Before we discuss types of kidney stones, this fact must be kept in mind that different types of stone occur in different parts of the world, for example, bladder stones occur mostly in countries with hot climates, and this fact also must not be ignored that dietary factor probably plays vital part in determining the varying patterns of renal stones.
Now we will discuss different types of stones one by one along with their peculiar characteristics:
1. Calcium Oxalate Stone (75 %)
Among all renal stones, this one is the most common. It is also called as “Mulberry” calculi. It is hard, single and has irregular sharp projections or spikes just like sea urchin. And due to these sharp projections, it causes hematuria (blood in the urine) very early, resulting in deposition of blood over the stone giving a dark color to the stone. Usually, it occurs in infected urine and contains alternate layer of calcium and bacterial vegetation. It is easily visualized in plain X-Ray KUB (Kidney, Ureter and Bladder)
2. Phosphate Stone (15%)
This stone is smooth and round in shape while dirty white to yellow in color. It consists of triple phosphate of calcium, magnesium and ammonium and commonly occurs in renal pelvis and tends to grow in alkaline urine. As it enlarges in the pelvis, it grows within the major and minor calyces and slowly forms Staghorn calculus. This calculus produces recurrent urinary tract infection and hematuria and slowly damages the renal parenchyma. This stone is common in women with recurrent urinary tract infection. It is also known as Struvite or Infection Stone.
3. Uric Acid Stone or Urate Calculi (5%)
These are multiple, small hexagonal, faceted and yellow to light brown colored stones containing calcium oxalate, which makes them opaque. It must be noted that pure uric acid stones are radiolucent. These stones occur in acidic urine and are common in those patients who consume red meat.
4. Cystine Calculus (2%)
Cystinuria is an inborn error of metabolism, which occurs due to decreased resorption of cystine from renal tubules. Such stones occur in young girls at puberty. Whenever there is an increased excretion of cystine in urine, it will result in cystine calculus. These stones are hard. Their color is white, pink or yellow when first removed but on exposure, color changes to a greenish hue. Although, they are translucent but it must be kept in mind that these stones are radio-opaque due to sulphur content.
5. Xanthine and Pyruvate Stones
These stones are usually rare and they happen if there is an inborn error of metabolism. They are smooth and round, brick red in color and show a lamellar (flat and thin) structure.
6. Indigo Calculi
These calculi are blue in color and the name is derived from indican. These calculi occur very rarely.