|Year : 2004 | Volume
| Issue : 2 | Page : 36-41
Diagnosing bladder outlet obstruction can we do away with pressureflow studies?
Abraham Vinod Peedikayil, NK Shyamkumar, Nitin Kekre
Christian Fellowship Hospital, Rajnandgaon, Chhattisgarh, and CMC, Vellore, India
Abraham Vinod Peedikayil
Division of Urology, Christian Fellowship Hospital, Rajnandgaon, Chhattisgarh
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objective: To compare pressure-flow study on one hand with BWT, prostate volume, urine flow rate PVR and IPSS index in the other arm for diagnosis of BOO.
Materials and methods: A prospective cross-sectional study was carried out in 48 men with lower urinary tract symptoms (LUTS). International prostate symptom score was completed by the patient who then underwent free urine flow study. Pressure-Flow study was performed as per recommendations of International continence Society. Abrams-Griffiths nomogram and number were used to diagnose BOO. Patients with diabetes, neurovesical dysfunction, acute urinary retention, prior pelvic surgery and known prostate cancer were excluded. Suprapubic ultrasonography was performed independently by a consultant radiologist, who was blinded to findings of Pressure-Flow study. Prevoid bladder volume, postvoid residue (PVR), prostate volume and bladder wall thickness (BWT) were noted.
Results: Based on objective evidence from Pressure-Flow study, 35 patients were obstructed, 13 were not. Multivariate analysis was performed using Backward Stepwise Logistic Regression Model. Bladder wall thickness, prostate volume and urine flow rate had statistically significant relationship with BOO. Their coefficients of correlation were +0.794, +0.084 and 0.393 respectively. Bladder outlet obstruction could be defined by using a mathematical formula as detailed in the text (Positive Predictive Value 96.97%). Post-void residue and IPSS index were statistically insignificant.
Conclusion: In a select group of patients presenting with LUTS, it should be possible to diagnose BOO without the use of Pressure-Flow study.
Keywords: bladder outlet obstruction; bladder wall thickness; prostate volume; uroflowmetry; suprapubic ultrasonography; benign prostatic hyperplasia.
|How to cite this article:|
Peedikayil AV, Shyamkumar N K, Kekre N. Diagnosing bladder outlet obstruction can we do away with pressureflow studies?. Indian J Urol 2004;20:36-41
|How to cite this URL:|
Peedikayil AV, Shyamkumar N K, Kekre N. Diagnosing bladder outlet obstruction can we do away with pressureflow studies?. Indian J Urol [serial online] 2004 [cited 2019 Nov 17];20:36-41. Available from: http://www.indianjurol.com/text.asp?2004/20/2/36/37166
| Introduction|| |
Management of patients presenting to an outpatient clinic with lower urinary tract symptoms (LUTS) is a complex problem. A proportion of these patients suffer from obstructive benign prostatic hyperplasia. Men proved to have obstruction on the basis of pressure-flow measurements applied to a nomogram have better outcomes after transurethral resection of the prostate; hence there is a growing need to accurately define bladder outlet obstruction. ,, Pressure-flow study is presently the gold standard for diagnosing bladder outlet obstruction but it is invasive. Newer modalities of investigation are being tried and reported in the literature. ,,,,,
Clinicians all over the globe have associated presence of bladder wall thickness, with the presence of significant obstruction in men with lower urinary tract symptoms. ,,, Detrusor hypertrophy has been described in association with many different disorders of the lower urinary tract and is not specific for any disease. A significant association between bladder wall mass and outlet obstruction has been described in patients with urinary symptoms. ,, Measurement of bladder wall thickness by suprapubic ultrasound appears to be a useful predictor of outlet obstruction with a diagnostic value exceeding free uroflowmetry, although it does not represent a substitution to invasive urodynamics. ,,,, The bladder thickness index is a sensitive sonographic predictor of infravesical obstruction. Application of this index as a noninvasive screening tool for the patient with persistent voiding dysfunction may prove beneficial for identifying infravesical pathology. 
| Materials and Methods|| |
We have carried out a cross-sectional study in patients presenting with LUTS. The objective of this study was to investigate the association between bladder outlet obstruction as proved by pressureflow studies on one hand, and ultrasonographic parameters viz. bladder wall thickness, post void urinary residue, and prostate volume, as also PVR and IPSS index on the other hand.
Forty-eight men with lower urinary tract symptoms attending urology outpatient department of the Christian Medical College & Hospital, Vellore, were recruited for the study. Cases were chosen at random. All subjects were above 40 years of age and the study was performed in the period between 15 th October 1998 and 31s` August 1999. International prostate symptom score questionnaire was completed by the patient who then underwent free-flow study. Patients with diabetes, neurovesical dysfunction, acute urinary retention on continuous bladder drainage, prior pelvic surgery and known prostate cancer were excluded. Pressureflow study was performed according to the recommendations of the International Continence Society. Bladder outlet obstruction was diagnosed and graded according to Abrams-Griffiths nomogram and Abrams-Griffiths number. Patients in the equivocal group were further re-allocated to the two sides, based on detrusor pressure at minimum flow. All urodynamic data used in the study were machine-read, unless there was obvious artifact. This was done in order to avoid observer bias.
All men were subjected to suprapubic ultrasonography by a consultant radiologist and note was made of prevoid bladdervolume at normal desire, postvoid residue, prostate volume and bladder wall thickness (BWT). All readings were taken single; bladder wall thickness was measured in the posterior wall. Ultrasound studies were carried out independently by the examiner, who was blinded to freeflow tracings and urodynamic findings. Bladder thickness index was obtained by dividing bladder wall thickness in millimeters by prevoid bladdervolume in liters.
| Results|| |
Patient characteristics and data overview are shown in [Table - 1].
Patients were divided into three groups according to Abrams-Griffith nomogram and number as depicted in [Table - 2]
Of the patients in the equivocal group, those with p(det)Qmin greater than 40cm H20 were further categorized as obstructed. Hence, based on objective evidence from Pressure-Flow study, there were 35 patients who were obstructed while 13 patients were not. These two groups were then compared with regard to various variables as shown in [Table - 3].
| Analysis|| |
International prostate symptom score, free flow, prostate volume, post void residue, bladder wall thickness and bladder thickness index were analyzed in order to define their contribution to obstruction. Since bladder thickness index was a function of bladder wall thickness, Univariate Analysis was carried out between the two at the outset. Our study did not shows Significant linear correlation between bladder wall thickness and bladder thickness index. Bladder thickness index was subsequently omitted from analysis, since its contribution to obstruction was less as compared to bladder wall thickness. Remaining independent variables were then subjected to multivariate analysis using Backward Stepwise Logistic Regression Model. Bladder wall thickness and prostate volume had significantly positive correlation, while free flow correlated negatively with obstruction. The coefficients of correlation were +0.794, +0.084 and 0.393 respectively. It was possible to derive a formula predicting the probability (P) of a case "y" being obstructed, and was given as follows:
X1--Bladder Wall Thickness
Receiver operated Characteristic (ROC) curve was plotted for obstruction as a function of bladder wall thickness, prostate volume and urinaryflow rate. [Figure - 1] For the case to be obstructed at a probability (P) of 0.62 and above,
Sensitivity was 91.43%,
Specificity was 92.31 %,
Positive Predictive Value was 96.97% and
Negative Predictive Value was 80%.
| Discussion|| |
Bladder wall thickness
Measurement of Bladder wall thickness is a simple and non-invasive technique. It depends upon age and sex of the individual, and volume of urine present in the bladder. Hakenberg et al. looked at normal values of bladder wall thickness. According to them, normal values of bladder wall thickness in adults with normal urinary tracts are on the average 3.0 +/_ 1 mm in women and 3.3 +/_ 1.1 mm in men. They have further shown that bladder wall thickness bears a negative linear co-relation to bladder volume. Change in BWT with increasing bladder volume is small and for practical purposes, negligible. 
In our study, we carried out univariate analysis between BWT and Bladder thickness Index (BTI) using SPSS computer programme. There was no linear correlation. BTI was subsequently omitted from further analysis.
Measurement of bladder thickness can be accomplished easily and is an office procedure. Geisse et al carried out this measurement in dogs using suprapubic ultrasonography to demonstrate its feasibiIity.  Muller et al standardized transabdominal ultrasound measurement of bladder wall thickness in children and evaluated its reliability. According to them, it was possible to determine the thickness of the low echogenic layer of the bladder wall with a systematic and anatomically defined method of acceptably reliable measurement.  Manieri et al carried out a study to investigate specificity and sensitivity of bladder wall thickness in the diagnosis of bladder outlet obstruction. A significant correlation (r > 0.6, p < or = 0.00.7) was found between bladder wall thickness and all parameters of the pressure-flow study. In their study, bladder wall thickness of 5 mm. appeared to be the best cutoff point to diagnose bladder outlet obstruction. They concluded that measurement of bladder wall thickness appeared to be a useful predictor of outlet obstruction with a diagnostic value exceeding free uroflowmetry although it did not represent a substitution to invasive urodynamics.  Kojima and associates concluded that ultrasound estimated bladder weight correlated significantly (p < 0.0001) with the Abrams-Griffiths number, urethral resistance factor and the Schaefer grade of obstruction. Ultrasound estimated bladder weight was calculated from bladder wall thickness measured ultrasonically and intravesical volume. It can be measured noninvasively at the bedside and is a reliable predictor of infravesical obstruction.  In the present study, BWT contributed significantly to presence of outlet obstruction; its contribution exceeding that of free uroflow. Taken as a single parameter in this select group of patients, a cutoff value of BWT of 4.5mm and above predicted obstruction with a sensitivity of 80 per cent and specificity of 92 per cent.
Does size of prostate gland contribute to obstruction?
Size of Prostate gland can be measured transrectally or suprapubically. In the present study, volume of the prostate was recorded suprapubically. Although suprapubic measurement of prostate volume is less than ideal, it correlates linearly with transrectal measurement. 
Effect of prostate volume on BOO is not well defined.
Lepor et al concluded that total prostate and transition zone volumes were not directly related to AUA symptom score and only weakly related to peak flow rate  Although there is no direct evidence of large prostates causing BOO in noncatheterized patients, those presenting with acute retention had successful trial without catheter provided the prostate size was smaller.  Thus, there is indirect evidence that larger prostates tend'to be obstructive. In our series, there was modest correlation (coefficient of correlation +0.084) between prostate volume as measured by suprapubic ultrasonography and BOO.
Free Urine Flow
Free-flow studies are used as a basis for deciding the clinical management of men with LUTS. They may be particularly useful for urologists with limited facilities for pressure-flow studies. Peak flow rate is significantly lower in those with BOO than in those with no obstruction. In the ICS-BPH study, threshold value of Qmax of 10 mL/s had a specificity of 70%, a positive predictive value (PPV) of 70% and a sensitivity of 47% for BOO.  Low urine flow rates may be either due to obstruction or due to detrusor weakness .  Conversely, high urine flow rates with high pressure voids may suggest obstruction. In our study, urine flow rate had an inverse relationship to BOO with coefficient of correlation of -0.393.
PVR and IPSS Index
Post void residue (PVR) and International Prostate Symptom Score (IPSS) have also been evaluated for defining BOO as non-invasive tools. High residual urine is a sign of abnormality of bladder function rather than the result of urethral obstruction. ,
There is no correlation between severity of obstruction and AUA symptom index. They are not reliable for screening populations and cannot diagnose obstruction. , In the present study, there was no significant association of PVR and IPSS index to BOO.
All non-invasive parameters evaluated so far have shown some or no correlation to BOO. Is it possible to combine some of these parameters to define BOO?
Combination of non-invasive parameters to define BOO
A number of studies have been reported combining noninvasive investigations. Kuo HC attempted to establish a clinical prostate score. 
Homma and associates studied predictability of conventional tests for the assessment of bladder outlet obstruction in benign prostatic hyperplasia 
Madersbacher developed nomograms by multiple logistic regression analysis to obtain the probability of BOO in patients with LUTS.  Steele and associates showed that combining the AUA symptom index, maximum urine flow and prostate volume reliably predicted bladder outlet obstruction in a small subset of patients.  Bladder outlet obstruction number may be calculated with an easy to use expression composed of prostate size, maximum urinary flow and relative residual volume. In 50 per cent of men with prostatism, bladder outlet obstruction number will diagnose obstruction with a reliability of more than 90 percent ,
In our series, bladder wall thickness, prostate volume and urine flow rate were statistically significant predictors of obstruction. Bladder outlet obstruction could be defined mathematically in this select group of patients by substituting the values in the formula, obtained by Backward Stepwise Logistic Regression.
| Conclusion|| |
Our study shows that in a subset of patients with LUTS with predefined inclusion and exclusion criteria, it should be possible to define obstruction with simple noninvasive parameters, without using Pressure-Flow study.
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[Figure - 1]
[Table - 1], [Table - 2], [Table - 3]