Kidney Stones (aka, renal calculus)

Kidney Stones

Aka, renal calculi

Estimated to occur in 1 in 10 adults in the U.S.

Nephrolithiasis are stones that form within the kidney.

Urolithiasis are stones that form anywhere along the urinary tract, including the kidney.

Stones outside of the kidney can impair urine flow and cause renal colic and hematuria.

SIGNS & SYMPTOMS

Renal colic (flank colic); pain increases and subsides as stone moves. Hematuria

See CT Scan with Kidney Stones

RISK FACTORS

Low urine volume promotes supersaturation and crystal formation.

Dietary factors

High sodium and high protein diets.

Other health conditions

Anatomic factors

Medullary sponge kidney
Horseshoe kidney

TREATMENTS

When symptomatic, kidney stones can be quite painful, but most pass on their own in the urine within 48 hours; NSAIDs can be provided to alleviate the pain.

Increase fluid intake to 2-3 L/day.

When needed, alpha blockers or other medications can be used to relax the smooth muscle of the urinary tract and facilitate stone passage.

Larger stones may require lithotripsy, which breaks the stone into smaller pieces using ultrasound shock waves, or even surgical removal.

Refer to emergency department if patient has high fever, acute renal failure, large/impassible stone, inability to tolerate oral medications/fluids.

Urinary tract obstruction can lead to permanent damage and end-stage renal disease, so clearance is important.

Recurrence is common; it occurs in approximately 50% of patients. Ask about potential dietary factors that can be avoided.

KIDNEY STONE TYPES

Calcium oxalate stones: Approximately 80% of stones comprise calcium oxalate, with and without elements of calcium phosphate. On X-ray and CT these stones are radiopaque. Crystals look like envelopes, and they look like spiky balls on gross examination. Causes include low urine pH, hypercalciuria, and hyperoxaluria. Hypercalciuria can be idiopathic or secondary to hyperparathyroidism, vitamin D excess, etc.; hyperoxaluria can be due to diet or malabsorption.

Calcium phosphate stones: Radiopaque. Their crystals are needle or star-shaped, and they look like smoother versions of the calcium oxalate stones. They are associated with high urine pH.

Struvite stones: Comprise ammonia, magnesium, and phosphate. They are radiopaque with "coffin-lid" crystals. They tend to have large projections (staghorns). Struvite stones are caused by urease-positive pathogens that cause urinary tract infections; the bacteria convert urea to ammonia, one of the key elements of the stone.

Uric acid stones: Radiolucent on X-ray and visible on CT. Crystals are rhomboid-shaped, and they have a pitted appearance. Uric acid stones are associated with low urine pH, gout (which is associated with uricemia), cancer, and metabolic syndromes.

Cystine stones: Faintly radiopaque. Hexagonal crystals and irregularly-shaped; they can become large. Cystine stones are caused by an autosomal hereditary disorder in which the renal tubules cannot reabsorb cystine (due to defects in the genes SLC3A1 and SLC7A). Because the defect is genetic, stone formation is recurrent, difficult to prevent, and causes renal insufficiency in affected patients.

Kidney Stones (aka, renal calculus)

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