Renal · Urolithiasis
The facts most likely to be tested
Non-contrast helical CT of the abdomen and pelvis is the gold standard diagnostic imaging modality for suspected nephrolithiasis.
Calcium oxalate stones are the most common type of kidney stone and appear as envelope-shaped crystals on urinalysis.
Struvite stones are associated with urease-producing organisms like *Proteus* and form staghorn calculi in the renal pelvis.
Uric acid stones are radiolucent on plain film radiographs 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.
Tamsulosin, an alpha-1 antagonist, is the preferred medical expulsive therapy for stones between 5 mm and 10 mm to facilitate passage.
Urgent urologic consultation is indicated for patients with a stone, fever, and signs of urosepsis or an obstructed solitary kidney.
Vignette unlocked
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 has microscopic hematuria on dipstick. His temperature is 98.8°F, blood pressure is 135/85 mmHg, and heart rate is 92 bpm. A non-contrast CT scan reveals a 6 mm stone at the ureterovesical junction with mild hydronephrosis.
What is the most appropriate initial management for this patient?
Tamsulosin and pain control with NSAIDs
This vignette tests the management of a small, uncomplicated ureteral stone (5-10 mm), where medical expulsive therapy with an alpha-blocker is indicated to facilitate passage.
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High yield triage
Etiology / Epidemiology
Most common is calcium oxalate. Risk factors include low fluid intake, high animal protein, and hyperparathyroidism.
Clinical Manifestations
Presents with renal colic: sudden, severe flank pain radiating to the groin. Patient is unable to find a comfortable position.
Diagnosis
Non-contrast CT abdomen/pelvis is the gold standard. Stones >10 mm rarely pass spontaneously.
Treatment
Stones <5 mm pass with tamsulosin and hydration. Fever with obstruction is a urologic emergency.
Prognosis
Recurrence is common. 24-hour urine collection is indicated for recurrent stone formers.
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Epidemiology & Etiology
Calcium oxalate is the most common stone type, often associated with hypercalciuria. Uric acid stones are associated with gout and acidic urine. Struvite stones are triple phosphate stones caused by urease-producing bacteria like Proteus.
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 growth. Low urine volume and pH abnormalities (e.g., distal renal tubular acidosis) promote stone formation. Obstruction leads to increased hydrostatic pressure, causing the classic radiating pain.
Clinical Manifestations
Patients exhibit writhing behavior, constantly shifting to find comfort. Hematuria is present in 85% of cases. Fever, chills, or hypotension suggest pyelonephritis with obstruction, requiring immediate decompression.
Diagnosis
Non-contrast CT abdomen/pelvis is the diagnostic test of choice. Ultrasound is preferred in pregnancy to avoid radiation. Stones >10 mm have a low probability of spontaneous passage.
Treatment
Manage pain with NSAIDs (e.g., ketorolac) or opioids. Tamsulosin (alpha-1 blocker) facilitates stone passage for distal stones. Do not use NSAIDs in patients with renal insufficiency or active peptic ulcer disease.
Prognosis
Most stones <5 mm pass within 4 weeks. Hydronephrosis and acute kidney injury are primary complications. Patients with recurrent stones require metabolic workup including 24-hour urine collection.
Differential Diagnosis
Pyelonephritis: presence of fever and pyuria
Appendicitis: RLQ pain without radiation to groin
Ectopic pregnancy: positive beta-hCG in females
Abdominal aortic aneurysm: pulsatile mass and hypotension
Testicular torsion: scrotal pain without flank radiation