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Nephro-Urology Interventions in Children
Nephro-Urology Interventions in Children Alex M. Barnacle, BM, MRCP, FRCR,* Derek J. Roebuck, MRCPCH, FRCR, FRANZCR,* and John M. Racadio, MD† Nephro-urological interventions developed in adult practice are highly transferable to the pediatric setting, and their use has widened the role of interventional radiology in the management of renal tract pathology in spheres such as oncology and urolithiasis. The emerging evidence is that these procedures are safe and effective in children and their use should be encouraged. Many of the techniques are similar to those used in adults. There are, however, subtle but important pediatric tips and tricks available that serve to minimize risk to the child and increase the chances of technical success. This article covers the indications, techniques, aftercare, and complications for renal biopsy, nephrostomy insertion, percutaneous nephrolithomy procedures, and ureteric stent insertion. Renal biopsy and nephrostomy insertion are commonly performed in most pediatric centers. Percutaneous nephrolithomy may be limited to centers with a significant urology workload, but are complex procedures ideally performed as joint cases between urology and interventional radiology. Tech Vasc Interventional Rad 13:229-237 © 2010 Elsevier Inc. All rights reserved. KEYWORDS pediatric, renal biopsy, nephrostomy, ureteric stent, percutaneous nephrolithotomy
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ephro-urology interventions are commonly performed in children. Many of the techniques are similar to those used in adults. There are, however, subtle but important pediatric tips and tricks available that serve to minimize risk to the child and increase the chances of technical success.
Renal Biopsy Renal biopsy is performed in children to establish a pathologic diagnosis, to monitor disease progression, and to assess response to treatment. Indications for biopsy are similar to those in adults. The patient’s coagulation status must be normalized preoperatively, and the platelet count should be above 50-100,000 ⫻ 106/L. Antibiotic prophylaxis is not routinely required. In small children, sedation or general anesthesia (GA) is required. Children older than about 8 years will often tolerate biopsy without sedation by breathing an equimolar mixture
*Department of Radiology, Great Ormond Street Hospital, London, UK. †Department of Radiology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH. Address reprint requests to Alex M. Barnacle, BM, MRCP, FRCR, Department of Radiology, Great Ormond Street Hospital, London WC1N 3JH, UK. E-mail: [email protected] 1089-2516/10/$-see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1053/j.tvir.2010.04.005
of nitrous oxide and oxygen (Entonox; BOC Health Care, Manchester, UK) via a demand valve. Transplant renal biopsy patients can lie supine for the procedure. Native kidneys are ideally approached with the patient in the lateral position, facing away from the operator. A supportive wedge should be placed under the patient, just above the iliac crest, to widen the space between it and the 12th rib, to optimize views of the kidney. Standard biopsy techniques are covered elsewhere; the following points relate to renal biopsies in particular. We use a 16-gauge noncoaxial semiautomated core needle system (Quick Core; William Cook Europe, Bjaeverskov, Denmark) for renal biopsies. Semiautomated devices are probably better than manual biopsy systems, with better yields of tissue and fewer complications reported.1-4 The automated systems seem to penetrate scarred kidneys with thickened capsules more cleanly. Two cores of tissue are usually required. Native kidneys can be approached via the lower pole, while imaging the kidney in longitudinal section, or by using transverse imaging, with a biopsy trajectory from the flank toward the midline, coring the superficial cortex of the kidney (Fig. 1). Note that adult allografts are often placed intraperitoneally in very small children, so a flank approach is strongly recommended to avoid the peritoneal cavity.5 Whatever the approach, it is 229
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A.M. Barnacle, D.J. Roebuck, and J.M. Racadio number of glomeruli in the sample (Fig. 1). Ideally, a pathology technician should assess each sample in the operating room to confirm that an adequate number of glomeruli are present in the core(s). The use of real-time ultrasound guidance for each throw of the needle is strongly supported in the literature4,6-8 and is arguably now the standard of care for renal biopsy. Postbiopsy ultrasound is not routinely recommended, although some operators will perform a brief on-table ultrasound at the end of the biopsy procedure to ensure that that there is no active bleeding at the biopsy tract and that a significant subcapsular hematoma is not developing. If bleeding is seen, manual pressure at the biopsy site is recommended until Doppler shows cessation of active bleeding. The patient should be aware of the possibility of hematuria, which is very common in the first 48 hours after biopsy. We recommend bed rest for 4 hours. Vital observations should be measured every 30 minutes during that time. The rate of major complications in children is 1.5%-3.4%, the most common being hemorrhage requiring transfusion.6,9 The rate of arterial injury is unknown, as many small arteriovenous fistulae and pseudoaneurysms are asymptomatic and may not be specifically sought on follow-up imaging. The reported incidence of such complications varies widely between 0.34% and 9%.10,11 Transplant biopsy in children is as safe as native renal biopsy.5
Nephrostomy Insertion
Figure 1 Biopsy of a native kidney. (A) Transverse ultrasound image of the right kidney. The anterior aspect of the kidney is punctured from the right flank. (B) Once the biopsy needle is within the renal parenchyma, it is partially withdrawn and “flattened out,” so the coring part of the needle samples the superficial cortex, which is rich in glomeruli. (Color version of figure is available online.)
prudent to puncture the renal capsule at a steep angle, so that there is no risk of tearing the capsule by too shallow an approach. A breath hold at this stage is also very useful, minimizing movement of the kidney and subsequent trauma to the capsule as the needle swings with respiration. Once the needle is safely in the renal parenchyma, it can be partially withdrawn, to lie just inside the capsule, and redirected at a more shallow trajectory, so that it slides along the superficial portion of the cortex, maximizing the
Ultrasound-guided nephrostomy insertion is usually more straightforward in children than in adults, as visualization of the kidney is often easier, but this procedure remains one that should be approached with caution. The abdominal wall and the kidney are more pliable in small children, and there is less space within the collecting system to maneuver guidewires and drainage tubes. The simplest possible technique should be used, because factors such as extravasation of urine and clot formation in the collecting system can quickly render the procedure very difficult. The most common and most urgent indication for drainage of the upper renal tract, as in adults, is an infected obstructed kidney. Causes of upper tract obstruction in children include renal calculi, clot, mycetoma, anatomic pelviureteric junction obstruction (PUJO), ureterovesical junction obstruction, an extrinsic abdominal or pelvic mass, or an obstructing ureterocele. Infection may be the first presentation of a previously undiagnosed obstructed system, and decompression is therefore the priority. Drainage may be required as part of the management of a dysfunctional renal tract, allowing assessment of renal function pre- and postdecompression. All patients should have their coagulation normalized and a platelet count of at least 50-80,000 ⫻ 106/L is usually acceptable. Antibiotic prophylaxis is mandatory.12,13 Nephrostomy insertion can be painful and requires a great deal of accuracy by the operator, so we would recommend seda-
Nephro-urology interventions in children tion or GA.12,13 Even when GA is used, long-acting local anesthetic (eg, levobupivacaine 2.5 mg/mL) should be infiltrated all the way along the track, including the renal capsule. This improves the patient’s postoperative experience. The patient is positioned semiprone on the operating table, facing away from the operator.12 Cushioning may be required to stabilize the patient and to support the kidney from the front so that it is not pushed anteriorly during puncture. There is no evidence to suggest a difference in technical success or complication rates in adults between single-stick and double-stick techniques. This may not be true for children, however, for the reasons given below. The single-stick technique is straightforward and is strongly recommended in grossly distended systems. The collecting system is punctured from a dorsal subcostal approach. Care should be taken not to approach from too laterally, to avoid the colon. A one-part 18-gauge needle (Trocar; William Cook Europe) is recommended. This is well visualized on ultrasound and allows a large (0.035- or 0.038inch) guidewire to be advanced into the collecting system (Fig. 2). Ideally, the tip of the guidewire should be advanced down the ureter, so the stiff part of the wire is in the pelvicalyceal system. The guidewire should be relatively stiff (Amplatz Extra Stiff; Boston Scientific, Waterdown, MA) so the nephrostomy tube can be advanced over it as the next and final stage of the procedure.12 This obviates the need for repeated guidewire exchanges, each of which increases the risk of inadvertent loss of access or decompression of the collecting system into the perinephric space. In marked hydronephrosis, the renal parenchyma is usually markedly thinned and the kidney mobile, so the kidney tends to push away from the needle, resisting puncture (Fig. 3).12 As the needle tip approaches and begins to indent the targeted calyx, a short, decisive acceleration of the needle may be necessary to successfully pierce into the collecting system. In these situations, it is vital to puncture the collecting system cleanly and minimize the number of dilatations or exchanges required; it should be possible to advance a 5-Fr nephrostomy tube, on its stiffener, without the prior use of dilators. For larger tubes, a single dilatation to the same gauge as the final tube may be required, using a hydrophilic dilator. The double-stick technique involves initial puncture of any part of the collecting system with a small-caliber (22-gauge) two-part needle (Chiba; William Cook Europe), followed by opacification of the pelvicalyceal system. A suitable calyx is selected for the second puncture, using fluoroscopy (Fig. 4). Puncture of a nondilated system is occasionally required, such as in kidneys containing staghorn calculi, before percutaneous nephrolithotomy (PCNL). Accessing a nondilated system is often easier in a child than an adult as the kidney is nearer the skin surface and therefore better visualized with ultrasound. The lumen of even the narrowest of collecting systems can usually be identified using a high-frequency linear probe. Here, the initial use of a 0.018-inch system (Universal Microintroducer kit; Bard Access Systems, Salt Lake City, UT) and a subsequent hydrophilic 0.035-inch guidewire is recommended. If initial attempts to access the system fail, the 22-gauge punc-
231 ture needle can be advanced into the kidney, just beyond where the calyx is expected to be, and the guidewire tip gently advanced as the needle is withdrawn, so the wire tip is constantly probing for the collecting system. A 0.018-inch wire should fall into the calyx. Slowly injecting very small quantities of contrast while withdrawing the needle, and monitoring this under direct fluoroscopy, can help to identify the lumen of the collecting system; and, at that point, further contrast can be injected to dilate the system further. Some operators advocate hydrating the child before the procedure and administering a single dose of diuretic at the start of the procedure to maximize physiological distension of the collecting system. Nephrostomy in pelvic or horseshoe kidneys and crossedfused ectopia may require computed tomography (CT) guidance. Locking, self-retaining catheters are preferentially used as nephrostomy tubes. A 5- to 6-Fr catheter is almost always sufficient in children, but tubes up to 10 Fr have been used.13 The catheter should be sutured to the skin and fixed with a wide adhesive dressing. Care should be taken to ensure the catheter is not kinked under the dressing and that the tube and drainage bag pass laterally, so the child can lie comfortably supine. If the tube is likely to be removed by another team at a later date, clear instructions as to how to release the locking device must be provided on the operating note. Overall complication rates of nephrostomy are dependent on patient selection. The major complications of bleeding, sepsis, and injury to the renal pelvis have been reported in 0%-4% of children.14-17 Sepsis is the most serious systemic complication but is rare in children.15 Any obstructed system should be considered infected. Prolonged manipulation of guidewires and drainage tubes and overdistension of the collecting system should be avoided as they are likely to increase the risk of bacterial seeding. Formal nephrostogram studies can be postponed until the child is stable. Bleeding may occur due to trauma to renal parenchymal or intercostal vessels. The incidence of bleeding requiring transfusion is approximately 2%.15 Venous bleeding is usually self-limiting and if necessary can be controlled by the use of a larger nephrostomy tube to tamponade the track. Arterial injury can result in an arterio-venous or arterio-calyceal fistula, the true incidence of which is unknown but certainly under-reported. Larger fistulas or pseudoaneurysms are seen on imaging, but more subtle sources of bleeding are often only detected at angiography. Transarterial management of such complications is required.
Percutaneous Nephrolithotomy PCNL involves percutaneous access for minimally invasive, nephroscopic management of upper tract renal calculi. Renal stone disease is uncommon in children. Young children usually present with nonspecific abdominal pain rather than renal colic, which often leads to delay in diagnosis. Infection is now less likely to be the causative process behind stone formation than in the past. Recent studies confirm that over
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Figure 2 Nephrostomy drainage using a “single-stick” technique, following clot obstruction secondary to transplant renal biopsy 12 hours previously. (A) Transverse ultrasound (US) image of the transplant kidney in the right iliac fossa, demonstrating a dilated anterior calyx suitable for puncture. Note clot debris within the calyx (arrow). (B) US-guided puncture of the anterior calyx. (C) US is used to monitor insertion of the 0.035-inch stiff guidewire, which is advanced into the dilated proximal ureter. (D) Fluoroscopy and contrast injection through a short dilator shows the site of clot obstruction. The guidewire is manipulated to break down the clot. (E) An 8.5-Fr pigtail nephrostomy is sited in the decompressed renal pelvis. There is now better contrast filling of the renal pelvis and proximal ureter. (Color version of figure is available online.)
Nephro-urology interventions in children
Figure 3 Decompression of the collecting system following unsuccessful attempt at access. (A) Ultrasound in a 6-month-old boy with pelvic neuroblastoma shows a dilated right pelvicalyceal system. (B) Unsuccessful puncture of a lower pole calyx has resulted in extravasation of urine into the perinephric space, with decompression of the collecting system. If this occurs, it is usually best to stop the procedure and bring the patient back at 24-48 hours, when the system is likely to have redilated. (Color version of figure is available online.)
40% of Western children have an identifiable metabolic predisposition for urolithiasis.18 Children presenting with repeat urinary tract infections or with hematuria require evaluation with a renal tract ultrasound and abdominal radiograph. Unlike in adults, even ureteric calculi are clearly defined sonographically in younger children, and, in most cases, CT is unlikely to provide useful
233 additional information. CT may underestimate renal parenchymal disease and importantly does not define the collecting system anatomy. Intravenous urograms, although considered outdated, have significant value in delineating the collecting system, a key concept on which management decisions are based.19 Increasingly, MR urography may have a role to play as a radiation-free method of achieving highquality imaging of the upper tracts.20 Preoperative radioisotope studies give an estimate of divided renal function. Metabolic assessment should be postponed until stones are retrieved at PCNL. Upper tract stones are treated almost exclusively by extracorporeal lithotripsy or PCNL and often by a combination of the two. PCNL is generally indicated for large stones, stones located in dependent calyces, and in children with a large stone burden, in whom PCNL offers the chance of complete stone clearance in one procedure. PCNL is performed using GA and antibiotic prophylaxis. The urologist usually places a ureteric catheter via a cystoscopic approach and the patient is then positioned prone. Initial access is the same as for nephrostomy, although the choice of calyx is governed by the need to optimize nephroscopic access to the calculi, and an upper pole approach is often required. The PCNL track approach should be always be discussed in detail with the urologist involved, so that both nephroscopic and radiological factors are considered when creating an optimal approach to the stone burden. In children with severe scoliosis or ectopic kidneys, a CT-guided approach may be required. Opacification of the system via the ureteric catheter, before puncture, can be useful (similar to a double-stick approach). An 18-gauge three-part (sheathed) needle (eg, Kellett needle; Rocket Medical, Watford, UK) allows the guidewire to be placed through the sheath once the needle has been withdrawn. Ideally, the guidewire should be placed well into the ureter, although this is not always possible in children with a large stone burden. Tract dilatation requires either serial telescopic metal dilators or a balloon dilatation system (Fig. 5). An 18- to 28-Fr track size is created. Calculi are then removed nephroscopically, either with forceps or a basket, or after preliminary stone fragmentation using ultrasonic lithotripsy or laser. Ideally, an additional safety wire should be in place, as the original wire can often be inadvertently displaced during nephroscopy. Occasionally, complex stone burdens or atypical pelvicalyceal anatomy mean that multiple PCNL tracks are required. In such cases, all necessary punctures should be made at the start of the procedure while the system is distended and clot-free, before dilatation of the primary track and nephroscopic intervention. In most cases, a temporary 6-Fr nephrostomy tube and/or double-J ureteric stent is placed at the end of the procedure. Tubeless PCNL, with only the placement of a double-J stent, and totally tubeless (tubeless and stentless) PCNL are well documented in adult series and appear to be safe and effective but are not yet well described in children. Stone clearance rates range from 68% to 100%.21 Complications occur in 8%-43% of children, although
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Figure 4 Nephrostomy in a 15-year-old female with Crohn’s disease and obstruction of the right ureter secondary to a pelvic abscess. The patient is prone. (A) A posterior calyx has been punctured with a 22-gauge Chiba needle under US guidance, and the grossly dilated system opacified with dilute contrast medium. (B) An upper pole calyx is then punctured, in an attempt to provide a straighter guidewire route into the ureter. A dilator placed over the guidewire has allowed more contrast to be instilled into the system, outlining the tortuous upper ureter. (C) The ureteric obstruction could not be crossed, despite the use of hydrophilic guidewires. A nephrostomy tube was inserted. Subsequent stenting of the ureter the following day was straightforward, after the system had been adequately decompressed.
most are minor, such as fever.21 In small children, the length of the procedure and the use of adult-sized instruments mean that transfusion requirement and hypothermia remain potential issues, with reported transfusion rates of up to 23.9%.21
Ureteric Stent Insertion Insertion of ureteric stents is commonly performed at our institution by urologists, using a retrograde approach. Indications for antegrade stenting, by interventional radiology, include PCNL with a large stone burden, failure of access from below (such as extrinsic ureteric compression by a pelvic tumor), and ureteric reimplantation (including following renal transplantation). The antegrade technique is essentially the same as that employed in adults. The initial nephrostomy track is ideally placed via an interpolar or upper pole calyx to simplify the subsequent angles for accessing the upper ureter. This also
means a reasonable amount of antegrade force can be applied along the guidewire with less risk of buckling the wire or perforating the renal pelvis. Often, however, puncturing an upper pole calyx involves steep upward angulation of the needle from beneath the 12th rib, and this angle is suboptimal for the remainder of the procedure, so a compromise has to be reached. In grossly dilated upper tracts with a tight PUJO or tortuous upper ureter, it may be very difficult to advance a guidewire into the ureter, as only the floppy tip of the wire will engage the ureter and further pushing buckles the wire in the dilated pelvis (Fig. 4). In such cases, a 0.014inch or even a 0.010-inch hydrophilic guidewire can be very useful. Alternatively, a temporary nephrostomy can be placed and ureteric stent insertion performed after a 1- to 2-day delay. This allows the upper tract to decompress to some degree, and the PUJO almost invariably becomes easier to cross. Once the ureter is accessed, a guidewire is advanced well into the bladder and a peel-away or angiographic sheath is inserted (Fig. 6). This may require a number of exchanges,
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Figure 5 An 8-year-old female with several calculi in the lower pole of the right kidney. (A) With the patient prone, an interpolar calyx has been punctured and the guidewire coiled in the renal pelvis (short white arrow), as the upper ureter was too narrow to be crossed by the guidewire. Contrast has been instilled via the ureteric catheter which is coiled via an obstructed upper pole calyx that has not filled with contrast (black arrow). A metal dilator has been advanced over the guidewire into the renal pelvis (long white arrow). (B) Successive metal dilators have been advanced over the wire to dilate the track and a 26-Fr plastic sheath placed over the final dilator. (C) The calculi have been cleared nephroscopically via the PCNL sheath. A temporary JJ stent has been placed before removal of the sheath; the proximal part of the JJ stent can be seen (arrow).
beginning with a small-caliber hydrophilic guidewire and ultimately exchanging for a stiff wire, using a short dilator or angled catheter to give direction when advancing the hydrophilic wire along the ureter. Ureteric strictures may need to be dilated using a conventional angioplasty balloon (Fig. 6) or even a cutting balloon. Variable length silicone stents (William Cook Europe) will suffice in most children up to the age of 10-12 years and avoid the need to measure ureteric length. The stent is orientated so that its tapered end is advanced into the bladder. The other end commonly has a suture through it. If not, a polypropylene or nylon suture can be passed through the proximal end of the straight part of the stent, using a round-bodied needle. Once the stent is advanced
partway along the guidewire, it is followed by a “pusher” catheter with a radio-opaque distal tip. The pusher is used to advance the distal end of the stent into the bladder. Then, the proximal end of the stent is fully advanced into the renal pelvis, using the radio-opaque marker to determine the end of the pusher and therefore the top of the stent. If the stent inadvertently advances further into the ureter rather than coiling in the pelvis, the guidewire is withdrawn and the tip of the pusher used to encourage the top of the stent to coil appropriately. The suture can be used to pull the stent back up from the ureter if required. Once a satisfactory position is achieved, the suture and peel-away sheath are removed.
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Figure 6 Dilatation and stenting of an idiopathic ureteric stricture. (A) Access has been obtained via an existing lower pole nephrostomy. It may well have been better to repuncture, to gain access from an interpolar or upper pole calyx. There is complete occlusion of the upper ureter (arrow). (B) The stricture has been crossed with a 0.014-inch guidewire. Its tip (not shown) is in the bladder. An angioplasty balloon has been advanced to the midureter. This required the use of a 6-Fr renal double curve guiding catheter (black arrow). Note the use of a safety wire (white arrow). (C) The 4-mm angioplasty balloon has been fully inflated. (D) A 5.2-Fr variable length (80-200 mm) silicone double-J stent has been advanced and the guidewire withdrawn. The distal pigtail (arrow) is forming in the bladder. (E) After withdrawal of the pusher catheter the upper pigtail (white arrow) has formed in the renal pelvis. There was significant bleeding during the procedure, so the safety wire was used to insert a precautionary nephrostomy tube (black arrow).
Nephro-urology interventions in children Complications in children include technical failure, infection, and stent malposition. In children with a propensity for stone formation, stent encrustation is a serious concern, and stents should not be placed for longer than 4-6 weeks without regular monitoring.
References 1. Nyman RS, Cappelen-Smith J, Al Suhaibani H, et al: Yield and complications in percutaneous renal biopsy. Acta Radiol 38:431-436, 1997 2. Webb NJ, Pereira JK, Chait PG, et al: Renal biopsy in children: Comparison of two techniques. Pediatr Nephrol 8:486-488, 1994 3. Nahas WC, Mazzucchi E, Henrique A, et al: Percutaneous needle biopsy of the renal allograft using the automated needle system: Evaluation of 87 procedures. J Urol 150:313-315, 1993 4. Feneberg R, Schaefer F, Zieger B, et al: Percutaneous renal biopsy in children: A 27 year experience. Nephron 79:438-446, 1998 5. Vidhun J, Masciandro J, Varich L, et al: Safety and risk stratification of percutaneous biopsies of adult-sized renal allografts in infant and older pediatric recipients. Transplantation 76:552-557, 2003 6. Tang S, Li JH, Lui SL, et al: Free-hand, ultrasound-guided percutaneous renal biopsy: Experience from a single operator. Eur J Radiol 41:65-69, 2002 7. Cozens NJ, Murchison JT, Allan PL, et al: Conventional 15G needle technique for renal biopsy compared with ultrasound-guided springloaded 18G needle biopsy. Br J Radiol 65:594-597, 1992 8. Bogan ML, Kopecky KK, Kraft JL, et al: Needle biopsy of renal allografts; comparison of two techniques. Radiology 174:273-275, 1990 9. Davis ID, Ochlenschlager W, O’Riordan MA, et al: Pediatric renal bi-
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14. 15. 16. 17. 18. 19. 20. 21.
opsy: Should this be performed in an outpatient setting? Pediatr Nephrol 12:96-100, 1998 Bilge I, Rozanes I, Acunas B, et al: Endovascular treatment of arteriovenous fistulas complicating percutaneous renal biopsy in three pediatric patients. Nephrol Dial Transplant 14:2726-2730, 1999 Hergesell O, Felten H, Andrassy K, et al: Safety of ultrasound-guided renal biopsy: Retrospective analysis of 1090 consecutive cases. Nephrol Dial Transplant 13:975-977, 1998 Koral K, Saker MC, Morello FP, et al: Conventional versus modified technique for percutaneous nephrostomy in newborns and young infants. J Vasc Interv Radiol 14:113-116, 2003 Hogan MJ, Coley BD, Jayanthi VR, et al: Percutaneous nephrostomy in children and adolescents: Outpatient management. Radiology 218:207210, 2001 Winfield AC, Kirchner SG, Brun ME, et al: Percutaneous nephrostomy in neonates, infants, and children. Radiology 151:617-619, 1984 Stanley P, Diament MJ: Pediatric percutaneous nephrostomy: Experience with 50 patients. J Urol 135:1223-1226, 1986 O’Brien WM, Matsumoto AH, Grant EG, et al: Percutaneous nephrostomy in infants. Urology 36:269-272, 1990 Laurin S, Sandstrom S, Ivarsson H: Percutaneous nephrostomy in infants and children. Acad Radiol 7:526-529, 2000 Cameron MA, Sakhaee K, Moe OW: Nephrolithiasis in children. Pediatr Nephrol 20:1587-1592, 2005 Hiorns MP: Imaging of urinary tract lithiasis: Who, when and why? Pediatr Radiol 38:S497-S500, 2008 (suppl 3) Grattan-Smith JD: MR urography: Anatomy and physiology. Pediatr Radiol 38:S275-S280, 2008 (suppl 2) Zeren S, Satar N, Bayazit Y, et al: Percutaneous nephrolithotomy in the management of pediatric renal calculi. J Endourol 16:75-78, 2002
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ephro-urology interventions are commonly performed in children. Many of the techniques are similar to those used in adults. There are, however, subtle but important pediatric tips and tricks available that serve to minimize risk to the child and increase the chances of technical success.
Renal Biopsy Renal biopsy is performed in children to establish a pathologic diagnosis, to monitor disease progression, and to assess response to treatment. Indications for biopsy are similar to those in adults. The patient’s coagulation status must be normalized preoperatively, and the platelet count should be above 50-100,000 ⫻ 106/L. Antibiotic prophylaxis is not routinely required. In small children, sedation or general anesthesia (GA) is required. Children older than about 8 years will often tolerate biopsy without sedation by breathing an equimolar mixture
*Department of Radiology, Great Ormond Street Hospital, London, UK. †Department of Radiology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH. Address reprint requests to Alex M. Barnacle, BM, MRCP, FRCR, Department of Radiology, Great Ormond Street Hospital, London WC1N 3JH, UK. E-mail: [email protected] 1089-2516/10/$-see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1053/j.tvir.2010.04.005
of nitrous oxide and oxygen (Entonox; BOC Health Care, Manchester, UK) via a demand valve. Transplant renal biopsy patients can lie supine for the procedure. Native kidneys are ideally approached with the patient in the lateral position, facing away from the operator. A supportive wedge should be placed under the patient, just above the iliac crest, to widen the space between it and the 12th rib, to optimize views of the kidney. Standard biopsy techniques are covered elsewhere; the following points relate to renal biopsies in particular. We use a 16-gauge noncoaxial semiautomated core needle system (Quick Core; William Cook Europe, Bjaeverskov, Denmark) for renal biopsies. Semiautomated devices are probably better than manual biopsy systems, with better yields of tissue and fewer complications reported.1-4 The automated systems seem to penetrate scarred kidneys with thickened capsules more cleanly. Two cores of tissue are usually required. Native kidneys can be approached via the lower pole, while imaging the kidney in longitudinal section, or by using transverse imaging, with a biopsy trajectory from the flank toward the midline, coring the superficial cortex of the kidney (Fig. 1). Note that adult allografts are often placed intraperitoneally in very small children, so a flank approach is strongly recommended to avoid the peritoneal cavity.5 Whatever the approach, it is 229
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A.M. Barnacle, D.J. Roebuck, and J.M. Racadio number of glomeruli in the sample (Fig. 1). Ideally, a pathology technician should assess each sample in the operating room to confirm that an adequate number of glomeruli are present in the core(s). The use of real-time ultrasound guidance for each throw of the needle is strongly supported in the literature4,6-8 and is arguably now the standard of care for renal biopsy. Postbiopsy ultrasound is not routinely recommended, although some operators will perform a brief on-table ultrasound at the end of the biopsy procedure to ensure that that there is no active bleeding at the biopsy tract and that a significant subcapsular hematoma is not developing. If bleeding is seen, manual pressure at the biopsy site is recommended until Doppler shows cessation of active bleeding. The patient should be aware of the possibility of hematuria, which is very common in the first 48 hours after biopsy. We recommend bed rest for 4 hours. Vital observations should be measured every 30 minutes during that time. The rate of major complications in children is 1.5%-3.4%, the most common being hemorrhage requiring transfusion.6,9 The rate of arterial injury is unknown, as many small arteriovenous fistulae and pseudoaneurysms are asymptomatic and may not be specifically sought on follow-up imaging. The reported incidence of such complications varies widely between 0.34% and 9%.10,11 Transplant biopsy in children is as safe as native renal biopsy.5
Nephrostomy Insertion
Figure 1 Biopsy of a native kidney. (A) Transverse ultrasound image of the right kidney. The anterior aspect of the kidney is punctured from the right flank. (B) Once the biopsy needle is within the renal parenchyma, it is partially withdrawn and “flattened out,” so the coring part of the needle samples the superficial cortex, which is rich in glomeruli. (Color version of figure is available online.)
prudent to puncture the renal capsule at a steep angle, so that there is no risk of tearing the capsule by too shallow an approach. A breath hold at this stage is also very useful, minimizing movement of the kidney and subsequent trauma to the capsule as the needle swings with respiration. Once the needle is safely in the renal parenchyma, it can be partially withdrawn, to lie just inside the capsule, and redirected at a more shallow trajectory, so that it slides along the superficial portion of the cortex, maximizing the
Ultrasound-guided nephrostomy insertion is usually more straightforward in children than in adults, as visualization of the kidney is often easier, but this procedure remains one that should be approached with caution. The abdominal wall and the kidney are more pliable in small children, and there is less space within the collecting system to maneuver guidewires and drainage tubes. The simplest possible technique should be used, because factors such as extravasation of urine and clot formation in the collecting system can quickly render the procedure very difficult. The most common and most urgent indication for drainage of the upper renal tract, as in adults, is an infected obstructed kidney. Causes of upper tract obstruction in children include renal calculi, clot, mycetoma, anatomic pelviureteric junction obstruction (PUJO), ureterovesical junction obstruction, an extrinsic abdominal or pelvic mass, or an obstructing ureterocele. Infection may be the first presentation of a previously undiagnosed obstructed system, and decompression is therefore the priority. Drainage may be required as part of the management of a dysfunctional renal tract, allowing assessment of renal function pre- and postdecompression. All patients should have their coagulation normalized and a platelet count of at least 50-80,000 ⫻ 106/L is usually acceptable. Antibiotic prophylaxis is mandatory.12,13 Nephrostomy insertion can be painful and requires a great deal of accuracy by the operator, so we would recommend seda-
Nephro-urology interventions in children tion or GA.12,13 Even when GA is used, long-acting local anesthetic (eg, levobupivacaine 2.5 mg/mL) should be infiltrated all the way along the track, including the renal capsule. This improves the patient’s postoperative experience. The patient is positioned semiprone on the operating table, facing away from the operator.12 Cushioning may be required to stabilize the patient and to support the kidney from the front so that it is not pushed anteriorly during puncture. There is no evidence to suggest a difference in technical success or complication rates in adults between single-stick and double-stick techniques. This may not be true for children, however, for the reasons given below. The single-stick technique is straightforward and is strongly recommended in grossly distended systems. The collecting system is punctured from a dorsal subcostal approach. Care should be taken not to approach from too laterally, to avoid the colon. A one-part 18-gauge needle (Trocar; William Cook Europe) is recommended. This is well visualized on ultrasound and allows a large (0.035- or 0.038inch) guidewire to be advanced into the collecting system (Fig. 2). Ideally, the tip of the guidewire should be advanced down the ureter, so the stiff part of the wire is in the pelvicalyceal system. The guidewire should be relatively stiff (Amplatz Extra Stiff; Boston Scientific, Waterdown, MA) so the nephrostomy tube can be advanced over it as the next and final stage of the procedure.12 This obviates the need for repeated guidewire exchanges, each of which increases the risk of inadvertent loss of access or decompression of the collecting system into the perinephric space. In marked hydronephrosis, the renal parenchyma is usually markedly thinned and the kidney mobile, so the kidney tends to push away from the needle, resisting puncture (Fig. 3).12 As the needle tip approaches and begins to indent the targeted calyx, a short, decisive acceleration of the needle may be necessary to successfully pierce into the collecting system. In these situations, it is vital to puncture the collecting system cleanly and minimize the number of dilatations or exchanges required; it should be possible to advance a 5-Fr nephrostomy tube, on its stiffener, without the prior use of dilators. For larger tubes, a single dilatation to the same gauge as the final tube may be required, using a hydrophilic dilator. The double-stick technique involves initial puncture of any part of the collecting system with a small-caliber (22-gauge) two-part needle (Chiba; William Cook Europe), followed by opacification of the pelvicalyceal system. A suitable calyx is selected for the second puncture, using fluoroscopy (Fig. 4). Puncture of a nondilated system is occasionally required, such as in kidneys containing staghorn calculi, before percutaneous nephrolithotomy (PCNL). Accessing a nondilated system is often easier in a child than an adult as the kidney is nearer the skin surface and therefore better visualized with ultrasound. The lumen of even the narrowest of collecting systems can usually be identified using a high-frequency linear probe. Here, the initial use of a 0.018-inch system (Universal Microintroducer kit; Bard Access Systems, Salt Lake City, UT) and a subsequent hydrophilic 0.035-inch guidewire is recommended. If initial attempts to access the system fail, the 22-gauge punc-
231 ture needle can be advanced into the kidney, just beyond where the calyx is expected to be, and the guidewire tip gently advanced as the needle is withdrawn, so the wire tip is constantly probing for the collecting system. A 0.018-inch wire should fall into the calyx. Slowly injecting very small quantities of contrast while withdrawing the needle, and monitoring this under direct fluoroscopy, can help to identify the lumen of the collecting system; and, at that point, further contrast can be injected to dilate the system further. Some operators advocate hydrating the child before the procedure and administering a single dose of diuretic at the start of the procedure to maximize physiological distension of the collecting system. Nephrostomy in pelvic or horseshoe kidneys and crossedfused ectopia may require computed tomography (CT) guidance. Locking, self-retaining catheters are preferentially used as nephrostomy tubes. A 5- to 6-Fr catheter is almost always sufficient in children, but tubes up to 10 Fr have been used.13 The catheter should be sutured to the skin and fixed with a wide adhesive dressing. Care should be taken to ensure the catheter is not kinked under the dressing and that the tube and drainage bag pass laterally, so the child can lie comfortably supine. If the tube is likely to be removed by another team at a later date, clear instructions as to how to release the locking device must be provided on the operating note. Overall complication rates of nephrostomy are dependent on patient selection. The major complications of bleeding, sepsis, and injury to the renal pelvis have been reported in 0%-4% of children.14-17 Sepsis is the most serious systemic complication but is rare in children.15 Any obstructed system should be considered infected. Prolonged manipulation of guidewires and drainage tubes and overdistension of the collecting system should be avoided as they are likely to increase the risk of bacterial seeding. Formal nephrostogram studies can be postponed until the child is stable. Bleeding may occur due to trauma to renal parenchymal or intercostal vessels. The incidence of bleeding requiring transfusion is approximately 2%.15 Venous bleeding is usually self-limiting and if necessary can be controlled by the use of a larger nephrostomy tube to tamponade the track. Arterial injury can result in an arterio-venous or arterio-calyceal fistula, the true incidence of which is unknown but certainly under-reported. Larger fistulas or pseudoaneurysms are seen on imaging, but more subtle sources of bleeding are often only detected at angiography. Transarterial management of such complications is required.
Percutaneous Nephrolithotomy PCNL involves percutaneous access for minimally invasive, nephroscopic management of upper tract renal calculi. Renal stone disease is uncommon in children. Young children usually present with nonspecific abdominal pain rather than renal colic, which often leads to delay in diagnosis. Infection is now less likely to be the causative process behind stone formation than in the past. Recent studies confirm that over
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Figure 2 Nephrostomy drainage using a “single-stick” technique, following clot obstruction secondary to transplant renal biopsy 12 hours previously. (A) Transverse ultrasound (US) image of the transplant kidney in the right iliac fossa, demonstrating a dilated anterior calyx suitable for puncture. Note clot debris within the calyx (arrow). (B) US-guided puncture of the anterior calyx. (C) US is used to monitor insertion of the 0.035-inch stiff guidewire, which is advanced into the dilated proximal ureter. (D) Fluoroscopy and contrast injection through a short dilator shows the site of clot obstruction. The guidewire is manipulated to break down the clot. (E) An 8.5-Fr pigtail nephrostomy is sited in the decompressed renal pelvis. There is now better contrast filling of the renal pelvis and proximal ureter. (Color version of figure is available online.)
Nephro-urology interventions in children
Figure 3 Decompression of the collecting system following unsuccessful attempt at access. (A) Ultrasound in a 6-month-old boy with pelvic neuroblastoma shows a dilated right pelvicalyceal system. (B) Unsuccessful puncture of a lower pole calyx has resulted in extravasation of urine into the perinephric space, with decompression of the collecting system. If this occurs, it is usually best to stop the procedure and bring the patient back at 24-48 hours, when the system is likely to have redilated. (Color version of figure is available online.)
40% of Western children have an identifiable metabolic predisposition for urolithiasis.18 Children presenting with repeat urinary tract infections or with hematuria require evaluation with a renal tract ultrasound and abdominal radiograph. Unlike in adults, even ureteric calculi are clearly defined sonographically in younger children, and, in most cases, CT is unlikely to provide useful
233 additional information. CT may underestimate renal parenchymal disease and importantly does not define the collecting system anatomy. Intravenous urograms, although considered outdated, have significant value in delineating the collecting system, a key concept on which management decisions are based.19 Increasingly, MR urography may have a role to play as a radiation-free method of achieving highquality imaging of the upper tracts.20 Preoperative radioisotope studies give an estimate of divided renal function. Metabolic assessment should be postponed until stones are retrieved at PCNL. Upper tract stones are treated almost exclusively by extracorporeal lithotripsy or PCNL and often by a combination of the two. PCNL is generally indicated for large stones, stones located in dependent calyces, and in children with a large stone burden, in whom PCNL offers the chance of complete stone clearance in one procedure. PCNL is performed using GA and antibiotic prophylaxis. The urologist usually places a ureteric catheter via a cystoscopic approach and the patient is then positioned prone. Initial access is the same as for nephrostomy, although the choice of calyx is governed by the need to optimize nephroscopic access to the calculi, and an upper pole approach is often required. The PCNL track approach should be always be discussed in detail with the urologist involved, so that both nephroscopic and radiological factors are considered when creating an optimal approach to the stone burden. In children with severe scoliosis or ectopic kidneys, a CT-guided approach may be required. Opacification of the system via the ureteric catheter, before puncture, can be useful (similar to a double-stick approach). An 18-gauge three-part (sheathed) needle (eg, Kellett needle; Rocket Medical, Watford, UK) allows the guidewire to be placed through the sheath once the needle has been withdrawn. Ideally, the guidewire should be placed well into the ureter, although this is not always possible in children with a large stone burden. Tract dilatation requires either serial telescopic metal dilators or a balloon dilatation system (Fig. 5). An 18- to 28-Fr track size is created. Calculi are then removed nephroscopically, either with forceps or a basket, or after preliminary stone fragmentation using ultrasonic lithotripsy or laser. Ideally, an additional safety wire should be in place, as the original wire can often be inadvertently displaced during nephroscopy. Occasionally, complex stone burdens or atypical pelvicalyceal anatomy mean that multiple PCNL tracks are required. In such cases, all necessary punctures should be made at the start of the procedure while the system is distended and clot-free, before dilatation of the primary track and nephroscopic intervention. In most cases, a temporary 6-Fr nephrostomy tube and/or double-J ureteric stent is placed at the end of the procedure. Tubeless PCNL, with only the placement of a double-J stent, and totally tubeless (tubeless and stentless) PCNL are well documented in adult series and appear to be safe and effective but are not yet well described in children. Stone clearance rates range from 68% to 100%.21 Complications occur in 8%-43% of children, although
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Figure 4 Nephrostomy in a 15-year-old female with Crohn’s disease and obstruction of the right ureter secondary to a pelvic abscess. The patient is prone. (A) A posterior calyx has been punctured with a 22-gauge Chiba needle under US guidance, and the grossly dilated system opacified with dilute contrast medium. (B) An upper pole calyx is then punctured, in an attempt to provide a straighter guidewire route into the ureter. A dilator placed over the guidewire has allowed more contrast to be instilled into the system, outlining the tortuous upper ureter. (C) The ureteric obstruction could not be crossed, despite the use of hydrophilic guidewires. A nephrostomy tube was inserted. Subsequent stenting of the ureter the following day was straightforward, after the system had been adequately decompressed.
most are minor, such as fever.21 In small children, the length of the procedure and the use of adult-sized instruments mean that transfusion requirement and hypothermia remain potential issues, with reported transfusion rates of up to 23.9%.21
Ureteric Stent Insertion Insertion of ureteric stents is commonly performed at our institution by urologists, using a retrograde approach. Indications for antegrade stenting, by interventional radiology, include PCNL with a large stone burden, failure of access from below (such as extrinsic ureteric compression by a pelvic tumor), and ureteric reimplantation (including following renal transplantation). The antegrade technique is essentially the same as that employed in adults. The initial nephrostomy track is ideally placed via an interpolar or upper pole calyx to simplify the subsequent angles for accessing the upper ureter. This also
means a reasonable amount of antegrade force can be applied along the guidewire with less risk of buckling the wire or perforating the renal pelvis. Often, however, puncturing an upper pole calyx involves steep upward angulation of the needle from beneath the 12th rib, and this angle is suboptimal for the remainder of the procedure, so a compromise has to be reached. In grossly dilated upper tracts with a tight PUJO or tortuous upper ureter, it may be very difficult to advance a guidewire into the ureter, as only the floppy tip of the wire will engage the ureter and further pushing buckles the wire in the dilated pelvis (Fig. 4). In such cases, a 0.014inch or even a 0.010-inch hydrophilic guidewire can be very useful. Alternatively, a temporary nephrostomy can be placed and ureteric stent insertion performed after a 1- to 2-day delay. This allows the upper tract to decompress to some degree, and the PUJO almost invariably becomes easier to cross. Once the ureter is accessed, a guidewire is advanced well into the bladder and a peel-away or angiographic sheath is inserted (Fig. 6). This may require a number of exchanges,
Nephro-urology interventions in children
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Figure 5 An 8-year-old female with several calculi in the lower pole of the right kidney. (A) With the patient prone, an interpolar calyx has been punctured and the guidewire coiled in the renal pelvis (short white arrow), as the upper ureter was too narrow to be crossed by the guidewire. Contrast has been instilled via the ureteric catheter which is coiled via an obstructed upper pole calyx that has not filled with contrast (black arrow). A metal dilator has been advanced over the guidewire into the renal pelvis (long white arrow). (B) Successive metal dilators have been advanced over the wire to dilate the track and a 26-Fr plastic sheath placed over the final dilator. (C) The calculi have been cleared nephroscopically via the PCNL sheath. A temporary JJ stent has been placed before removal of the sheath; the proximal part of the JJ stent can be seen (arrow).
beginning with a small-caliber hydrophilic guidewire and ultimately exchanging for a stiff wire, using a short dilator or angled catheter to give direction when advancing the hydrophilic wire along the ureter. Ureteric strictures may need to be dilated using a conventional angioplasty balloon (Fig. 6) or even a cutting balloon. Variable length silicone stents (William Cook Europe) will suffice in most children up to the age of 10-12 years and avoid the need to measure ureteric length. The stent is orientated so that its tapered end is advanced into the bladder. The other end commonly has a suture through it. If not, a polypropylene or nylon suture can be passed through the proximal end of the straight part of the stent, using a round-bodied needle. Once the stent is advanced
partway along the guidewire, it is followed by a “pusher” catheter with a radio-opaque distal tip. The pusher is used to advance the distal end of the stent into the bladder. Then, the proximal end of the stent is fully advanced into the renal pelvis, using the radio-opaque marker to determine the end of the pusher and therefore the top of the stent. If the stent inadvertently advances further into the ureter rather than coiling in the pelvis, the guidewire is withdrawn and the tip of the pusher used to encourage the top of the stent to coil appropriately. The suture can be used to pull the stent back up from the ureter if required. Once a satisfactory position is achieved, the suture and peel-away sheath are removed.
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Figure 6 Dilatation and stenting of an idiopathic ureteric stricture. (A) Access has been obtained via an existing lower pole nephrostomy. It may well have been better to repuncture, to gain access from an interpolar or upper pole calyx. There is complete occlusion of the upper ureter (arrow). (B) The stricture has been crossed with a 0.014-inch guidewire. Its tip (not shown) is in the bladder. An angioplasty balloon has been advanced to the midureter. This required the use of a 6-Fr renal double curve guiding catheter (black arrow). Note the use of a safety wire (white arrow). (C) The 4-mm angioplasty balloon has been fully inflated. (D) A 5.2-Fr variable length (80-200 mm) silicone double-J stent has been advanced and the guidewire withdrawn. The distal pigtail (arrow) is forming in the bladder. (E) After withdrawal of the pusher catheter the upper pigtail (white arrow) has formed in the renal pelvis. There was significant bleeding during the procedure, so the safety wire was used to insert a precautionary nephrostomy tube (black arrow).
Nephro-urology interventions in children Complications in children include technical failure, infection, and stent malposition. In children with a propensity for stone formation, stent encrustation is a serious concern, and stents should not be placed for longer than 4-6 weeks without regular monitoring.
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