Kidney Stones

Image: news-medical.net

Dr. Anand Deo

MBBS, KU

Kidney stones, commonly known as renal stones in medical science, imply presence of stones anywhere in urinary tract. Urinary Tract starts from kidney and ends at urethra. It comprises of two kidneys (Right and left), a ureter arising from each kidney, one urinary bladder, and finally urethra. As urethra forms part of passage through which semen travels during ejaculation in male, it is also known as Genito-urinary system. Stones can be present anywhere in this system, commonly found in kidney, ureter and bladder where they’re technically termed as Nephrolithiasis, Ureterolithiasis, Cystolithiasis/Vesical Calculus respectively (lith- meaning stone). Calculus (pleural: calculi) is another term commonly used for stones.

Types of Renal Stones

Oxalate stones:  It is the commonest variety of renal stones. These stones primarily comprise of calcium deposits. They are usually irregular, spiculated, mulberry shaped. The tiny spicules can cause damage to surrounding blood vessels (capillaries mainly) and cause slight bleeding. The stones are therefore mostly brown in color owing to their mineral composition and also staining with pigments of blood. By virtue of spicules, it causes pain even in early stages and hence when detected are usually small. These are usually found in acidic urine as oxalates are insoluble in acidic ph.

Phosphate stones: These contain calcium, magnesium and ammonium deposits and hence commonly called triple stones. They are smooth surfaced, white in color and can grow considerably in size before causing symptoms. They are commonly found in infected, alkaline urine. Bacterial enzymes are probably necessary for the formation of ammonium deposits. Also, phosphates are insoluble in alkaline ph.

Other varieties are Uric acid stones, Urate stones, Xanthine stones, Cystine stones.

Prevalence of Renal Stones in Nepal

A study conducted by A. Pandeya et. al in 2008-2010 on 99 cases of renal stones, 61 were males (61.6%) and 38 were females (38.4%). This is in accordance with the study results published by Stapleton FB. Larger muscle mass and complex structure of genito-urinary tract in males may be responsible for pre-ponderance of stone formers among males; higher the muscle mass, more the metabolic waste and hence higher the likelihood of stone formation. Majority of the cases (52.5% of the total cases) were of age group of 21-40 years followed by 25.2% in age group of 41-60 years. This result is supported by a study of Asplin et. al. The least number of stone formers were present beyond their 60s. The composition of most of the stones analyzed were oxalate (98.9%) followed by uric acid (62.6%) as an organic constituents while as an inorganic constituents, stones were composed of calcium (95.9%), phosphate (85.8%), ammonium (46.4%) and very few numbers of stones were composed of carbonate (5.0%).

 

Cause of Renal Stones

Decreased water intake, hot weather, dehydration, consuming water with higher level of calcium and other minerals causes relative excess of solute in urine. These super saturate to form small deposits (microliths) especially in areas where the lining cells (epithelium) in urinary tract are damaged. Over time, the deposits increase in size and form stones. Citrate level in urine keeps calcium and other minerals in soluble state in urine. Decrease in citrate level favors super saturation of urine and predisposes to stone formation. Sodium contained in common salt can increase the risk of stone formation, probably by increasing the urinary excretion of calcium. Vitamin A deficiency causes poor healing of damaged epithelium and increases chance of stone formation. Oxalate is oxidized product of Vitamin C and hence excess of this vitamin may predispose one to renal stones. Increased blood calcium level causes increased level of calcium in urine and hence favors stone formation. High protein diet, high oxalate diet also predisposes to stone formation. Various disease cause increased level of variety of minerals in blood (eg. Blood calcium level increases due to increased bone resorption in primary hyperparathyroidism) and predisposes to formation of respective stones in urinary tract. Acidic urine favors formation of oxalate and uric acid stones while alkaline urine favors formation of phosphate stones.

Symptoms

Many of us have small deposits of these minerals in our urinary tract. Only a fraction of individuals experience discomfort due to renal stones though. Symptoms due to stones depend primarily on size, location and shape of stone. A small stone in kidney may not cause any symptom but the same stone if dislodged into ureter can cause severe symptoms because ureter is narrow tubular structure. Oxalate stones cause symptoms even when small because of its irregular shape. A phosphate stone usually attains large size before causing symptoms.

The most common symptom is pain abdomen, especially in flanks and lower abdomen. Some experience dull aching pain while others experience excruciating pain starting from flanks and going down towards groin. One may feel nauseated or may even vomit due to severe pain. There may be burning sensation while passing urine, unable to pass urine freely. Some may pass blood mixed urine. Infected urine may cause headache, fever, lower backache. Some may feel urge to pass urine repeatedly but passing only small volume each time. This urge is due to local irritation caused by stones and infected urine. Sometimes these stones may partially or completely obstruct the flow or urine down its tract resulting in accumulation of urine in areas before the site of stone(hydronephrosis : accumulation of water/urine in kidney causing it to swell up; hyderoureter : accumulation of water/urine in ureter causing it to swell up). In such cases people experience a great deal of distress. The accumulated urine may get infected and pus may develop in these structures (pyonephrosis ; pyo- referring to pus). This situation may progress and cause dame to kidney.

Investigations

The common modalities of investigation are X-ray (commonly called X-ray KUB; kidney ureter bladder), Ultrasound abdomen, Biochemical and microbiological analysis of urine. Depending on severity there may be need of assessing the capacity of kidney to filter blood and form urine (Renal function tests). Advanced imaging techniques like CT scan may be occasionally necessary. Most of the renal stones are radiopaque thereby meaning it appears on plain x-ray. Non-radio opaque stones can be found on abdominal ultrasound.

Treatment

Most important home remedy for asymptomatic cases and as preventive measure is drinking enough of clean water. There are several foods that have been implicated to facilitate stone formation while another list of food that facilitates stone dissolution. Normal-Calcium, Low-Sodium, and Low Animal-Protein Diets are recommended for Stone Prevention.

Other treatment options depend upon the symptomatology and findings on investigation. Pain relieving medications, antibiotics for infected urine are commonly prescribed. Various non-invasive techniques like fragmenting the stones into smaller pieces (lithotripsy) to facilitate their spontaneous expulsion in urine are available. Larger stones may require surgical intervention varying from endoscopic procedures, minimally invasive to extensive surgeries.

References:

Assessment of kidney stone and prevalence of its chemical compositions by A. Pandeya, R. Prajapati, P. Panta, and A. Regmi. (Nepal Med College Journal 2010; 12(3): 190-192).

Stapleton FB. (Childhood stones. Endocrinol Metabol Clin North America 2002; 31: 1001-15).

Asplin et. al (Nephrolithiasis. In: Brenner BM, ed. Brenner and Rector’s the kidney. 5th ed. Philadelphia: Saunders, 1996)

 

 

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