Renal · Nephrolithiasis
The facts most likely to be tested
Non-contrast helical CT of the abdomen and pelvis is the gold standard diagnostic modality for suspected nephrolithiasis.
Calcium oxalate stones are the most common type and appear as envelope-shaped crystals on urinalysis.
Struvite stones (magnesium ammonium phosphate) are associated with urease-producing organisms like Proteus and form staghorn calculi.
Uric acid stones are radiolucent on plain film radiography and are associated with gout or high cell turnover states.
Cystine stones are caused by a genetic defect in renal transport of dibasic amino acids and appear as hexagonal crystals.
Medical expulsive therapy using alpha-1 blockers like tamsulosin facilitates the passage of stones between 5 mm and 10 mm.
Urgent urologic consultation is mandatory for patients presenting with a stone accompanied by fever, signs of sepsis, or acute kidney injury.
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A 34-year-old male presents to the emergency department with sudden onset of severe, colicky left-sided flank pain radiating to the groin. He is restless, pacing the room, and appears in significant distress. Physical examination reveals tenderness to percussion at the costovertebral angle. Urinalysis demonstrates microscopic hematuria but is negative for nitrites and leukocyte esterase. The patient has no history of fever or chills.
What is the most appropriate initial diagnostic imaging study to confirm the diagnosis?
Non-contrast helical CT of the abdomen and pelvis
The patient's presentation of flank pain radiating to the groin with hematuria is classic for nephrolithiasis, and non-contrast CT is the gold standard for diagnosis as it is highly sensitive and specific for detecting stones.
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High yield triage
Etiology / Epidemiology
Most common is calcium oxalate; risk factors include low fluid intake and hyperparathyroidism.
Clinical Manifestations
Presents with renal colic: sudden-onset, severe flank pain radiating to the groin.
Diagnosis
Non-contrast CT abdomen/pelvis is the gold standard; hematuria is present in 85% of cases.
Treatment
Stones <5mm pass spontaneously; tamsulosin is first-line medical expulsive therapy.
Prognosis
Recurrence is common; 24-hour urine collection is required for metabolic workup.
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Epidemiology & Etiology
Stones are most common in males aged 30-50. Calcium oxalate accounts for 80% of cases, often linked to hypercalciuria or hypocitraturia. Uric acid stones are associated with high protein intake and gout.
Pertinent Anatomy
Stones typically lodge at the ureterovesical junction (UVJ), the narrowest point of the ureter. Obstruction here causes hydronephrosis and intense renal colic due to ureteral distension.
Pathophysiology
Supersaturation of urine leads to crystal nucleation and stone growth. Struvite stones are associated with Proteus or Klebsiella infections, forming staghorn calculi that act as a nidus for persistent infection.
Clinical Manifestations
Patients exhibit writhing behavior, unable to find a comfortable position. Flank pain radiating to the groin is classic. Fever with obstruction is a urologic emergency requiring immediate decompression.
Diagnosis
Non-contrast CT abdomen/pelvis is the diagnostic test of choice. Urinalysis typically shows microscopic hematuria. Ultrasound is preferred in pregnancy to avoid radiation.
Treatment
Initial management includes aggressive hydration and NSAIDs (e.g., ketorolac) for pain. Tamsulosin facilitates stone passage for distal stones. Surgical intervention (stent or nephrostomy) is indicated for infection, intractable pain, or renal failure.
Prognosis
Most stones <5mm pass within 4 weeks. Recurrence is high, necessitating dietary changes like increased fluid intake and reduced sodium. 24-hour urine collection identifies metabolic abnormalities in recurrent stone formers.
Differential Diagnosis
Pyelonephritis: presence of fever and pyuria
Appendicitis: RLQ pain without radiation to groin
Ectopic pregnancy: positive beta-hCG in females
AAA rupture: pulsatile abdominal mass and hypotension
Testicular torsion: scrotal pain without flank radiation