Current Surgical Management of Branched Renal Calculi

Symposium on Surgery at the Lahey Clinic

Current Surgical Management of Branched Renal Calculi Robert A. Roth, M.D. *

Branched renal calculi occupy the renal pelvis and contiguous calices. Calculous material may involve one calyx and infundibulum or progress to form a complete cast of the entire collecting system (Fig. 1), Although any calculus can form in a branched manner, the struvite calculus is the commonest and most serious type that may require operation. Cystine and uric acid calculi also tend to branch; however, medical management is preferred for these. While abnormalities of calcium, uric acid, oxalate, and cystine metabolism often contribute to formation of calculi, struvite calculi are usually caused by infection. It is speculated that infection may be either the primary event leading to formation of struvite calculi or that a preexisting calculus becomes secondarily infected and grows as a struvite calculus. At times no cause may be discovered or diagnosis must wait until the calculus is carefully analyzed qualitatively to reveal the origin of its nucleus. Women have a 2% times greater incidence of struvite calculus disease than do men, a fact which parallels women's increased incidence of urinary tract infection. 9

INDICATIONS FOR OPERATION When planning operation for branched calculi, it should be remembered that these calculi are usually a manifestation of a basic underlying renal disorder. Although operation relieves certain sequelae of the calculi, it seldom alters the basic disorder. Because of this, our practice is to remove calculi as part of a vigorous overall medical management program. Operation is usually indicated for the presence of an upper urinary tract infection (especially when urease-producing bacteria are identified), persistent pain of renal origin, pyelocaliceal obstruction with resultant parenchymal atrophy, progressive decrease in renal function, or failure of medical management to reduce the symptoms or size of uric acid or

'i'Department of Urology, Lahey Clinic Foundation, Boston, Massachusetts

Surgical Clinics of North America-Vol. 56, No.3, June 1976

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Figure 1. Kidney ureter bladder film. Complete cast of left collecting system by struvite calculus of20 years' duration. Right kidney shows a new branched calculus of the lower pole.

cystine calculi. These same criteria apply to branched calculi that form either bilaterally or in a solitary kidney. Although the surgical techniques to be described have an acceptably low morbidity rate and nephrectomy rate, the possibility of irretrievable renal loss is still present. Therefore, before attempts are made to remove a difficult calculus in a solitary kidney or in bilaterally poorly functioning kidneys, adequate support, such as vascular access and renal dialysis, should be available. When the indications for surgical intervention are absent, these patients should have follow-up studies without operation rather than to risk permanent loss of renal reserve. 7

PREOPERATIVE EVALUATION Generally, sufficient time is available before operation to evaluate and to correct metabolic abnormalities that may influence formation of calculi. These abnormalities should be corrected before operation or the

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same cause will persist in promoting reformation of calculi, thereby negating the beneficial effects of operation. An excellent review of the metabolic evaluation of renal lithiasis is presented by Smith. 18 As a result of formation of calculi, renal function may be depressed sufficiently to cause azotemia and acidosis. These disorders can usually be corrected with proper attention to fluid and electrolyte replacement; but, in severe disease, preoperative dialysis may be required. Precise identification of bacteria and treatment of urinary tract pathogens are essential. Proteus species and, less commonly, species of Pseudomonas, Staphylococcus, and E. coli are associated with infected calculi. Certain strains of these bacteria have the ability to produce urease; this enzyme splits urea to form ammonia, which causes urine to become alkaline. Urine is constantly saturated with phosphates, and these salts become insoluble in the alkaline pH range. The salts precipitate as magnesium ammonium phosphate or struvite calculi. Bacteria become embedded within the calculus as it grows and remain viable, thereby being a source of constant infection. 13 These bacteria are seldom eradicated with appropriate antibiotics, although associated pyelitis and pyelonephritis may be controlled. After the offending bacteria are identified, antibiotic treatment is begun 72 hours before operation. An antibiotic should be selected on the basis of sensitivity studies, mode of antibiotic excretion, toxic side effects, and degree of renal impairment. We prefer antibiotics that attain tissue levels in order to treat infection within the parenchyma of the kidney. In general, ampicillin or a cephalosporin is used for Proteus and E. coli species. Carbenicillin, gentamicin, or tobramycin is preferred for Pseudomonas or resistant proteus strains. Routine screening for urinary tuberculosis is performed, and if results are positive, appropriate antituberculosis therapy is instituted well in advance of operation.

RADIOGRAPHIC STUDIES Most branched calculi are radiopaque except for the uric acid calculi,14 and accordingly plain films (kidney, ureter, bladder-KUB), posterior oblique views, and nephrotomograms are obtained to quantitate the exact number, size, and location ofthe calculi in each kidney. Not uncommonly a previously unsuspected calculus is found in an apparently normal opposite kidney. Pyelography after infusion or high-dose infusion demonstrates the relationship of the calculi to the calices, the amount of renal parenchyma present, and the functional status of the pelvis and ureters. Retrograde pyelography may be necessary to visualize the ureters and the ureteropelvic junction to rule out the existence of obstruction. A voiding cystourethrogram is obtained to exclude the possibility of vesicoureteral reflux. Although renal angiography is not routinely performed, it is extremely valuable if the operative procedure is to include an extensive nephrotomy, if calculi are present in solitary kidneys, or ifreoperation for calculi is necessary. Renal function studies using endogenous creatinine

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clearance and quantitative isotopic renal scans are useful for providing baseline evaluation of renal function and of any postoperative changes. Information regarding individual renal function can be obtained by catheterized split renal function studies or can be estimated from renal isotopic studies. Both of these studies can be helpful in deciding whether nephrectomy or removal of calculi is preferable and, when calculi are bilateral, in deciding which kidney is to be operated on first (in general, it is the kidney with poorer function),u

OPERA TIVE TECHNIQUE Each significant operative technique developed in recent years was designed to offer the surgeon the best chance of removing all calculi within the kidney while conserving maximally functioning renal parenchyma. Although the proponents of each procedure tend to exclude the techniques of the other, I believe these techniques are often complementary and seldom exclusive. The surgeon should be prepared to integrate procedures or to apply the most appropriate procedure for the individual patient. A briefreview of currently used techniques and their indications is presented, followed by a description ofthe combined method used most frequently at the Lahey Clinic. Nephrectomy Nephrectomy may be the most conservative procedure in the properly selected patient; it eliminates the risk of recurrence of calculi and the attendant risk and hazards of second and third operations. I reserve this procedure for elderly high-risk patients with unilateral calculus disease, patients with poor or total nonfunction with a relatively normal contralateral kidney, patients with calculous pyelonephrosis with abscess, and for patients with multiple recurrences after failure of medical and surgical management. Nephrectomy should be extraperitoneal whenever possible. At times, perirenal fibrosis may be so extensive that only transperitoneal or subcapsular nephrectomy will prevent serious damage to neighboring structures. Partial Nephrectomy In partial nephrectomy, polar areas of the kidney are removed along with the branched calculus. This technique is used when the overlying parenchyma is markedly atrophic and when the associated calices are badly destroyed. The remaining calices and parenchyma should be relatively normal. Recurrent formation of calculi originating in abnormal polar calices is also managed with resection of the involved area. Routine partial nephrectomy is not recommended as a method of preventing recurrence of calculi. 12 The main renal artery or appropriate segmental arterial branch is occluded in partial nephrectomy. The renal capsule is reflected, and the

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renal parenchyma is divided bluntly in a guillotine fashion. The cut edge of the calix or infundibulum is then closed with fine absorbable sutures. Individual vessels are ligated with figure-of-eight sutures. If hemostasis is adequate, the capsule is then closed snugly over the incision. The artery is unclamped, and the nephrotomy is inspected for bleeding. Throughand-through mattress sutures will control arterial bleeding at this point if bleeding persists. Gentle pressure usually controls venous bleeding. U sually, cooling of the kidney is not necessary as resection seldom takes longer than 30 minutes.

Intrasinusal Pyelolithotomy This procedure was popularized by Gil-Vernet4 in 1965 and was a major innovation in the removal of renal calculi. The basic proced ure is to expose the kidney through a verticallumbotomy incision; the kidney is left in situ, and only the posterior hilar area is exposed (Fig. 2A). A plane is developed between the adventitia of the renal pelvis and the renal parenchyma (renal sinus), exposing the infundibula and caliceal anatomy (Fig. 2B). Wide exposure is afforded so that pelvic calculi and even projections into infundibula and into calices can be removed through appropriate incisions in the collecting system (Fig. 3, A and B). Calculi are teased from the calices with gentle traction (Fig. 4), After all of the calculus is removed, the pyelocaliceal incisions are closed with interrupted atraumatic absorbable sutures. Either no drainage or a small nephrostomy tube is used. A Penrose drain is placed in the peripelvic area.

Figure 2. Intrasinusal pyelolithotomy. A and B. An avascular plane is developed between the adventitia of the renal pelvis and renal parenchyma (renal sinus). Obliteration of this space by infection or previous operation precludes this approach.

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The major advantage of this procedure is that renal parenchyma need not be incised. The procedure is usually bloodless if the proper plane is developed, and adjunctive measures of ischemia and hypothermia are unnecessary. Difficulty in developing an adequate intrasinus plane when it has been obliterated by fibrosis secondary to chronic infection, previous operation, or a small intrarenal pelvis precludes this approach ..

Anatrophic Nephrotomy Smith and Boyce 19 refined the technique of making incisions into the kidney based on the predictable renal arterial supply. They utilized the observation that there are usually four major renal segmental areas based on arterial supply. A segmental artery goes to each pole and posterior renal segments. Two segmental arteries usually supply the anterior segments (Fig. 5), Because these arteries are end arteries and do not collateralize, anatrophic incisions can be made between the segments without damaging major intrarenal branches or collaterals. 5 The segmental blood supply is determined by preoperative renal angiography and by intra-operative identification of segmental vessels using intra-arterial injection of dye indicators. Intrarenal veins collateralize profusely and can be divided without causing venous infarction.5 After identification of segmental anatomy, the renal artery or segmental artery is occluded to provide a dry operative field, and hypothermia is induced to delay the onset of ischemic damage. A blunt nephrotomy is made between the segments on the identified anatrophic area (Fig. 6).

Figure 3. A, Gentle blunt dissection and retraction of renal parenchyma can expose infundibula. B, An incision is made into the pelvis to expose the calculus. A flap is formed with the base toward the calyces.

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Figure 4. Branched sions of the calculus are grasped and removed from fundibulum at a time until tire calculus is removed.

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The collecting system is sharply incised, and the calculus is removed. When all of the calculous material has been removed, abnormalities of the collecting system may be repaired by plastic reconstruction of calices or infundibula. Individual arteries and veins are ligated with sutures under direct vision. Drainage is provided by an internal Silastic stent from the

Figure 5. Posterior aspect of the kidney demonstrating the segmental arterial supply. The arterial distribution may vary, but the basic segmental supply is usually present. There are usually single arteries to the apical, basilar, and posterior segments. Two arteries commonly supply the anterior segment.

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ANTERIOR

Figure 6. Anteroposterior intersegmental line defined by intraarterial dye indicator (indigo carmine or methylene blue). Anatrophic nephrotomy is made along this line. The incision is not carried into the apical or basilar segments.

POSTERIOR

renal pelvis to the bladder. Nephrotomy incisions are closed with a minimally necrosing mattress suture or sutures of the capsule alone. The four major advantages of anatrophic nephrotomy are that intrarenal arterial damage is minimal (thus eliminating segmental infarction); large hemostatic mattress sutures, notorious for causing large amounts of parenchymal necrosis, are unnecessary;8 the intrarenal collecting system can be reconstructed; and exposure of the collecting system is possible in the presence of perinephritis or after previous surgical procedures. The major disadvantages are that, in many instances, the parenchyma need not be incised for complete removal of the calculus and that parenchymal necrosis (although minimal) is still present along with the possibility of delayed hemorrhage. Ex Vivo (Bench) Surgery Removal of the kidney with protective cold arterial perfusion is a technique derived from wide experience with renal homotransplantation. Ideal exposure, accurate removal of the calculus, and excellent intraoperative radiographs can be achieved with this approach. However, several problems arise. The majority of branched calculi requiring operation are infected with virulent gram-negative organisms. Vascular anastomoses made in the presence of these organisms may lead to infection at the suture line with its associated morbidity. In addition, many urologists have limited experience with the necessary vascular techniques. For these reasons I believe that most branched calculi should be approached in situ and that ex vivo surgery should be used only in highly selective patients and only by surgeons who are familiar with renovascular techniques.

ADJUNCTIVE TECHNIQUES Renal Ischemia and Hypothermia Occlusion of the renal artery enables the surgeon to work in a bloodless field, preventing excessive blood loss and the need for transfusion. It

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also provides for almost complete visualization ofthe collecting system so that all visible calculus may be removed. Tissue turgor is reduced, facilitating palpation of calculi and removal of caliceal calculi through narrowed infundibula. The problem, of course, is a trade between ischemic cell injury and the benefit of a dry operative field. Fortunately, cooling of the kidney greatly reduces the rate of ischemic cell injury, and kidney core temperatures of 15 to 20° C provide approximately two hours of operating time without significant reduction in renal function. 21 Two hours is sufficient time for most procedures. Mannitol, 25 gm given intravenously five minutes before clamping of the renal artery, helps to protect the kidney from cold injury and ischemic damage. Hypothermia can be induced by several methods. The most widely used technique, described by Metzner and Boyce,10 is to surround the kidney with a rubber dam into which iced saline slush is poured. This slush is made by freezing sterile containers of saline or Ringer's solution. Appropriate core temperatures are obtained in approximately 15 minutes. Because the kidney warms in approximately 30 minutes, repeat applications of slush are necessary. A more sophisticated technique, intra-arterial cold perfusion with egress of the perfusate through the renal vein, is an attractive idea. 3 A technique used at the Lahey Clinic employs a coronary artery angiographic catheter inserted percutaneously through the femoral artery and placed into the renal artery with the aid of fluoroscopy (Fig. 7), The kidney is then exposed in a routine manner, and a venotomy is made for egress of the perfusate. The kidney can then be cooled with a constant core temperature, eliminating cyclic temperature change. In addition, blood loss is less because a colored perfusate is used to identify transected vessels so that they may be sutured accurately. This procedure requires a small

Figure 7. Percutaneous in vivo cold perfusion of kidney using a coronary artery balloon catheter. A small venotomy is necessary for egress of the perfusate. The kidney is kept at a con· stant core temperature. Suture liga· tion of vessels divided by nephrotomy is facilitated by adding a dye to the perfusate.

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venotomy which must be repaired, and some risk of morbidity is associated with percutaneous transfemoral catheter placement. This technique has been of proved value in our experience. 6 British surgeons use a continuous cooling pump with two heat transfer paddles to encircle the kidney. This system appears to be efficient and provides a dry operative field. It does, however, require expensive equipment not generally available to the practitioner. 22

Intraoperative Radiography Small sterile kidney cassettes* are readily available for radiography of the kidney at operation. After all calculous fragments are removed, the cassette is placed against the kidney. Radiographic exposures are obtained, and residual calculous fragments can be localized with the aid of the radiograph and thus removed. In practice, this procedure may be difficult. The fragment may be enclosed in a stenosed calix or within the renal parenchyma itself. Despite the most valiant efforts, extraction of fragments may not be possible within acceptable ischemic time. Resolution power of the film is not high with smallfragments; they may therefore be overlooked or not visible on the film.1s The use of mammography film is expected to improve this problem. The milliampere seconds, kilovolt, and distance techniques must be decided on before operation so that time is not wasted and technically poor films are not obtained.

Nephroscopy Endoscopic instruments are now commercially available that permit examination of the inner reaches of the collecting system. The Storz nephroscope** is a fixed, right-angle endoscope with an operating tip capable of identifying and grasping small calculous fragments. Although the principle is excellent, in our experience we have found the instrument cumbersome and difficult to manipulate when looking for small retained calculi. There still remains a great need for a small caliber flexible instrument of this type. Postoperative Nephrostomy Irrigation Even in the best of hands"residual fragments are left in up to 25 per cent of patients. 4 , 16, 23 Controversy persists over the importance of this mishap; I believe every attempt should be made to remove residual infected calculiP A nephrostomy tube is best left in patients with retained fragments as, on occasion, the fragment may be irrigated or manipulated through the tube out of the pelvis. 1, 2 Recently, encouraging results have been reported with 10 per cent Renacidin (a complex organic acid) irrigation to dissolve retained struvite calculi,13 It should be used only in patients with sterile urine because of several reported deaths resulting from sepsis after irrigation of infected kidneys with Renacidin. Routine postoperative irrigation with Renacidin *Eastman Kodak Corporation, Rochester, N. Y. '·Storz Instrument Co., St. Louis, Mo.

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or with similar solutions may prove to be beneficial for dissolving small fragments or mucosal plaques not visible radiographically that may playa major role in the cause of recurrence of calculi.

CURRENT OPERATIVE METHOD I prefer to use the intrasinusal exposure of Gil-Vernet whenever possible. The kidney is approached extraperitoneally through a twelfth rib or supracostal eleventh or twelfth rib incision. The kidney is totally dissected out of the renal fossa. Renal artery and vein are identified and looped with Silastic vascular tapes. The intrasinusal dissection is then performed using vein retractors and malleable brain retractors of various sizes. A generous pyelotomy flap is made with the base toward the calices; the size ofthe incision depends on the configuration ofthe pelvis. Caliceal projections of the calculus are gently teased from one calix at a time until the entire calculus is removed. Occlusion ofthe renal artery at this point will often reduce parenchymal tissue turgor sufficiently that calculi can gently be pried out of the calices without fracturing the calculus. Caliceal projections frequently have a dumbbell configuration and cannot be removed through the narrow infundibulum without excessively traumatizing the structure. In such instances, the calculus is fractured at the narrow portion of the dumbbell and the main portion of the pelvic calculus is removed (Fig. SA). If the overlying parenchyma is scarred and atrophic, individual nephrotomies are performed over the involved calices and the calculus is removed through these incisions (Fig. 8R). If

Figure 8. A. Ifadumbell-shaped calculus is present in the calyx that will not pass through the infundibulum, the calculus is fractured at the narrowed neck. B, The calyceal projections are removed by isolated nephrotomy.

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the parenchyma is thick, nephrotomies are created as much as possible according to the segmental distribution of the renal arterial supply and then limited to one segment. When nephrotomies are necessary through thick parenchyma, I institute hypothermia and renal ischemia. Partial nephrectomy is performed when the polar caliceal and parenchymal areas are markedly atrophic and damaged and when the remainder of the kidney is relatively normal. Should the calculus be localized to the lower pole infundibulum and calices, extension of the pyelotomy incision through the posterior intersegmental line is useful. This technique provides wide exposure of the inferior portion of the collecting system without causing major arterial damage. After all the calculous material is removed, reassembly of the calculus and comparison of its appearance to that on preoperative radiographs is helpful to determine if all calculous material has been retrieved. Each infundibulum and calix should be irrigated thoroughly to remove either chips or fragments of soft calculi. Several irrigation systems are available for this purpose; the malleable metal nasal antral irrigator is readily obtainable and works well. The kidney is placed on a calibrated metallic grid and radiographed to determine the location of retained fragments. The fragments are identified and removed after location by reference to the radiographic grid or by gentle palpation with a malleable metal probe or by both methods. If fragments are retained, a nephrostomy tube is placed for postoperative manipulation of the calculus and Renacidin irrigation. I prefer to use a pyelostomy tube for a solitary kidney to avoid possible secondary complications from the insertion of the drainage tube through the renal parenchyma. Pyelotomy incision is closed with 5-0 interrupted absorbable sutures. Closure is routine, and Penrose drains are placed in the peripelvic area. If intrasinusal exposure is not possible or more than three isolated nephrotomies are necessary, I favor a posterior anatrophic nephrotomy using ischemia and hypothermia. A total renal bivalve procedure is not performed because complications far exceed the small benefit of increased exposure. Regardless of the type of procedure performed, the kidney is surrounded with perirenal fat and sutured back into its normal position. This placement is important to prevent scar formation with ensuing pelvic or ureteral obstruction.

POSTOPERATIVE MANAGEMENT After removal of the calculus, the patient should be given along-term medical program to aid in preventing regrowth of the calculus. Obvious metabolic abnormalities should be corrected. It is imperative that the calculus be submitted for careful qualitative and quantitative analysis of both major calculous substance and, if present, the nucleus of the calculus." Once the type of calculus is determined, medical treatment is *Two laboratories conducting these studies are the Louis C. Herring Co., P.O. Box 2191, Orlando, Florida 32802 and the Laboratory for Research, 81 Wyman St., Waban, Massachusetts 02168.

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directed first at eradication or suppression of infection if present. Sterile urine is essential and should be checked by culture on a monthly basis. Antibiotics are used in the immediate postoperative period and should be continued on a long-term basis. Effective treatment means sterile urine. Second, medical treatment entails reducing the urinary concentration of the substances identified from analysis of the calculus. Calcium, uric acid, cystine, and oxalate excretion can be reduced by appropriate medication or by dietary restriction. In addition, concentration can be reduced by intake of 4 to 5 liters of water spaced evenly over a 24-hour period. 20 Most patients will thereby urinate approximately 3 liters of urine a day, which is beneficial in reducing formation of calculi. Third, altering the solubility of calculous substances is part of the medical plan. Uric acid and cystine solubility are greatly increased in the urinary alkaline pH range. At times, alkalinization of the urine along with diuresis is sufficient to prevent recurrence of calculi. Similarly, struvite becomes soluble in the acid pH range and these patients should maintain acid urine pH. The physician has the responsibility to impress upon the patient the necessity offollowing this treatment program. Patient cooperation is essential as the program can be difficult to maintain and is sometimes a life-long project.

SUMMARY Patients with branched renal calculi present challenging problems to the renal surgeon. Techniques are now available that offer a reasonably good chance of total removal of calculi while causing minimal damage to the functioning renal parenchyma. In our experience, a combination of intrasinusal dissection and isolated nephrotomy incisions using ischemia and hypothermia provides the necessary procedures to remove calculi in the majority of patients. Surgical treatment of calculi should be only part of the overall management of the patient with renal calculi. Incumbent upon both surgeon and patient is the maintenance of a vigorous postoperative medical regimen to aid in preventing recurrence of calculi.

REFERENCES 1. Bissada, N. K., Meacham, K. R, Redman, J. F.: Nephrostoscopy with removal of renal pelvic calculi. J Urol., 112:414-416 (Oct.) 1974. 2. Brantley, R G., Shirley, S. W.: U-tube nephrostomy: an aid in the postoperative removal of retained renal stones. J. Urol., 111 :7-8 (Jan.) 1974. 3. Farcon, E. M., Morales, P., al-Askari, S.: In vivo hypothermic perfusion during renal surgery. Urology, 3 :414-420 (April) 1974. 4. Gil-Vernet, J.: New surgical concepts in removing renal calculi. Urol. Int., 20:255-288, 1965. 5. Graves, F. T.: The Arterial Anatomy of the Kidneys; the Basis of Surgical Techniques. Baltimore, Williams and Wilkins Co., 1971, 101 pp. 6. Libertino, J. A., Zinman, L.: Personal communication. 7. Libertino, J. A., Newman, H. R, Lytton, B., et al.: Staghorn calculi in solitary kidneys. J. Urol., 105:753-757 (June) 1971. 8. Maddem, J P.: Surgery of the staghorn calculus. British Association of Urological Surgeons Prize Essay. Br. J. Urol., 39:237-275 (June) 1967. 9. Metzner, P. J., Boyce, W. H.: The staghorn calculus. An immediate indication for nephrolithotomy. Med. J. Aust., 2:1062-1066 (Nov. 2011971.

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10. Metzner, P. J., Boyce, W. H.: Simplified renal hypothermia: an adjunct to conservative renal surgery. Br. J. Urol., 44:76-85 (Feb.) 1972. 11. Mogensen, P., Rossing, N., Giese, J.: Glomerular filtration rate measurement and 131 I-hippuran renography before unilateral nephrectomy. Scand. J. Urol. Nephrol., 6:228-231, 1972. 12. Myrvold, H., Fritjofsson, A.: Late results of partial nephrectomy for renal lithiasis. Scand. J. Uroi. Nephrol., 5:57-62, 1971. 13. Nemoy, N. J., Staney, T. A.: Surgical, bacteriological, and biochemical management of "infection stones." J.A.M.A., 215:1470-1476 (March 1) 1971. 14. Roth, R., Finlayson, B.: Observations on the radiopacity of stone substances with special reference to cystine. Invest. Urol., 11 :186-189 (Nov.) 1973. 15. Singh, M., Marshall, V., Blandy, J.: The residual renal stone. Br. J. Urol., 47:125-129 (April) 1975. 16. Singh, M., Tresidder, G. C., Blandy, J: The long-term results of removal of staghom calculi by extended pyelolithotomy without cooling or renal artery occlusion. Br. j. Urol., 43 :658-664 (Dec.) 1971. 17. Singh, M., Chapman, R., Tressider, G. C., et al.: The fate of the unoperated staghom calculus. Br. J. Urol., 45:581-585 (Dec.) 1973. 18. Smith, L. H.: Medical evaluation of urolithiasis; etiologic aspects and diagnostic evaluation. Urol. Clin. North Amer., 1 :241-260 (June) 1974. 19. Smith, M. J., Boyce, W. H.: AnatIOphic nephrotomy and plastic calyrhaphy. J. Urol., 99:521-527 (May) 1968. 20. Thomas, W. C., Jr.: Medical aspects of renal calculous disease; treatment and prophylaxis. Uroi. Clin. North Amer., 1 :261-278 (June) 1974. 21. Ward, J. P.: Determination of the optimum temperature for regional renal hypothermia during temporary renal aschaemia. Br. J. Urol., 47:17-24 (Feb.) 1975. 22. Wickham, J. E., Mathur, V. K.: Hypothermia in the conservative surgery ofrenal disease. Br. J. Urol., 43 :648-657 (Dec.) 1971. 23. Williams, R. E.: The results of conservative surgery of stone. Br. J. Urol., 44 :292-295 (June) 1972. Lahey Clinic Foundation 605 Commonwealth A venue Boston, Massachusetts 02215