INFRAVESICAL OBSTRUCTION AND BLADDER WEIGHT 479

is well known that when the bladder outlet is obstructed, the detrusor muscle develops hyperplasia, hypertrophy or colla- gen deposition which then leads to detrusor dysfunction in some 2o Accordingly increased ultrasound estimated bladder weight in patients without obstruction may suggest impaired detrusor secondary to prolonged infravesical ob- struction.

Also, there may be another cause of bladder hypertrophy in the absence of infravesical obstruction. In our previous study relating ultrasound estimated bladder weight to bladder compliance and deformity in patients with detrusor areflexia, ultrasound estimated bladder weight increased as bladder compliance and deformity Thus, histopathologi- cal changes of the detrusor caused by neurogenic factors may cause bladder hypertrophy or an abnormal increase in ultra- sound estimated bladder weight. When considered together, although ultrasound estimated bladder weight can be used as a predictor of infravesical obstruction in the majority of patients, it may sometimes be difficult to distinguish cor- rectly the cause of bladder hypertrophy using only ultra- sound estimated bladder weight measurement. Therefore, further studies are necessary to establish a method for cor- rectly distinguishing the cause of bladder hypertrophy.

CONCLUSIONS

Ultrasound estimated bladder weight is a reliable tool for predicting infravesical obstruction. It seems particularly use- ful for monitoring therapeutic effects in men with urinary symptoms caused by infravesical obstruction because of sig- nificant correlation with the degree of obstruction. Consider- ing its noninvasiveness and easy use at the bedside, ultra- sound estimated bladder weight is promising as an auxiliary technique but it requires further followup to determine whether it can replace pressure flow studies.

1.

2.

3.

4.

5.

6

REFERENCES

Kojima, M., Inui, E., Ochiai, A,, Ukimura, 0. and Watanabe, H.: Quantitative evaluation of estimated bladder weight (EBW) in men with infravesical obstruction using transabdominal sonography-a preliminary study. Neurourol. Urodyn., 14 453, 1995.

Kojima, M., Inui, E., Ochiai, A., Naya, Y., Ukimura, 0. and Watanabe, H.: Ultrasonic estimation of bladder weight as a measure of bladder hypertrophy in men with infravesical ob- struction. A preliminary report. Urology, 47: 942, 1996.

Barry, M. J., Fowler, F. J., O'Leary, M. P., Bruskewitz, R. C., Holtgrewe, H. L., Mebust, W. K., Cockett, A. T. K. and Meas- urement Committee of the American Urological Association: The American Urological Association Symptom Index for be- nign prostatic hyperplasia. J. Urol., 148: 1549, 1992.

Lim, C. S., Reynard, J., Cannon, A. and Abrams, P. H.: The Abrams-Griffiths number. A simple way to quantify bladder outlet obstruction. Neurourol. Urodyn., 1 3 475, 1994.

Griffiths, D., van Mastrigt, R. and Bosch, R.: Quantification of urethral resistance and bladder function during voiding, with special reference to the effects of prostate size reduction on urethral obstruction due to benign prostatic hyperplasia. Neurourol. Urodyn., 8: 17, 1989.

Schafer, W.: Principles and clinical application of advanced uro- dynamic analysis of voiding function. Urol. Clin. N. Amer., 17: 553,1990.

7. Abrams, P. H. and Grifiths, D. J.: The assessment of prostatic obstruction from urodynamic measurements and from resid- ual urine. Brit. J. Urol., 51: 129, 1979.

8. Abrams, P.: Objective evaluation of bladder outlet obstruction. Brit. J. Urol., suppl., 76: 11, 1995.

9. Cockett, A. T. K., Khoury, S., Aso, Y., Chatelain, C., Denis, L.. Griffiths, K. and Murphy, G.: The 2nd International Consul- tation on Benign Prostatic Hyperplasia. Channel Island: Sci- entific Communication International Ltd., pp. 624-631, 1994.

10. Netto, N. R., Jr., D'Ancona, C. A. L. and de Lima, M. L.: Corre- lation between the international prostatic symptom score and a pressure-flow study in the evaluation of symptomatic benign

prostatic hyperplasia. J. Urol., 155 200, 1996. 11. Chai, T. C., Belville, W. D., McGuire, E. J. and Nyquist, L.:

Specificity of the American Urological Association Voiding Symptom Index. Comparison of unselected and selected sam- ples of both sexes. J. Urol., 150: 1710, 1993.

12. Lepor, H. and Machi, G.: Comparison of AUA Symptom Index in unselected males and females between fifty-five and seventy- nine years of age. Urology, 4 2 36, 1993.

13. Chancellor, M. B., Rivas, D. A,, Keeley, F. X., Lotfi, M. A. and Gomella, L. G.: Similarity of the American Urological Associ- ation Symptom Index among men with benign prostate hyper- plasia (BPH), urethral obstruction not due to BPH and detru- sor hyperreflexia without outlet obstruction. Brit. J. Urol., 74: 200, 1994.

14. Shoukry, I., Susset, J. G., Elhilali, M. M. and Dutartre, D.: Role of uroflowmetry in the assessment of lower urinary tract ob- struction in adult males. Brit. J. Urol., 47: 559, 1975.

15. Siroky, M. B., Olsson, C. A. and Krane, R. J.: The flow rate nomogram. 11. Clinical correlation. J. Urol., 123 208, 1980.

16. Gleason, D. M., Bottaccini, M. R., Drach, G. W. and Layton, T. N.: Urinary flow velocity as an index of male voiding func- tion. J. Urol., 128: 1363, 1982.

17. Chancellor, M. B., Blaivas, J. G., Kaplan, S. A. and Axelrod, S.: Bladder outlet obstruction versus impaired detrusor contrac- tility. The role of uroflow. J. Urol., 145: 810, 1991.

18. McConnell, J. D., Barry, M. J., Bruskewiz, R. C., Bueschen, A. J., Denton, S. E., Holtgrewe, H. L., Lange, J. L., McClennan, B. L., Mebust, W. K., b i l ly , N. J., Roberts, R. G., Sacks, S. A. and Wasson, J. H.: Benign Prostatic Hyperplasia: Diagnosis and Treatment. Rockville, Maryland: Agency for Health Care Policy and Research, Public Health Services, United States Department of Health and Human Services, pp. 36-42,1994.

19. Turner-Warwick, R., Whiteside, C. G., Arnold, E. P., Bates, C. P., Worth, P. H. L., Milroy, E. G. J., Webster, J. R. and Weir, J.: A urodynamic view of prostatic obstruction and the results of prostatectomy. Brit. J. Urol., 45: 631, 1973.

20. McGuire, E. J.: Detrusor response to outlet obstruction. World J. Urol., 2: 208, 1984.

21. Koiima. M.. Inui. E.. Ochiai. A., Ukimura. 0. and Watanabe, H.: ' h e possible &e of ultrasonic measurement of estimated blad- der weight in patients with underactive neurogenic bladder. Neurourol. Urodyn., 14: 430, 1995.

EDITORIAL COMMENT

Every urologist knows that older men have thicker bladders than older women and this difference has always been attributed to an enlarged prostate in elderly men with associated bladder outlet obstruction. It has also long been observed that the severity of obstruction correlates with the findings of trabeculation, cellule and diverticula formation, which are also associated with bladder wall thickening. Physiologists have long recognized that muscles grow and hypertrophy with increased activity or work, and because the bladder must work harder to empty itself in the presence of bladder outlet obstruction it only stands to reason that this param- eter (bladder wall thickness, a measure of work) may correlate with bladder outlet obstruction. This assumption led to the current study.

These authors cleverly used objective parameters to demonstrate this correlation using bladder weight (wall thickness and volume) as a measure of detrusor activity and pressure-flow studies to document the presence of bladder outlet obstruction. The study has practical implications in that measurements of bladder weight, a relatively simple determination with abdominal ultrasonography, could allow one to predict noninvasively bladder outlet obstruction without the necessity of invasive examinations, such as pressure-flow studies. Although it is known that conditions other than outlet obstruction can result in a thickened bladder (for example neurogenic bladder) and I doubt that this examination will replace pressure-flow studies in all patients, it has the potential for reducing the need for this study in those with obstructive symptoms who are being evaluated. Obviously further experience is needed but this innovative approach certainly warrants further study.

Martin I. Resnick Department of Urology Case Western Reserve University Cleveland, Ohio