Radio-Contrast Enhancement of Urinary Tract Stones

0022-534 7/91/1453-0618$03.00/0 THE JOURNAL OF UROLOGY Copyright© 1991 by AMERICAN UROLOGICAL ASSOCIATION, INC.

Vol. 145, 618-623, March 1991

Printed in U.S.A.

RADIO-CONTRAST ENHANCEMENT OF URINARY TRACT STONES J. CORCOS,* L. PICARD, S. GROLEAU, P. MADARNAS AND E. ESCHER From the Departments of Surgery (Urology), Pharmacology, Radiology and Pathology, Centre Hospitalier Universitaire de Sherbrooke, Sherbrooke, Quebec, Canada

ABSTRACT

Most urologists treating stone disease with any method (ESWL, PCL, URS) have encountered problems of poor stone visualization with fluoroscopy. This difficulty to localize urinary tract (UT) stones or fragments may result in incomplete stone extraction, prolonged surgery and increased risk of recurrence and post-operative complications. We have sought and found means to increase the radioopacity of mineral UT stones by a simple pre-operative perfusion technique. The capacity of radioopacification has first been demonstrated in in vitro incubations of fragments of human mineral stones with aqueous solutions of barium, of the lanthanides and of the two natural actinides. Most of the incubations led to considerable radio-contrast enhancement and heavy metal incorporation, measured by X-ray fluorescence analysis. Dogs with implanted human stone fragments were used as an in vivo model. The UT were perfused through a retrograde pyelic catheter with heavy metal salts solutions, the ensuing radioopacification of the implanted UT-stones was estimated by abdominal radiographies and the metal incorporation was measured on the retrieved stones. Considerable radioopacity enhancement together with heavy metal incorporation was observed for the following elements: Sr, Ba and the lanthanides Gd and Yb. The pathological evaluation of the urothelial linings from animals treated with lanthanide salt showed no toxic effects. KEY WORDS: calculus, radioopacification All modern surgical treatments of urinary tract (UT) stone disease (extracorporeal shock wave lithotripsy, percutaneous lithotripsy, ureteroscopy) depend on good visualization of the stones. Duration of surgery, recurrence, morbidity and complication rate depend to a high degree on good visibility of the stone by fluoroscopy during the procedure. More than 25% of all UT stones are too radio-translucent to permit straightforward extraction or lithotripsy1 under simple fluoroscopic control. But even the most radioopaque mineral stones, (Ca-oxalate, Ca-phosphate) tend to become poorly visible once they have been shattered into smaller fragments. The use of ultrasound, generally more powerful than fluoroscopy in its ability to localize stones or their fragments, is however limited by the stone size (detection limit around four mm.) and, in the case of multiple stones or fragments, due to screen effects. 2 Moreover, simultaneous stone manipulation is difficult under ultrasound visualization. After lithotripsy, most fragments generated (84%) are smaller than five mm. in diameter3 and, if some are not expulsed spontaneously, they are difficult to visualize. Residual stones after any surgical treatment are the single most important cause of recurrence 4 and of complications. Improved radiological methods for stone localization and manipulation would therefore significantly improve the results of UT stone surgeries. Several clinical situations could benefit from such a diagnostic procedure. Radioopacification could be carried out before the actual surgery if the stones are poorly visible under fluoroscopy. This will facilitate any surgery by percutaneous or ureteroscopic approaches and will permit better positioning for ESWL. On the other hand, radioopacification could be very useful after an initial stone disintegration. This would simplify and accelerate the detection of remaining and potentially pathogenic fragments. It would also permit to evaluate accuAccepted for publication September 19, 1990. *Requests for reprints: J. C. Urology Unit, C. H. U. S., Sherbrooke, Sherbrooke, Quebec, Canada JlH 5N4. Supported by Grants from the Quebec chapter of the Canadian Kidney Foundation.

rately the opportunity and type of any further intervention (repetitive surgery, ESWL, stone dissolution). To our knowledge to date, there is no technique available which allows the enhancement of radioopacity of UT stones. Generally, radio contrast media are either highly insoluble heavy metal salts, for example BaS0 4 , or iodinated organic molecules with the appropriate pharmacodynamic behaviour, like meglumine diatrizoate (Renografin-76). 5 None of these compounds is specifically incorporated into the inorganic matrix of UT stones. On the contrary, frequently stones can be visualized by exclusion of the contrast medium (negative imaging). An agent for potential positive stone visualization must specifically interact with the matrix of the stone, incorporate into it and thus, increase its radioopacity. In our search of potential compounds with such properties we decided to look at heavy metals which a) form highly insoluble oxalates and phosphates, b) are weakly or not toxic to the ureteral lining and c) form highly water soluble salts. We investigated the capacity of radioopacification and incorporation of heavy metals into UT stones in two assays. First, we incubated human UT stones in vitro in aqueous heavy metal salt solutions. The heavier elements of class 2 of the periodic system (Sr and Ba), class 3 (Y, La, and all the lanthanides) and the natural actinides U the Th were evaluated and compared to several reference solutions. In a more refined model, selected elements were tested in vivo. Stone fragments were implanted in the renal pelvis of anaesthetized dogs and perfused with heavy metal solutions. The effectiveness of this procedure was evaluated by the observed radioopacity enhancement and by the heavy metal incorporation into the stone fragments; The innocuousness of the perfusion was assessed by pathological evaluation of the treated urothelium. MATERIALS AND METHODS

Fresh human urinary tract stones of various mineral compositions were obtained either from open surgery or endoscopic extraction and were stored in gamma-ray sterilized human urine at 4C or as dry samples. In this group, a giant bladder stone (hydroxyl apatite, 8.1 cm. diameter, 162 gm. dry weight)

618

RADIO-CONTRAST ENHANCEMENT OF URINARY STONES

was fragmented and used for the in vitro incubation experiments. This material was however unappropriate for the ensuing in vivo studies due to its extreme brittleness. Heavy metal salts were purchased in the hydrated nitrate form from Alfa inorganics with the exception of Th and U salts which were obtained from Atomic Energy Canada. In vitro incubations were carried out without stirring in 2.5 cm. petri dishes at 37C for 40 hr. with small hydroxylapatite stone fragments (three to five mm.) and 4.0 ml. of a 2.5% w/v solution of hydrated heavy metal nitrate. The supernatant was discarded, the stone was rinsed carefully several times with water and dried in a dessicator. Before and after incubation the stone fragments were radiographed under identical conditions (Picker PX 1500, Curix RPI-L film at 42 KV, 20 mAmps at 81 cm. distance). Heavy metal incorporation was assessed by X-ray fluorescence analysis (Kevex 700 instrument coupled to a 8000-computer, two mA, 60 kV with a rhodium tube) of intact stone fragments or pellets of powdered samples. The elementary composition is expressed in % of sample weight. As controls, incubations with potassium nitrate, sodium iodide, and the conventional radiocontrast agent Renografin-76 (Sqibb) were performed. In vivo perfusion experiments were carried out on non-gravid, nonestrous female mongrel dogs (23 to 35 kg.). The animals were fasted for 24 hr. with water ad libidum, sedated with xylazine (one mg./kg.) and atropine (0.05 mg./kg.) subcutaneously, then anaesthetized with pentobarbital (BDH, 30 mg./kg.) by infusion into the cephalic vein. After intubation, the animal was mechnically ventilated, kept normovolemic by continuous i.v. administration of 0.9% NaCl and a sternum-to-pubic laparotomy was performed. The ureters were mobilized and sectioned approximately 10 cm. below the kidneys. Several (three to five) small fragments (1.5 to three mm. diameter) of Ca-oxalate UTstones were placed into the renal pelvis by retrograde insertion, followed by a dual-lumen catheter. The abdominal wound was sutured and a first abdominal radiography was taken (Picker PX1500, Curix RPl-L films at 54-56 KV, 40 mAmps, 102 cm.). Calculi superfusion was performed with 5% w/v metal salt through the infusion catheter (0.4 ml./min.) with a Harvard syringe pump. Urine output was monitored continuously and the experience was aborted if the urine output was equal or lower to the input volume. Urine pH and osmolarity was also recorded, the first being in the range of 5.0 to 7.0 and the second in the range of 200 to 525 mOsm. After one to two hr., the catheters and the renal pelvis were rinsed with 0.9% NaCl for 15 min. and a second abdominal radiography was taken under identical conditions. Finally, the animal was sacrificed by an overdose ofpentobarbital, the kidneys removed, the pelvis opened, the calculi recovered and the UT tissues prepared for pathological evaluation. The heavy metal content of the UT stone fragments was assessed by X-ray fluorescence as mentioned above. Pathological evaluation was carried out on tissue samples of ureter and pelvis. For this purpose, kidney, pelvis and ureter were fixed in 10% formol solution for two days, the tissue samples were dehydrated with alcohol washes and finally with toluene. The tissues were embedded in paraffin blocks and prepared as three to five µ. thick sections, stained with hematoxylin and eosin for optical microscopy. RESULTS

The in vitro experiments with statically incubated struvite fragments showed several dramatically increased radioopacities and very high metal incorporations (see Fig. 1 and Table 1) of up to 40% w/w. In table 1 are presented the results obtained with the in vitro incubations of struvite stone fragments from the same giant UT-stone. In general, a good correlation is visible between the incorporation rate and the radioopacity enhancement for all compounds tested. Good results were obtained with the higher group 2 elements strontium (Sr) and barium (Ba), both Ca-homologuous elements. Among the group

619

3 elements, the aluminium homologuous yttrium (Y) showed some weak incorporation and radioopacification. The Y homologuous lanthanum (La), the first lanthanides cerium (Ce), praseodymium (Pr), neodymium (Nd), and samarium (Sm) proved rather disappointing with weak or no effect at all. Good results were obtained with three lanthanides, europium (Eu), gadolinium (Gd) and ytterbium (Yb), all three produced consistently good incorporation and visibility. The remaining lanthanides terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm) and the rarest, lutetium (Lu) showed the same effect but with less efficiency. On the other hand, the two natural actinides thorium (Th) and uranium (U in its form as uranyl-salt) produced dramatic results which led to almost total radioopacification (fig. 1). In this group, the element gadolinium (Gd) is especially promising, since chelated salts of this element are now used clinically as contrast agents in magnetic resonance imaging. 7•8 Non-chelated salts of Gd have however some moderate toxicity if administered systemically; 9 the use within the UT however should prevent in principle such a systemic distribution and toxic effects should be limited to the urothelial linings. As reference compounds were used Reno-76, sodium iodide and potassium nitrate, but none of these produced any incorporation nor radioopacification (table 1 and fig. 1). Incubation of calculi fragments with sodium tungstat (W04 -) solutions did however not produce any significant incorporation nor radioopacification. The tungstat treated calculi however had a pronounced tendency to disintegrate during incubation and the following operations. The analysis of the results obtained with the in vivo dog model has shown that indeed, small UT calculi are visualized by this technique (table 2). It also appears, although a numerical evaluation of the radiological findings is rather problematic, that radioopacity enhancement is proportional to heavy metal incorporation, and that such contrast enhancement is obtained even with only moderate incorporations. The ensuing in vivo experiments were carried out with some heavy metal salts successful in the in vitro studies. The in vitro highly successful actinides Th and U were not considered further. The Ca homologuous Sr and Ba were studied only preliminarily because of the toxicity of Ba6 and the smaller atomic weight of Sr. In the remaining lanthanides the three elements that gave the best results in the in vitro studies, namely Eu, Gd and Yb proved to be the most suitable also in the in vivo studies. The relatively inexpensive Gd and Yb consistently produced good incorporation and stone fragment visibility. With the third element Eu, only preliminary results were carried out but without abdominal radiography. The pathological evaluation of dog tissues treated with heavy metal salt solutions has been made difficult by the always present injuried to the urethelial linings caused by the retrograde stone fragment insertion (fig. 2). Therefore experiments on the in vivo model were carried out that did not involve stone fragments but otherwise identical conditions for the perfusion experiments. As controls were utilized completely non-treated urinary tracts and urinary tracts perfused with the struvite stone dissolving formulation Renacidin 10 (Guardian Chemical, Smithtown, N.Y.). In the untreated, the Renacidin treated and the Gd-treated caliceal and pelvic tissues, no cytological alteration nor damage could be detected (fig. 3), suggesting, a posteriori, the low toxicity of Gd to the urothelial linings. DISCUSSION

The success of UT stone surgery is only assured if a truly stone-free kidney and UT can be achieved: Recurrence and complication rate is directly related to the residual stone burden after surgery. 4 The only means however to assure effectively a stone-free state of the UT are radiological techniques but they are limited by stone fragment size and/or opacity. 1·2 Without the assurance of more sensitive detection methods, the relative

--

--620

CORCOS AND ASSOCIATES TABLE

Metal

K Sr

y

I Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu W (Wo.-) Th

u

1. In vitro incubation of struvite fragments

A.N.

A.W.

Incorporation

Radio Opacification

19 38 39 53 56 57 58 59 60 62 63 64 65 66 67 68 69 70 71 74 90 92

39.10 87.62 88.91 126.90 137.34 138.91 140.12 140.91 144.24 150.35 151.96 157.25 158.92 162.50 164.93 167.26 168.93 173.04 174.97 183.85 232.04 238.04 809.00*

0 ++ + 0 +++ 0 0 + + + ++ ++ + + + + + +++ + 0 +++ +++ 0

0 ++ + 0 ++ 0 0 + 0 + ++ ++ + + + + + ++ + 0 +++ +++ 0

Reno-76

n 3 11

5 14 8 10 4 4 10 6 4 10 8 6 6 4 2 13 2 8 6 7 4

A.N. is the Atomic number. A.W. is the Atomic weight, and n is the Number of experiments. Incorporation values were determined with X-ray fluorescence on the intact stones and are expressed as follows: +++ is for incorporation above 20% w/w, ++ is for incorporation above 10%, but below 20%, + is for incorporations between 2 and 10%, and Oindicates incorporations below 2%. Radio-opacification is expressed as: 0 = no change, + = overall density somewhat higher, border lines visible, ++ = overall density much higher, very good contrast, +++ = almost totally radioopaque. TABLE 2.

Metal Sr Ba Eu Gd Dy Yb

In vivo perfusion of small UT-stones

Incorporation ++ + ++ + + ++

Radiovisibility

n

+ ++ No radiography ++ 0 +to++

1 1 2 3 2 5

The incorporation rate of heavy metals into fragments of Ca- containing UT stones was determined by X-ray fluorescence analysis of diluted powder samples or intact stone fragments. The incorporation rate is expressed by the ratio of Metal-to-Ca in% w/w. ++ indicates incorporation superior to 10%, + is 2-10%, and O indicates an incorporation rate below 2%. The in vivo radiovisibility of stone fragments is expressed by ++ for good visibility with high contrast, by + for fair visibility with weak contrast. 0 indicates no notable improvement of fragment visibility. n indicates the number of experiments.

Fm. 1. In vitro incubation of struvite stones. Stone fragments were radiographed before (left) and after (right) incubation with corresponding heavy metal salt. Plate A is treatment with potassium, plate B is lutetium, plate C is ytterbium and plate D is thorium. Scale bar is 5 mm. Radioopacification obtained in A corresponds to O (as in table 1), inB to+, in C to++ and in D to+++.

high frequency of recurrence is a direct consequence of these diagnostic shortcomings; they are responsible for the presence of residual stones, overlooked during the actual surgery. Our research goal was therefore that of a general radioopacity enhancement of mineral UT stones which should facilitate general fluoroscopic visibility during any approach for UT stone surgery. A successful method should assure the visibility also of smaller fragments in the two to five mm. range, stone fragments generally too small to be detected even under favor-

able conditions, by ultrasonography and fluoroscopy but still capable to induce stone disease recurrence. Our approach to use heavy metal salt-solution as UT stone radioopacity enhancers has been oriented by the chemical nature of mineral UT stones and the required high atomic weight of radioopaque elements. The working hypothesis of a specific heavy element incorporation into the lattice of Caoxalate and/or Ca, Mg-NH4-phosphate stones is that of a specific cationic exchange reaction or of a precipitation reaction. Therefore the choice of elements was concentrated on elements of the third period with atomic numbers above 54, all forming insoluble oxalates and phosphates, and, last but not least, being void of known toxic effects on the urothelial linings. As prime candidates were available the lanthanides or rare earth elements, atomic numbers from 58 to 71 and lanthanum itself. Also considered were the Ca-homologuous Ba and Sr of element group II, the La homologuous Y of group III and the lanthanide homologuous natural actinides U and Th of period IV. The two latter are the best con,trast media due to their ultra-high atomic weight (232 and 238) and are therefore well suited as experimental models but they cannot be utilized clinically due to their inherent radioactive nature. Soluble Ba salts are known to be systemically toxic 6 but no report on

RADIO-CONTRAST ENHANCEMENT OF URINARY STONES

621

FIG. 2. Abdominal radiography of implanted UT-calculi fragments. Abdominal radiographies were taken before (left panels) and after (right panels) lanthanide salt perfusion of implanted UT-stone fragments in dogs. Perfusions were carried out with Gd (upper panels) and Yb (lower panels). Calculi locations are indicated by arrows, scale bars are 10 mm.

eventual epithelial toxicity could be found, therefore Ba and also Sr salts were included in this study. A heavy metal anion, forming insoluble Mg and Ca salts is the tungstat ion (W04 -), therefore calculi incubations were also carried out with sodium tungstat solutions. Other high atomic weight metals were not considered, although they may form insoluble oxalates and

phosphates, because of their well known toxicity; for instance, lead, thalllium, mercury and cadmium. An interesting observation was made on a particular dog during the initial phase of this research where, prior unknown to us, an endogenous UT stone was already present in the pelvis. Unfortunately, during this phase, abdominal radiogra-

622

CORCOS AND ASSOCIATES

FIG. 3. Cytology of lanthanide treated UT-epithelia. First row: control section of untreated renal calyx (A, X400) and renal pelvis (B, X400) normal cytology. Second row: cross section of Renacidin-treated caliceal (C, Xl60) and pelvic urothelium (D, X400). No significant changes visible. Third row: cross section of 5% Gd-treated urothelium. In caliceal (E, X400) and pelvic (F, X400) tissue samples urothelium is well preserved. Stromal fracture in F is artefactual.

phy was not yet a standard procedure due to technical restrictions. The concomitant analysis of the introduced stones and the endogenous stone showed a six-fold higher incorporation into the endogenous stone, suggesting a more efficient captation of a native and active stone surface over a fragmented, dried and then re-hydrated stone. This serendipitous finding promotes us to investigate animal models of chronic stone disease which might reduce the necessary time of contrast media instillation even further; these studies are currently under way. In conclusion, we claim to have found a new and relatively simple, non-invasive and effective method for the radiological detection of hitherto undetectable pathogenic UT stones.

Acknowledgments. L. P. is the holder of a partial studentship from the Faculty of Medicine. We would like to thank Dr. R. Zamojska from the department of chemistry, Faculty of Sciences, University of Sherbrooke for the X-ray fluorescence analysis of UT stones. REFERENCES 1. Davidson, A. J.: lntraluminal Abnormalities. W. B. Saunders Com-

pany, Toronto, p. 424, 1985. 2. Kellum, C. D., Tegtmeyer, C. J., Jenkins, A. D., Barr, J. D., Gillenwater, J. Y., Wyker, A. W. and Lippert, M. C.: The role of

RADIO-CONTRAST ENHANCEMENT OF' URINARY STONES

radiology in extracorporeal shock wave therapy. Radio!., 165: 431, 1987.

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