CT Scan in the Diagnosis of Urinary Tract Stones

Saturday, April 1, 2017

    Imaging plays an essential role in the diagnosis and initial management of urolithiasis. The imaging methods used have undergone considerable evolution in recent years. One major advance is the use of plain non-contrast helical computed tomography (NCHCT) in patients who are suspected of having a renal colic. The various aspects of the formation, diagnosis and management of urolithiasis are discuss below.
    The term kidney stones, renal stones, renal calculi, nephrolithiasis and urolithiasis are often used interchangeably to refer to the gravel like deposits that may appear in any part of the urinary system, from the kidney to the bladder. These deposits may small or larger, single or multiple. Sometimes this stones are barely bigger than the sugar granules, whereas in other cases cases they are so big that can fill the entire renal pelvis. The term nephrolithiasis is derived from the greek word nephros means kidney and lithos meaning stone. Urolithiasis is from the greek word ouron (urine), and the term calculus (plural calculi) is the Latin word for pebble. Specifically, the term renal calculi is used when the stones is located in the kidney, whereas the term ureterolithiasis is used when the stone is located in the ureter.

Symptoms of Stone in Urinary Tract

    The passage of the renal stones from the kidney to the urinary tract is always accompanied by an acute, or usually sever pain, and this pain is referred to as renal colic. This urethral stone can sometimes cause obstruction, distention and enlargement of the collection system in the kidney; this changes is sometime referred to as hydronephrosis. However, renal and bladder stones are sometimes not painful and sometimes it remains undetected for many years. In most rare cases, this stones are discovered as incidental findings when a patient undergoes ultrasound or plain xray examination of the abdomen or KUB.
    The pain of renal colic often begins as vague flank pain. Patients will often ignore this early symptom until the pain advances into waves of severe pain. The symptoms the patient experiences will vary depending on the stone’s location as shown on the table below. Typically, the pain tends to migrate caudally and medially as the stone works its way down the ureter.
    Many other conditions can cause symptoms similar to those of renal colic. In women, gynecologic conditions such as ovarian torsion, ovarian cyst, and ectopic pregnancy must be considered. In men, symptoms of testicular tumor, epididymitis, prostatitis may result to have the same symptoms of distal ureteral stones. Other general causes of abdominal pain such as appendicitis, cholecystitis, diverticulitis, colitis, constipation or hernia may present with similar discomfort. In patient’s older than 60 years with no prior history of stones, abdominal aortic aneurysm must be ruled out before the diagnosis of nephrolithiasis is pursued. Finally, other urologic conditions, such as renal or ureteral tumors, must also be excluded.

urinary tract stone
Relationship of Stone Location to
Symptom Presentation

What are the Causes of Stones?

    Unlike many other medical conditions such as diverticulitis, kidney stones are not a result of moderm lifestyle. In fact, stone disease can be traced back to the earliest human records. Scientist have found evidence of kidney stones in a 7000 year old Egyptian mummy.
    When there is no clear precipitating factor identified that can be linked to stone formation, the condition is referred to as idiopathic nephrolithiasis. Urinary tract infection and kidney disorder such as polycystic kidney disease are associated with stone formation. A number of metabolic disease are associated with nephrolithiasis like for example, hyperparathyroidism, hyperoxaluria. In general, the development of stones is related to decreased urine volume or increased excretion of stone forming components such as calcium, oxalate, urate, cysteine, xanthine, and phosphate. The stone form in the urine collecting system of the kidney. For many patients, hereditary factors are important. A person with a family history of kidney stone is more likely to develop stones. Genetic factors may play a role in up to 45% of calcium stone cases.
    Normal urine is supersaturated with calcium oxalate, the primary constituent of most kidney stones. However, stones will not form unless there is one of a number of abnormalities such as overexcretion of stone constituents, a persistent imbalance in urinary pH, or an obstruction or infection in the urinary tract. In some cases, the underlying problem is simply poor fluid or water intake leading to concentrated urine.
    Although certain foods may promote stone formation in people who are susceptible, researchers do not believe that eating any specific food causes stones to form in people who are not susceptible. Therefore, there are no specific dietary recommendations to prevent stone formation. However, once a stone has been analyzed, the patient’s diet can be evaluated, and then changes can be recommended that will reduce the likelihood of recurrence.

Types of Renal Stones

    Stone composition often provides clues to an underlying metabolic abnormality. There are four basic types of urinary stones.
  • Calcium Salts
  • Uric Acid
  • Magnesium Ammonium Phosphate – called struvite

 

Cystine

    These four types of renal calculi are associated with more than 20 different causes. A fifth type of stone is drug-induced. A number of medications can precipitate in urine causing stone formation. These include indinavir, guaifenesin, triamterene, silicate (this is an overuse of antacids cointaining magnesium silicate), and sulfa drugs.
    Calcium salts stones are the most common type of stone, according for approximately 75% of stone cases. They occur when there is too much calcium in the urine or blood. There are a variety of conditions that result in excessive urine calcium (hypercalciuria) or excessive blood calcium (hypercalcemia). Defective kidney function may allow too much calcium in the urine, or excessive calcium may be absorbed from the stomach and intestine. Some calcium stones are caused by an excess of a chemical called oxlate that is present in many foods such as spinach or chocolate. Oxalate binds easily with calcium to form a stone. It is interesting to note that excessive dietary calcium is not though to be a factor in stone formation, so calcium restriction is no longer recommended.

Struvite Stones

    Struvite stones form when the urinary tract is infected with certain bacteria that secrete specific enzymes. These bacteria, called urea-splitting bacteria, have the ability to precipitate a chemical reaction that results in the formation of struvite stones. The women are twice as likely to have struvite as men. Because struvite stones are almost always caused by urinary tract infections, they are often called infection stones.

Uric Acid Stones

    Uric acid stones most often form a result of high concentration of uric acid crystals, a condition known as hyperuricuria. These stones are associated with urine pH less than 5.5, high purine intake, like organ meats, legumes, fish, meat extracts, gravies, or malignancy. Approximately 25% of patients who have a kidney stone composed of uric acid have gout.

Cystine Stones

    Cystine stones are found in patient with an inherited disorder that causes abnormal transport of the amino acids cysteine, ornithine, lysine, and arginine in the kidney and gastrointestinal tract.

Stone Natural Passage

    It is estimated that 80 to 85% of urinary calculi will pass spontaneously. There are several factors that influence the ability to pass a stone, including the person’s size, prior stone passage, prostate enlargement, pregnancy, and the stone’s size. A 4-mm stone has an 80% chance of passage, whereas a 5 mm stone has a 20% possibility of passage.

Presentation and Differential Diagnosis

    In some situations, the presence of renal stones will be accompanied by considerable discomfort. Urolithiasis should always be considered in the differential diagnosis of abdominal pain. The classic patient with renal colic is in excruciating unilateral flank or lower abdominal pain, pacing about and unable to lie still. The pain is not related to any precipitating event such as trauma, and is not relieved by postural changes. This presentation is in contrast to a patient with peritoneal irritation who will typically remain as motionless as possible to minimize discomfort. Some patients with urolithiasis complain of nausea and vomiting that is caused by stimulation of the celiac plexus. Fever is not part of the uncomplicated nephrolithiasis. If fever is present, hydronephrosis with infection, pyonephrosis, or perinephric abscess should be suspected.
    It should be noted that the size of the stone does not necessarily predict the severity of the pain: a very tiny crystal with sharp edges can cause intense pain, whereas a larger round stone may not be a problematic. If the stone is too large to pass easily, pain continues as the muscles in the wall of the tiny ureter try to squeeze the stone along into the bladder. As the stone moves down the ureter closer to the bladder, the patient may complain of urinary frequency or a burning sensation during urination.

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