Percutaneous Genitourinary Intervention

Kidney

The kidneys are paired organs located in the retroperitoneum surrounded by fat. They are usually located between the level of the 11th or 12th thoracic to the second or third lumbar vertebral bodies. The left kidney usually lies 1-2 cm higher than the right. The pleura is attached to the 10th rib laterally and the 12th rib posteriorly. Normally the 12th rib crosses over the upper pole of the right kidney, whereas on the left side the upper renal pole is often covered by the 11th and 12th ribs. Because of this anatomy, percutaneous intervention through the upper pole will almost certainly be transpleural, so the risk of pneumothorax or hydropneumothorax is increased. The lower poles of both kidneys are located more anteriorly than the upper poles, such that, when performing percutaneous nephrostomy, it is important to remember that the lower poles are further away from the skin than the mid and upper poles when the patient is in the prone position.

At the renal hilum, the renal vein is situated anteriorly. The renal artery lies posterior to the renal vein and the renal pelvis lies posterior to both. Therefore, in the prone position, the renal pelvis is the most posterior structure of the renal pedicle and nearest the skin. The renal artery separates into anterior and posterior divisions as it approaches the renal hilum, with the anterior division dividing into three or four segmental branches and the posterior division giving rise to one segmental branch. The segmental renal arteries become interlobar arteries in the renal sinus, cross through the septum of Bertin, course along the medullary pyramid, and arch around the distal end of the pyramids to divide into arcuate arteries. The arcuate arteries are located at the base of the pyramids and give rise to interlobular arteries, which supply the peripheral renal cortex.

The Brödel line is a relatively avascular plane in the posterolateral aspect of the kidney between the posterior and anterior intrapolar vascular territories. Because of the absence of large arterial branches, this avascular plane is theoretically safer for placing catheters into the renal pelvicaliceal system. However, in practice this plane cannot be routinely identified and placement of a catheter into a calyceal fornix is usually adequate and safe for percutaneous nephrostomy ( Fig. 22-1 ).

Percutaneous puncture and placement of a catheter directly into the renal pelvis is not recommended because of the proximity of the renal vascular pedicle and the propensity to cause arterial damage and major hemorrhage. Placement of a catheter through the peripheral cortex of the kidney is the recommended route for percutaneous access because of the proximity to the avascular plane of Brödel and the presence of smaller blood vessels in this region (see Fig. 22-1 ).

Renal calyceal anatomy is also important for planning percutaneous nephrostomy. Because percutaneous nephrostomy is performed with the patient in the prone position, gaining access to a posterior calyx is the preferred entry point into the renal pelvicaliceal system. Because the posterior calyces are closer to the skin surface in the prone position, the angle of entry from a posterior calyx into the renal pelvis is more direct and less acute than that associated with an anterior calyx ( Fig. 22-2 ). The location of anterior and posterior calyces in relation to the lateral contour of the kidney is not constant. Brödel proposed that anterior calyces are located medially and posterior calyces laterally, while Hodson proposed the opposite; that is, anterior calyces are located laterally and posterior calyces medially. However, more recently Kaye and Reinke studied calyceal location using computed tomography imaging. They found that the Brödel description is far more common on the right, whereas the Hodson calyceal description is more often present on the left ( Fig. 22-3 ).

Because of the variation in the anterior and posterior calyces, in the author’s unit we tend to use either carbon dioxide or air to outline the posterior calyces ( Fig. 22-4 ). When there is marked hydronephrosis, differentiation of anterior from posterior calyces is usually not of any technical advantage. However, in renal collecting systems that are moderately or minimally dilated, delineation of the posterior calyces with air or CO ₂ may make placement of the percutaneous nephrostomy catheter technically easier.

The colon is occasionally positioned laterally or even posterior to the kidney. Posterior colonic location is rare and if present may well result in colonic transgression ( Fig. 22-5 ). However, it is so rare that routine pre-nephrostomy imaging with computed tomography (CT) or barium studies is not warranted. Lateral colonic location is more frequent and mitigates against using a lateral access route for percutaneous nephrostomy. Therefore, in practice, a posterolateral route is chosen for gaining access to the kidney so that if the colon is located laterally it will be avoided ( Box 22-1 ).

Ureter

The ureter descends from the renal hilum on the anteromedial surfaces of the psoas muscle. As it passes over the common iliac artery, a slightly more medial course is assumed, followed by a posterolateral course in the pelvis. Finally, as the ureter approaches the bladder, the ureter turns medially and enters the bladder at the ureterovesical junction. There are three areas of physiologic narrowing in the ureter. These are located at the UPJ, the common iliac artery, and the ureterovesical junction.

Bladder

The urinary bladder is located behind the symphysis pubis. The superior wall or dome of the bladder is the only portion of the bladder covered by peritoneum. The neck is fixed in position and as the bladder fills and distends it becomes elevated well above the symphysis pubis. As the bladder fills, all bowel loops are pushed superiorly out of the pelvis, allowing for safe percutaneous access. The vascular supply of the bladder enters through the posterior and lateral aspects of the bladder wall, which also makes for safe percutaneous access through the anterior wall. When planning a percutaneous suprapubic cystostomy, it is important to remember that the inferior epigastric vessels run down the anterior abdominal wall on each side of the rectus muscles and are avoided by selecting an entry site close to the midline.

Antegrade Pyelography

Antegrade pyelography refers to the insertion of a needle into the pelvicaliceal system and the injection of contrast material to delineate the anatomy of the pelvicaliceal system and ureter ( Fig. 22-6 ). It currently forms a starting point for many percutaneous genitourinary interventions. It was widely used in the 1980s as a diagnostic technique when intravenous urography failed to adequately opacify the pelvicaliceal system or ureter. However, with the advent of cystoscopy and retrograde injection of contrast medium into the ureter, its popularity has declined. Moreover, with the more extensive use of modalities such as ultrasound, computed tomography, and magnetic resonance imaging (MRI), many renal and ureteric abnormalities can be fully evaluated without recourse to either antegrade pyelography or retrograde pyelography. However, it still remains the mainstay for performance of the Whittaker test and for delineating the anatomy and cause of obstruction before percutaneous nephrostomy.

Technique

The patient is positioned prone on the fluoroscopy table and the kidney is located with ultrasound. Because only a single needle is being placed, the renal pelvis or a calyx can be chosen as a target. It is easier to access the renal pelvis in most instances and in the author’s unit we generally choose the renal pelvis as a target. The needle can be directed into the renal pelvis using fluoroscopy alone. The commonly chosen landmark is approximately 2-3 cm lateral to the transverse process of L2. Alternatively, some authors prefer to use ultrasound alone to direct the needle into the renal pelvis or renal calyx using a freehand technique. We prefer to use ultrasound to mark the location and if there is marked dilatation of the pelvicaliceal system the needle is inserted into the renal pelvis without ultrasound guidance. If there is mild or moderate hydronephrosis, ultrasound guidance is used. A 20- or 22-gauge needle can be used, but a 20-gauge needle is preferred because it is a little stiffer and can be directed through the muscles and perinephric tissues without the tip becoming deflected as can happen with 22-gauge needles. Once urine is aspirated from the needle, the needle hub is connected to extension tubing and contrast material is injected. If there is high-grade obstruction, it is important to remove adequate amounts of urine before injecting contrast material to avoid overdistention of the collecting system. A tilting table may help delineate the lower level of the obstruction, particularly in the severely hydronephrotic collecting system. By placing the patient semierect, the heavier contrast material will gravitate toward the lower end of the ureter and delineate the level of the obstruction.

Complications

Complications encountered with antegrade pyelography are rare. Bacteremia can be induced by injecting contrast material into a high-pressure collecting system particularly if the urine is infected. If the urine is cloudy on visual inspection, it is important to decompress and remove an adequate amount of urine before contrast material is injected.

Whittaker Test

The Whittaker or ureteral perfusion test is used to determine whether or not a dilated urinary system is obstructed. It has been regarded as the gold standard for this determination but is performed rarely. Lasix renography can often determine the presence or absence of an obstruction but does have a 10%-15% false-positive rate, particularly in patients with dilated collecting systems. The Whittaker perfusion test was devised to evaluate the presence or absence of obstruction to flow in the presence of a dilated but nonrefluxing upper urinary track. It is more commonly used in pediatric patients where dilated nonrefluxing ureters can pose a diagnostic dilemma. Its most common use in adults is to determine whether pelvicaliceal dilatation due to pelviureteric junction (PUJ) dysfunction is causing obstruction. Similarly, it can be used in adults to evaluate the adequacy of pyeloplasty for the treatment of PUJ obstruction.

The Whittaker test is basically a ureteral stress test. The ureter is perfused with known volumes of fluid at known flow rates. An antegrade needle is placed in the pelvicaliceal system and a Foley catheter placed in the bladder. Manometers are attached to both the antegrade needle and the bladder catheter, and contrast material is infused through the antegrade needle using a pump at known flow rates.

On placement of the antegrade needle, a sample of urine is aspirated for bacteriologic assessment. If the urine appears cloudy, it is best to delay the procedure until the Gram stain can be obtained. An opening pressure is recorded by connecting a water manometer to the antegrade needle. A water manometer is also connected to the bladder catheter ( Fig. 22-7 ). An opening pressure from the bladder is recorded. It is important to have the base of the manometers at the same level as the tip of the antegrade needle. Water manometers are usually strapped to drip infusion stands and can be set to a similar level as the tip of the antegrade needle by calculating the amount of needle length within the patient. The ureter is then perfused with contrast material diluted to a 20% concentration at a flow rate of 10 mL/min for 5 minutes. Then the perfusion is halted and pressures are again taken from the kidney and bladder. If no evidence of obstruction is present the ureter can be further stressed at a higher flow rate of 15-20 mL/min for another 5 minutes. The subtraction of the recorded bladder pressure from the renal pressure provides the differential pressure. Normal and abnormal pressure differentials are listed in Table 22-1 .

Lastly, the ureteral perfusion test is repeated with the bladder full to evaluate the effect of increased bladder pressure on the urinary track. This is important in situations where the bladder pressure is high owing to either outlet obstruction or neurogenic disease. Intermittent or continuous high bladder pressures greater than 20 cm H ₂ O places the kidney at risk even in the absence of ureteral obstruction.

The ureteral perfusion test is abandoned if the opening pressure in the kidney is greater than 35 cm H ₂ O or if the patient develops pain during the procedure.

Percutaneous Nephrostomy

Percutaneous nephrostomy remains the most common procedure performed on the kidney by the interventional radiologist. The most common indications for percutaneous nephrostomy include obstruction from ureteric stones and malignant obstruction from carcinomas of the bladder and prostate. The ureters may also be involved by secondary malignant deposits from cancers of the uterus, colon, breast, and abdominal lymphoma. Other indications for percutaneous nephrostomy include postsurgical damage to the ureter, ureteral fistulas, and idiopathic retroperitoneal fibrosis.

Nephron damage and parenchymal atrophy can begin as early as a few days to a week following the onset of obstruction. Undoubtedly, nephron damage occurs much earlier if the urine is infected. Information on how long the kidney can tolerate high-grade obstruction is incomplete, but nephron damage is influenced by whether the obstruction is unilateral or bilateral, whether there is superimposed infection, and whether there is preexisting renal or vascular disease. Because of the uncertainty as to when irreversible nephron damage begins, an obstructed urinary system should be drained as soon as possible after diagnosis.

Technique

Pelvicaliceal Access

The patient is placed prone on the fluoroscopy table and the obstructed kidney is imaged with ultrasound to determine its location and the degree of hydronephrosis. An antegrade pyelogram is performed as previously described and contrast material injected to outline the pelvicaliceal system. During antegrade pyelography, the level and cause of obstruction is determined, if not known already. The only exception is when a pyonephrosis is encountered. If a pyonephrosis is encountered, the minimum amount of contrast material is injected and minimal manipulation of the pelvicaliceal system is carried out. Once the pelvicaliceal system is outlined by contrast material, a calyx is chosen for puncture. The calyx chosen depends on the anatomy of the kidney and on the likelihood of any future procedures such as antegrade ureteral stent insertion. If antegrade stent insertion is likely, then a midpole calyx is preferable; if not, a lower pole calyx can be chosen.

Having decided on the calyx of choice, the next step is to decide whether the calyx seen is an anterior or posterior calyx. The best way to do this is to inject either carbon dioxide or air via the antegrade needle into the pelvicaliceal system ( Fig. 22-8 ). If CO ₂ is not available, 10-15 cc of air can be injected through the antegrade needle. It is important to ensure that the antegrade needle is not in communication with a vein, so that air embolus is avoided. The air or CO ₂ will rise into the posterior calyces, which can then be readily identified. At this stage, some operators like to turn the patient into the prone oblique position, which theoretically makes the angle from the calyx into the infundibulum and renal pelvis more shallow and easier to negotiate. In the author’s unit we prefer to leave the patient in the prone position because usually there is little or no difficulty in negotiating a wire from a posterior calyx into the pelvis.

A single-stick needle access system (Neff Set, Cook, Bloomington, Ind.; Acustick, Meditech, Watertown, Mass.) is used to gain access into the calyx. These needle access sets are composed of a 22-gauge, 15-cm needle, a 0.018-inch guidewire, a metal cannula, a 4-French plastic cannula, and a 5-French sheath. A skin position is marked using fluoroscopy 1.5-2.0 cm lateral to the calyx chosen. The skin is infiltrated with local anesthetic, an incision is made with a #11 scalpel, and the needle is inserted under fluoroscopic guidance into the calyx. The depth of insertion can usually be gauged by the depth of the antegrade needle inserted to gain access to the renal pelvis; because the lower pole of the kidney is more anterior, the second needle is inserted a little deeper than the antegrade needle to gain access to the collecting system. A 10-mL syringe with 2 mL of saline is placed on the hub of the needle. The stylet is removed and the needle is slowly withdrawn until urine or air bubbles appear in the syringe. The 0.018-inch guidewire is then manipulated down through the needle into the calyx and into the renal pelvis. Occasionally, difficulty is encountered in advancing the guidewire from the tip of the needle, even though urine has been aspirated through the needle. Often this is because the needle tip is up against the wall of the calyx. Withdrawing the needle slightly and turning the needle so that the bevel points in different directions may aid in negotiating the guidewire into the renal pelvis. When the 0.018-inch guidewire is in the renal pelvis, the needle is removed over the guidewire and the 5-French sheath assembly is placed over the wire into the pelvicaliceal system. It is important to detach the metal stiffening cannula when the sheath system has entered the calyx. The metal cannula is too stiff to traverse the angle between the calyx and renal pelvis. Once the metal cannula is withdrawn, the 5-French sheath and inner plastic cannula are flexible enough to follow the guidewire into the renal pelvis. If the metal cannula is left in place, attempts to force the sheath system into the renal pelvis result in guidewire kinking in the calyx and further pushing may cause the guidewire to slip out of the kidney altogether. Once the 5-French sheath is in the renal pelvis, a 0.035-inch J-guidewire is inserted through the 5-French sheath and is coiled in the renal pelvis, placed in the upper pole calyx, or manipulated down the ureter ( Fig. 22-9 ).

Placing the Nephrostomy Catheter

When the 0.035-inch J-guidewire is present in the renal pelvis, the track is dilated. Some others prefer using a stiffer guidewire such as a 0.035-inch Ring-Lunderquist (Cook, Bloomington, Ind.) guidewire, but with experience the J-guidewire is usually adequate. If an 8-French catheter is being placed, the track is dilated with 8- and 10-French dilators. If a 10-French catheter is being placed the percutaneous track is dilated with 8-, 10-, and 12-French dilators and so on. An 8-French nephrostomy catheter is placed for the vast majority of percutaneous nephrostomies. Only if one encounters a pyonephrosis should a 10- or 12-French catheter be placed. It is important to fluoroscopically monitor the guidewire while dilating the track to ensure that kinking of the guidewire does not take place. When the track is dilated the nephrostomy catheter (Cook, Bloomington, Ind.; Meditech, Watertown, Mass.) is passed over the guidewire into the renal pelvis. The nephrostomy catheters usually come with a metal stiffening cannula, which is used to provide stability for the catheter as it passes through the subcutaneous tissues, muscles, and retroperitoneal tissues on the way to the kidney. Once the catheter has entered the kidney, it is important again to detach the metal stiffening cannula and withdraw it slightly while sliding the catheter forward over the guidewire. Failure to do this will result in kinking of the wire and/or loss of purchase within the kidney.

Depending on where the guidewire is coiled, the catheter is placed in the upper pole calyx, coiled in the pelvis, or placed down the ureter over the wire. The string on the end of the catheter is then pulled to form the pigtail loop. If the catheter is down the ureter, pulling the catheter back until the tip is approximately 4-5 cm from the PUJ ensures that, when the string is pulled, the catheter flipped back into the renal pelvis, forming a nice pigtail ( Fig. 22-10 and Box 22-2 ).

Box 22-2

Percutaneous Nephrostomy

• 20-gauge antegrade needle first placed in renal pelvis

• CO ₂ or air injected to identify posterior calyces

• Single-stick needle system used to access chosen calyx

• Nephrostomy catheter metal stiffener withdrawn at calyceal level

• Minimal contrast injection and manipulation in infected system

Aftercare

Catheter fixation to the skin is important and can be done in a number of ways. The author uses a Hollister ostomy disk, which is placed on the patient’s skin with the catheter threaded through the opening in the center of the Hollister disk. Adhesive tape is placed around the catheter and the adhesive tape is then sutured to the ostomy disc. Alternatively, the adhesive tape that is first placed around the catheter can be sutured directly to the patient’s skin. Unless there has been a lot of bleeding and clot formation, it is usually not necessary to irrigate a nephrostomy catheter. Urine contains proteolytic enzymes that will tend to break down any clot forming in the catheter and keep the catheter patent. The author’s unit tends to use irrigation only when there is thick pus in the collecting system or when there is significant clot formation after the procedure.

Results

The success rate for percutaneous nephrostomy approaches 100% in experienced hands. Difficulties may be encountered with the nondilated collecting system, but these are surmountable by appropriate placement of an antegrade needle and adequate distention.