Kidney stones: what we should know

Part1
By Dr Vineet Naja, MS(G.Surgery);MCh(Urology) (Consulting Urologist and Andrologist)


Introduction

Kidney stones are a common occurrence in the general population of Guyana. Kidney stones are hard, solid particles that form in the urinary tract. In many cases, the stones are very small and can pass out of the body without any problems. However, if a stone (even a small one) blocks the flow of urine, excruciating pain may result, and prompt medical treatment may be needed. Today, treatment for stones is much less invasive than in the past. Open surgery (making a cut for the removal of stone) is performed in less than 2% of patients worldwide. This article will be in two parts. Today we will discuss problems associated with stones. In the subsequent article we will focus on minimally invasive and non-invasive methods for stone removal.


Kidney, ureter & bladder

The two kidneys are located deep behind the abdominal organs, below the ribs and towards the middle of the back. The process of urination begins in the kidneys. The kidneys filter out fluids and waste from the body, producing urine. As the urine passes through the kidneys, it becomes more concentrated. From the kidneys, urine flows from through thin tubes called ureters into the bladder. The bladder’s elastic walls expand to store the incoming urine until it leaves the body through a tube called the urethra.

Type of stones and causes

Occasionally, various salts build up on the inside surfaces of the kidney and form crystals. Eventually these crystals become large enough to form stones in the kidney, a condition called nephrolithiasis. Kidney stones (renal calculi) may also form in the ureter or the bladder. Combinations of minerals and other chemicals, some derived from a person’s diet, make up the salts in these stones.
Calcium Stones: About 70-90% of all kidney stones are made of calcium, usually combined with oxalate, or oxalic acid. About 6% of calcium stones are made of calcium phosphate (called brushite).
Uric Acid Stones: Uric acid is responsible for close to 10% of kidney stones. It is the breakdown product of purines, nitrogen compounds found in our bodies and in certain foods. Often, uric acid stones occur with calcium stones.
Struvite Stones: Struvite stones are made of magnesium ammonium phosphate. They are almost always associated with certain urinary tract infections.
Cystine Stones: A build-up of the amino acid cystine, a building block of protein, causes 1% of kidney stones in adults and up to 8% of stones in children. The tendency to form these stones is inherited.
Xanthine Stones: Other kidney stones are composed of xanthine, a nitrogen compound. These stones are extremely uncommon and usually occur as a result of a rare genetic disorder.
Causes

The key process in the development of kidney stones is presence of high concentration of certain substances in the urine (supersaturation). The urine carries salts, including calcium oxalate, uric acid, cystine, or xanthine. These salts can become extremely concentrated if there is not enough urine, or if unusually high amounts of crystal-forming salts are present. When salt concentration levels reach the point at which they no longer dissolve, these salts form crystals.

Different factors may be involved in either reducing urine amount, or increasing the levels of the salts.

Deficiencies in protective factors: Normally, urine contains substances that may protect against stone formation, including magnesium, citrate, pyrophosphate, enzymes, etc. These substances allow salt in the urine to be at higher-than-normal concentrations without forming crystals, prevent crystal formation and coat the crystals and prevent them from sticking to the surface of kidney tubes. Not having enough of these protective substances can cause stones.
Imaging Techniques

Various imaging techniques are helpful in determining the presence of kidney stones. The best approach uses spiral (or helical) computed tomography scans. If these scans are not available, the patient will need an ultrasound or standard x-rays.
X-Rays: A standard x-ray of the kidneys, ureters, and bladder may be a good first step for identifying stones, since many are visible on x-rays. Bowel preparations are required before a good quality of X-rays otherwise bowel gases may obscure the stone.
Computed Tomography: A type of computed tomography (CT) scan called a spiral or helical CT scan is currently the best method for diagnosing stones in either the kidneys or the ureters. This test is fast, does not require any bowel preparation, and provides detailed accurate images of even very small stones. If stones are not present, a spiral CT scan can often identify other causes of pain in the kidney area. It is better than x-rays, ultrasound, and an intravenous pyelogram – the previous standard test for detecting kidney stones.
Ultrasound: Ultrasound can detect clear uric acid stones and obstruction in the urinary tract. It is not useful for finding very small stones present in the ureter. It may be a useful first diagnostic aid in the emergency room to help diagnose a stone.
Intravenous Pyelogram: With an intravenous pyelogram (IVP), the doctor injects a special dye into the patient. A technician will then take x-rays as the dye enters the kidneys and travels down the urinary tract. IVP is invasive but, until recently, was the most cost-effective method for detecting stones. Where it is available, spiral CT is now preferred, since it gives a faster diagnosis and is more accurate and safer. IVP should not be used on patients with kidney failure. There is also a risk for an allergic reaction to standard dyes, although newer, less allergenic ones are becoming available.
We will continue this article on treatment and prevention of urinary tract stones in the next edition of this column.

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