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Nephrology - Kidney Stones - Fast Facts | NEJM Resident 360

Acute renal colic typically presents with intermittent colicky flank pain that may radiate to the groin, s often associated with nausea and vomiting and may be associated with lower urinary tract symptoms such as dysuria.

• Acute management and workup of kidney stones (renal calculi [nephrolithiasis]) and ureteric calculi (ureterolithiasis) is covered in Abdomiopelvic Emergencies in the Emergency Medicine rotation guide.

Kidney Stone Composition

• Calcium: Most kidney stones contain calcium combined with either oxalate, phosphate, or uric acid and all calcium-containing stones are radio-opaque. Conditions causing hypercalciuria can contribute to the formation of calcium stones. These include diseases such as primary hyperparathyroidism, certain malignancies, granulomatous diseases, sarcoidosis and thyrotoxicosis.

(Source: Calcium Kidney Stones. N Engl J Med 2010.)

• Uric acid: Unless combined with calcium stones, uric acid stones are radiographically transparent. Causes include gout, myeloproliferative disorders, tumor lysis syndrome that result in hyperuricemia and hyperuricosuria.

• Struvite: The characteristic appearance of a “staghorn” calculi is caused by struvite stones, which are associated with significant morbidity and symptoms including bleeding, obstruction, and infection.

• Cystine: Cystine stones are found in children with cystinuria, and the stones are moderately radio-opaque.

Workup

• Urinalysis: All patients require urinalysis, which may show microscopic hematuria as well as signs of urinary tract infection.

• Blood work: In the acute setting, blood work is useful to evaluate electrolytes and renal function, and in the chronic setting, it can help identify underlying causes of stones.

• Imaging: CT is still considered by many as the best imaging modality for both evaluating the presence, size, and location of stones, and the surrounding anatomy. Its use is debatable for monitoring and follow up of chronic or recurrent stones, given the high exposure to radiation. Intravenous urography was the gold standard but has since been superseded by CT scans.

  • Plain abdominal radiographs are useful for radio-opaque stones and to monitor disease activity.

  • Renal ultrasonography is useful in follow up or in pregnant patients. Although historically, ultrasonography was not been used in the acute evaluation of renal colic, given its low sensitivity, a recent study reported no difference in rates of missed high-risk diagnoses or adverse events between ultrasound or CT in patients with renal colic.

Treatment

Acute management of renal colic involves adequate analgesia and fluids and is covered in the emergency medicine guide. Kidney stones are generally conservatively managed and do not need active removal or fragmentation unless they cause acute obstruction, infection, bleeding, or persistent pain. Acute surgical management aims to decompress the urinary tract through ureteral catheters, ureteral stents, and percutaneous nephrostomy tubes. Choosing the type of urological surgical intervention will depend on the stone size, location, and composition of the stone.

• Shock wave lithotripsy directs a shock wave onto the stone, causing it to fragment. This technique is generally used for smaller stones (<2 cm diameter).

• Ureteroscopy is an endoscopic method used to visualize the renal and ureteric tract and allows instruments to fragment or remove stones. This technique is generally used for smaller stones (<2 cm diameter). Stone-free rates are higher than shock wave lithotripsy but ureteroscopy is associated with a higher complication rate, including sepsis and ureteral injury.

• Percutaneous nephrolithotomy involves the creation of an access tract into the renal collecting system, that allows for nephroscopy and subsequent fragmentation and removal of stones using laser or lithotrite. This technique is generally used for larger stones (>2 cm diameter), complex stones (e.g., staghorn calculi), or when shock wave lithotripsy fails.

• Medical management is targeted at treating or preventing recurrent or chronic stones.

  • General measures include an increase in oral water intake to at least 2 liters per day and a diet low in animal protein and calcium.

  • Thiazide diuretics (e.g., hydrochlorothiazide and indapamide) decrease urine calcium excretion and reduce recurrence of calcium stones.

  • Alpha-adrenergic blockers (e.g., tamsulosin) aid in the spontaneous passage of ureteral calculi by inhibiting basal ureteral tone and peristaltic frequency.

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