Kidney stones

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Introduction0:00–0:30

With nephrolithiasis, “nephro-” refers to the kidneys, and “-lithiasis” means stone, so nephrolithiasis means kidney stones, sometimes also referred to as renal calculi or urolithiasis.
Kidney stones form when solutes in the urine precipitate out and crystalize, and although these most commonly form in the kidneys themselves, they can also form in the ureters, the bladder, or the urethra.
Now, urine’s a combination of water, which acts as a solvent, and all sorts of particles, or solutes. In general, when certain solutes become too concentrated in the solvent, they become supersaturated.

Pathophysiology0:30–1:19

Urinary supersaturation of certain solutes results in precipitation out of the solution and formation of crystals. Those crystals then act as a nidus, or place where more solutes can deposit and over time it builds up a crystalline structure.
This can happen if there’s an increase in the solute, or a decrease in the solvent, as would be the case with dehydration.
In addition, there are substances like magnesium and citrate that inhibit crystal growth and aggregation, preventing kidney stones from forming in the first place.

Calcium containing stones1:19–1:59

In the majority of cases, the inorganic precipitate is calcium oxalate, formed by a positively charged calcium ion binding to a negatively charged oxalate ion, which results in a black or dark brown colored stone that is radio-opaque on an Xray, meaning that it shows up as a white spot.
Sometimes, instead of oxalate, the calcium binds a negatively charged phosphate group to form calcium phosphate stones which are dirty white in color and alsop radiopaque on an Xray.
Calcium oxalate crystals are more likely to form in acidic urine, whereas calcium phosphate crystals are more likely to form in alkaline urine.

Risk factors of calcium containing stones1:59–2:53

The exact reason why these stones form is usually unknown, but there are some known risk factors like hypercalcemia and hypercalciuria, having too much calcium in the blood and urine, respectively.
Hypercalcemia can result from increased calcium absorption in the gastrointestinal tract as well as hormonal causes like primary hyperparathyroidism.
Hypercalciuria can result from impaired renal tubular reabsorption of calcium, which leaves a lot of calcium behind in the tubule.
For the calcium oxalate stones, hyperoxaluria is a risk factor as well, and it can be due to a genetic defect that increases oxalate excretion, a defect in liver metabolism, or a diet heavy in oxalate-rich foods like rhubarb, spinach, chocolate, nuts, and beer.
There are also uric acid stones which are red-brown in color and radiolucent under an Xray, meaning that they’re transparent to x-rays and don’t show up very well.

Uric acid stones2:53–3:40

At a physiologic pH, uric acid loses a proton and becomes a urate ion, which then binds sodium, forming monosodium urate which crystallizes and ultimately forms uric acid stones.
Since uric acid is a breakdown product of purines, a very common reason for high levels of uric acid is consuming lots of purines.
Purine-rich foods include shellfish, anchovies, red meat or organ meat. High levels of uric acid can also cause gouty arthritis, most commonly in the first metatarsal joint which is the base of the big toe.

Struvite stones3:40–4:39

A fourth type are struvite stones, sometimes called infection stones, which are a composite mix of magnesium, ammonium, and phosphate.
These form when bacteria like Proteus mirabilis, Proteus vulgaris, and Morganella morganii use the enzyme, urease, to split urea into ammonia and carbon dioxide.
The ammonia makes the urine more alkaline and favors precipitation of magnesium, ammonium, and phosphate into jagged crystals called “staghorns” because they often branch into the several of the renal calyces and look like the horns of a staghorn deer.
Like the calcium phosphate stones, struvite stones are dirty white and radiopaque under an X-ray. Risk factors include urinary tract infections, as well as vesicoureteral reflux and obstructive uropathies, both of which are also risk factors for urinary tract infections.

Cystine and xanthine stones4:39–5:10

A tiny minority of stones are cystine stones, composed of the amino acid cystine which sometimes leaks into the urine to crystalize and form a yellow or light pink colored stone that is radiopaque under X-ray.
Finally, there are some rare stones made of xanthine, which, just like uric acid, is a byproduct of purine breakdown. These stones, also like uric acid stones, are red-brown in color and radiolucent under an X-ray.

Signs and symptoms5:10–5:43

Kidney stones can cause dull or localized flank pain in the mid to lower back on both sides, as well as renal colic, which is a sharp pain and is a bit of a misnomer because the pain is usually constant rather than intermittent.
The pain is caused by the dilation, stretching, and spasm caused by obstruction of the ureter, and is typically worse at the ureteropelvic junction and down the ureter, and subsides once the stone gets to the bladder.
Stones that are less than 5mm across are usually passed within hours. Diagnosis involves a history and physical exam, as well as imaging studies like ultrasound and CT scans, and finally urinalysis because it might show microscopic or gross hematuria or blood in the urine.

Diagnosis5:43–6:00

Treatment6:00–6:34

Treatment or management includes hydrating an individual to reverse the process of precipitation. Also, medications might be given, to help reduce pain, reduce stone formation, like potassium citrate, and to help stones pass through, like alpha adrenergic blockers and calcium channel blockers.
Also shockwave lithotripsy might be used, which is a noninvasive treatment that uses high-intensity acoustic pulses that travel through the body to break up the kidney stones.
Finally, surgery and stent placement might be needed for larger stones. Alright, as a quick recap, nephrolithiasis is the formation of kidney stones, which form when solutes precipitate out into crystals in the urine.

Review6:34–7:06

The most common type of stones are calcium oxalate stones, though other types include uric acid stones and struvite stones.
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