Uday Patel, Lakshmi Ratnam The genitourinary (GU) tract is especially prone to anatomical and morphological variations and successful intervention relies on careful anatomical appreciation and planning. This chapter describes the various interventional procedures currently used in the GU tract, but commences with a review of the anatomy relevant to renal access, as this is the cornerstone of most GU interventions. The kidneys lie in the perinephric space at the level of T12 to L2/3 vertebral bodies. The upper pole is more medial than the lower, with a coronal axis tilt of about 15°. The upper pole is also more posterior facing than the lower. In the short axis the renal pelvis points anteromedially. Anatomical disposition in the 3 planes is illustrated in Fig. 91-1. The important relations regarding renal access are those adjacent structures that may be inadvertently injured—the liver, spleen, diaphragm, pleura/lung and the colon. Variant anatomy should also be remembered: for example, the splenic flexure of the descending colon may be abnormally high and posterior (said to be more common in obese women). Pre-procedure ultrasound (US) will identify these hazards. The adult kidney has approximately 8–9 calyces. Typically, the upper and lower pole calyces are fused; and therefore larger and easier to access. Calyces will also vary in orientation, facing either relatively anterior or posterior. The posterior calyx is ideal for access, being closer to the skin surface. Posterior calyces also allow better intrarenal navigation; e.g. the route from a posterior to an adjacent anterior calyx or the renal pelvis is more or less in a straight line forward. However, access to the pelviureteric junction (PUJ) and ureter is easier from an interpolar or upper pole calyx. These points are illustrated in Fig. 91-2. The main renal artery divides into a (larger) anterior division and smaller posterior division, and each division further separates into segmental and lobar divisions (Fig. 91-3). Peripherally, the lobar and arcuate arteries skirt around the calyx. Thus, the safest place to puncture a calyx is its middle.1,2 Puncture into the infundibulum or renal pelvis may lacerate larger arterial branches. A further potential hazard is the posterior division, which is the only major renal arterial division that lies posterior to the collecting system. Typically it lies behind the upper renal pelvis but occasionally it is behind the upper pole infundibulum, where it may be injured if entry is misdirected towards the infundibulum rather than the upper pole calyx. Normally there is a single renal artery and vein, but up to 25% of kidneys have more than one renal artery and variant renal veins are seen in 3–17%. These do not influence access, but may explain the occasional vascular injury that occurs despite adherence to safe anatomical principles. Part of either kidney will lie above the eleventh/twelfth rib, especially the left kidney, and upper pole access may require an intercostal entry, placing the intercostal artery or pleura at risk. The intercostal artery runs in a groove underneath the rib and is vulnerable with angled cephalad needle puncture. The posterior reflection of the parietal pleura is horizontal and reflected off the lateral portions of the ribs, and puncture through the latter half of the intercostal space is theoretically safer (Fig. 91-4). From this discussion, it can be appreciated that there are numerous factors to consider when planning safe, effective percutaneous renal access. The important considerations are summarised in Table 91-1. The safest point for calyceal puncture is the centre of the calyx, approached through the relatively avascular plane (Brödel’s line) between the branches of the anterior and posterior divisions of the renal artery. Puncturing the centre of the calyx avoids injury to the arcuate divisions that course around the infundibulum. This is the ideal, and is illustrated in Fig. 91-5. TABLE 91-1 Anatomical Considerations That Influence Renal Access in a Normally Sited Kidney a. The upper pole is more posterior. b. The short axis lies posterolaterally. 2. The Calyces a. The calyces lie either anterior or posterior. b. Upper or lower calyces are often compound or fused and so bigger. 3. Vascular a. There is a theoretically ‘avascular’ line along the lateral margin of the kidney. b. The lobar branches course in a curvilinear fashion around the calyx and papilla. c. The posterior segmental division may lie behind the upper pole infundibulum. a. Pleura lies above the 12th and 11th ribs laterally. b. Intercostal artery lies underneath the rib. c. Liver, spleen and (left) colon may overlie the upper pole. Personal preference may determine choice of equipment, but some general principles can help guide selection. The two broad choices are a one-part 21G needle system (sometimes known as a micropuncture access system) or a one-part 18G/4Fr sheath system. With the former, the puncture is with a 21G needle, through which a 0.018-inch. platinum-tipped wire is inserted, followed by a 4Fr dilator and finally a 0.035-inch. working guidewire. A one-part system is an 18G diamond point needle, over which is a 4Fr sheath and the whole is inserted as a single unit. The puncture size is smaller with the two-part system (21G vs 18G or 0.032 inch vs 0.048 inch diameter) and should be safer, but this has not been proven.3 The ideal puncture site is the centre of a calyx, but the calyx is a small structure with a usually even smaller outlet. Thus to navigate out of the calyx, a soft flexible wire with good torque is important, whereas rigidity is less vital. We favour either a straight-tipped Bentson wire or an angled-tipped hydrophilic wire. With the former wire, the floppy tip should not be too long. Once the guidewire has been manipulated out of the calyx (ideally down into the ureter, or at least into the renal pelvis), rigidity becomes more important, and a stiffer Amplatz-type wire is useful, especially if the track is being dilated for PCNL or a stent is being inserted through a malignant stricture. A stiff shaft hydrophilic wire has particular merits, being both rigid and kink resistant, whereas the other guidewires can kink. Kinks impede catheter advancement and lead to rupture of the renal pelvis.4 The standard diameter is 0.035 inch, but thinner wires, especially with stiff inner cores, e.g. nitinol core, can be useful with tight ureteric strictures. Used for either navigation or drainage. For the former, a short angled-tip (e.g. Kumpe) or Cobra shape, high-torque catheter is best. Hydrophilic catheters are useful for bypassing tight ureteric strictures. For drainage, a pigtail catheter with large holes along the inner surface of the pigtail is chosen, as these are less likely to obstruct once the system decompresses. Any size > 6Fr should suffice, but the pigtail may not easily form in a small renal pelvis. The location and size of the drainage holes in the pigtail ensures good drainage. The pigtail should assist anchorage, especially with a locking system, but they do still fall out, and we routinely also further secure them in place (see below). Drainage catheters less frequently used are straight catheters or those with a Malecot-type tip, both useful with the small renal pelvis. Percutaneous nephrostomy insertion is a commonly performed interventional procedure, most frequently for the relief of renal obstruction, with or without associated infection, and some further indications are listed in Table 91-2. TABLE 91-2 Indications for Insertion of PCN Ideally, a nephrostomy should be performed within working hours, on a stable, well-resuscitated and monitored patient. However, it is also important not to unnecessarily delay renal decompression, especially in those with suspected pyonephrosis or infected hydronephrosis, as these patients can rapidly deteriorate.4 Our practice is to only perform out-of-hours nephrostomy in infected obstructed kidneys and obstructed single or transplant kidneys, but this is an area of debate and department policies differ. Discussion between the urology and radiology department is important, and an agreement reached depending on local skill sets and resources. The only two published randomised studies comparing nephrostomy and ureteric stents showed them to be equally effective.5,6 The technical success rate for PCN is quoted as 98–99% of patients, but it is possible that previous series may have under-represented non-dilated kidneys as the success rate is reduced in patients with non-dilated collecting systems, complex stone disease or staghorn calculi.7–9 Available practice guidelines quote a success rate of 98% for dilated systems and transplants and 85% for non-dilated systems and staghorn calculi.10 There are no absolute contraindications to performing a PCN. Severe coagulopathy is a relative contraindication but this can be corrected. In patients with a limited life expectancy, a nephrostomy should be inserted only if this would lead to improved quality of life and survival. In all cases a multidisciplinary approach and close liaison with referring clinicians is essential. Written consent should be obtained for all PCNs. Acceptable thresholds for complications are listed in Table 91-3. Where local complication rates are known, these should inform the consent process. Intravenous access and adequate hydration should be established; metabolic acidosis and hyperkalaemia should be corrected. A normal coagulation profile, with an INR <1.3 and platelet count of >80,000/dL, should be ensured. Antibiotic prophylaxis should be given,11 especially if there is clinical evidence of infection. A single dose of a wide-spectrum agent is sufficient for low-risk patients. In high-risk cases, (elderly, diabetic, indwelling urinary catheter, bacteriuria, ureteroenteric conduit), antibiotics may have to be continued and modified appropriately once urine culture results are known. TABLE 91-3 Accepted Thresholds for Major Complications for PCN From ref 10. Insertion is usually performed in the prone or prone oblique position. A true lateral or supine/oblique position is feasible; however, this increases the technical difficulty, with a greater risk of trauma to the liver, spleen or bowel. CT guidance may help if there is concern about variant anatomy. The procedure is usually performed under monitored sedo-analgesia. In addition, a local anaesthetic agent is infiltrated down to the renal capsule. Occasionally, when dealing with a confused or restless patient it may be safer to perform the procedure with the assistance of an anaesthetist, who can maintain a deeper level of sedation with safety, whilst the interventionist focuses on performing the procedure. Following puncture of an appropriate calyx, a small amount of urine is aspirated to confirm the position of the needle. If the urine is clear, and the patient does not demonstrate any signs of sepsis, a small volume of iodinated contrast medium (approximately 10 mL) is injected into the collecting system. Over-distension should be avoided as this greatly increases the risk of bacteraemia. If the puncture site is acceptable, a wire is inserted and the track dilated for catheter insertion (single puncture PCN—Fig. 91-6). If the puncture site is revealed to be unsuitable (i.e. entry is into an infundibulum or the renal pelvis) then a second puncture should be performed into a more suitable calyx (double puncture PCN—see below). On ultrasound, the posterior calyces are the most superficial and medial with the patient lying prone. With advances in ultrasound equipment and technique, primary puncture of a target calyx has become more common and is usually uneventful in a dilated system,7 allowing for a single puncture PCN. Intravenous iodinated contrast medium can be used to opacify and select a suitable calyx. On fluoroscopy of an opacified collecting system, the calyces that demonstrate the largest range of movement when viewed on continuous screening (with tube below couch) from +30 to −30 oblique positions are the most posterior calyces. Being non-dependent, posterior calyces will be also be the least densely opacified in a prone position. Double contrast pyelography can also be used to highlight the posterior calyces as any gas (air or CO2), being buoyant, will preferentially gravitate into the non-dependent parts of the collecting system. Not more than 20 mL of gas should be injected slowly and under continuous fluoroscopy. Care should be taken to avoid gaseous extravasation into the surrounding tissues, vessels or the retroperitoneum. Once a suitable calyx is identified, the needle is inserted under fluoroscopic guidance (Fig. 91-7). The collecting system is initially punctured under ultrasound guidance. Ideally the definitive calyx for PCN should be punctured and subsequent tract dilatation and catheter insertion carried out under fluoroscopic guidance. However, if definitive calyceal entry is not feasible (e.g. when the calyces are small), then any part of the collecting system visualised on ultrasound is entered with a 22G needle, a single or double contrast pyelogram performed and the pyelographic information used to select a target calyx. The chosen calyx is then punctured under fluoroscopic guidance, the tract dilated and a catheter inserted. This technique is useful and safer when variant renal anatomy is suspected: e.g. horseshoe kidney, pelvic kidney or suspected retrorenal colon. A planning pyelographic phase CT is performed in the prone or supine/oblique position. The procedure can be performed under sole CT guidance or as a combined CT/fluoroscopy method. Needle access is gained under CT guidance and a guidewire inserted. Subsequent tract dilatation and catheter insertion is done under fluoroscopic control. For the latter, care should be taken to ensure the access is secure before transferring the patient to the interventional suite12 (Fig. 91-8). Displacement of a nephrostomy catheter is a constant hazard, particularly with long-term drainage. Definitive management (e.g. ureteric stenting) should not be delayed. The catheter should also be meticulously secured. Most nephrostomy tubes have a self-retaining suture, which once pulled forms a ‘locked’ pigtail within the collecting system. However, anchorage is not guaranteed and we further secure the tube to the skin (Fig. 91-9). A single anchoring suture through skin should be made close to the tube entry site. A small piece of tape is secured around the tube. The suture is then wrapped around the tube in a ‘roman sandal’ configuration with knots at every turn going away from the skin entry site. The suture should be firmly tightened against the catheter but not so tightly as to kink the tube. Once the top of the tape is reached, the suture is returned towards the skin entry site, as a reversed ‘roman sandal’ pattern. In addition we also apply a standard ‘drain-fix’ dressing. Removal of a nephrostomy tube should be performed under fluoroscopic control and, using a guidewire. The pigtail should be unlocked and, if this fails, the nephrostomy tube can be cut at the hub; however, this increases the likelihood of the suture being caught in the soft tissues on withdrawal of the nephrostomy tube, leaving a fragment behind. A retained suture acts as a foreign body and a nidus for stone formation.13 Therefore, it is preferable to unlock the catheter whenever possible and not to cut the suture.13 Non-dilated calyces are not visualised on ultrasound examination and, being small, they are difficult to puncture. Also the space is too restricted for wire/catheter manipulation. The double contrast technique can be used in these cases. If the renal pelvis can be seen on US then this can be punctured with a 22G needle and a double contrast pyelogram performed to identify and distend the posterior calyces. If no part of the collecting system can be seen on US, then intravenous contrast medium is used to opacify the system and a posterior calyx selected and punctured. Using this technique, a success rate of up to 96% can be achieved in the non-dilated system.14 Because of its anatomical disposition, the horseshoe kidney is prone to impaired drainage, infection and stone formation but the orientation of the calyces and vessels are such that percutaneous access is relatively safe. As horseshoe kidneys are located more inferiorly, the upper poles are usually well below the ribs. The lower pole and pelvis are usually more anterior facing and a lower pole lateral entry may damage large anterior division arteries or accessory branches from the iliac artery. Thus a medial lying, upper pole calyx entry should be chosen for PCN (Fig. 91-10). Ultrasound-guided PCN is usually relatively straightforward in a transplant kidney as it is superficial and good views can be obtained.15 The procedure is performed with the patient supine. A lateral, upper pole entry is preferred to avoid puncturing the peritoneum. An upper pole or interpolar anterior-facing calyx is ideal as this allows more favourable access to the PUJ and ureter for subsequent ureteric stenting. Careful ultrasound technique helps reduce the risk of bowel injury or puncture of the inferior epigastric artery. Often, there is marked capsular fibrosis around the transplant and this can make dilation and catheter insertion difficult. Over-dilatation of the tract by 2Fr will facilitate catheter passage. Percutaneous nephrostomy in children should be performed under general anaesthesia. Ultrasound-guided PCN is technically straightforward as the collecting system is well seen, as it is superficial and usually generously dilated. However, in children the collecting system can rapidly decompress on needle entry and access may be lost. Decompression may occur because the system is under high pressure or because it is non-compliant. Therefore, the catheter must be inserted as swiftly as feasible. In straightforward cases with a dilated collecting system, initial puncture is performed with a sheathed needle, a stiff 0.035-inch. guidewire is inserted and the nephrostomy catheter advanced directly over this, as previous dilatation is not necessary. Special neonatal nephrostomy catheters (5Fr) are available; however, a standard 6Fr pigtail system works well. Care should be taken to minimise radiation dose to the patient by using low-dose techniques, good collimation and fluoroscopic image capture with minimal screening.16 Urolithiasis is the common cause of true ureteric obstruction in pregnancy and will usually resolve with conservative measures. If this fails, nephrostomy may be required and an ultrasound-guided procedure should be performed. Fluoroscopy should be used sparingly and only if necessary. A lateral or supine/oblique approach may be used and intravenous opiates alone utilised to minimise fetal respiratory depression.
Non-Vascular Genitourinary Tract Intervention
Introduction
Percutaneous Renal Access—Important Anatomical Factors
Renal Position
Relations of the Kidney
Pelvicalyceal Anatomy of the Kidney
Renal Vascular Anatomy
Other Anatomical Factors Important for Renal Access
Renal Anatomy and Percutaneous Entry
To summarise: A lower pole, posterolateral puncture of the centre of the calyx is theoretically the safest. The upper pole is more posterior and allows for easier navigation but must be approached with due care.
General Equipment for Renal Access
Access Needle
Guidewires
Catheters
Percutaneous Nephrostomy (PCN)
Techniques
Patient Preparation and Procedure
Complication
Incidence (%)
Septic shock requiring major increase in level of care
4
Septic shock (in setting of pyonephrosis)
10
Haemorrhage requiring transfusion
4
Vascular injury (requiring embolisation or nephrectomy)
1
Bowel transgression
<1
Pleural complications
<1
Complications resulting in unexpected transfer to an intensive care unit, emergency surgery or delayed discharge
5
Single Puncture Ultrasound-Guided PCN
Single Puncture Fluoroscopically Guided PCN
Double Puncture Combined Ultrasound and Fluoroscopy-Guided PCN
CT-Guided Nephrostomy
Catheter Fixation and Removal
Difficult or Complicated Nephrostomy
Non-dilated Kidneys
Horseshoe Kidney
Transplant Kidney
Paediatric Nephrostomy
Pregnancy
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Non-Vascular Genitourinary Tract Intervention
Chapter 91
