Hann-Chorng Kuo, Department of Urology, Buddhist Tzu Chi General Hospital, No. 707, Section 3, Chuang Yang Road, Hualien City, Taiwan. Tel: 886-3-8561825 ext. 2117; Fax: 886-3-8560794. Email: firstname.lastname@example.org
Objective: To analyze the lower urinary tract symptoms (LUTS) and video-urodynamic characteristics of women with clinically unsuspected bladder outlet obstruction (BOO).
Methods: From 1997 to 2010, a total of 1605 women with bothersome LUTS received video-urodynamic study in our unit. We reviewed the charts of 212 women diagnosed with BOO based on video-urodynamic criteria and 264 women without abnormal findings. LUTS and urodynamic parameters were compared between obstructed and unobstructed cases and among the BOO subgroups.
Results: The mean ages of the BOO (58.2 years) and control groups (58.8 years) were similar. The mean values of detrusor pressure at maximum urinary flow rate (PdetQmax)/maximum flow rate (Qmax) of the BOO and control groups were 51.83 cm H2O/10.22 mL/s versus 18.81 cm H2O/20.52 mL/s. In the BOO group, cinefluoroscopy revealed dysfunctional voiding in 168 patients (79.2%), urethral stricture in 17 (8.0%), and bladder neck dysfunction in 27 (12.7%). Patients with dysfunctional voiding had significantly lower urethral resistance compared with the other two BOO subgroups. Combined lower urinary tract symptoms were present most often in all BOO patients (69.3%), followed by isolated storage symptoms (30.2%) and isolated voiding symptoms (0.5%). Seventy-seven patients (37.3%) had dysuria and 79 patients (36.3%) had frequency as their main symptom.
Conclusion: Women with BOO usually have nonspecific LUTS. Dysfunctional voiding was the most common form among women with clinically unsuspected BOO, but the degree of obstruction was less severe than with primary bladder neck obstruction and urethral stricture.
Bladder outlet obstruction (BOO) is an underestimated urological condition in women with lower urinary tract symptoms (LUTS), which may be predominantly voiding, storage, or a combination of both. Voiding symptoms relevant to BOO are nonspecific, and a full urodynamic evaluation is essential in making the correct diagnosis.1
The etiologies for BOO in women include a combination of anatomic and functional origins.2–5 Groutz et al. reported that previous anti-incontinence surgery and severe genital prolapse were the most common etiologies, accounting for half of BOO in women.1 Clinicians can detect these two conditions without difficulty with detailed history taking and alert thinking about the unfavorable sequelae of previous anti-incontinence surgery, along with a physical examination. With less common etiologies of BOO, such as dysfunctional voiding, bladder neck dysfunction and urethral stricture, the precise differential diagnosis depends on detailed urodynamic study and voiding cystourethrography. Most urethral strictures in women are iatrogenic and result from previous urethral or periurethral surgery, or in some cases, from previous urethral dilatation. These pathologies can be identified with cystoscopy.2 Primary bladder neck obstruction (PBNO) is due to a lack of relaxation of the smooth muscle at the bladder neck during voiding. Dysfunctional voiding is an abnormality of bladder emptying in neurologically normal individuals caused by external sphincter dyssynergia and/or pelvic floor hyperactivity.6,7 These patients tend to have decreased flow, increased voiding pressure, and high postvoid residual (PVR) urine volume.
There is a wide variation of voiding pressures and flow parameters between women with or without obstruction. Nitti et al. proposed video-urodynamic criteria to diagnose obstruction and to identify the etiology as the point of obstruction existing at the level of the bladder neck, urethral sphincter, or pelvic floor muscles.8 We conducted this study to analyze LUTS presentations and video-urodynamic characteristics of women with BOO that is not clinically suspected.
From 1997 to 2010, a total of 1605 women visiting the urology clinic of Buddhist Tzu Chi General Hospital with bothersome LUTS received thorough baseline evaluations including International Prostate Symptom Score questionnaire for patients to pick their most bothersome LUTS, medical history, physical examination, urine analysis, urine culture, and necessary diagnostic imaging examinations. Video-urodynamic study (VUDS) was performed according to the recommendations of the International Continence Society9 to identify the underlying pathophysiology of LUTS when patients had poor responses to first-line treatment. Patients with neurological disease, iatrogenic BOO caused by anti-incontinence surgery, and pelvic organ prolapse greater than stage II were excluded from the study. This retrospective study has been approved by the Institution Review Board of the Tzu Chi General Hospital under number IRB100-06.
We reviewed the charts of subjects with BOO diagnosed by VUDS. Subjects with normal VUDS findings served as the control group. BOO was defined as radiographic evidence of obstruction between the bladder neck and distal urethra in the presence of a sustained detrusor contraction of any magnitude, plus a voiding detrusor pressure (Pdet) of greater than 35 cmH2O in combination with a Qmaxof less than 15 mL/s.8,10 The urodynamic parameters were compared between the BOO group and the control group.
After the initial comparison of the BOO and control groups, the secondary aim of this study was to analyze the characteristics of BOO in women, including the variations of urodynamic parameters and main symptoms and related LUTS among the subgroups of BOO. Women with BOO were categorized into the following three subgroups according to the findings of voiding cystourethrography (Fig. 1): (a) dysfunctional voiding (b) bladder neck dysfunction and (c) urethral stricture. Patients were considered to have dysfunctional voiding if they had dilatation of the proximal urethra combined with a “spinning top” appearance in the middle urethra or narrowing of the distal urethra, and increasing or no concomitant relaxation of electromyography (EMG) activities during micturition. Bladder neck dysfunction was defined as absence of opening of the bladder neck during voiding. A urethral stricture was noted if there was a segmental narrowing of the urethra. Bladder neck dysfunction and urethral stricture have coordinated sphincteric-EMG relaxation during micturition. All patients with urodynamically confirmed BOO also underwent cystoscopic examinations to identify the absence or presence of urethral strictures.
Statistical analyses among groups were performed using analysis of variance and χ2 test. A P-value of less than 0.05 was considered statistically significant.
The medical records of 212 women with BOO diagnosed by VUDS criteria and 264 women with normal VUDS findings were retrospectively reviewed. The mean ages of women in the BOO and control groups were similar (58.2 ± 18.0 vs 58.8 ± 18.4 years). All the urodynamic parameters, including cystometric bladder capacity (CBC), voiding detrusor pressure at Qmax (PdetQmax), Qmax, PVR and bladder compliance at full sensation were significantly different between the BOO and control groups (P < 0.001) (Table 1). The mean values of the urethral resistance relationship (PdetQmax/Qmax, URR) of the BOO and control groups were 9.3 ± 15.5 and 1.1 ± 0.8, respectively.
Table 1. Comparison of urodynamic parameters between control group and bladder outlet obstruction (BOO) patients
PdetQmax (cm H2O)
Compliance at full sensation (mL/cm H2O)
CBC, cystometric bladder capacity; Pdet Qmax, detrusor pressure at the maximum flow rate; PVR, postvoid residual; Qmax, maximum flow rate; URR, urethral resistance relation. Data are presented as mean ± standard deviation.
Control (n = 272)
58.78 ± 18.43
482.31 ± 100.11
18.81 ± 0.55
20.52 ± 0.49
1.08 ± 0.81
25.74 ± 44.00
120.54 ± 121.22
BOO (n = 212)
58.16 ± 17.98
284.09 ± 160.97
51.83 ± 1.38
10.22 ± 0.50
9.34 ± 15.50
86.22 ± 120.37
60.13 ± 79.66
According to cinefluoroscopic findings during the voiding phase, women with BOO were categorized into the following three groups: (i) 168 patients (79.2%) with dysfunctional voiding; (ii) 17 patients (8.0%) with urethral stricture; and (iii) 27 patients (12.7%) with bladder neck dysfunction (Table 2). Comparison of the urodynamic parameters among the BOO three subgroups showed that PdetQmax and Qmax were the parameters that differed significantly. There was no significant difference in the detrusor condition among BOO subgroups. The relationship of PdetQmax and Qmax among the three subgroups of BOO and normal controls is shown in the pressure-flow plots in Figure 2. From the pressure-flow plot, the points represent schematically the values of maximum flow rate and detrusor pressure at maximum flow for different voids in the three subgroups of BOO and in normal controls. It is remarkable that the plots of normal controls fell over the side of high Qmax and low PdetQmax, while the plots of BOO subgroups of bladder neck dysfunction and urethral stricture fell over the side of low Qmax and high PdetQmax.
Table 2. Comparison of age and urodynamic parameters among subgroups of bladder outlet obstruction (BOO)
PdetQmax (cm H2O)
Compliance at full sensation (mL/cm H2O)
BND, bladder neck dysfunction; BO, bladder oversensitivity; CBC, cystometric bladder capacity; DO, detrusor overactivity; DV, dysfunctional voiding; ND, normal detrusor function; PdetQmax, detrusor pressure; PVR, postvoid residual; Qmax, maximum flow rate; URR, urethral resistance relation; US, urethral stricture. Data presented as mean ± standard deviation, or number of patients, with percentages in parentheses.
DV (n = 168)
285.67 ± 12.32
49.07 ± 1.34
11.27 ± 0.58
8.04 ± 13.40
77.41 ± 8.68
63.00 ± 6.34
US (n = 17)
219.88 ± 32.68
65.35 ± 7.08
5.94 ± 0.74
16.87 ± 29.71
92.94 ± 19.49
29.11 ± 6.27
BND (n = 27)
314.70 ± 34.17
60.44 ± 4.46
6.41 ± 0.79
13.17 ± 14.30
136.78 ± 32.8
61.82 ± 16.18
Seventy-seven patients (37.3%) had dysuria and 79 patients (36.3%) had frequency as their main symptoms (Table 3). Combined LUTS were present most often in all BOO patients (69.3%), followed by isolated storage symptoms (30.2%) and isolated voiding symptoms (0.5%). There was no significant difference in the prevalence of main symptoms (P = 0.2) or related LUTS symptoms (P = 0.54) among BOO subgroups of BOO.
Table 3. Main symptoms and related lower urinary tract symptoms (LUTS) among subgroups of bladder outlet obstruction (BOO)
Stress urinary incontinence
Storage + voiding
Storage + pain
Storage + voiding + pain
BND, bladder neck dysfunction; DV, dysfunctional voiding; US, urethral stricture. Data presented as number of patients, with percentages in parentheses.
DV (n = 168)
US (n = 17)
BND (n = 27)
Total (n = 212)
According to the VUDS definition of BOO in women, we demonstrated statistically significant differences in the parameters of CBC, PdetQmax, Qmax, URR, PVR urine volume, and bladder compliance between obstructed and non-obstructed groups. We also found large standard deviations for values of age, CBC, PVR, and bladder compliance in each group. It is difficult to draw cutoff values for these parameters to define BOO. However, narrow standard deviations for PdetQmax and Qmax in each group were calculated, suggesting the possibility of assigning cutoff values for these two parameters in women with BOO.
There are many previously proposed pressure flow urodynamic definitions of BOO in women.4,11–13 Kuo reported cutoff values for PdetQmax≥ 35 cmH2O combined with Qmax≤ 15 mL/s, which yielded specificity of 93.9% and sensitivity of 81.6% for women with BOO.10 The mean values of PdetQmax/Qmax of our control group and BOO group were 18.8 cmH2O/20.5 mL/s versus 51.8 cmH2O/10.2 mL/s, respectively; the parameters met all the cutoff values mentioned by other references and showed negative correlation for PdetQmax and Qmax in the BOO group. These findings were compatible with the gold standard pressure-flow relationship for diagnosing BOO.14,15
Of the 212 women who had BOO diagnosed based on VUDS criteria, up to 79.2% (n = 168) had dysfunctional voiding, followed by 12.7% (n = 27) who had bladder neck dysfunction, and 8% (n = 17) who had urethral stricture. Dysfunctional voiding is a condition of increased external urethral sphincter and/or pelvic floor activity during voiding in the absence of known neurological disease.16,17 Nitti et al. reported that dysfunctional voiding was the most common abnormality of the voiding phase in women presenting with LUTS.8 Compatible with this finding, our study, which excluded patients with pelvic organ prolapse and anti-incontinence surgery-induced BOO, also showed that dysfunctional voiding was the most prevalent pathophysiology among women with BOO.
Another functional cause of BOO, PBNO (primary bladder neck obstruction), is due to a lack of relaxation of the smooth muscle at the bladder neck during voiding. The prevalence of PBNO is reported at 9–16% among women with BOO in previous studies.8,18 Among our patients, bladder neck dysfunction was identified in 12.7% (n = 27) of women with BOO. Urethral stricture was a relatively uncommon cause of BOO. Most urethral strictures in women are iatrogenic and result from previous urethral or periurethral surgery, or in some cases from previous urethral dilatation.2
In this series of patients, we also found that the urodynamic parameter of PdetQmax was relatively lower and Qmax was relatively higher in the dysfunctional voiding group than in the bladder neck dysfunction or urethral stricture groups. It is clearer to represent the outlet resistance by the parameter of URR, which differed significantly among the BOO subgroups (P = 0.04). The mean value of URR in each subgroup was 8.04 in dysfunctional voiding, 16.87 in urethral stricture and 13.17 in bladder neck dysfunction. A significant difference was noted between dysfunctional voiding and urethral stricture (P = 0.022), but not between other subgroups. This finding suggested that the degree of obstruction was relatively less serious in women with dysfunctional voiding. In other words, if we found higher urethral resistance with higher PdetQmax and lower Qmax, we must have a high suspicion of bladder neck dysfunction or urethral stricture.
Regardless of the etiology, BOO produces resistance upon the bladder outflow channel and results in LUTS, which may be predominantly voiding, storage, or often a combination of both.5 Groutz et al. reported that symptomatology was defined as mixed voiding and storage in 63% of 38 women with BOO, isolated storage in 29%, and isolated voiding in another 8%.1 Our study showed that near 70% of all the women with BOO had combined variant lower urinary tract symptoms, and about 30% presented with isolated storage symptoms. There was no significant difference in the distribution of presenting symptoms among the three BOO subgroups, suggesting that it is not possible to make an accurate diagnosis according to presenting symptoms. Women with LUTS need careful survey of these etiologies. Effective therapeutic strategies are based on an accurate diagnosis of the various etiologies of BOO.
The limitation of this study is the retrospective analysis. However, our study provides the concept of different degrees of urethral resistance among subgroups of clinically unsuspected bladder outlet obstruction. This finding can help differential diagnosis of the pathophysiology of BOO in clinical practice.
More than half of the women with BOO had combined storage and voiding symptoms. VUDS was an identical tool to define the etiologies of BOO in women. When we excluded the conditions of pelvic organ prolapse and previous anti-incontinence surgery, dysfunctional voiding was the most common cause of women with clinically unsuspected bladder outlet obstruction. The degree of obstruction in dysfunctional voiding was less severe than in primary bladder neck obstruction and urethral stricture.
The authors appreciate Miss Ching-Hui Tien for her contribution in preparing relevant information in this paper.