Treatment. Radiologic Evaluation

Radiologic Evaluation

Approximately 90% of urinary tract stones are radioopaque and can be seen on plain radiographs. Stones comprised of uric acid, struvite, or xanthine are typically radiolucent. Stones less than 0.5 mm may be difficult to detect on plain films due to overlying bowel gas and fecal material, and tomograms may be helpful to localize radiodensities to the urinary tract. IVP (intravenous pyelogram) can usually demonstrate the calcification within the urinary tract, as well as provide functional evidence of obstruction due to the stone. IVP also provides the best delineation of the anatomy of the calyceal system, pelvis, and ureter that may be important in planning treatment. Ultrasound is often the preferred initial examation in children because of its lack of need for radiation, intravenous access, and contrast injection. The sensitivity of ultrasound for detection of renal calculi has been reported as high as 96%, and detection of ureteral calculi is aided by the presence of obstruction proximal to the calculus. Sonography can miss stones in the absence of hydroureteronephrosis, in the presence of overlying bowel gas or large body habitus, or with small stone size (less than 0.5 mm). CT scanning has become the gold standard for stone detection for a variety of reasons. Technological advances of spiral CT have allowed rapid scanning with 3- to 5-mm section images during a single breathhold. CT can detect nearly all stones due to their high density, even when radiolucent or as small as a few millimeters. Evidence of obstruction is easily seen, and body habitus is unimportant. Typically, intravenous constrast is not needed to localize the density within the urinary tract. Additional intrabdominal pathology can be noted when obtained in the setting of an acute abdomen.

Note! Radiologic evaluation may include plain abdominal radiography, US, intravenous pyelography, and noncontrast CT. In adults, the standard imaging study is noncontrast CT because of its sensitivity and specificity. In children, however, these studies are limited, although some authors recommend CT as the first-line imaging study. Others recommend initial abdominal US because of the varied presentation of urolithiasis in children and because of concerns about radiation exposure. Plain abdominal radiography may not be helpful in the initial diagnosis but may assist in planning treatment on the basis of the ability to visualize the stone.

Four main factors affect initial treatment decisions: the clinical scenario, stone composition, stone size, and stone location (Table 8.2).

During the acute phase (acute renal colic) when the stone is being passed, management is directed toward pain control and facilitating passage or removal of the stone(s). Nonsteroidal anti-inflammatory drugs (NSAIDs) and opioids can be cautiously used to control acute pain. Medical expulsive therapy for an acute stone episode includes tamsulosin and alpha blockers such as doxazosin.

Oral fluids and analgesic (NSAIDs - e.g., Ibuprofen) should be encouraged to facilitate the passage of stones and to reduce any risk of permanent damage to renal function. Many stones in the renal tract will pass spontaneously but large ones may require removal. Of ureteral stones, 95% of those 2-4 mm in diameter pass spontaneously but passage may take as long as 40 days. Intervention may be required in 50% of ureteral calculi greater than 5 mm. Those larger than 7 mm are unlikely to pass spontaneously.

The degree of pain, and patient gender and age appear to have no bearing on the time taken to pass a stone.

If the child passes a stone or stone fragment, save it in a clean container. A lab can analyze the stone to determine the type, which can guide treatment.

In the hospital, the child will be given intravenous (IV) pain medications and IV fluids. If the stone is small, this treatment may be continued for several days, until the stone passes. During this time, the location of the stone is usually monitored with ultrasound.

In the setting of potential urinary tract obstruction with fever or complete obstruction, urgent relief of the obstruction is warranted, either by placement of a ureteral stent or by percutaneous nephrostomy. The decision between ureteral stent placement and percutaneous nephrostomy is dependent on physician preference, available resources, and patient size and anatomy. In children, nephrostomy drainage may be performed without general anesthesia and may be the procedure of choice.

After relief of the obstruction and subsequent treatment of infection, definitive therapy directed at stone clearance can be undertaken.

Table 8.2

Factors Affecting the Treatment of Stones (by Anthony A. Caldamone, Robert Shamberger, 2012)

Factor	Treatment Consideration
Clinical scenario
Bilateral obstruction	For all scenarios, urgent relief of obstruction via stent or nephrostomy
Obstruction of a solitary kidney
Fever/UTI with potential obstruction
Intractable pain
Stone composition
Uric acid	Consider chemodissolution
Struvite	Continue antibiotic therapy throughout treatment
Cystine	Responds poorly to ESWL
Calcium oxalate	Radiopaque; may respond well to ESWL
Stone size
<4 mm	Approximately 90% chance of spontaneous passage
4-6 mm	Approximately 50% chance of spontaneous passage
>6 mm	Approximately 10%-20% chance of spontaneous passage
Stone location
Renal	ESWL or PCNL
Proximal ureteral	Ureteroscopic extraction (antegrade) or ESWL
Distal ureteral	Ureteroscopic extraction (retrograde) or ESWL

The most common composition of upper tract calculi is calcium oxalate. The stones are radiopaque and do not respond to dissolution therapy. Calcium oxalate monohydrate stones may be resistant to extracorporeal shock wave lithotripsy (ESWL), whereas calcium oxalate dihydrate calculi, which are more common, generally respond well.

Uric acid calculi are radiolucent and form at a low urinary pH. They are often identified by their characteristic Hounsfield units (the Hounsfield scale, named after Sir Godfrey Newbold Hounsfield, is a quantitative scale for describing radiodensity) on noncontrast CT. Uric acid stones may be dissolved and prevented by alkalinization of the urine (pH > 6.5) using sodium bicarbonate or potassium citrate. If symptoms are present, a ureteral stent or nephrostomy tube may be used for temporary relief during dissolution therapy.

Struvite stones are usually associated with infection, and antibiotics should be continued throughout treatment. Because struvite stones are generally large or staghorn in shape, percutaneous nephrostolithotomy (PCNL) is often the first-line treatment for these stones.

Cystine stones are typically difficult to treat and frequently recur. Small renal cystine stones may be treated by ESWL, whereas larger stones will likely require PCNL or ureteroscopic extraction.

Stone size can be used to predict whether the stone will pass without intervention. Therefore supportive care in the form of vigorous hydration (oral or intravenous, as needed) and analgesic therapy is a reasonable first step in a child with a small stone in the absence of fever or complete ureteral obstruction.

Studies demonstrate that partial obstruction is well tolerated in the short term; thus this treatment may be continued for 3 to 4 weeks on an outpatient basis to allow spontaneous passage of the stone.

In the case of an obstructing stone 4 mm or greater in size, the likelihood of spontaneous passage is significantly lower, and intervention may be indicated sooner.

Nonobstructing stones can be treated electively. Stones larger than 2 cm have demonstrated a poor stone-free response to ESWL, and a National Institutes of Health Consensus Conference in 1998 recommended that stones larger than 2 cm be approached by PCNL as first-line treatment. "Sandwich therapy," which is a combination of PCNL and ESWL, is an addition to the treatment armamentarium for large calculi.

Calculi are most commonly located within the renal pelvis or calices, proximal ureter, distal ureter, or bladder. Each location lends itself to different treatment approaches. For renal calculi, ESWL or PCNL is suitable. ESWL or ureteroscopic stone extraction is an appropriate choice for ureteral stones, whereas cystolitholapaxy or cystolithotomy is recommended for bladder calculi.

ESWL, first described in the early 1980s, is noninvasive and well-tolerated but requires general anesthesia in many young children and special precautions in infants. This procedure may be suitable for proximal ureteral stones and even some distal ureteral stones; however, treatment of calculi more distal than the midureter is contraindicated in females because of the unknown effects of shock waves on the developing ovary. Stone-free rates after one to two treatments generally range from 70% to 97% (mean 85%).

Complications of ESWL therapy include incomplete fragmentation of the stone, retained fragments, Steinstrasse (a complication of ESWL for urinary tract calculi in which stone fragments block the ureter to form a “stone street”), perinephric hematoma, fever, renal colic, and abrasion or ecchymosis at the site of shock wave entry and exit. Although the distant and long-term effects of ESWL are unknown, short-term follow-up studies suggest no demonstrable complications with regard to renal function or hypertension.

PCNL requires nephrostomy tube placement, general anesthesia, and inpatient hospitalization. Once the nephrostomy tube is placed, the tract is dilated to a size appropriate for the nephroscope and electrohydraulic or ultrasonic lithotriptor. It is a good choice for a large renal stone associated with hydronephrosis or one refractory to ESWL treatment (cystine or calcium oxalate monohydrate). PCNL and ESWL can be combined for optimal treatment in some cases, so-called sandwich therapy. Stone-free rates may approach 100%.

Complications of PCNL include perforation of the collecting system, bleeding, extravasation of irrigant, pneumothorax, intestinal injury, and retained fragments.

Ureteroscopic stone extraction in children has become feasible with the development of progressively smaller uretero-scopes and working instruments. Ureteroscopic treatment of ureteral calculi may be approached in an antegrade or retrograde fashion, and the stone may be extracted intact or fragmented using a laser, ultrasound, or hydraulic lithotriptor (Swiss Lithoclast). Success rates for ureteroscopic stone extraction may exceed 95%. An indwelling ureteral stent may be left in place for 24 to 72 hours to prevent obstruction secondary to ureteral spasm or edema.

Complications include ureteral perforation, ureteral stricture, reflux, proximal migration of the stone, and loss of the stone through a perforated ureter.

Despite the success of minimally invasive treatment for pediatric stone disease, open surgical treatment is still required in up to 17% of patients, which may result in decreased renal function in up to 45%.

Anatomic abnormalities such as ureteropelvic junction obstruction or obstructed megaureter may be addressed concurrently with stone treatment and must be dealt with eventually to prevent recurrence and optimize renal function.

Cystolitholapaxy, or transurethral lithopexy of bladder stones, has been the preferred approach for all but large bladder calculi. The stone is fragmented using the electrohydraulic lithotriptor, and the fragments are irrigated from the bladder. Bladder calculi are becoming more common in children who have undergone augmentation cystoplasty, and in this population, open removal of the intact calculi may be a more prudent approach to minimize the risk of recurrence due to retained fragments, although this remains controversial.

Note! Litholapaxy referred to the process of breaking stone and removal of them, consequently. But, lithotripsy is just action of breaking the stone. Practically, litholapaxy is used almost exclusively in the bladder, and refers to mechanical or physical destruction of the stone. Lithotripsy implies an energy source (ESWL or laser).

Lithos = stone in (Greek); Tripsis = to rub or pound (Greek); Lapaxis = emypting out (Greek).

Дата добавления: 2014-10-15