Noninvasive Quantitative Estimation of Infravesical Obstruction Using Ultrasonic Measurement of Bladder Weight

0022-534719711572-0476$03.00/0 W E JOCRWAL OF U R O r M Y Copyright 0 1997 by AVERIC.W UROLCCICAL ASSNIATION.IK.

February 1997 Printed in US&

V O ~ .157, 476-479,

NONINVASIVE QUANTITATIVE ESTIMATION OF INFMVESICAL OBSTRUCTION USING ULTRASONIC MEASUREMENT OF BLADDER WEIGHT MU"EKAD0 KOJIMA," EM1 INUI, ATSUSHI OCHIAI, YOSHIO NAYA, OSAMU UKIMURA HIROKl WATANABE

AND

From the Department of Urology, Kyoto Prefectural University of Medicine, Kyoto, Japan

ABSTRACT

Purpose: Ultrasound estimated bladder weight w a s compared to pressure-flow studies t o test the ability of ultrasound estimated bladder weight to predict infravesical obstruction. Materials a n d Methods: A total of 65 m e n with urinary symptoms underwent ultrasonic measurement of bladder weight and pressure-flow studies. Assuming the bladder is a sphere, ultrasound estimated bladder weight w a s calculated from bladder wall thickness measured ultrasonically and intravesical volume. Results: Ultrasound estimated bladder weight correlated significantly ( p <0.0001) with the Abrams-Griffiths number, urethral resistance factor and the Schafer grade of obstruction. A cutoff value of 35 gm. for ultrasound estimated bladder weight revealed a diagnostic accuracy of 86.2% (56 of 65 cases) for infravesical obstruction with 12.1 (4 of 33) a n d 15.6% (5 of 32) false-positive and false-negative rates, respectively. Conclusions: Ultrasound estimated bladder weight c a n be measured noninvasively at the bedside and it is promising as a reliable predictor of infravesical obstruction. KEY WORDS:bladder, ultrasonography, urination disorders Currently pressure-flow studies are recognized as the gold standard for the diagnosis of infravesical obstruction. Although pressure-flow studies can provide specific insight into detrusor function, their prevalent application in mandated clinical use is limited due to the invasive nature of the procedure. Recently we developed a new method capable of estimating bladder weight on transabdominal sonography. In our preliminary studies ultrasound estimated bladder weight was shown to increase significantly in men with obstructive diseases, such as benign prostatic hyperplasia (BPH), prostatic cancer and urethral stricture, compared to those with normal urinary conditions.1.2 These results suggest that ultrasound estimated bladder weight can predict infravesical obstruction noninvasively. The aim of our study was to reveal the usefulness of ultrasound estimated bladder weight in diagnosing infravesical obstruction in men with substantial urinary symptoms by comparing ultrasound estimated bladder weight to urodynamic parameters obtained on pressureflow studies. MATERIALS A N D METHODS

Between November 1994 and January 1996 urodynamics, including ultrasound estimated bladder weight measurement and pressure-flow studies, were performed on 65 men 45 to 89 years old (mean age 71) with moderate to severe urinary symptoms evaluated by the American Urological Association symptom index for BPH.3 Ultrasound estimated bladder weight was measured as previously described.1.2 Transabdominal sonography was performed with the patient supine. A longitudinal section of the bladder was obtained by scanning the midline of the lower abdomen above the pubic symphysis using a 7.5 MHz. probe. The thickness of the Accepted for publication June 14, 1996. Supported by a grant-in-aid for scientific research (C) from the Ministry of Education, Science and Culture, Japan. * Requests for reprints: Department of Urology, Kyoto Prefectural University of Medicine, Kawaramachi-Hirokoji,Kamikyo-Ku, Kyoto 602, Japan.

anterior bladder wall at the midline was measured a t 3 points approximately 1cm. apart and the average value was recorded. Following ultrasonic measurement intravesical volume was calculated by adding voided and post-void residual urine volumes estimated by ultrasound or catheterization. Ultrasound estimated bladder weight was calculated from bladder wall thickness and intravesical volume, assuming the bladder is a sphere (fig. 1). Pressure flow studies were performed with the Polygraph System.? Intravesical and intrarectal pressures were recorded to allow derivation of detrusor pressure (Pdet).Intravesical pressure was obtained via a 5F catheter placed in the bladder through the urethra. Opening pressure a t the start of flow and detrusor pressure at the maximum flow rate (Q,,) were determined from pressure-flow studies. The AbramsGriffiths number was then calculated according to the formula, PdetQm.--2Qmm.4 Patients were divided into obstructed and unobstructed groups using the AbramsGriffiths number and a cutoff value of 40. In addition, a group specific urethral resistance factor was calculated from detrusor pressure and maximum flow rate.6 By plotting detrusor pressure and maximum flow rate on the Schafer nomogram6 cases were divided into 7 grades of obstruction (0 to VI). Detrusor contractility was classified as strong, normal or weak by plotting the measurements of PdetQ,,JQ,,, on the Abrams-Grimths nomogram.7 Values were expressed as means plus or minus standard deviation. Pearson's correlation coefficient was used to evaluate the relationship between ultrasound estimated bladder weight and urodynamic parameters. An unpaired t test was used to compare data among the groups. The chi-square test for trend was applied to assess any correlation between dtrasound estimated bladder weight and infravesical obstruction with p c0.05 considered statistically significant.

476

i Nihon Koden, Tokyo, Japan,

INFRAVESICAL OBSTRUCTION AND BLADDER WEIGHT

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FIG. 1. Ultrasonogram of anterior bladder wall. A, in 68-year-old man without infravesical obstruction ultrasound estimated bladder weight was calculated as 26.4 gm.Abrarns-Griffiths number, urethral resistance factor and Schafer grade were 6, 16 and 0, respectively. €3, in 70-year-old man with infravesical obstruction ultrasound estimated bladder wei ht was calculated as 55.6 gm. Abrams-Griffiths number, urethral resistance factor and Schiifer grade were 84, 47 and IV,respectively. Refiuced from X 1.8. RESULTS

In the 65 men ultrasound estimated bladder weight ranged from 16.8to 79.5gm.(average 38.1 +- 14.3,fig. 1).Ultrasound estimated bladder weight correlated significantly with opening (R = 0.478,p <0.0001, fig. 2,A)and maximum pressures (R = 0.463,p = 0.0001)but not with maximum flow rate (R = 0.037). A significant positive correlation was noted when ultrasound estimated bladder weight was compared to the Abrams-Griffiths number (p <0.0001),the Schiifer grade of obstruction (p <0.0001) and urethral resistance factor (p <0.0001,fig. 2,B to D,respectively). The highest correlation coefficient was observed between ultrasound estimated bladder weight and the Schafer grade (R = 0.5431,followed by urethral resistance factor (R = 0.486)and the AbramsGriffiths number (R = 0.478). Based on the Abrams-Griffiths number 34 patients (52.3%) were diagnosed with and 31 (47.7%) were diagnosed without infravesical obstruction. In unobstructed and obstructed cases ultrasound estimated bladder weight ranged from 16.8

A

to 58.4 and 21.2 to 79.5 gm.,respectively (fig. 3,A) with a significant difference between unobstructed and obstructed cases (29.3 -t 9.4 versus 46.2 -+ 13.3 gm., p <0.0001).Receiver operator characteristics curve analysis demonstrated that the most suitable ultrasound estimated bladder weight cutoff value was 35 gm.for predicting infravesical obstruction (fig. 3, B ) . Of the 33 patients with an ultrasound estimated bladder weight greater than 35 gm.29 (87.9%)proved to have infravesical obstruction on pressure-flow studies compared to 5 of the 32 (15.6%)with an ultrasound estimated bladder weight of 35 gm. or less (p <0.0001, fig. 3, C and table 1). Using the cutoff value a diagnostic accuracy as high as 86.2% (56 of 65 cases) was obtained, and false-positive and false-negative rates were 12.1 (4of 33) and 15.6% (5of 32), respectively (table 2). There was no significant difference in maximum flow rate between the unobstructed and obstructed groups. Ultrasound estimated bladder weight in patients with a was significantly less than weak detrusor (30.3f 12.5 gm.)

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INFRAVESICAL OBSTRUCTION AND BLADDER WEIGHT

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Unobstructed "-31

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FIG.3. A, distribution of ultrasound estimated bladder weight (UEBW) in unobstructed and obstructed patients. Ultrasound estimated bladder weight was si ificantly greater in obstructed than unobstructed cases (p <0.0001). B , receiver operator characteristics curve of ultrasound estimatedsadder weight in diagnosis of infravesical obstruction in 65 men with mild to moderate unnary symptoms. C , Abrams-Griffiths nomogram versus ultrasound estimated bladder weight. Pdet, detrusor pressure. Qmax, maximum flow rate.

to BPH makes it unreliable for predicting infravesical obstruction. Because it is noninvasive and easy to perform, uroflowNo. pts. Bladder Wt. (gm.) metry has commonly been used in the diagnostic evaluation Obstruction No Obstruction Total No. of infravesical obstruction but with confusing results.14-17 Siroky e t al developed a flow rate nomogram relating bladder 4 33 Greater than 35 29 5 22 32 35 or Less volume to maximum flow rate and reported a clear separa31 65 Totals 34 tion of patients with infravesical obstruction from the normal population using the n o m ~ g r a mIn . ~contrast, ~ uroflowmetry showed no predictive value for infravesical obstruction in OUT TABLE2 patients. Currently i t is generally considered that uroflow% (No. ptaJtotal No.) metry as a single test cannot distinguish between infravesical obstruction and impaired detrusor contractility.18 Sensitivity 85.3 (29/34) Specificity 87.1 (27/31) Although pressure-flow studies are believed to be the only Pos. oredictive value 87.9(29/33) method for proving the presence or absence of infravesical Neg..predichve value 84.4(27/32) obstruction, invasive features involved in the procedure limit False-pos.rate 12.1 (4/33) its further application in urology clinics. Therefore, a noninFalse-neg.rate 15.6 (332) Diagnostic accuracy 86.2(56/65) vasive methodology sufficiently sensitive to detect infravesical obstruction remains to be developed. Our study demonstrates that ultrasound estimated bladder weight predicts infravesical obstruction with a diagnostic accuracy of 86.2% in those with a normal (41.8% 14.6 gm., p <0.005) or strong using a cutoff value of 35 gm.,which was determined based (44.7 % 10.6 gm.,p <0.001)detrusor. Ultrasound estimated on analysis of a receiver operator characteristics curve. The bladder weight was greater than 35 gm.in 80,65.4and 16.7% cutoff value was considered proper because it almost exactly of patients with a strong, normal and weak detrusor, respec- corresponded to the value of mean +2 standard deviations of ultrasound estimated bladder weight (25.6 2 5.7 gm.) in tively (p <0.0001). normal male controls 52 to 86 years old, a s shown in our previous study.2 DISCUSSION In the last decade there have been many advances in The definitive preoperative diagnosis of infravesical ob- urodynamics of the lower urinary tract using pressure-flow struction would contribute much toward consideration of studies, as summarized by Abrarnss Of several parameters treatment options for patients with urinary symptoms and designed to date the Abrams-Griffiths number? urethral redecrease the number of surgical treatment failures signifi- sistance factold and Schafer grade of obstruction6 are comcantly. In the past many efforts have been made to establish monly used for evaluating the degree of infravesical obstrucdiagnostic standards capable of evaluating infravesical ob- tion. In our study ultrasound estimated bladder weight was related to these numeric parameters with the aim of testing struction objectively.8 Recently the American Urological Association symptom quantitatively the predictability of ultrasound estimated index for BPH was reported to show a high correlation to bladder weight for the degree of infravesical obstruction. patient global ratings of the magnitude of urinary distur- Since ultrasound estimated bladder weight correlated signifbance caused by BPH and to discriminate strongly between icantly with these parameters, as shown in this study, it was BPH and control subjects.3 Netto e t a1 examined the relation- also considered to be a reliable tool for evaluating the degree ship between the International Prostatic Symptom Score of infravesical obstruction. The measurement of ultrasound (I-PSS)gand infravesical obstruction caused by BPH.10 Of estimated bladder weight provides a continuous variable that their 111 patients with severe symptoms (scores 20 to 35) 92 allows statistical analysis in conjunction with other urody(82.9%)had bladder outlet obstruction caused by BPH com- namic parameters, such as symptom score, flow rate or postpared to 53.4% of those with moderate symptoms (scores 8 to void residual urine volume. Ultrasound estimated bladder 19).They concluded that I-PSS cannot be used for diagnosing weight seems particularly promising for monitoring theraprostatic obstruction but it can provide an important means peutic effects on infravesical obstruction because ultrasound of selecting patients who should undergo further urodynam- estimated bladder weight can be measured noninvasively at ics, that is pressure-flow studies. The authors recommended the bedside. pressure-flow studies only in patients with a total I-PSS of In 2 of our patients ultrasound estimated bladder weight less than 28.However, it is likely that the well-known lack of was substantiallv increased over 50 em.desnite the absence the index tzender11.12 and disease13 swcificities of .~ .~ . svmntnm ..r.._. . .___ . of.infravesical o6struction proved by Gressur; flow studies. It TMLE 1. Ultrasound estimated bladder weight predictability infravesical obstruction

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INFRAVESICAL OBSTRUCTION AND BLADDER WEIGHT

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is well known that when the bladder outlet is obstructed, the prostatic hyperplasia. J. Urol., 155 200, 1996. detrusor muscle develops hyperplasia, hypertrophy or colla- 11. Chai, T. C., Belville, W. D., McGuire, E. J. and Nyquist, L.: Specificity of the American Urological Association Voiding gen deposition which then leads to detrusor dysfunction in Symptom Index. Comparison of unselected and selected sam2o Accordingly increased ultrasound estimated some ples of both sexes. J. Urol., 150: 1710,1993. bladder weight in patients without obstruction may suggest impaired detrusor secondary to prolonged infravesical ob- 12. Lepor, H.and Machi, G.: Comparison of AUA Symptom Index in unselected males and females between fifty-five and seventystruction. nine years of age. Urology, 4 2 36, 1993. Also, there may be another cause of bladder hypertrophy in 13. Chancellor, M. B., Rivas, D. A,, Keeley, F. X., Lotfi, M. A. and the absence of infravesical obstruction. In our previous study Gomella, L. G.: Similarity of the American Urological Associrelating ultrasound estimated bladder weight to bladder ation Symptom Index among men with benign prostate hypercompliance and deformity in patients with detrusor areflexia, plasia (BPH), urethral obstruction not due to BPH and detruultrasound estimated bladder weight increased as bladder sor hyperreflexia without outlet obstruction. Brit. J. Urol., 74: compliance and deformity Thus, histopathologi200, 1994. cal changes of the detrusor caused by neurogenic factors may 14. Shoukry, I., Susset, J. G., Elhilali, M. M. and Dutartre, D.: Role of uroflowmetry in the assessment of lower urinary tract obcause bladder hypertrophy or an abnormal increase in ultrastruction in adult males. Brit. J. Urol., 47: 559, 1975. sound estimated bladder weight. When considered together, although ultrasound estimated bladder weight can be used 15. Siroky, M. B., Olsson, C. A. and Krane, R. J.: The flow rate nomogram. 11. Clinical correlation. J. Urol., 123 208, 1980. as a predictor of infravesical obstruction in the majority of D. M., Bottaccini, M. R., Drach, G. W. and Layton, patients, it may sometimes be difficult to distinguish cor- 16. Gleason, T. N.: Urinary flow velocity as an index of male voiding funcrectly the cause of bladder hypertrophy using only ultration. J. Urol., 128: 1363,1982. sound estimated bladder weight measurement. Therefore, 17. Chancellor, M.B., Blaivas, J. G., Kaplan, S. A. and Axelrod, S.: further studies are necessary to establish a method for corBladder outlet obstruction versus impaired detrusor contracrectly distinguishing the cause of bladder hypertrophy. tility. The role of uroflow. J. Urol., 145: 810,1991. 18. McConnell, J.D., Barry, M. J., Bruskewiz, R. C., Bueschen, A. J., CONCLUSIONS

Ultrasound estimated bladder weight is a reliable tool for predicting infravesical obstruction. It seems particularly useful for monitoring therapeutic effects in men with urinary symptoms caused by infravesical obstruction because of significant correlation with the degree of obstruction. Considering its noninvasiveness and easy use at the bedside, ultrasound estimated bladder weight is promising as a n auxiliary technique but it requires further followup to determine whether it can replace pressure flow studies. REFERENCES

1. 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., 1 4 453, 1995. 2. 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 obstruction. A preliminary report. Urology, 47:942,1996. 3. Barry, M. J., Fowler, F. J., O'Leary, M. P., Bruskewitz, R. C., Holtgrewe, H. L., Mebust, W. K., Cockett, A. T. K. and Measurement Committee of the American Urological Association: The American Urological Association Symptom Index for benign prostatic hyperplasia. J. Urol., 148: 1549, 1992. 4. 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. 5. 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. 6 Schafer, W.: Principles and clinical application of advanced urodynamic 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 residual 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 Consultation on Benign Prostatic Hyperplasia. Channel Island: Scientific Communication International Ltd., pp. 624-631, 1994. 10. Netto, N. R., Jr., D'Ancona, C. A. L. and de Lima, M. L.: Correlation between the international prostatic symptom score and a pressure-flow study in the evaluation of symptomatic benign

Denton, S. E., Holtgrewe, H. L., Lange, J. L., McClennan, B. L., Mebust, W. K., b i l l y , 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 bladder 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 parameter (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