Chapter IV - Urinary System
Ureters and Kidney Stones
The ureters are the ducts that carry urine from the kidneys to the urinary bladder. The ureters are muscular tubes that can propel urine along by the motions of peristalsis. In the adult, the ureters are usually 25 to 35cm long.
The ureters enter the bladder posteriorly, running within the wall of the bladder for a few centimeters. There are no valves in the ureters, backflow being prevented by pressure from the filling of the bladder, as well as the tone of the muscle in the bladder wall.
The ureter has a diameter of about 3 millimeters, and the lumen is star-shaped. Like the bladder, it is lined with transitional epithelium, and contains layers of smooth muscle.
The epithelial cells of the ureter are stratified (in many layers), are normally round in shape but become squamous (flat) when stretched. The lamina propria is thick and elastic (as it is important that it is impermeable).
There are two spiral layers of smooth muscle in the ureter wall, an inner loose spiral, and an outer tight spiral. The inner loose spiral is sometimes described as longitudinal, and the outer as circular, (this is opposite to the situation in the gastrointestinal tract).
The adventitia of the ureter, like elsewhere is composed of fibrous connective tissue, that binds it to adjacent tissues.
Diseases and disorders
Medical problems that can affect the ureter include:
· Cancer of the ureter
· Passage of kidney stones
Megaureter is a descriptive term aptly applied to the ureter that is dilated out of proportion to the rest of the urinary tract. The term implies a congenital disorder, and since the neonatal ureter contains a large amount of elastic fibers, it can become enormously wide. Congenital ureteral dilatation may be caused by vesicoureteral reflux, obstructive disease, high urine flow from non-concentrating kidneys, and maldevelopment of ureteral musculature.
A ureterocele is a congenital abnormality found in the urinary bladder. In this condition called ureteroceles, the distal ureter balloons at its opening into the bladder, forming a sac-like pouch. It is most often associated with a double collector system, where two ureters drain their respective kidney instead of one. Ureteroceles strikes only one in 4,000 individuals, atleast four fifths of whom are female. Since the advent of the ultrasound, most ureteroceles is diagnosed prenatally. The pediatric and adult conditions are often found only through diagnostic imaging performed for reasons other than suspicious ureteroceles.
Kidney stones, also known as nephrolithiases, urolithiases or renal calculi, are solid accretions (crystals) of dissolved minerals in urine found inside the kidneys or ureters. They vary in size from as small as a grain of sand to as large as a golf ball. Kidney stones typically leave the body in the urine stream; if they grow relatively large before passing (on the order of millimeters), obstruction of a ureter and distention with urine can cause severe pain most commonly felt in the flank, lower abdomen and groin.
Conventional wisdom has held that consumption of too much calcium can aggravate the development of kidney stones, since the most common type of stone is calcium oxalate. However, strong evidence has accumulated demonstrating that low-calcium diets are associated with higher stone risk and vice-versa for the typical stone former.
Other examples of kidney stones include struvite (magnesium, ammonium and phosphate), uric acid, calcium phosphate, or cystine (the amino acid found only in people suffering from cystinuria). The formation of struvite stones is associated with the presence of urease splitting bacteria (Klebsiella, Serratia, Proteus, Providencia species) which can split urea into ammonia, most commonly Proteus mirabilis.
Types of Stones:
· Calcium - most common type
· Struvite - infection stone
· Uric acid stone
· Cystine stone
Kidney stones are usually idiopathic and asymptomatic until they obstruct the flow of urine. Symptoms can include acute flank pain (renal colic), nausea and vomiting, restlessness, dull pain, hematuria, and possibly fever if infection is present. Acute renal colic is described as one of the worst types of pain that a patient can suffer from.
Diagnosis & Investigation
Diagnosis is usually made on the basis of the location and severity of the pain, which is typically colic in nature (comes and goes in spasmodic waves). Radiological imaging is used to confirm the diagnosis and a number of other tests can be undertaken to help establish both the possible cause and consequences of the stone.
The relatively dense calcium renders these stones radio-opaque and they can be detected by a traditional X-ray of the abdomen that includes Kidneys, Ureters and Bladder—KUB. This may be followed by an IVP (Intravenous Pyelogram) which requires roughly about 50ml of a special dye to be injected into the bloodstream that goes straight to the kidneys and helps outline any stone on a repeated X-ray. Computed tomography, a specialized X-ray, is by far the most accurate diagnostic test for the detection of kidney stones.
Investigations typically carried out include:
· Culture of a urine sample to exclude urine infection (either as a differential cause of the patient's pain, or secondary to the presence of a stone)
· Blood tests: Full blood count for the presence of a raised white cell count, (Neutrophilia) suggestive of infection, a check of renal function and if raised blood calcium blood levels (hypercalcemia).
· 24 hour urine collection to measure total daily urinary calcium, oxalate and phosphate.
Stones less than 5 mm in size usually will pass spontaneously, with diclofenac usually proving effective pain management. However the majority of stones greater than 6 mm will require some form of intervention, especially so if the stone is stuck causing obstruction and infection of the urinary tract.
In many cases non-invasive Extracorporeal Shock Wave Lithotripsy may be used. Otherwise some form of invasive procedure is required; with approaches including retrograde ureteral, percutaneous nephrolithotomy or open surgery, and using laser, ultrasonic and mechanical (pneumatic, shock-wave) forms of energy to fragment stones.
· Preventive strategies include dietary modifications and sometimes also taking drugs with the goal of reducing excretory load on the kidneys.
· Drinking enough water to make 2 to 2.5 liters of urine per day.
· A diet low in protein, nitrogen and sodium intake.
· Restriction of oxalate-rich foods and maintaining an adequate intake of dietary calcium is recommended. There is no convincing evidence that calcium supplements increase the risk of stone formation.
· Taking drugs such as thiazides, potassium citrate and allopurinol depending on the cause of stone formation.
Extracorporeal Shock Wave Lithotripsy (ESWL)
A lithotriptor is a medical device used in the non-invasive treatment of kidney stones (urinary calculosis) and biliary calculi (stones in the gallbladder or in the liver). The scientific name of this procedure is Extracorporeal Shock Wave Lithotripsy (ESWL). Lithotripsy was developed in the early 1980s.
Lithotripsy attempts to break up the stones with minimal collateral damage by using an externally applied, focused high-intensity acoustic pulse. The sedated or anesthestized patient lies down in the apparatus' bed, with his back supported by a water-filled coupling device placed at the level of kidneys, for instance. A fluoroscopic x-ray imaging system or an ultrasound imaging system is used to locate the stone and aim the treatment head such that the F1 of the shock wave is focused upon the offending stone. The treatment usually starts at the equipment's lowest power level, with a long gap between pulses, in order to accustom the patient to the sensation. The frequency of pulses & power level will then be gradually increased, in order to break up the stone more effectively. The successive shock wave pressure pulses result in direct shearing forces, as well as cavitation bubbles surrounding the stone, which fragment the stones in smaller pieces, which then can pass easily through the ureters or the cystic duct. Extracorporeal lithotripsy works best with stones between 4 mm and 2 cm in diameter that are still located in the kidney. It can be used to break up stones, which are located in a ureter, too, but with less success.
ESWL is the least invasive of the commonplace modalities for definitive stone treatment, but provides a lower stone-free rate than other more invasive treatment methods, such as ureteroscopic manipulation with laser lithotripsy or percutaneous nephrolithotomy (PCNL).
ESWL is not without risks. The shock waves themselves, as well as cavitation bubbles formed by the agitation of the urine medium can lead to capillary damage, renal parenchymal or subcapsular hemorrhage. This can lead to long-term consequences such as renal failure and hypertension. Overall complication rates of ESWL range from 5-20%.
Percutaneous nephrolithotomy is a technique that may be used to remove stones from the kidney or upper ureter. It avoids the morbidity of an open procedure.
A needle is passed through the skin into the renal pelvis under ultrasound or radiological guidance. A guide-wire is then threaded through the needle into the kidney to create a track. Using graduated dilators, the track is then enlarged to a diameter of approximately 30 mm. The stone may then be removed immediately or following drainage for 48 hours with a nephrostomy tube.
Small stones can be removed through the nephrostomy track under direct vision using special nephroscope and a variety of grasping instruments. Stones larger than the tract must be fragmented prior to removal, either with ultrasound or electrohydraulic probes.
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Chapter IV - Urinary System