India has high incidence of calculus especially
in Gujarat, Rajasthan, Punjab and Madhya Pradesh. Different
types occur with different frequencies in different parts of
the world probably as a consequence of dietary and environmental
factors but genetic factor may also make a significant contribution.
Major crystalline substances identified in renal stones could
be categorized in 6 groups:
· Calcium oxalate(monohydrate dehydrate)
· Calcium Phosphate
· Uric Acid and other metabolites of purine metabolism.
· Bacterial induced magnesium ammonium phosphate(struvite)
· Others eg:drugs(triamterene) and matrix
Out of these radios translucent stones are uric acid, xanthine,
and triametrene stone
Radiopaque stones are calcium oxalate and calcium phosphate
Cystine and struvite are less dense giving ground glass appearance
Majority of stones are admixture of two or more of the above
Urinary tract stone formation is a multi factorial complex process
dependent on loss of physical chemistry which governs crystallization
of sparingly soluble salts in aqueous solution. The process
of precipitation leading to crystallization of any mineral stone
constituents in urine super saturation in urine. Normal urine
has several inorganic as well as macromolecular inhibitors of
crystal formation. The kidney’s important function is
to conserve the water and also excrete minerals which have low
solubility. Thus a delicate balance exists between crystal formation
and its inhibitors. Whenever this delicate balance is disturbed
in favor of crystallization condition exists for stone formation.
1) CALCIUM OXALLATE:
These are irregular in shape, usually single. It’s covered
with sharp projection which tends to cause bleeding. The surface
of calculus is discolored by blood. A calcium oxalate monohydrate
stone is hard and radio dense commonly known as MULBERY STONES.
2) PHOSPHATE CALCULUS:
Phosphate calculus (calcium phosphate often with ammonium magnesium
phosphate) struvite is smooth and dirty white. It tends to grow
alkaline urine especially when urea splitting proteus organisms
are present. These stones can grow to a large size and fill
the renal pelvis and calyces to produce a staghorn appearance
and are radiopaque
3) URIC ACID AND URATE CALCULI:
These are hard, smooth and often multiple. The colours vary
from yellow to dark brown and are typically faceted. These are
radiolucent common in men. Half of the patients with uric acid
stones have gout.
4) CYSTENE CALCULUS:
These are uncommon; appear in urinary tract of the patients
with a congenital error of metabolism that leads to cystinuria.
These are radiopaque often multiple, hexagonal. White crystals
of cystine appear only in acid urine.
5) XANTHENE CALCULUS
These are extremely rare. They are smooth and round, brick red
in colour and show lamellation on cross-section.