25 Monica A. Farcas1 & Kenneth T. Pace2 1 Department of Surgery, Division of Urology, St. Michael’s Hospital, Toronto, ON, Canada 2 Department of Surgery, University of Toronto, Toronto, ON, Canada A “staghorn” calculus is defined as stone within the renal pelvis extending into two or more calyceal systems. A “partial staghorn,” as the name suggests, occupies part, but not all, of the collecting system, while a “complete staghorn” occupies essentially the entire collecting system. Staghorn calculi composition is commonly struvite (magnesium ammonium phosphate) and/or calcium carbonate apatite. These stone compositions are often referred to as “infection stones” due to their strong association with recurrent urinary tract infections caused by urea‐splitting bacteria. Cultures of infection stones have shown that bacteria are harbored within the stone material itself, rather than on the surface [1]. This explains why once an infection stone is present, urine infections tend to recur. Calcium phosphate, uric acid, calcium oxalate, and cysteine also commonly form staghorns, particularly in the metabolic patient. Although traditionally it was thought that the majority of staghorns were infection stones, contemporary studies have shown that metabolic stone staghorns are just as, and perhaps even more, common [2]. Preoperative knowledge of stone composition can potentially play an important role in treatment decisions. The holmium:YAG laser, for example, is a very effective lithotrite for fragmenting struvite stones and less effective for calcium oxalate monohydrate (COM) stones. Cysteine, brushite, and COM stones, for example, are also resistant to fragmentation via shock‐wave lithotripsy (SWL). Possible complications of untreated staghorn calculi include urinary tract infections, sepsis, progressive decline in renal function, renal failure, and death. Traditionally, it has been taught that patients with untreated staghorn calculi have a mortality of up to 30%. This was largely based on the landmark Blandly and Singh study in 1976 which reported a mortality rate of 28% at 10 years for 60 patients managed conservatively for staghorn calculi, compared to a 7% mortality rate for those treated surgically [3]. In 1995, Teichman et al. reviewed 177 patients with staghorn calculi followed for a mean of 7.7 years, and found that no patients with complete stone clearance died of kidney‐related causes, compared to 67% of patients who refused treatment [4]. As a result, active aggressive management of staghorn calculi has become the standard of care, with percutaneous nephrolithotomy (PCNL) being the mainstay surgical treatment option. With advances in PCNL technique and its more widespread adoption, as well as better urinary drainage and antibiotic treatment, current mortality rates are likely far lower than initially reported, although a large body of literature on the subject matter is lacking. Furthermore, these older studies involved large cohorts of patients with infection stones, whereas more recent studies demonstrate that the majority of patients have metabolic stones, with lower risks of urosepsis [2, 5, 6]. Recently, Deutsch and Subramonian reported on their single‐center experience with conservative management of staghorn calculi in 22 patients [7]. In this small series, patients were managed conservatively due to comorbid conditions, poor access/anatomy, or patient choice. Complications included recurrent urinary tract infections (UTIs) in 50%, progressive renal failure in 14%, disease‐specific mortality in 9%, and dialysis dependence in 9%. Disease‐specific mortality and morbidity were significantly different between the unilateral and bilateral staghorn groups, at 0 versus 40% and 12 versus 20%, respectively. They concluded that candidates for conservative management would ideally have unilateral asymptomatic stones with minimal infection, in addition to specific indications preventing more aggressive therapy. The American Urological Association (AUA) best practice guidelines on the surgical management of stones recommend active treatment of all staghorn stones, if comorbidities do not preclude treatment [5, 6]. Medical therapy and supportive therapy are to be considered only for those not thought to be operative candidates. The 2005 AUA report on the management of staghorn calculi recommends discussion of all treatment options with patients [8]. This includes PCNL, retrograde ureteroscopic approaches (URS), SWL, combined therapies, and open or laparoscopic or robotic surgery, where applicable. PCNL is recommended as the initial modality of choice for treatment of struvite staghorn calculi. This can thereafter be followed by SWL, URS, or repeat PCNL, as required to render patients stone free. In patients not considered candidates for PCNL, clinicians may offer staged ureteroscopy [5, 6]. Unlike adults, the pediatric population has been shown to have great success with SWL in fragmenting even very large stones. In adults, however, SWL and open surgery are not recommended as first‐line therapies, with laparoscopic or robotic or open surgery being reserved for situations in which there is expected to be poor success with PCNL and SWL procedures. The aim of treatment, particularly for struvite calculi, is complete surgical stone removal, as any remaining stone debris may lead to bacterial persistence, recurrent infection, and stone regrowth. Achieving stone‐free status also prolongs time to stone recurrence. Stone‐free rates for staghorn calculi are widely variable in the literature, but approach 85%, with or without adjunct SWL therapy [9], versus only 51% for SWL monotherapy [10]. Lifshitz et al. reported stone‐free rates of 78% with an average of 2.9 procedures [11]. Stone‐free rates are lower following PCNL for staghorn calculi, than they are for nonstaghorn stones. When choosing and planning stone treatment, the urologist must consider stone factors (stone burden, composition, location), renal anatomical factors (obstruction, hydronephrosis, ureteropelvic junction (UPJ) obstruction, calyceal diverticulum, renal ectopia or fusion, lower pole location, reconstructed urinary tracts), and patient and clinical factors (infection, obesity, body habitus, coagulopathy, patient age, hypertension, neurogenic bladder, spina bifida, and renal failure). Current AUA guidelines recommend preoperative workup with computed tomography (CT) of the abdomen and pelvis, urinalysis, urine culture and sensitivity, serum electrolytes, estimated glomerular filtration rate (eGFR), and complete blood count (CBC) [5, 6]. Coagulation parameters are not routinely necessary unless the patient has a history of bleeding diathesis or is on anticoagulant therapy. Further preoperative preparation includes an extended period of antibiotics for actively infected collecting systems and cessation of anticoagulants and antiplatelet agents in preparation for therapeutic procedures. Current AUA guidelines emphasize the importance of obtaining preoperative CT scan in all patients planned for PCNL [5, 6]. In general, a noncontrast CT scan is sufficient, but in patients with anatomic anomalies or UPJ obstruction a triphasic contrast‐enhanced CT scan with delayed urographic phase and 3D reconstructions can be very helpful in surgical planning. A differential renal scan can provide clinical useful information, particularly in patients who may have a nonfunctioning kidney with a staghorn stone. They may be better served with nephrectomy (rather than PCNL), particularly for symptomatic or infected stones, and a normal contralateral kidney. Preoperative assessment of stone complexity is vital, particularly for staghorn calculi. A number of scales have been developed to assess preoperative stone complexity with the aim of predicting postoperative stone‐free rates and complications. These scoring systems, such as Guy’s stone score [12], S.T.O.N.E. nephrolithometry [13], the CROES nomogram [14], and the Seoul National University Renal Stone Complexity score for PCNL [15], have noted the importance of numerous factors in determining operative success. These include: surgeon case volume, prior stone treatment, presence of staghorn calculi, presence of calyceal diverticula, stone location, stone count, stone size, number of involved calyces, stone density, presence of obstruction, PCNL tract length, anatomical abnormalities, and patient factors (such as spina bifida or spinal injury). These scores, however, are not specific for staghorn calculi. In patients with staghorn calculi, variants of the collecting system anatomy have an important impact on the expected procedural complexity and preoperative, as well as intraoperative, planning. Figure 25.1 illustrates intraoperative images obtained from three patients undergoing PCNL. Figure 25.1a shows a bifid system, which limits the ability to use an upper pole puncture. Figure 25.1b reveals a favorable clinical situation in which the main stone is situated within the renal pelvis, while the calyces are short and dilated. Figure 25.1c shows an unfavorable system with long calyces and relatively narrow infundibula, which will likely require treatment, at least in part, with flexible nephroscopy and laser lithotripsy or multiple punctures to use rigid instruments efficiently and without excessive torque on the renal parenchyma. Figure 25.1 Fluoroscopic images from three patients undergoing PCNL illustrating variation in collecting system anatomy. (a) A bifid system which limits the ability to access the lower pole via an upper pole puncture. (b) A hydronephrotic system with favorable anatomy and short dilated calyces. (c) An unfavorable bifid system with long spidery infundibula. Various percutaneous techniques and modifications have been developed with the aim of improving stone‐free rates and patient safety. These include variations in patient positioning, number and size of tracts, and instruments for stone removal and fragmentation. In this chapter we review possible difficulties encountered in the treatment of staghorn calculi with PCNL and present our approach, as well as alterative modifications, to treating staghorn calculi via PCNL. Obtaining appropriate access to the pelvicalyceal system is the most challenging and crucial part of PCNL. Technically, access can be obtained by a trained urologist in the operating room or a radiologist preoperatively. Percutaneous renal access, in fact, is not uncommonly performed by interventional radiology preoperatively in the face of obstruction, infection, or complex renal anatomy. Other situations in which radiology‐placed access may be quite beneficial include failed retrograde access and inability to opacify the collecting system where fluoroscopic (rather than ultrasound‐guided) access is employed, prior urinary diversion which can make retrograde access difficult, or preoperative decompression of an obstructed and/or infected system inadequately drained by stenting. In these cases there should be clear communication between urologist and radiologist to ensure placement of the tract through a posterior calyx ideal for maximizing access to the stone in preparation for PCNL. If the radiologist‐placed nephrostomy tube is not ideally placed, it is vital that a new tract be placed intraoperatively, using opacification of the collecting system via the nephrostomy to select and puncture the best calyx (or calyces if multiple tracts are needed). Urologic surgeon access for PCNL has been shown to be safe and effective. Some studies have reported lower complication rates and improved stone‐free rates compared to access obtained by interventional radiology [16]. This can likely be explained by the fact that urologists have intimate knowledge of intrarenal anatomy and angulation of the calyces, the stone complexity, and potential difficulties which can arise during the surgical procedure. Thus, urologists more closely focus on achieving end‐on calyceal access through a posterior papilla with a direct access to the stone, as opposed to a potential dangerous tract through the infundibulum or renal pelvis, which, if dilated, can cause significant bleeding and postoperative complications. Urologist percutaneous access has traditionally been obtained fluoroscopically in the prone position using a bullseye technique, although various modifications have been developed. Ureteroscopic‐assisted puncture, usually in the prone split‐leg position, has also recently become more commonplace. Its advantages include the ability to directly visualize a posterior papilla for puncture, as well as decreased fluoroscopy time compared to traditional PCNL [17–19]. Consideration must also be given to the location of the puncture. At our center, we prefer upper pole punctures, when feasible, as this can facilitate single access for staghorn calculi. The upper pole tract tends to be more in line with the axis of the kidney, and allows the efficient treatment of high stone volumes in the upper pole, renal pelvis, and lower calyces with rigid instruments and minimal torque through a single access. The disadvantage, however, of upper pole puncture is that of potential pleural complications. In contrast, although lower pole punctures have a number of advantages including low risk of pleural, liver, and splenic injuries, they involve a longer tract, with a greater skin‐to‐stone distance, poorer access to the UPJ, and a slightly higher risk of colonic injures. Lower pole punctures are, therefore, more suited for lower pole nonstaghorn stones or lower pole partial staghorns, particularly in bifid collecting systems. Options for patient positioning during PCNL include: prone, prone‐flexed, prone split‐leg, lateral, lateral‐flexed, and supine. The prone position is the standard positioning technique for PCNL. The various modifications to this position change the relative positioning of the kidneys and their surrounding structures, thus altering the incidence of procedural complications. The prone‐flexed position reduces lumbar lordosis and increases working space between the costal margin and iliac crest, which can minimize instrument clashes (Figure 25.2) [20]. In the prone‐flexed position, the position of the left kidney is lowered 92% of the time, converting what would have been supra‐11th rib punctures in the prone position to supra‐12th rib punctures in the prone‐flex position 46% of the time, thus minimizing the risk of intrathoracic complications [21]. In addition, the skin‐to‐kidney distance is shortened (8.4 mm for the right kidney and 13.4 mm for the left kidney) [21]. The kidneys tend to “fall away” from adjacent organs, leading to 11.3° further trajectory to the spleen on the left side and 13.6° further trajectory to the liver on the right side, leading to decreased risk of injury to these organs [21]. Lastly, the prone‐flex position sets up an easier trajectory from an upper pole puncture to access the entire collecting system for treatment of staghorn calculi with minimal infundibular torque, as the renal axis is favorably altered in this position. For these reasons, the flexed‐prone position is the position most commonly used at our center for PCNL. Figure 25.2 Compared to the prone position, the prone‐flexed position for PCNL increases the available flank area for puncture, flattens the back, and decreases instrument clashes with the buttocks. The prone‐flex position can thus facilitate the multiple punctures often needed for staghorn calculi. Note the widening of the area between the lines drawn on the flank. Source: Ray AA, Chung D, Honey J. Percutaneous nephrolithotomy in the prone and prone‐flexed positions: anatomic considerations. J Endourol 2009;23(10). Reproduced with permission of Mary Ann Liebert, Inc. The prone split‐leg position is advantageous for performing concomitant retrograde cystoscopy and ureteroscopy without need for repositioning the patient while under anaesthesia. Prone endoscopy, however, has a steep, but easily overcome, learning curve. This positioning also allows for initial attempted treatment via ureteroscopy, in cases where a percutaneous procedure may or may not be necessary and is to be determined based on intraoperative findings.
Percutaneous Nephrolithotomy: Special Problems with Staghorns
Introduction
Access
Patient positioning
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