Int Urogynecol J (2009) 20:1445–1449
DOI 10.1007/s00192-009-0964-0
ORIGINAL ARTICLE
Is ultrasound estimation of bladder weight a useful tool
in the assessment of patients with lower urinary
tract symptoms?
Demetri C. Panayi & Vikram Khullar &
G. Alessandro Digesu & Caroline Hendricken &
Ruwan Fernando & Paris Tekkis
Received: 10 March 2009 / Accepted: 8 July 2009 / Published online: 3 September 2009
# The International Urogynecological Association 2009
Abstract
Introduction and hypothesis The aim of this study was to
assess the relationship between ultrasound estimation of
bladder weight (UEBW), symptoms and urodynamic
diagnosis.
Methods Women with lower urinary tract symptoms
underwent urodynamics studies and measurement of
UEBW at a fixed bladder volume.
Results Women with overactive bladder symptoms had a
median UEBW of 48.3 g (95% CI 44–52), with stress
urinary incontinence a median UEBW of 35.1 g (95% CI
30–41) and with mixed urinary incontinence a median
UEBW of 40.0 g (95% CI 37–43) (p<0.001). Women with
detrusor overactivity had a median UEBW of 48.0 g (95% CI
46–51), with urodynamic stress incontinence a median
UEBW of 30 g (95% CI 29–31) and detrusor overactivity
and urodynamic stress incontinence a median UEBW of
37.3 g (95% CI 33–41) (p<0.001).
Conclusions UEBW is higher in women with overactive
bladder and detrusor overactivity. UEBW may be a useful
tool in women with lower urinary tract symptoms.
Electronic supplementary material The online version of this article
(doi:10.1007/s00192-009-0964-0) contains supplementary material,
which is available to authorized users.
D. C. Panayi (*) : V. Khullar : G. A. Digesu : C. Hendricken :
R. Fernando : P. Tekkis
Department of Urogynaecology, St. Marys Hospital,
Imperial College Healthcare NHS Trust,
Praed Street,
London W2 1NY, UK
e-mail: drpanayi@gmail.com
Keywords Detrusor overactivity .
Ultrasound estimation of bladder weight .
Urodynamic stress incontinence . Urodynamics studies
Introduction
Women who have lower urinary tract symptoms undergo a
range of assessments and investigations to obtain a diagnosis
and initiate treatment.
Urodynamics may form part of the investigation of women
with lower urinary tract symptoms; however, urodynamic
findings do not always correspond with the patient symptoms.
In a study of a large number of women attending urodynamics
clinic, approximately 55% of women with overactive bladder
symptoms had a diagnosis of detrusor overactivity and of the
women with a urodynamic diagnosis of detrusor overactivity,
only 30% gave symptoms of overactive bladder [1]. Women
with a history of overactive bladder symptoms and urodynamics that are inconclusive provide a challenge to the
clinician, and the application of other diagnostic tools has
been the subject of recent research.
Ultrasonography has been used increasingly in the
assessment of women with lower urinary tract symptoms.
Two-dimensional ultrasound has assessed bladder neck
mobility in women with stress urinary incontinence,
investigated the aetiology and extent of pelvic organ
prolapse, and in three dimensions, measurement of urethral
sphincter volume and the levator hiatus [2–6]. Ultrasound
imaging has also been used to assess the thickness of the
bladder wall and its correspondence with detrusor overactivity based on the principle that involuntary detrusor
contractions in an inappropriate situation where urinary
leakage does not occur leads to isometric contractions
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producing detrusor muscle hypertrophy and an increased
thickness of the bladder wall. Measurement of detrusor wall
thickness has been previously demonstrated as being strongly
associated with detrusor overactivity [7–9]. However, a recent
large study of 686 women demonstrated that whilst women
with detrusor overactivity had a statistically significantly
higher mean detrusor wall thickness than those without
detrusor overactivity using translabial ultrasound measurement, receiver operator characteristic analysis gave a low
sensitivity (37%) for diagnosing detrusor overactivity [8].
Yang and co-authors, in a study of 1,049 women with
lower urinary tract symptoms, found a statistically significant difference between women with detrusor overactivity
and a control group but no difference between women
with detrusor overactivity and urodynamic stress urinary
incontinence [10].
Ultrasound estimation of bladder weight (UEBW) has
already been reported as a measure of bladder outlet
obstruction in conditions such as benign prostatic hyperplasia as this condition can also result in hypertrophy of the
detrusor muscle which would manifest as an increase in
bladder weight [11, 12].
Kojima and co-workers have estimated bladder weight by
measuring the bladder wall thickness on high-resolution
B-mode ultrasound images at fixed volumes of bladder filling
[12, 13]. From this data, using a complex mathematical
formula, the bladder weight is determined but it is an estimate
as it assumes the bladder to be a sphere. Further studies have
improved accuracy of bladder weight measurement by
categorising the bladder into one of five different shapes
and applying different correction coefficients to the formula
depending on the shape of the individual’s bladder [14].
Subsequent to this work, the BladderScan 6500 BVM
device (Diagnostic Ultrasound, Bothell, WA, USA) has
been developed (see electronic supplementary Fig. s1). The
device uses a 3.7-MHz probe and takes 24 ultrasound
planes over 5 s through 130°. It estimates the bladder weight
in a different manner to the original method because the
device uses three-dimensional ultrasound as opposed to the
two-dimensional ultrasound originally used to calculate
bladder weight and also calculates the surface area of the
bladder rather than assuming the bladder is a sphere.
The ultrasound estimation of bladder weight is arrived at
by the following calculation: UEBW ¼ S t p(S=bladder
surface area, t=distance between the outer and inner wall of
the bladder and p=the bladder muscle specific gravity) [11].
The aim of the study was to assess whether ultrasound
estimation of bladder weight could be correlated to lower
urinary tract symptoms or urodynamic diagnoses and
therefore whether it would be a useful tool in assessing
women with lower urinary tract symptoms. We believe this
is the first study investigating the role of UEBW in lower
urinary tract symptoms in women.
Int Urogynecol J (2009) 20:1445–1449
Materials and methods
Women were recruited from attenders to a urodynamics
clinic and were direct referrals from primary care or from
the urogynaecology clinic. After obtaining a symptom
history using the Kings Health Questionnaire and examination, the women would undergo urodynamic studies.
Women who gave a history of voiding difficulties, poor
stream or straining to void were excluded from the study.
Women were asked to attend urodynamic studies with a
comfortably full bladder and the first part of the test consisted
of voiding on a flowmeter in private. Women were included in
the study if their uroflowmetry was normal, that is, showed a
normal flow pattern and had a Qmax of greater than or equal
to 15 ml/s after voiding at least 150 ml. Urinalysis was then
carried out and if there was no evidence of urinary tract
infection; filling cystometry was then performed. This
consisted of insertion of a 10F filling catheter and 4.5F
pressure catheter into the bladder and a 4.5F pressure catheter
into the rectum. After quality control was checked using
voluntary coughing, filling was commenced at a rate of
100 ml/min unless slower filling was indicated.
At a bladder volume between 200 and 400 ml, filling
was stopped and the woman underwent an ultrasound scan
of her bladder using the BladderScan 6500 BVM UEBW
Scanner according to manufacturers’ guidelines.
The scanner was placed approximately 2 to 3 cm
superior to the symphysis pubis with the scan head aimed
slightly towards the coccyx with the woman supine. The
3D ultrasound data are collected upon pressing the scan
button on the scanner. Once the scan is complete, the LCD
on the device displays accuracy of scan taken in the form of
arrows which may indicate repositioning of the scan head.
A flashing arrow indicates to the operator to reposition the
aim of the probe in the direction of the arrow and rescan.
If this occurred, the scan was repeated until the device
displayed a solid arrow or no arrow. The LCD on the
device also displayed the calculated bladder volume. The
scanner was inserted into a cradle and ultrasound data
was uploaded to the manufacturer’s server and a report
was obtained. For accurate UEBW measurement, the required bladder volume is between 200 and 400 ml [11].
Filling would continue until the sensation of maximum
bladder capacity was reached. The filling catheter was then
removed and the women underwent provocative manoeuvres
such as coughing or running on the spot and listening to
running water [15]. Women voided on a flowmeter with the
pressure lines in place to obtain pressure/flow studies.
Women with pressure/flow studies that had abnormal flow
pattern and/or a Qmax of less than 15 ml/s were also
excluded from the study.
Twenty two women were recruited and scanned by two
independent blinded operators using the BladderScan BVM
Int Urogynecol J (2009) 20:1445–1449
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Table 1 UEBW inter- and intra-operator data
Table 3 UEBW according to women’s symptoms
N=22
History
Operator 1
Operator 2
Operator 1 (visit 2)
Mean UEBW in grams (standard deviation)
39.0 (10.5)
40.9 (10.6)
41.4 (11.4)
6500. This was repeated by one of the operators after at
least a 2-week interval by means of validating the technique
before recruitment of women into the main study.
Women’s lower urinary tract symptoms were subdivided into overactive bladder symptoms, stress urinary
and mixed urinary incontinence (MUI). Urodynamics
diagnoses were subdivided into detrusor overactivity
(DO) and urodynamic stress urinary incontinence (USI).
These terms were according to standard definitions
established by the International Continence Society
(ICS) [16]. Women with both urodynamic stress incontinence and detrusor overactivity were described as having
urodynamic mixed urinary incontinence, which is not a
standard ICS definition. Symptomatic women without a
urodynamics diagnosis are described as having negative
urodynamics.
The lower urinary tract symptoms were compared with
the ultrasound estimation of bladder weight as determined
by the scanning device. Urodynamic diagnosis and UEBW
was compared in each patient. Median values and 95%
median confidence intervals were quoted for each group
and statistical significance was determined using the
Kruskal–Wallis test. Bland Altman analysis was used to
determine the validity of the technique by comparing the
mean difference between operators and between two
separate visits by the same operator.
The bladder volume was determined by the scan report
generated from the data uploaded from the scanner and the
infused volume.
Results
Twenty two women were scanned by two blinded operators
and on a second visit by one operator. The mean, standard
deviation as well as the mean difference and 95%
Table 2 UEBW inter- and intra-operator mean difference and 95%
confidence interval of the mean
N=22
Mean difference in grams
(95% CI of the mean difference)
Inter-operator
−1.90 (−0.31 to −3.51)
Intra-operator
−2.41 (−4.33 to −0.35)
SUI
OAB
MUI
Mean UEBW (95% CI)
35.1 (30–41)
48.3 (44–52)
40.0 (37–43)
confidence intervals of the mean difference are shown in
Tables 1 and 2.
One hundred and twenty nine women were recruited and
were scanned and had urodynamics carried out. Seventeen
women were excluded from the study on the basis that they
gave a history of voiding difficulties or had an abnormal
uroflow pattern with or without a reduced Qmax or had a
Qmax of less than 15 ml/s.
The mean age of the women was 59 years (41–79). Of
these women, 118/129 (91%) were successfully scanned
and in 11 women, despite several attempts, the scanner was
unable to successfully obtain an image that could be used to
produce an UEBW. This problem most commonly occurred
in women with an increased body mass index, but in two
cases there was no clear explanation as to why a successful
scan was not obtained.
Of the 118 women who were successfully scanned, 33/118
(28%) reported a history of overactive bladder symptoms,
35/118 (30%) reported a history of stress urinary incontinence
and 50/118 (42%) gave a history of mixed urinary incontinence. Of the 118 women who underwent urodynamic
studies, 36/118 (31%) had detrusor overactivity, 48/118
(41%) had a urodynamic diagnosis of urodynamic stress
incontinence and 24/118 (20%) had urodynamic mixed
incontinence. The remaining ten women had negative
urodynamics.
When considering UEBW according to patient history,
the 33 women with a history of overactive bladder
symptoms had a median UEBW of 48.3 g (95% CI 44–52),
the 35 women with stress urinary incontinence had a median
UEBW of 35.1 g (95% CI 30–41) and patients with mixed
urinary incontinence had a median UEBW of 40.0 g (95% CI
37–43). There was statistical significance between the groups
(p<0.001; Table 3).
UEBW according to urodynamic diagnosis showed that
the women with detrusor overactivity had a median UEBW
Table 4 UEBW according to urodynamic diagnosis
Urodynamics
USI
DO
USI and DO
Inconclusive urodynamics
Median UEBW (95% CI)
30.0
48.0
37.3
45.5
(29–31)
(46–51)
(33–41)
(38–49)
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of 48.0 g (95% CI 46–51). Women with urodynamic stress
incontinence had a median UEBW of 30 g (95% CI 29–31),
and those with both detrusor overactivity and urodynamic
stress incontinence had a median UEBW of 37.3 g (95% CI
33–41). There was statistical significance between the
groups (p<0.001). The ten women who had negative
urodynamics had a median UEBW of 45.5 (95% CI 38–49)
(see Table 4).
UEBW was unrelated to bladder volume between 200
and 400 ml and mean bladder volume was 298 ml (SD=55)
(see Fig. 1).
Discussion
Our technique of measurement of UEBW demonstrated
good inter- as well as intra-operator repeatability. We
demonstrated a statistically significant difference between
ultrasound estimated bladder weight in women according to
symptoms. Women with overactive bladder symptoms have
a higher UEBW than women with stress urinary incontinence, and those women with mixed urinary incontinence
are in between the other two groups. The same pattern is
reflected when comparing urodynamic diagnoses. Women
with detrusor overactivity have higher ultrasound estimated
bladder weights when compared to those women with
urodynamic stress incontinence with the mixed group
falling between the two. This is consistent with the
hypothesis that women who suffer with involuntary
detrusor contractions and the symptoms associated with
this have bladders with higher weight. This may occur
Fig. 1 Scattergraph showing
the relationship between
UEBW and volume of filling at
which the UEBW was obtained
Int Urogynecol J (2009) 20:1445–1449
secondary to isometric detrusor contractions against a
closed sphincter leading to hypertrophy of the detrusor
muscle and a resultant increase in bladder weight [7]. At
present, there is no published study of UEBW in women
with lower urinary tract symptoms or in women with no
lower urinary tract symptoms. The value of UEBW in 216
asymptomatic men has been at 42 g. This value is lower
than the women with overactive bladder symptoms and
those with detrusor overactivity but data on asymptomatic
women is still required to ascertain the relationship between
our results and normality. It may be the UEBW in women
with urodynamic stress incontinence is lower than in
asymptomatic normals.
Other proposed markers of detrusor overactivity have
shown a similar pattern to our results. Opening detrusor
pressure (ODP) has been demonstrated as a urodynamic
finding that may have further clinical application. In
women with urodynamic stress incontinence, the ODP is
lower than in women with normal urodynamics studies and
women with detrusor overactivity have a higher ODP when
compared to women with normal urodynamics studies [17].
This pattern is reflected in our data comparing UEBW and
urodynamics diagnoses.
Women with stress urinary incontinence and urodynamic
stress incontinence have a lower UEBW when compared to
the mixed groups or the OAB and DO groups. This may be
explained by a small urethral sphincter in women with
urodynamic stress incontinence [18]; this results in a lower
outlet resistance. Women with urodynamic mixed incontinence have both pathologies of detrusor overactivity and
low urethral outlet resistance and this may produce an
Int Urogynecol J (2009) 20:1445–1449
UEBW that is lower than the pure DO group but higher
than the pure USI group.
As with other diagnostic markers or tools, it is important
to ascertain the clinical application of UEBW. It may be
useful to follow the progression of symptoms, the severity
of a diagnosed condition or the response to treatment.
UEBW was related to overactive bladder symptoms and
detrusor overactivity. Presence of preoperative detrusor
overactivity is associated with poorer outcomes after
continence surgery [19], thus it may also have a role in
predicting the outcome of continence surgery and therefore
preoperative counselling of patients.
Conclusion
UEBW is related to urodynamic diagnosis. It is elevated in
detrusor overactivity and lower in urodynamic stress urinary
incontinence, and in women with urodynamic mixed incontinence the UEBW is between the other two pure diagnoses.
Although we have provided a test–retest series in this
paper, this technique has not been formally validated prior
to our work. The use of UEBW as a useful parameter would
be further strengthened by means of comparing it to twodimensional measurement of bladder wall thickness as well
as comparing it to actual bladder weight in bladders obtained
from cadavers. Further study is required to ascertain its
application to women with lower urinary tract symptoms in
line with other diagnostic tools and urodynamic parameters.
Conflicts of interest D.C. Panayi: funded by Pfizer travel and
accommodation: International Continence Society Cairo 2008. V.
Khullar: paid consultant to Astellas, Lilly, Allergan, Pfizer, Gynecare,
Cook, Bioxell. G.A. Digesu: paid consultant to Astellas, Bioxell. C.
Hendricken: no disclosures. R. Fernando: paid consultant to Astellas,
Pfizer. P. Tekkis: no disclosures
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