intraoperative imaging in renal calculus surgery

Urol Radiol 6:144-151 (1984) Urologic Radiology

© Springer-Verlag 1984

Intraoperative Imaging in Renal Calculus Surgery

Michael Berte and Mart in I. Resnick Division of Urology, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA

Abstract. Renal calculus surgery requires metic- ulous detail to ascertain the presence o f residual stones. This paper summarizes past and present methods for the accurate localization o f renal calculi in the surgically exposed kidney.

Key words: Kidney, intraoperat ive radiography-- Kidney, intraoperat ive ultrasonography -- Kidney, intraoperat ive nephroscopy.

Address reprint requests to: Martin I. Resnick, M.D., Professor and Chairman, Division of Urology, Case Western Reserve Uni- versity School of Medicine, University Hospitals, 2065 Adelbert Road, Cleveland, OH 44106, USA

Management of the patient with renal stones in- volves the identification and correction o f any met- abolic conditions that predispose to stone forma- tion, the control o f urinary tract infections, and, when surgical intervent ion is necessary, the total removal o f all calculi. The surgical management o f renal calculi can be rewarding when successfully performed but frustrating when the elusive calculus cannot be found. Though they are believed to be solid uniform stones, staghorn calculi are more typ- ically composed o f multiple fragments (Fig. 1). Mul- tiple direct maneuvers are available to locate renal stones intraoperatively. These include direct pal- pation, use o f needles for localization, and various stone forceps or metal probes. Various adjuvant techniques, such as intraoperat ive radiography, in-

Fig. 1. A seemingly uniform staghorn calculus is often composed of multiple fragments

M. Berte and M.I. Resnick: Intraoperative Imaging in Renal Calculus Surgery 145

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Fig. 2. Intraoperative radiograph using standard Kodak X-Omat KS film

Fig. 3. Diagram demonstrating use of a portable x-ray unit in obtaining intraoperative radiographs. The extension cone is draped with a sterile plastic bag which permits a tube-object distance of 30.5 cm. Note the correct orientations of the kidney and film to the cone

traoperative ultrasonography, and direct visualization via nephroscopy are also available to the urologic surgeon. Because these techniques usually result in less t rauma to the kidney, they are preferable to the methods outlined above, especially during sur-

gery for multiple or branched calculi, which often fragment during removal.

When these ancillary techniques are not utilized the incidence of residual or retained stones increases to an undesirably high rate. Typical recurrence rates range from 25 to 35% [1, 2]. Therefore, the total removal of all renal calculi should always be the goal of surgery. Reliance on postoperative irrigation with stone-dissolving irrigants should be avoided because of the low success rate, particularly with calcium oxalate and calcium phosphate stones [1].

Intraoperative Radiography

Following Roentgen's description of the surgical ap- plications of x-rays, the possibility ofintraoperat ive x-rays to locate renal calculi was first suggested by Robson in 1898 [3]. The first clinical application, however, was reported in 1919 by Braasch and Car- men who used fluoroscopy during stone surgery [4]. Fluoroscopy at that period was time-consuming, utilized nonsterilizable equipment, and probably exposed operating room personnel and patients to excessive radiation. A method of sterile intraoperative fluoroscopy was reported in 1957 by Baskin and associates and was made possible by a fluoro- scopic screen which was sterilized by immersion in aqueous zepharin for 20 minutes [5]. The screen measured 10 x 7.5 x 1.5 cm and was placed directly behind the fully mobilized kidney [5]. Baskin also utilized a sterile beam-limiting cone to reduce radiation scatter and exposure of operating room personnel. The use of fluoroscopy in the operating room waned somewhat in the 1920s with the im- provement of static radiographs. However, it has recently increased because of its usefulness in per-

146 M. Berte and M.I. Resnick: Intraoperative Imaging in Renal Calculus Surgery

Fig. 4. Sequential intraoperative radiographs. A Initial films. B, C Subsequent films, which aided in complete removal of the stone


cutaneous nephroureteral stone manipulation and with the availability of C-arm intensifying imaging systems. While images produced with C-arm flu- oroscopes are satisfactory, their quality is still believed to be less than that of static radiographs. Ra- diation exposure with C-arm use may be in the range of 5 rads per minute at a 30.5-cm distance with some units. This emphasizes the need for strict adherence to the principles of radiation protection [6, 7].

Various types of radiographic imaging films have been used for intraoperative radiography. Static intraoperative radiography has been utilized since 1925, when it was first reported by Quinby [8]. Con- ventional x-ray film wrapped in light-tight paper and then held closely to the kidney was used. Asepsis was maintained by placing the paper-covered x-ray films in a sterile rubber bag. Image quality improved and radiation exposure decreased with the addition of intensifying screens [9]. A special metal cassette and double intensifying screens measuring 9.5 x 12 cm were developed by Jaches in 1929 [10]. The metal cassette was inflexible (in contrast to Quinby's system) but with the addition of intensifying screens, the system allowed exposure times to be decreased to 1/~0 of their previous values. Adequate exposures could be obtained at 0.5 sec at a distance of 30.5- 48 cm.

Linke utilized the simultaneous exposure of 2 sheets of mammography film to facilitate exposures of different densities, with exposure factors of 50 mA at 50 kVl5 at a distance of 25 cm [11].

Probably the most common film in use today is Kodak X-Omat KS film, which is contained in a light-tight plastic envelope (Fig. 2). Two sheets of radiographic film of different emulsion speeds are housed within it, permitting some latitude in exposure [12]. The cassette has a notch in 1 side to accommodate the renal pedicle, although not all surgeons place the cassette as originally intended. At our institution this type of film is used routinely and exposures are made at 60 mA, and 54 kV15 with a portable x-ray unit. A sterile bag placed over the extension cone allows the tube to be brought within 30.5 cm of the kidney (Fig. 3). Feldman and associates further described the use of mammography film in renal stone surgery [13]. Exposure settings of 200 mA at 40 kV for 2 seconds at a tube distance of 30.5-35.5 cm were utilized [13]. Advantages in- cluded improved resolution of less dense stones, including the visualization of uric acid calculi in vitro. This advantage is limited, however, when one considers that the primary treatment of uric acid calculi is nonoperative. Marshall also reported the use of mammography film in renal stone surgery

and consistently identified 2-mm stones, with good visualization of stones in the 1-2-mm range. Mar- shall et aL, however, reported that they could not visualize uric acid calculi with this technique [14].

Polaroid film has also been used for renal surgery and offers the advantages of low-cost, imme- diate processing in the operating suite, and images of relatively good quality [ 15, 16]. Roth has reported the use of Polaroid Type 57 film, a single 10 x 12.7- cm sheet placed inside a sterile bag and exposed at 40-48 mA, 65-70 kV15, and a 46-76-cm distance [14]. Koshiba et al. used an entire Polaroid Type 107 Land film pack. The film pack measured 8.3 x 10.8 cm and contained 8 separate prints. Exposure was made at 70-80 kVI5 and 40 mA, and a distance of 80 cm [16]. Dental film has been used for renal stone surgery in children by Braren [ 17]. Kodak Oc- clusal Ultraspeed Safety film is placed in a sterile container and operative radiographs are obtained at the same settings as in adult kidney cassettes. Pan- orex Type film has been used by Leusch [18] and Baur [19]. A vacuum kidney cassette system was described by Pochaczevsky and was intended to insure optimal intensifying screen contact with the radiographic film [20].

Energy sources for static radiography include standard portable x-ray machines found in almost all hospitals. With an extension tube attached which can either be sterilized or covered with a sterile plastic bag or drape, distance from tube to kidney is consistent [21]. If however, this distance can be kept constant without the cone excellent film quality can be obtained. Portable dental x-ray generators have also been used, apparently with good results [221.

A unique method of exposing static renal radiographs reported by Burke in 1956 consisted of a hand-held radioisotope energy source, thulium 170 [23]. The apparatus containing the isotope was held in 1 hand while the spring-loaded plunger was held in the other hand, much like a cable release mech- anism for 35-mm cameras. The unit weighed 15.4 kg and required relatively long exposures (up to 4 seconds, nearly 2 half-lives of the isotope). This method of exposing radiographs has not withstood the test of time and is no longer used.

Whatever method of radiography is used, obtaining serial intraoperative radiographs greatly aids urologists in searching for the elusive renal stone. The first film can be used as a road-map when planning the initial nephrotomy. Subsequent films aid in total stone removal (Fig. 4). However, other methods have been devised to enhance further the likelihood of localizing a stone. The easiest and least


Fig. 5. Intraoperative radiograph demonstrating the use of surgical clips and radiopaque thread to aid in stone localization

Fig. 6. Intraoperative real-time sonogram demonstrating a staghorn calculus. Strong acoustical reflections from branches of the calculus (c) produce bright echoes and distal shadowing (ar- rowheads), p, renal parenchyma

ably the most definitive radiographic technique for intraoperative stone localization was developed by Gil-Vernet and reported in 1981 [26]. This method involved taking 2 radiographs at 90 ° to each other, thereby localizing the stone 3-dimensionally. His system utilized standard x-ray film, image-intensifying screens, and special cassettes, which also held the kidney. Radiographs were taken at 45-50 kV15 50 mA at a distance of 70 cm [26]. Intraoperative pneumopyelography with air insufflated via a Teflon catheter placed within the renal pelvis and secured with a pursestring suture has been described [27]. The technique was performed in 45 patients with complex renal lithiasis and resulted in a change in operative strategy in 10 cases. In 2 of the 10 patients concretions were left behind when it was shown that no communications existed with the collecting system. No complications were observed [27].

expensive method is probably localizing needles in association with intraoperat ive radiography. A straight Keith needle or small-gauge intravenous needle is utilized. Once the stone is localized a nephrotomy is made over the tract of the needle lead- ing to the stone. Other useful materials include metal surgical clips and the radiopaque threads obtained from surgical sponges (Fig. 5) [12]. Various radiopaque grid systems have also been developed. Hanley developed a low-cost grid system made from picture wire which measured 10 x 12.7-cm and which was placed in front of the kidney [24]. Roth described a more elaborate grid system utilizing a radiolucent polytetrafluorethylene sheet slightly larger than a Kodak KS cassette which was per- manently photoengraved in 1 cm 2 blocks [25]. Prob-

Intraoperative Ultrasonography

Ultrasonography in urologic practice has been used for evaluating disorders of the testes, bladder, pros- tate and seminal vesicles, and the kidney and ureter. The use of ultrasonography has become more wide- spread due to its ease of use, relatively low cost, and safety. One-dimensional imaging reflection ultrasound systems include M-mode and A-mode types. M-mode is used mainly for echocardiography. A-mode ultrasonography was used intraoperatively for the first time by Schlegel in 1961 [28]. This "flaw" detector emitted a pulsating sound wave with a frequency of 1.6 megacycles per second, and a pulse frequency of 1,000 per second. A-mode sonograms consist of spikes or peaks in which stones are located. Measuring the distance between the anterior


A B

/

Fig. 7. A Intraoperative real-time ultrasound transducer. B Sterile rubber sleeve covers transducer (courtesy of Matthew Rifldn, M.D.)

and posterior surface peaks and the peak produced by the stone revealed the depth of the stone. A-mode ultrasonography was used by others but fell into disuse because of the difficulty in interpretating the scans and clinicians' lack of familiarity with ultrasound.

Two-dimensional imaging ultrasonography as used intraoperatively today is otherwise known as real-time B-mode scanning, and was a major advancement in intraoperative ultrasonography. Ad- vantages include identification of radiolucent calculi, lack of radiation exposure, and delineation of a more anatomical display which is easier to inter- pret (Fig. 6).

B-mode scanning displays a cross-section of renal tissue and, with multiple scans at different angles, turns a 2-dimensional scan into a "3-dimensional" image which is useful in localizing stones. Depth of penetration and small-object discrimination are of fundamental importance but the sensi- tivity of one varies inversely with that of the other. Discrimination of a l-ram object within kidney tissue requires relatively high frequencies but, with increasing frequency, the depth of penetration de- creases [ 12]. This can be somewhat offset by varying the transducer size. Most ultrasound devices used in urologic surgery utilize a frequency of 7-10 MHz and are modifications of the small ophthalmic ultrasound probe. Experimentally it has been found that a 6-7-MHz transducer produces satisfactory echoes at a depth of 3.0-3.5 cm with resolution of stones in the 2-3 mm range [ 12]. Since echoes from deep objects are weaker than those from objects nearer the surface, intraoperative real-time B-mode scanners are equipped with time-variable gain to produce a clear display of objects in the scanned tissue (Fig. 6). Intraoperative real-time B-mode ul-

trasound of the kidney was first described by Cook and Lytton in 1977 [29]. Except for some equipment advances, it is basically the same technique as used today. Cook and Lytton used a 10-MHz frequency probe which visualized 2-3-mm stones. For 3-dimensional localization they utilized fine needles concomitantly, successfully employing the scanner in 7 of 11 patients [29].

In general, ultrasonography during renal surgery is relatively simple. The kidney is mobilized and the ultrasound probe is either applied directly to the kidney or transmitted through a thin layer of fluid to create an acoustic window of a few millimeters (Fig. 7). The kidney and pelvis are scanned in multiple planes to detect the best approach to nephrolithotomy. Needle probes are directed either "free- handed" along the probe or are guided via needle guides that attach to the ultrasound probes. The probe attachment is generally reserved for small stones while the "free-handed" method is reserved for larger and more superficially located stones. An incision is then made along the needle tract, the stone is exposed, and then grasped with an appropriate instrument. Ultrasonography is repeated to insure removal of all fragments. Prior to the second ultrasound exam, saline is reintroduced into the wound to displace any air bubbles that distort the image. Most surgeons advocate the use of pre- and postnephrolithotomy intraoperative radiography in addition to ultrasound.

A review of the literature by Lytton in 1983 revealed a total of 69 patients in whom intraoperative ultrasound was used in locating renal stones. Ultrasound was found to be useful in 52 of 69 cases, not particularly helpful in 5 cases, and failed to detect the stone is 12 cases [30].

Another ultrasonographic method utilized in


renal surgery is the Doppler ultrasound probe to locate the branches of the renal artery in planning the nephrotomy incision [31]. Advantages in the use of Doppler probe include the ability to make the nephrotomy in a relatively avascular plane thus avoiding the need for renal artery clamping and renal cooling. Additionally the shortest parenchymal incision can be made to effect stone removal, therefore reducing damage to renal tissue. The series by Riedmiller and associates reported use of the Dopp- ler probe in 35 patients [31]. Avoidance of renal artery clamping was accomplished in 33 patients with complete stone removal in all patients.

Utilizing cadavaric kidneys, a comparison of radiography and ultrasonography was made by Mar- shall and associates [12]. They compared radiography made with mammography film exposed at 55 kV~, 200 mA with a sequential linear array real- time unit with a 7-MHz frequency transducer probe. Both methods consistently identified 3-mm stones. Stones of various composition were used and the depth varied. Radiography did have an advantage in identifying smaller stones (1-2-ram) but did not visualize uric acid stones nor was the information immediately displayed as in real-time ultrasonography.

more advantageous than an intrarenal pelvis. Ap- proximately 60% of calculi were seen, with the mid- dle calyceal system being the most difficult to vis, ualize. It was believed that nephroscopy was most advantageous in localizing and removing fragments less than 2 mm, the practical limit ofintraoperative radiography [36].

The development of the flexible nephroscope improved the range of visualization of calyces [37]. Although a bloodless field is ideal for nephroscopy, clamping of the renal artery and kidney cooling are generally not required. Various instruments can be passed via the operating port of the flexible nephroscope, including the electrohydraulic lithotriptor, which is a device for fragmenting stones [37]. The injection of intravenous indigo carmine has helped identify calyces that are otherwise difficult to see.

In conclusion, intraoperative identification and localization of all stone fragments are mandatory when performing stone surgery. Intraoperative radiography should be utilized routinely and, when appropriate, combined with the use of needles or other radiopaque guides to aid in localizing a stone. Ultrasonography and nephroscopy are adjuncts to these techniques and can often greatly aid the surgeon in localizing and subsequently removing elusive stones.

Nephroscopy

Although nephroscopy was utilized during renal surgery as early as 1925, Trattner in 1948 was the first to popularize its use with the development of a 22- Fr rigid, straight nephroscope [32]. In 1950, Lead- better developed a right-angle nephroscopy unit [33]. Basic design of the rigid nephroscope has essentially remained unchanged for 20 years except for im- provements in optics and light sources. A major advancement in rigid nephroscopy was the development by Hertel in 1973 of an atraumatic stone forceps [34]. The indications for intraoperative nephroscopy include assistance in diagnosing the site of renal hemorrhage, visualization and biopsy of diseases of the renal pelvis, and as an aid in identifying and removing residual stones during renal stone surgery [35]. The advancements in nephroscope design have permitted therapy as well as diagnosis and are a unique advantage in comparison to the use ofultrasonography or radiography in renal stone surgery.

In a recent study by Zingg and Futterlieb the rigid nephroscope was used in 130 renal stone op- erations [36]. In general, a wide transverse pyelo- lithotomy was made for the introduction of the nephroscope, with a large extrarenal pelvis being

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intraoperative imaging in renal calculus surgery

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