Pelvic congestion syndrome: In females – pelvic pain, dysmenorrhea, varicose veins.
- Gonadal vein reflux: Varicoceles in males.
- Psychosocial impact: Due to chronic symptoms and school absences.
• Outcome: Most patients improve with conservative management (weight gain).

✅ Model Answer:
• Prognosis:
- Excellent with conservative management (weight gain).
- Spontaneous resolution: Most patients improve as they gain weight (increase retroperitoneal fat).
- Recurrence: Uncommon if BMI normalizes.
- Renal function: Usually remains normal.
- Surgical outcome: Good if needed (LRV transposition, stenting).
• Long-term follow-up:
- Monitor BMI: Encourage weight gain (goal BMI >18.5).
- Monitor hematuria: Urinalysis every 3-6 months until resolved.
- Monitor BP: Annually.
- Monitor proteinuria: Spot urine protein/creatinine ratio annually (if persistent).
- Patient education: Hydration, avoid prolonged standing, and recognize worsening symptoms.

✅ Model Answer:
• Nutcracker syndrome:
- Cause: Left renal vein compression (aorta-SMA).
- Clinical: Left flank pain, gross hematuria, orthostatic proteinuria, thin body habitus.
- Urine calcium: Normal (Ca:Cr <0.2).
- Doppler ultrasound: Shows LRV compression.
- Treatment: Weight gain, conservative; surgery if severe.
- Prognosis: Usually resolves with weight gain.
• Idiopathic hypercalciuria:
- Cause: Excessive urinary calcium excretion (normal serum calcium).
- Clinical: Hematuria, dysuria, abdominal pain, nephrolithiasis.
- Urine calcium: Elevated (Ca:Cr >0.2).
- Doppler ultrasound: Normal.
- Treatment: Hydration, low sodium diet, thiazide if refractory.
- Prognosis: Good with treatment; risk of nephrolithiasis.