August 2010|Vol 7|Issue 8

August 2010 | Volume 7 | Issue 8

 

Article
 
Pathogenesis... Kidney stones
 



 




Dr. Sarita Umadi,
Lecturer, Dept. of Surgery,
BBHMC&H,
Bangalore.

    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)
    · Cystine
    · 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 components.

    PATHOGENESIS:
    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.


    TYPES:
    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.