Urolithiasis

Urolithiasis (from Greek oûron, "urine" and lithos, "stone") is the condition where urinary stones are formed or located anywhere in the urinary system.^[1] The term nephrolithiasis (or "renal calculus") refers to stones that are in the kidney, while ureterolithiasis refers to stones that are in the ureter. The term cystolithiasis (or vesical calculi) refers to stones which form or have passed into the urinary bladder.^[2]

Urinary stones are typically classified by their location or by their chemical composition (calcium-containing, struvite, uric acid, or other compounds). In humans, calcium oxalate is a major constituent of most urinary stones. About 80% of those with kidney stones are men. Men most commonly experience their first episode between 20-30 years of age, while for women the age at first presentation is somewhat later.

Nephrolithiasis and ureterolithiasis

Kidneys, ureters, and bladder x-ray with bilateral kidney stones

A kidney stone, also known as a renal calculuoos is a solid concretion or crystal aggregation formed in the kidneys from dietary minerals in the urine. Kidney stones typically leave the body by passage in the urine stream, and many stones are formed and passed without causing symptoms. If stones grow to sufficient size (usually at least 3 millimeters (0.12 in)) they can cause obstruction of the ureter. Ureteral obstruction causes postrenal azotemia and hydronephrosis (distension and dilation of the renal pelvis and calyces), as well as spasm of the ureter. This leads to pain, most commonly felt in the flank (the area between the ribs and hip), lower abdomen, and groin (a condition called renal colic). Renal colic can be associated with nausea, vomiting, fever, blood in the urine, pus in the urine, and painful urination. Renal colic typically comes in waves lasting 20 to 60 minutes, beginning in the flank or lower back and often radiating to the groin or genitals. The diagnosis of kidney stones is made on the basis of information obtained from the history, physical examination, urinalysis, and radiographic studies. Ultrasound examination and blood tests may also aid in the diagnosis.

When a stone causes no symptoms, watchful waiting is a valid option. For symptomatic stones, pain control is usually the first measure, using medications such as nonsteroidal anti-inflammatory drugs or opioids. More severe cases may require surgical intervention. For example, some stones can be shattered into smaller fragments using extracorporeal shock wave lithotripsy. Some cases require more invasive forms of surgery. Examples of these are cystoscopic procedures such as laser lithotripsy or percutaneous techniques such as percutaneous nephrolithotomy. Sometimes, a tube (ureteral stent) may be placed in the ureter to bypass the obstruction and alleviate the symptoms, as well as to prevent ureteral stricture after ureteroscopic stone removal.

Cystolithiasis

A star-shaped stone can be seen in the urinary bladder on this radiograph of the pelvis

Cystolithiasis refers to stones which form or have passed into the urinary bladder, which are also referred to as vesical calculi.^[2]

Signs and symptoms

In the kidney, fixed renal pain (flank pain) is common. In the ureter (according to localisation of stone): If in the upper one-third of the ureter - pain radiates to the perineum, if at the pelvic brim - pain radiates to the inner aspect of the thigh, if present in the middle one-third of ureter - pain radiates to the iliac fossa. If the stone is localised in the bladder neck or urethra - pain may present as tip of penis pain. Frequency of urination, oliguria, dribbling of urine, and hematuria may increase.

Causes

The development of urinary stones is most commonly related to:

• Decreased urine volume
• Increased excretion of stone-forming components
• Inadequate urine drainage, which may lead to stasis
• Decrease in urinary citrate levels leading to deposition of calcium
• Deficiency of vitamins A or C - these conditions can also lead to the "hyper triad": hyperparathyroidism, hypercalcaemia, and hyperuricosuria.

In ruminants

Among ruminants, uroliths more commonly cause problems in males than in females; the sigmoid flexure of the ruminant male urinary tract is more likely to obstruct passage. Early-castrated males are at greater risk, because of lesser urethral diameter.^[3]

Low Ca:P intake ratio is conducive to phosphatic (e.g. struvite) urolith formation.^[3] Incidence among wether lambs can be minimized by maintaining a dietary Ca:P intake ratio of 2:1.^[4][3]

Alkaline pH favors formation of carbonate and phosphate calculi. For domestic ruminants, dietary cation:anion balance is sometimes adjusted to assure a slightly acidic urine pH, for prevention of calculus formation^[3]

Differing generalizations regarding effects of pH on formation of silicate uroliths may be found. ^[5][3] In this connection, it may be noted that under some circumstances, calcium carbonate accompanies silica in siliceous uroliths.^[6]

Pelleted feeds may be conducive to formation of phosphate uroliths, because of increased urinary phosphorus excretion. This is attributable to lower saliva production where pelleted rations containing finely ground constituents are fed. With less blood phosphate partitioned into saliva, more tends to be excreted in urine.^[7] (Most saliva phosphate is fecally excreted.^[8])

Oxalate uroliths can occur in ruminants, although such problems from oxalate ingestion may be relatively uncommon. Ruminant urolithiasis associated with oxalate ingestion has been reported.^[9] However, no renal tubular damage or visible deposition of calcium oxalate crystals in kidneys was found in yearling wether sheep fed diets containing soluble oxalate at 6.5 percent of dietary dry matter for about 100 days.^[10]

Conditions limiting water intake can be conducive to urolith formation.^[11]

Various surgical interventions, e.g. amputation of the urethral process at its base near the glans penis in male ruminants, perineal urethrostomy, or tube cystostomy may be considered for relief of obstructive urolithiasis.^[11]

References

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