Percutaneous nephrostomy (PCN) was first described by urologist Dr. Willard Goodwin in 1955 as a minimally invasive, x-ray guided temporary or permanent procedureal alternative to traditional surgery in patients with hydronephrosis. It has since become a common procedure but is now more frequently performed by radiologists starting in the late 1970s when ultrasound imaging technology made it easier to visualize the kidneys from a cross-sectional approach.
Assuming normal embryologic development, the human kidney normally is positioned between the T12 and L3 vertebrae (right usually slightly lower than left). It normally is angled with its superior pole more dorsal and medial while its lower pole is more ventral and lateral. The kidneys have their own sagittal plane (through the hilum) directed toward the body's sagittal plane. In other words, the kidneys are tilted backward 30 to 50 degrees from the body's coronal plane and tilted inward 30 to 50 degrees from the sagittal plane.
The right kidney is typically one or two centimeters lower or inferior to the left kidney. When a patient is prone, both kidneys tend to move slightly superiorly.
PCN placement can potentially injure several surrounding organs and structures including the pleura, diaphragm, colon, spleen and liver. Of these, injuries to the pleura and diaphragm are the most common. The pleura extend to the lower margin of the 12th rib along the paravertebral line. Therefore, pleural injury is minimized when PCN placement is below the 12th rib. Placement above the 12th rib will usually puncture the diaphragm.
The renal collecting system is comprised of 8 to 15 minor calyces that join to form major calyces that in turn usually form a single renal pelvis that empties into a single ureter. The arterial supply is typically a single renal artery that divides into an anterior and posterior branch. However, due to genetic or other embryologic reasons, a person's kidney or kidneys may have variations in one or all of the factors discussed above.
A fairly constant aspect of a kidney is a relatively hypovascular plane (described by multiple researchers but often referred to as Brodel's line after medical illustrator Max Brodel) in the watershed region between the anterior and posterior renal artery divisions. This hypovascular area usually is oriented 20 to 30 degrees posteriorly from the body's sagittal plane. Puncturing this area theoretically results in reduced bleeding risk compared to other areas of the kidney.
The kidney is usually found within the perirenal space, an anatomic compartment that is completely or nearly completely separated by fascia from all the other internal organs except for the adrenal gland. Access to the kidney involves navigating instruments into this perirenal retroperitoneal space and staying away from the pleura, subcostal arteries, and nearby retroperitoneal structures such as the duodenum and ascending (on the right) and descending (on the left) portions of the colon.
Indications for PCN fall into several broad categories:
PCN is the procedure of choice when transurethral access is impossible or has already failed at relieving an obstructed urinary system from extrinsic mass effect (e.g., pregnancy, malignancy, fluid collections such as cysts, abscesses, or urinomas) or intrinsic blockage (e.g., benign or malignant strictures). Drainage of an obstructed renal unit is the most common indication for PCN accounting fo 85 to 90% of all nephrostomy placements.  Unless infected, establishing drainage of an obstructed, hydronephrotic kidney is not an acute emergency. Even with complete obstruction for a full week, complete renal recovery is likely. the longer the obstruction beyond one week, the lower the eventual recovery rate. After 12 weeks of complete outlet obstruction, very little recovery of renal function in that kidney can be expected. Bilateral nephrostomy drainage is rarely indicated and should be reserved for special cases such as patients with intractable, severe hemorrhagic cystitis or bilateral, treatable malignant or benign disease.
Pyonephrosis and Obstructive Pyelonephritis
The most common reason for emergency PCN placement is to provide drainage in an acutely obstructed, infected kidney (pyonephrosis or obstructive pyelonephritis) in a septic patient, due to the high mortality risk as well as the permanent renal impairment it can cause. In these cases, both percutaneous nephrostomy and transurethral retrograde Double J stenting are recommended. The decision of which one is preferred is usually determined by local technical expertise, equipment availability and individual patient factors. PCN is often preferred in the most seriously ill patients based on its reduced manipulation of the obstructed, infected ureter. The transurethral approach may not be successful in bypassing a severely obstructed ureteral stone which is not an issue for PCN. Even when transurethral bypass of an obstructing stone is accomplished, PCN generally offers the opportunity to use a larger caliber drainage catheter. However, in a morbidly obese patient with minimal hydronephrosis or in a patient with an uncorrected coagulopathy, transurethral Double J stenting would be preferred. Typically, urology will be involved in these emergency cases and make the final decision regarding the preferred therapeutic approach, usually in consultation with radiology.
PCN is the first step in accessing the renal collecting system to enable percutaneous insertion of devices to treat nephrolithiasis (percutaneous nephrolithotomy or PCNL) for:
PCN creates a tract through which lasers, ultrasonic probes, and retractable baskets can be inserted for mechanical crushing, vaporization and stone retreival. In this way, PCN can be an adjunct therapy to percutaneous lithotomy or extracorporeal shock wave lithotripsy, which may cause a large stone to fragment into many smaller pieces that are still large enough together to result in obstruction. The overwhelming majority (90%) of percutaneous renal access prior to definitive percutaneous nephrolithotomy surgery is now done by interventional radiology.
PCN rarely may need to be used as part of the "primary treatment strategy" in persons with the recurrent stone formation, such as in the setting of mineral-forming metabolic disease. In such cases, 24 hour urine testing and optimal prophylactic therapy is recommended.
Nephrolithiasis is the most common non-obstetrical complication of pregnancy. Double J stents and PCN are considered equally safe and effective in relieving pain in pregnant nephrolithiasis patients who are not manageable with conservative measures alone. Double J stents are less well tolerated by most patients and are associated with increased rates of ascending urinary infection.  PCN has been associated with higher rates of septic complications and may more easily become dislodged. Both will require frequent replacement, usually every 4-6 weeks, due to very rapid encrustation which is peculiar to pregnancy.
Healing of injured urinary tract tissue, such as in the setting of urinary leak or fistula and hemorrhagic cystitis, may be accelerated if urine is preferentially rerouted away from the region of inflammation through bilateral nephrostomies. Urinary urokinase tends to promote bleeding which can be eliminated with bilateral nephrostomies. This is limited to severe and refractory cases of hemorrhagic cystitis.
Other Therapeutic Ureteral Interventions
Direct access to the collecting system percutaneously may be the least invasive (i.e., less than surgery and when transurethral access is not feasible) manner for introducing tools for treating strictures, fistulas, or infections. Pyeloplasty or urethroplasty may relieve a stricture that developed secondary to inflammation from stones, trauma or other causes. Stent insertion may allow a fistula to heal. Direct administration of a highly concentrated medication may help treat resistant infections (e.g., fungal) while reducing systemic toxicity. Percutaneous renal access can also help with uretero-enteric anastomotic strictures in post-cystectomy patients as retrograde access across such strictures is very problematic. 
In some patients, particularly patients with only one functioning kidney (e.g., patients who have already undergone renal transplant), there may be a need for invasive testing to differentiate renal failure from intrinsic, autoimmune etiologies from obstruction; especially when imaging by other means does not provide a reliable diagnosis. Antegrade nephrostograms can readily identify the location and nature of ureteral obstructions not easily imaged otherwise.
The Whitaker test involves percutaneous puncture of the kidney with or without insertion of a catheter to measure pressure within the system. First described in 1973, the Whitaker test is designed to differentiate obstructed, hydronephrotic renal units from those with dilated but unobstructed ureters. Through a percutaneous catheter, fluid is infused while the intrapelvic pressure is measured via a catheter. A gradient pressure of 22 mm of water or more indicates obstruction while 15 mm or less indicates no obstruction. Pressures between 22 and 15 mm are considered indeterminate. The Whitaker test has largely been replaced by diuretic renography and is rarely used clinically today.
PCN should be avoided or delayed in certain circumstances but there are no absolute contraindications.
As for all procedures, it is advisable to start with the least potentially harmful manner of therapy. Transurethral access should generally be considered as the first line whenever feasible to avoid the risks inherent with new percutaneous access procedures. Reconsider the procedure if the patient has a predicted very short-term survival.
Untreated urinary tract infections are a relative contraindication.
Attempting PCN on a non-dilated system may be deferred temporarily if there is a chance that the calyces may increase in size with a short delay to make the procedure easier and possibly safer. Certain factors may need to be addressed prior to attempting the procedure, such as risk factors for hemorrhage and complications from sedation (as discussed below). Patients with obstructed urinary tracts may have renal dysfunction resulting in hyperkalemia, which can destabilize cardiac myocytes and cause a life-threatening arrhythmia if not addressed urgently. In the setting of severe hyperkalemia (i.e., potassium level greater than 7 mEq/L), hemodialysis should be performed before attempting PCN.
During informed consent for the procedure, make the patient aware of the likelihood of having a new foreign body that requires maintenance for weeks or months and may necessitate prolonged nursing or family medical support with limited lifestyle functionality. The unwillingness of a patient to accept this or to accept the risks of the procedure is a contraindication to the procedure.
Specific concerns must be addressed before attempting the procedure, such as the risks of hemorrhage and complications from sedation, with such risks mitigated if possible. The Society of Interventional Radiology (SIR) provides a list of recommendations for the cessation of antiplatelet and anticoagulant medications for interventional radiology procedures (which it categorizes based on hemorrhage risks from level 1 to level 3). The SIR classifies PCN as a level 3 procedure. These recommendations are discussed below under "Preparation."
The SIR provides recommendations for the cessation of a list of antiplatelet and anticoagulant medications for interventional radiology procedures, which it categorizes based on hemorrhage risks, from level 1 to level 3. The SIR classifies PCN as a level 3 procedure. For level 3 procedures, the SIR recommends that the international normalized ratio be no greater than 1.5, activated partial thromboplastin time be no greater than 1.5 times the particular hospital's standard of normal, and that the platelet count be at least 50,000 cells/cubic microliter.
The SIR also lists anticoagulants that should be withheld (or their side effects medically corrected) to reduce bleeding risks. Any dose of aspirin is recommended to be withheld for 5 days. Enoxaparin at prophylactic doses does not require delaying the procedure, but at therapeutic dosing should result in scheduling the procedure 24 hours later than the most recent dose when possible.
Determination of periprocedural anesthesia risk is site dependent. Many hospitals require physicians to assess the patient using the American Society of Anesthesiology (ASA) physical classification system and a Mallampati score. If the patient is ASA class 4 or higher and/or has any other anesthetic risk factors, such as an advanced airway, then some institutions and authors recommend that the patient should have anesthetic consultation prior even to "low risk" procedures such as PCN (Cohn S, ed. Perioperative Medicine. London: Springer-Verlag; 2011).
Pre-procedure antibiotics are given an hour before the procedure if there is a suspicion of an infected collecting system, which is frequently the setting in which the request for PCN is made. The main bacteria to cover empirically are gram-negative Escherichia coli, Proteus species, and Klebsiella species as well as gram-positive Enterococcus. Less common, but often resistant to early generation penicillins and cephalosporins, is Pseudomonas, a gram-negative rod with a beta-lactamase. Usually, anaerobic coverage is not needed. The SIR lists 4 first-line antibiotic options, all of which contain a cephalosporin or penicillin, but not all of which typically provide coverage for Pseudomonas. The AUA Best Practice Policy recommends a first or second generation cephalosporin, or clindamycin, or gentamycin and metronidazole. For patients who will be undergoing subsequent percutaneous nephrolithotomy (PCNL) procedures, renal pelvis urine cultures have been shown to be more sensitive and useful than bladder urine cultures in predicting urosepsis.  Also, several clinical studies have demonstrated a benefit of one week of antibiotic treatment prior to PCNL even when the initial urine culture is negative. 
The patient may have some degree of renal failure-related metabolic imbalances that should be sought out and potentially corrected prior to initiating the PCN procedure to decrease the risk of complications. Hyperkalemia or metabolic acidosis may induce arrhythmias. In this situation, it may be judicious to review an ECG. If no arrhythmia or symptoms/signs of hyperkalemia (usually nonspecific weakness, fatigue, and dyspnea; sometimes palpitations or chest pain) are present, then emergent treatment for hyperkalemia is not "needed" but should still be considered if the serum value is above 5.5 mEq/L. Due to the risk of sepsis/septic shock during the procedure, there should be a low threshold to request that an expert on the management of hypotension (such as an anesthesiologist) be present or immediately available.
When punctures are poorly placed, there is a greater risk of complications. This may impede the success of future interventions. Therefore, a cautious approach should be taken without too much guarantee of where needle placement will be attempted until imaging confirms the anatomic layout and what options for a planned puncture route are available and ideal. CT may be needed for treatment planning purposes in cases of aberrant anatomy, such as a horseshoe kidney or scoliosis causing the kidney to lie deeper than usual within the abdomen.
Ultrasound may be used in isolation to confirm that the colon is not in the line of puncture and to determine the degree of hydronephrosis. About 5% of patients will demonstrate a retrorenal colon when placed prone. This is more common in thinner patients with limited abdominal fat. It can be predicted by checking a cross-sectional axial CT image. If this is not available, the colon can usually be easily identified using fluoroscopy at the time of the PCN as it will typically contain gas when patients are in the prone position.
A target calyx is selected using either ultrasound or fluoroscopic guidance or both. Intravenous or retrograde contrast through a ureteral catheter can be used to help visualize the internal renal anatomy fluoroscopically.
Skin entry point selection is based on the renal anatomy, underlying problem and whether or not other associated procedures, such as PCNL, are being planned. In general, the entry point should be below the 12th rib to minimize pleural and diaphragmatic trauma. If too medial a site is chosen, the patient will likely suffer more pain as the paraspinal muscles will tend to kink the nephrostomy tube and make supine positioning more uncomfortable. Too lateral an access site will increase the chances for accidental trauma to the colon.
A posterior calyx is usually preferred for entry as this will utilize Brodel's line to minimize bleeding. Access through an infundibulum or renal pelvis is discouraged as it increases the risk of a vascular injury.
When PCNL is anticipated, discussion with urology is recommended to optimize placement for stone fragmentation and removal. The planned PCN approach should allow direct access to the area of largest stone burden with rigid instruments if possible, as this will greatly facilitate later stone fragmentation and removal by urology. Upper pole access is recommended for complex lower pole stones, calculi in horseshoe kidneys, complete staghorn stones and large proximal ureteral stones. If an intercostal approach (above the 12th rib) is used, a chest x-ray following the procedure is recommended
The most commonly performed technique for needle insertion is the "eye of the needle" approach. This uses the C-arm or fluoro placed so that the needle is parralel and pointed directly at the target calyx or stone. Depth of penetration is determined by rotation or angulation of the x-ray unit.
A one-stick or two-stick technique can be used. Typically, for PCNL, there is an existing, radio-opaque stone that can be used as a target allowing the one-stick technique. In the two-stick method, the first needle puncture is used only to opacify the collecting system with contrast so that the final or definitive stick with another needle can be optimally directed. Since the first stick is just for opacification, a smaller needle is suggested and it can be targeted directly at the renal pelvis. A small amount of air or carbon dioxide can be injected into the renal pelvis to help visualize the posterior calyces as the gas will preferentially fill them in prone patients providing an obvious target.
A needle (usually 18-gauge or 21-gauge size) is inserted followed by aspiration of renal pelvis urine, contrast (optional) and a guidewire. If a renal stone is present, the needle can be targeted directly to the calculus. An 18-gauge needle can easily transmit a 0.035-inch guidewire. If a 21 gauge needle is used, then a transitional dilator is used to allow for a 0.035-inch guidewire to be passed. 18 gauge needles tuypically track straighter, pass easier through soft tissue and are better visualized using ultrasound They also do not need further dilation to pass a 0.035-inch guide wire. No increase in significant bleeding complications was noted between 18-gauge and 21-gauge needles when used for PCN access.
The guidewire is directed to achieve stable purchase, ideally in the ureter, but sometimes out of necessity to a different calyx or the renal pelvis. An angled catheter may be used to redirect the guidewire. When the guidewire position is settled upon, sequential, transitional dilators (Amplatz) or a balloon dilator are used to open the track for the eventual nephrostomy catheter, which usually starts at about 8 French. Transurethrally placed double J stents are usually only 6 or 7 French but they can go up to a maximum of 8 French.
The SIR has published complication rates for PCN. The rate of major complications is around 2% to 10%. Major complications include:
Transgression of blood vessels during PCN is to be expected. Coagulation usually occurs successfully, and hemorrhage ceases entirely within 2 to 3 days. Bleeding through the catheter can occur if a catheter side hole is left in communication with a renal vessel or if a pseudoaneurysm develops. Minor, temporary bleeding after PCN placement is expected and occurs in about 95% of cases. Significant bleeding requiring transfusion has been reported in 1 to 4% of patients while small retroperitoneal hematomas have been found in 13%. 
In hemodynamically stable patients:
If arterial hemorrhage is obvious (such as bright red pulsatile blood is coming out of the tube), then the patient should be taken for emergent angiographic embolization.
If hemorrhage is suspected (such as from observing persistent hematuria, a falling hemoglobin level, or unstable vital signs), then CT angiography (CTA) can be considered as a first-line diagnostic tool. Digital subtraction angiography (DSA) via arterial puncture can be performed after that for embolization treatment if evidence of bleeding is seen on the CTA. However, whenever there is strong clinical suspicion of bleeding in the absence of hemorrhage seen on CTA, then a fluoroscopic tractogram should be performed next.
If no vessels are opacified or if the drainage catheter side holes are found to lie outside the kidney, then the catheter should be repositioned and the tractogram repeated. If a vein is opacified, then the catheter should be upsized to tamponade the vein. Time should be given to see if the intervention worked. If an artery is opacified, then the catheter should be upsized to tamponade the artery. If blood can still be aspirated through the larger catheter, then angiographic embolization of the renal artery branch involved should be performed urgently.
In hemodynamically unstable patients:
A decision must be reached between the radiologist and surgeon whether the patient should go to surgery, to angiography, or both (if angiography can be performed in the operating room).
PCN provides a conduit for bacteria to enter the urinary tract from an external source. Although PCN may be performed to treat the obstruction that is the cause of sepsis, PCN itself may also cause sepsis. Preventive measures include routine catheter exchange every 2 to 3 months and using a catheter that has a good chance at remaining patent. Pyelonephritis is treated with antibiotics (such as Unasyn). Intravenous (IV) fluids, oxygen, and vasopressors in the setting of an intensive care unit should also be considered.
Infections associated with PCN should be treated with culture specific antibiotics. Once appropriate antibiotics have been administered, it is recommended that the nephrostomy tube be changed within four days. 
Percutaneous nephrostomy catheters can become clogged with encrustations (usually calcium phosphate). Catheter flushing can help with an acute obstruction temporarily, but even routine flushing does not appear to affect the rate of encrustation. Only increased hydration has been shown to reduce the encrustation rate. In pregnancy, PCN catheters should be changed every 4-6 weeks. For most other patients, routine changes every 3 months is typically suggested.
Benefits of PCN include the following:
Percutaneous nephrostomy tube placement is a valuable medical resource for minimally invasive access to the renal collecting system for drainage and in preparation for percutaneous nephrolithotomy surgery. Proper patient selection and collaboration between urology and radiology physician and nursing specialist are essential to optimizing outcomes. Antibiotics are necessary in most cases of stones or suspected kidney infections. Short term low-grade fevers and some degree of bleeding are commonly seen after PCN, but overall serious complication rates are relatively low compared to its significant and potentially life-saving benefits.
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