Kidney stones, also called renal calculi, are solid concretions (crystal aggregations) of dissolved minerals in urine; calculi typically form inside the kidneys or bladder. The terms nephrolithiasis and urolithiasis refer to the presence of calculi in the kidneys and urinary tract, respectively.
Renal stone or calculus or lithiasis is one of the most common diseases of the urinary tract. It occurs more frequently in men than in women and in whites than in blacks. It is rare in children. It shows a familial predisposition.
Urinary calculus is a stone-like body composed of urinary salts bound together by a colloid matrix of organic materials. It consists of a nucleus around which concentric layers of urinary salts are deposited.
Renal calculi can vary in size from as small as grains of sand to as large as a golf ball.
Most calculi originate within the kidney and proceed distally, creating various degrees of urinary obstruction as they become lodged in narrow areas, including the ureteropelvic junction, pelvic brim, and ureterovesical junction. Location and quality of pain are related to position of the stone within the urinary tract. Severity of pain is related to the degree of obstruction, presence of ureteral spasm, and presence of any associated infection.
Cause of Kidney Stones
HYPEREXCRETION OF RELATIVELY INSOLUBLE RINARY CONSTITUENTS such as oxalates, calcium, uric acid, cystine and certain drugs (such as magnesium trisilicate in the treatment of peptic ulcer).
PHYSIOLOGICAL CHANGES IN URINE such as Urinary pH (which is influenced by diet and medicines), Colloid content, Decreased concentration of crystalloids, Urinary magnesium/calcium ratio.
ALTERED URINARY CRYSTALLOIDS AND COLLOIDS.
Either there is an increase in the crystalloid level or a fall in the colloid level, urinary stones may be formed.
If there is any modification of the colloids e. g. they lose their solvent action or adhesive property, urinary stones may develop.
DECREASED URINARY OUTPUT OF CITRATE.
VITAMIN A DEFICIENCY.
The desquamated cells form nidus for stone formation. This is more applicable to bladder stones.
URINARY INFECTION.
Infection disturbs the colloid content of the urine, also causes abnormality in the colloids (which may cause the crystalloid to be precipitated).
Infection also changes urinary pH and also causes increase in concentration of crystalloids.
URINARY STASIS.
It causes a shift of the pH of the urine to the alkaline side, predisposes urinary infection, and allows the crystalloids to precipitate.
HYPERPARATHYROIDISM.
Due to overproduction of parathormone the bones become decalcified and calcium concentration in the urine is increased. This extra calcium may be deposited in the renal tubules or in the pelvis to form renal calculus.
PROLONGED IMMOBILISATION.
NIDUS OF STONE FORMATION.
PREDISPOSING FACTORS
ENVIRONMENTAL AND DIETARY FACTORS
Low urine volumes.
High ambient temperatures.
Low fluid intake.
Diet.
High protein intake.
High sodium.
Low calcium.
High sodium excretion.
High oxalate excretion.
High urate excretion.
Low citrate excretion.
OTHER MEDICAL CONDITIONS
Hypercalcemia of any cause
Ileal disease or resection (leading to increased oxalate absorption and urinary excretion)
Renal tubular acidosis type I
CONGENITAL AND INHERITED CONDITIONS
Familial hypercalciuria
Medullary sponge kidney
Cystinuria
Renal tubular acidosis type I
Primary hyperoxaluria
Types of renal calculi
Basically the renal stones can be divided into two major groups
Primary stones
Secondary stones.
PRIMARY STONES
They appear in apparently healthy urinary tract without any antecedent inflammation.
· Calcium oxalate.
Uric acid calculi.
Cystine calculi.
Xanthine calculi.
Indigo calculi.
SECONDARY STONES
They are usually formed as the result of inflammation.
Triple phosphate calculus.
Mixed stones.