Effect of Lithotripsy on Immature Rabbit Bone and Kidney Development

0022-534 7 /91/1461-0213$03,00/0 'Vol. 146,

THE JOURNAL OF UROLOGY

Copyright © 1991 by AMERICAN UROLOGICAL ASSOC!ATION, INC,

EFFECT OF LITHOTRIPSY ON IMMATURE RABBIT BONE AND KIDNEY DEVELOPMENT KEITH N, VAN ARSDALEN,* STEVEN KURZWEIL, JANET SMITH AND ROBERT M, LEVIN From the Division of Urology, University of Pennsylvania, School of Medicine, and the Philadelphia Veterans Administration Medical Center, Philadelphia, Pennsylvania

ABSTRACT

Although extracorporeal shock waves have been used to treat kidney stones for several years, little is known of their effect on developing tissue. In order to determine if lithotripsy has any negative effects on development, immature rabbits were used to study the relationship of extracorporeal shock waves to renal and skeletal growth. Rabbits in both the control and treatment groups had metallic clips placed surgically to demarcate the kidneys. Following unilateral kidney and femoral head treatment of the respective study groups with the Dornier Lithotripter Model HM-3, the rabbits were allowed to grow to maturity (six months). Plain radiographs were taken at three months. There was no significant difference between control and study groups when length of the kidneys or femurs, the diameter of the femoral heads, or the rabbits weights were compared. At six months of age, the rabbits were weighed, then sacrificed. The kidneys and femurs were removed. Comparisons between the control and study groups were then made for weight of the rabbit, weight and volume of the individual kidneys, femoral length, and femoral head diameter. Following these measurements sectioning and histologic examinations were done. In all parameters grossly and histologically, there was no statistically significant difference. It is concluded from this study that treatment with extracorporeal shock waves does not adversely affect overt rabbit renal or bone growth, making treatment of pediatric patients with ESWL appear safe in regard to these parameters. Future studies will be directed at confirming these findings in children, KEY WORDS: calculi, lithotripsy

The initial in vitro and in vivo experiments and early clinical studies reported by Chaussy demonstrated minimal adverse effects of carefully directed high energy shock waves although potential tissue damage from misdirected shock waves was recognized, I The non-invasive nature ofthe technique, its clinical efficacy and its apparent safety lead to rapid, worldwide acceptance of extracorporeal shock wave lithotripsy (ESWL) as the primary method for the treatment of renal calculi. 2 ,3 With increasing clinical experience, the indications for ESWL expanded to more difficult calculi and to patients that were excluded from the original protocols. With minor modifications of the gantry and particular attention to shielding the lung, the same safety and effectiveness of ESWL was reported by Newman and associates in treating upper urinary tract calculi in children. 4 This has also been the experience at this institution noting, however, that each patient is treated with some trepidation and with the understanding that truly long-term, potentially adverse effects of ESWL may not be known at this time as the clinical experience with ESWL is still less than a decade in the making and unanticipated side effects may still be reported. The study, described herein was designed to evaluate the effects of high pressure shock waves on growing, developing tissue because of theoretical concerns raised in treating children. The investigation centered on the kidneys as the shock waves are most frequently focused directly at this organ and on bones because of the proximity of this type of tissue to the Accepted for publication January 23, 1991. * Requests for reprints: Division of Urology, 5 Silverstein, Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia PA 19104. Supported by Grants from the Veterans Administration, NIH Grants RO-1 DK 6508, RO-1 DK 33559, RO-1 DK 26508, RO-l DK 39086, P50 DK 39257 and the McCabe Fund. 213

kidney and to the path of the shock waves, and because of the known sensitivity of developing bone to other types of energy.5 MATERIALS AND METHODS

Nineteen weaned immature male New Zealand white rabbits, with a mean weight of two kilograms, were divided into control and treatment groups. Three of the control group and three of the kidney treatment group had metallic surgical clips placed in the perinephric fat adherent to the right kidney at the level of the poles and the lateral border to define the precise location of the kidney (fig. Three more control group rabbits and four of the treatment group had metallic clips similarly placed immediately adjacent to the left kidney. These surgical clips were placed via a flank incision while the rabbits were under general anesthesia using parenteral ketamine and xylazine. These clips subsequently allowed fluoroscopic localization of the kidneys for treatment with ESWL. Of the six remaining rabbits, three had their left femoral epiphysis and three had their right femoral epiphysis exposed to extracorporeal shock waves. Three weeks following placement of the metallic clips, all rabbits had plain radiographs taken while under general anesthesia. The rabbits in the treatment groups had either their kidney or hip treated in the Dornier Model HM-3 Lithotripter. This was performed with the anesthetized animals placed on a specially constructed "rabbit gantry" that attached to the standard lithotripter gantry (fig. 2). The rabbits were held securely in position by mesh netting, Prior to securing the rabbits to the gantry, the hair over the flank was clipped and then thoroughly wetted once they were placed in the water bath. The kidneys designated for treatment were properly positioned at F -2 by identifying the previously placed clips and by using standard biplanar fluoroscopic localization techniques that have been proven experimentally and clinically to set the

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waves for all of the treatments were triggered by attaching the EKG leads to one of the technical assistants. Following treatment, the rabbits were returned to their cages for recovery and observation. The rabbits were allowed to grow to full maturity (six months). Weekly weights were recorded. At three months of age, plain radiographs were taken to preliminarily assess bone and kidney growth. At six months of age, the rabbits were weighed and then sacrificed. The respective kidneys and/or femurs were removed intact. The kidneys were weighed and measured for length, width and diameter. The femurs were measured for length and diameter of the femoral head. The kidneys were then fixed in buffered formalin. They were routinely processed for paraffin embedding, sectioned at six microns, and then stained with: hematoxylin and eosin, Mallory's or PAS. The bones were fixed in formaldehyde, then decalcified in a mixture of hydrochloric acid, ethanol, acetic acid and chloroform. They were then split, embedded in paraffin, sectioned, and stained with hematoxylin and eosin. RESULTS

FIG. 1. KUB taken prior to ESWL treatment of left kidney which has been clearly demarcated by surgical clips placed at upper pole, lower pole and lateral border of kidney.

Acutely, all of the animals in the kidney treatment group developed gross hematuria which was noted immediately after each procedure. The blood persisted for 24 to 48 hours in each case and then the urine remained grossly clear thereafter. On examination, no obvious flank hematomas were identified in this group and no overt abnormalities were noted in the tissues surrounding the femurs which were treated. Three months after treatment, preliminary comparisons were made by plain radiographs. The rabbit's weight, length of the kidney and femur, as well as the diameter ofthe femoral head, were measured for the respective groups. Statistical analysis of these preliminary measurements showed no significant effect from ESWL. Six months following treatment, most rabbits were in a good state of health. Following sacrifice, the individual weights (fig. 3), kidney weight and kidney volume (fig. 4A, B), femoral length and femoral head diameter (fig. 5A, B) were measured. Each group studied contained either five or six animals (n = 5-6). No differences were noted in comparing results of "right" versus "left" sided treatment groups and therefore these were considered together simply as the "treatment" groups for comparison with the "control" groups. Analysis of variance was done and in each category, the statistical analysis showed no difference between the variables (p <0.05). Histologic analysis of the kidney and femoral head control groups versus the treatment groups showed no differences. In the kidney, there was no difference in the renal architecture or number of glomeruli and no increase in the amount of fibrous

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target at the area of maximum shock wave energy. Localization of the proximal femur for treatment was accomplished by directly identifying this segment of bone in the cross-hairs of the fluoroscopic monitors. All treatments consisted of one thousand shock waves administered at 18 kilovolts. The shock

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tissue in the treated versus the control groups (fig. 6A, B). The intact and split bones demonstrated similar gross anatomic external and internal anatomy. None of the animals had any gross or microscopic lesions noted in the epiphyses which had fused and calcified equally in the two groups. The end result, as noted in fig. 5, was therefore equal bone growth and development. DISCUSSION

The treatment of urolithiasis in adults and children changed dramatically since the advent of ESWL. In part, the rapid acceptance of this technique and the applicability to the pediatric age group has been based upon its apparent safety and the lack of obvious major adverse sequelae. Although numerous animal studies were conducted by the original investigators during the developmental stages,' more recent clinical radiographic studies, experimental and histological data suggest that intrarenal damage may occur as a result of this technique. 6 - 11 The effects of shock waves on renal and skeletal growth have not been established. The studies described above were designed to determine if ESWL had any negative gross or histologic effects on kidney and bone growth and development. As demonstrated in this experimental model, one thousand of the eighteen kilovolt shock waves delivered by the Dornier HM3 lithotripter had no effects on any of the parameters measured. The findings with regard to bone are in contradiction to a research study by McCullough and his colleagues that reported focal growth plate dysplasia in eight of 18 (44%) and impaired

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longitudinal growth in three of 18 (17%) treated rat tibias. '2 The disparate results may be attributed to the different animal models and to differences in the amount of shock wave energy applied in each experiment. In these two animals, the smaller overall size of the rats compared to rabbits and particularly the smaller absolute size ofthe rat tibias compared to rabbit femurs may have been important factors. Perhaps of greater significance is the amount of energy delivered at 20 KV by the Dornier XL-l experimentallithotripter. In our rabbit experiment, 1000 shock waves were delivered at 18 KV by the Dornier HM3 lithotripter. Not only did the rats receive L5 times the number of shock waves but also by using the authors' information,'2 the pressure at F2 would have been approximately 2.5 times higher with the XL-1 compared to the HM3 at the respective generator voltages. The significance ofthis and other similar experiments relates to the potential applicability of this information to the clinical management of pediatric patients with urolithiasis. Our experience with pediatric patients treated with the Dornier HM3 Iithotripter is that the amount of energy delivered to these patients (1,000 shock waves at 17 KV average) is similar to the levels delivered to these rabbits. Since the body weight of the rabbits and the size of their kidneys are both less than most children, the amount of energy delivered to the rabbit kidneys and femurs exceeds what one would expect is actually delivered to children simply based upon body habitus. Therefore, this model, at these average clinical energy levels, supports the use of ESWL to treat urolithiasis in children but certainly the ability to damage bone with high pressure shock waves,'2 regardless of the total amount of energy used, must be kept in

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FIG. 6. Light microscopy of renal parenchyma in control (A) or treated (B) rabbits (100X magnification).

mind. An effort must therefore be made to limit the shock wave exposure to the kidney and adjacent structures to the least amount necessary to effectively fragment calculi. Other clinical and experimental studies must be done and longer follow-up must be obtained to confirm that high energy shock waves are safe for use in pediatric patients. Acknowledgement. We would like to thank Ms. Lynn Hayes for her expert technical assistance.

6. 7.

8. REFERENCES

1. Chaussy, C.: Extracorporeal Shock Wave Lithotripsy. New Aspects in the Treatment of Kidney Stone Disease. New York, S. Karger, 1982. 2. Chaussy, C. and Fuchs, G.: Experience with extracorporeal shock wave lithotripsy after five years clinical use. Urology, 24: 305, 1985. 3. Drach, G. W., Dretler, S., Fair, W., Finlayson, B., Gillenwater, J., Griffith, D., Lingeman, J. and Newman, D.: Report of the United States Cooperative Study of extracorporeal shock wave lithotripsy. J. Urol., 135: 1127, 1986. 4. Newman, D. M., Coury, T., Lingeman, J. E., Mertz, J. H. 0., Mosbaugh, P. G., Steele, R E. and Knapp, P. M.: Extracorporeal shock wave lithotripsy experience in children. J. Urol., 136: 238, 1986. 5. Neuhauser, R B. D., Wittenborg, M. H., Berman, C. Z. and Cohen,

9.

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J.: Irradiation effects of roentgen therapy on the growing spine. Radiology, 59: 637, 1952. Kaude, J. V., Williams, M. C., Millner, M. R and Finlayson, B.: Renal morphology and function immediately after extracorporeal shock wave lithotripsy. AJR, 145: 305, 1985. Rubin, J. I., Arger, P. H., Pollack, H. M., Banner, M. P., Coleman, B. G., Mintz, M. C. and Van Arsdalen, K.: Kidney changes after extracorporeal shock wave lithotripsy: CT evaluation. Radiology, 162: 21, 1987. Knapp, P. M., Kulb, T. B., Lingeman, J. E., Newman, D. M., Mertz, J. H. 0., Mosbaugh, P. G. and Steele, R E.: Extracorporeal shock wave lithotripsy-induced perirenal hematomas. J. Urol., 139: 700, 1988. Bomanji, J., Boddy, S. A. M., Britton, K. E., Nimmon, C. C. and Whitfield, H. N.: Radionuclide evaluation pre- and postextracorporeal shock wave lithotripsy for renal calculi. J. Nucl. Med., 28: 1284, 1987. Newman, R, Hackett, R, Senior, D., Brock, K., Feldman, J., Sosnowski, J. and Finlayson, B.: Pathologic effects of ESWL on canine renal tissue. Urology, 29: 194,1987. Rigatti, P., Colombo, R, Centemero, A., Francesca, F., DiGirolamo, V., Montorsi, P. and Trabucchi, E.: Histological and ultrastructural evaluation of extracorporeal shock wave lithotripsy-induced acute renal lesions: preliminary report. Eur. Urol., 16: 207,1989. Yeaman, L. D., Jerome, C. P. and McCullough, D. L.: Effects of shock waves on the structure and growth of the immature rat epiphysis. J. Urol., 141: 670, 1989.