What causes kidney and urinary stones?
Urine is produced by the two kidneys situated high in the abdominal cavity, and comprises water associated with waste products of the body. It passes down narrow tubes called the ureters into the bladder, which stores urine until a convenient time for it to be excreted.
Stones in the kidneys and urinary tract occur commonly in Singapore and Southeast Asia, and usually occur in patients aged above 40 years. They affect men more often than women, and form as a as a result of urine with a high concentration of certain chemicals (such as calcium, oxalate, phosphate, uric acid and others) and a low concentration of substances that stop stone formation (urinary inhibitors such as citrate and magnesium). Most urinary stones are made up of calcium oxalate or calcium phosphate, whilst struvite, uric acid and cysteine stones are less commonly encountered. Risk factors for urinary stone formation include (1) urinary tract infections; (2) cystic kidney disease; and (3) various metabolic disorders such as gout1.
How are kidney stones diagnosed?
Kidney stones are often asymptomatic. They are usually detected when they cause severe cramping pain in the flanks, which may spread down to the lower abdomen. Nausea, vomiting, and blood in the urine may be accompanying symptoms. Fever, chills and painful urination suggest that the stone may be associated with a urinary infection. Urine analysis, X-rays of the abdomen and pelvis and ultrasonography of the kidneys are usually the first tests to confirm the diagnosis (figure 1). Computer tomography of the urinary tract, popularly known as a CT urogram, gives the most accurate information of the position of the stones and the associated anatomy of the kidneys, which may be swollen from the stone causing obstruction to passage of urine down the ureters.
Figure 1: Abdominal X-rays showing
(a) stone in the left upper ureter;
(b) staghorn stones in both kidneys.
What treatments are available for urinary stones?
Most urinary stones are small (<5mm), and will pass out of the body spontaneously without need for surgery. For larger or impacted stones, treatment objectives are to eradicate the stone and relieve obstruction to promote recovery of kidney function. In recent years, new approaches and technologies have been developed to eradicate such stones.
1. Medical expulsive treatment of ureteric stones
In the past decade, medical expulsive therapy (MET) for ureteric stones has become increasingly popular. Various medications, such as calcium channel blockers (nifedipine and verapamil), α-blockers (tamsulosin, alfuzosin, doxazosin, and terazosin), and corticosteroids have been investigated. Based on several published meta-analyses, tamsulosin appears to be the most effective in facilitating spontaneous stone expulsion. It is suitable as first-line treatment in patients with ureteric stones <10mm which are not causing upper tract obstruction or significant distress. Failure of stones to pass out after 4 to 6 weeks of medical treatment will necessitate intervention to remove these stones1-3.
2. Extracorporeal Shockwave lithotripsy (ESWL)
ESWL is a popular treatment for stones <2cm in size in the kidneys and upper ureter. It is performed as an outpatient procedure, and involves the patient lying on a specially constructed treatment platform. Shock waves of varying intensities are created outside the body and transmitted through the skin and body tissues to converge on these stones. The stones are then shattered into smaller particles that pass easily through the urinary tract in the urine (figure 2). Recovery time is relatively short, and most people can resume normal activities in a few days. Side effects of ESWL treatment include bruising and pain around the treated kidney; downstream blockage of stone fragments in the lower ureter; and incomplete stone clearance requiring multiple treatment sessions.
Figure 2. Extracorporeal shockwave lithotripter for kidney stones.
3. Ureterorenoscopy (URS)
For stones in the lower ureter <2cm, specially constructed small-calibre endoscopes are passed up the ureter to the stone's location with the aid of guide-wires under X-ray guidance. The stones may then be shattered using a Holmium laser probe under direct vision, and the fragments retrieved out of the ureter using special stone baskets. If the ureter or kidney is swollen from stone obstruction, a temporary plastic stent is left in the ureter to facilitate healing, and is subsequently removed using a cystoscope 4-6 weeks after the initial procedure. URS is usually performed as an outpatient procedure under general anaesthesia. Pain after URS usually resolves after 2-3 days, although blood in the urine will take slightly longer to clear up.
In recent years, advances in endoscope technology have enabled urologists to use small-calibre flexible ureterorenoscopes to steer all the way up the upper ureter into the kidney, and remove kidney stones using Holmium lasers and stone baskets (figure 3). This has proved most successful for definitive clearance of stones located in the lower chambers of the kidney, for which ESWL has poor stone clearance rates4.
(a) Urologist using a flexible ureterorenoscope to access stones in the urinary tract.
(b) Holmium laser and basket used to eradicate stones.
4. Percutaneous Nephrolithotomy (PCNL)
For kidney stones > 2cm in size or occupying a significant part of the kidney (known as staghorn stones), PCNL is the treatment of choice for definitive stone clearance. This procedure is performed under general anaesthesia, usually with the patient lying prone on the surgical table. Under X-ray or ultrasound guidance, the urologist makes a tiny incision in the back and creates a tunnel directly into the relevant chamber of the kidney. Rigid and flexible nephroscopes are used to locate to the stones, which are then shattered and removed using various devices (figure 4). A small nephrostomy tube is left in the kidney for a few days till residual bleeding clears up.
Figure 4. Use of rigid and flexible nephroscopes to access stones in the kidney through a small incision in the skin.
Which treatment is best for me?
Urinary stones are a common cause of visits to the emergency department. Patients are usually referred on to the urologist, who will then advise on the most appropriate treatment approach based on the stone's size, characteristics of the urinary tract anatomy, and clinical condition. Advances in medical therapy and surgical technologies now allow stones to be eradicated successfully with minimal scars, less pain and swift recovery.
About the Author
Dr Tan Yau Min, Gerald is a consultant urologist at Mt Elizabeth Hospital with over 17 years of clinical experience. He is internationally renowned for his expertise in minimally invasive and robotic surgery for prostate, kidney and bladder diseases. Dr Tan has received numerous top international awards for academic and clinical excellence, and was named the Outstanding YoungUrologist of Asia by the Urological Associations of Asia in 2012. He may be contacted via email at email@example.com.
1. C Turk, T. Knoll, A Petrik et al. EAU guidelines on urolithiasis 2013. http://www.uroweb.org/gls/pdf/21_Urolithiasis_LR.pdf
2. Bader MJ, Eisner B, Porpilgia F, Preminger GM, Tiselius HG. Contemporary management of ureteral stones. European Urology 2012; 61(4): 764-772.
3. Seitz C, Liatsikos E, Porpiglia F, Tiselius HG, Zwergel U. Medical therapy to facilitate the passage of stones: what is the evidence? European Urology. 2009; 56:455–471.
4. S Rajamahanty, M Grasso. Flexible ureteroscopy update: indications, instrumentation and technical advances. Indian Journal of Urology 2008; 24(4): 532-537.