Ultrasound measurement of detrusor wall thickness in healthy adults

Neurourology and Urodynamics 25:308^317 (2006)

Ultrasound Measurement of DetrusorWall Thicknessin Healthy Adults

Matthias Oelke,1,2* Klaus H˛fner,2,3 Udo Jonas,2 Dirk Ubbink,4

Jean de la Rosette,1 and Hessel Wijkstra11Department of Urology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands

2Department of Urology, Medical School Hannover, University of Hannover, Hannover, Germany3Department of Urology, Evangelical Hospital, Oberhausen, Germany

4Department of Statistics and Biometry, Academic Medical Centre, University of Amsterdam,Amsterdam, The Netherlands

Aims: Measurements of detrusor wall thickness (DWT) are used to diagnose bladder outletobstruction (BOO). No values of DWT exist in healthy adults so far. These values, however, arenecessary to judge DWT in patients with suspected BOO correctly. The aim of this study was todetermine DWT in healthy adults and to investigate if bladder ¢lling, gender, age, or body-massindex (BMI) in£uences DWT. Materials and Methods: In 55 healthy adult volunteers between 15and 40 years of age, DWT was measured at the anterior bladder wall with a 7.5 MHz ultrasoundprobe and with a full bladder. In nine of those volunteers, an urodynamic investigation was per-formed additionally during which DWT was measured in steps of 50 ml until 300 ml and in stepsof 100 ml until the maximum bladder volume. Results: DWT decreases rapidly during the ¢rst250 ml of bladder ¢lling but, thereafter, remains almost stable until maximal bladder capacity. Nostatistical di¡erence was found between DWT at 250 ml and DWT at a higher bladder ¢lling. Menhad a greater DWTcompared to women (1.4 vs. 1.2 mm, P < 0.001). The age and BMI did not have asigni¢cant impact on DWT. Conclusions: DWT remains stable at a bladder ¢lling of 250 ml. Atthis state of bladder ¢lling, DWT between di¡erent groups are comparable. Men have to be evalu-ated separately from women. Neurourol. Urodynam. 25:308 ^317, 2006. � 2006 Wiley-Liss, Inc.

Key words: bladder¢lling; bladderwall; detrusorwall thickness; gender;ultrasound

INTRODUCTION

Measurements of the bladder or detrusor wall thickness(DWT) have received increasing interest as a non-invasive testto diagnose bladder outlet obstruction (BOO). In experimen-tal animals with BOO,DWTand bladder weight increases dueto smooth muscle hypertrophy and deposition of connectivetissue [Uvelius et al., 1984; Levin et al., 2000]. These histologi-cal changes of the detrusor as a result of BOO have been con-¢rmed in humans [Gilpin et al., 1985; Elbadawi et al., 1993].Thickening of the detrusor occurs as a result of increasedworkload similar to the heart in which the muscular wallthickens due to a valve stenosis or arterial hypertension[Tubaro and Miano, 2002]. Consequently, it is hypothesizedthat DWTre£ects the workload of the bladder and gives infor-mation about urethral resistance.

The bladder wall as well as the di¡erent layers of the blad-der (mucosa, detrusor, and adventitia) can be imaged withultrasound technology. Sonographic measurements of thebladder wall have shown a low intra- and inter-observer varia-bility, which makes this technique suitable for the routine usein patients [Manieri et al., 1998; Naya et al., 1998; Mˇller et al.,

2000]. Before using DWT for determination of BOO, it isessential to know DWT of healthy individuals. Values ofhealthy individuals have to serve as a reference to judge mea-surements in patients correctly. All information about thenormal DWT is from ultrasound studies of BPH-patientswithout BOO [Manieri et al., 1998; Oelke et al., 2002] orwomen with urinary incontinence [Khullar et al., 1994]. How-ever, it is unclear if these values re£ect DWT in healthy indivi-duals correctly. Furthermore, it is unknown at what bladder¢lling DWT should be measured and if other factors mightalso in£uence DWT. Therefore, the aim of this study was to

No con£ict of interest reported by the author(s).Abbreviations used: ANOVA, analysis of variance; BMI, body-mass index;BOO, bladder outlet obstruction; DWT, detrusor wall thickness; Qmax,maximum urinary £ow.*Correspondence to: Matthias Oelke, MD, FEBU, Department of Urology,AcademicMedicalCentrum,University of Amsterdam,Meibergdreef 9, 1105AZ Amsterdam,TheNetherlands. E-mail: [email protected] 20 October 2005; Accepted 8 March 2006Published online 1May 2006 inWiley InterScience(www.interscience.wiley.com)DOI 10.1002/nau.20242

�2006Wiley-Liss, Inc.

determine DWT in healthy adults and to investigate if theparameters bladder ¢lling, gender, age, or body-mass-index(BMI) might also in£uence DWT.

MATERIALS AND METHODS

Volunteers

Fifty-¢ve healthy adult volunteers (30 women, 25 men)between 15^40 years of age were included in this study. Allvolunteers were investigated to show the relationship betweenDWTand age, gender, or BMI. Nine of these volunteers (¢vewomen, four men) were also studied to evaluate the relation-ship between DWTand bladder ¢lling. All examinations wereperformed in accordance to the regulations of the local ethicscommittee. All individuals were employees of the hospital(female andmale doctors, scientists, nurses, and probationers).The age of the male volunteers varied between 16 and 40 years(mean 28.2 years) and the age of the female volunteers between15 and 40 years (mean 26.5 years; P ¼ 0.394, t-test).None of thevolunteers had lower urinary tract symptoms, previous opera-tions at the urinary tract or small pelvis, a neurological de¢citor diabetes mellitus. Before including the volunteers in thestudy, normal bladder emptying was assessed by uro£owme-try and sonographic measurements of postvoid residual urine.All volunteers had amaximumurinary £ow (Qmax) of>15 ml/sec and postvoid residual volume of �10 ml (1^10 ml, mean4 ml). The average Qmax was 26.2 � 6.6 ml/sec in men and31.1 �10 ml/sec in women (P ¼ 0.038, t-test). The characteris-tics of volunteers are shown in theTable I.

Urodynamic Investigation

A computer-urodynamic investigation (Ellipse, ANDRO-MEDA,Taufkirchen, Germany) was performed in nine volun-teers to show the relationship between DWT and bladder¢lling. Under sterile conditions, a 6 French H2O-catheterwas inserted through the urethra in the bladder and a 10French H2O-catheter was placed in the rectum. Before start-ing the measurement, the bladder was emptied completely

through the transurethral catheter. Afterwards, the bladderwas ¢lled with physiologic saline solution of 37�C at a ¢llingrate of 25 ml per minute. During ¢lling and voiding phases,intravesical and intrarectal pressures were recorded simulta-neously, detrusor pressure was calculated by subtracting theintrarectal from the intravesical pressure. Methods, de¢ni-tions, and units conform to the standards recommended bythe International Continence Society, except where speci¢-cally noted [Abrams et al., 2002]. For sonographic determina-tion of DWT, the urodynamic measurement was interrupted.Immediately after the last DWTmeasurement, pressure-£ow-measurement was performed and the degree of BOO wascalculated using the algorithm of the Sch�fer-classi¢cation[Sch�fer et al., 1989; Sch�fer, 1995]. No volunteer showedany signs of BOO (all Sch�fer class 0); all volunteers had a‘‘normal’’detrusor strength (DAMPF).

Measurement of DetrusorWall Thickness

Sonographic measurement of DWT was performed atthe anterior bladder wall using a 7.5 MHz linear array(SonoDIAGNOST 360, Philips Medical Systems, Eindhoven,The Netherlands) positioned suprapubically in horizontaldirection. At low magni¢cation, anatomical structures of theanterior abdominal wall and the bladder wall were identi¢ed(Fig. 1). The digital picture was enlarged to factor 9.8, and thedetrusor wall was measured at least at three di¡erent sites withthe integral equipment of the ultrasound system (Fig. 2). Peri-vesical tissue, mucosa, and submucosal tissue appear hypere-chogenic; the detrusor appears hypoechogenic [Jequier andRousseau, 1987; Kojima et al., 1996]. The mean value of thosemeasurements was used for further calculations.In all volunteers with an urodynamic investigation, DWT

measurements were performed during cystometry in steps of50 ml up to a bladder ¢lling of 300 ml and every 100 ml up tothe maximum bladder ¢lling. In those volunteers without anurodynamic investigation, DWT was measured at the timewhen they felt the strong desire to void and would usuallyempty the bladder.

Statistical Evaluation

Non-linear regression analysis was used for evaluation ofDWT at di¡erent bladder ¢lling volumes. Non-parametrictests were used to show the relationship between DWT andbladder ¢lling, gender, or age (Kruskal^Wallis or Mann^Whitney test). Non-parametric correlation analysis and theSpearman coe⁄cient were used to demonstrate any relation-ship between DWTand BMI. Di¡erences of means of contin-uous variables were evaluated with the Student’s t-test anddi¡erences of categories were evaluated with ANOVA. AP-value of 0.05 or less was considered to be signi¢cant. TheStatistical Package for Social Sciences (SPSS, Version 12.0.2;Chicago, IL), and S-PLUS (Version 2000; Seattle, WA) wereused for statistical analyses.

Neurourology and Urodynamics DOI 10.1002/nau

TABLE I. Characteristics of the Volunteers WhoParticipated in This Study

GenderAge

(years)Number ofvolunteers

Height (cm)mean � SD

Weight (kg)mean � SD

BMI (kg/m2)mean � SD

Males 16^20 5 179 � 6.5 80.0 � 13.6 24.9 � 3.021^30 10 185 � 6.9 78.4 � 7.2 22.9 � 1.431^40 10 182 � 6.2 83.4 � 14.1 25.1 �4.5

Females 15^20 10 169 � 4.8 65.7 � 8.1 23.2 � 3.021^30 10 167 � 4.8 61.1 � 3.7 21.9 � 2.131^40 10 166 � 6.4 65.2 � 6.4 23.7 � 2.9

No signi¢cant di¡erences with regard to height, weight, or BMI were seenbetween the di¡erent age groups of one gender (P > 0.05). SD, standarddeviation; BMI, body-mass-index (weight (kg)/height x height (m2)).

DetrusorWall Thickness in Adults 309


Fig. 1. Ultrasound image of the anterior abdominal wall and anterior bladder wall with a 7.5 MHz linear

array positioned suprapubically. At lowmagnification of the ultrasound picture (3.5�), the anterior bladder

wall can be identified.

Fig. 2. After enlargement of the digital ultrasound image (9.8�), the structures of the anterior bladderwall

can be further analyzed. Mucosa and adventitia appear hyperechogenic, the detrusor appears

hypoechogenic. The distance between the two hyperechogenic lines represents the detrusor wall

thickness (DWT) that can bemeasuredwith the integratedmeasuring function of the ultrasounddevice (in

this example 1.4 and 1.5 mm).

RESULTS

DWTand Bladder Filling

In all nine volunteers, DWT decreased rapidly during the¢rst 250 ml of bladder ¢lling. This feature was similar in men(Fig. 3a) and women (Fig. 3b). At a bladder ¢lling of 50 ml,DWT varied between 2.2 and 4.4 mm in men and 2.5 and4.4 mm in women. At a bladder ¢lling of 250 ml, DWT was1.4 mm in men and between 1.4 and 1.5 mm in women. After250 ml of bladder ¢lling, DWT decreased only slightly untilthe maximum bladder ¢lling. DWTat maximum bladder ¢ll-ing was between 1.3 and 1.4 mm in men and between 0.9 and1.4 mm in women. Comparisons of DWT between di¡erentbladder ¢llings revealed that there were no signi¢cant di¡er-ences of DWT between bladder ¢llings of�250 ml (P > 0.05,Mann^Whitney test). DWT between 200 and 250 ml of blad-der ¢lling was still signi¢cantly di¡erent (P ¼ 0.008, Mann^Whitney test), whereas DWT between 250 and 300 ml of blad-der ¢lling did not show a statistical di¡erence anymore(P ¼ 0.139, Mann^Whitney test).

If bladder-¢lling volume was converted to percentage ofbladder capacity, DWT decreased rapidly during the ¢rst40%^50% of bladder capacity. Thereafter, DWT decreasesonly slightly until maximal bladder capacity. The characteris-tic of DWT with increasing bladder capacity was similar inboth men (Fig. 4a) and women (Fig. 4b).

DWTand Gender

DWTwas measured in 25 male and 30 female volunteers withfull bladder only. Men were measured with a bladder-¢llingvolume of 400� 131 ml and women with a bladder ¢llingvolume of 423� 137 ml (P¼ 0,361, t-test). DWTvaried between1.2 and 1.6 mm in men and 1.1 and 1.6 mm in women. MedianDWT in males (1.4 mm; 25%^75% percentiles 1.33^1.5 mm)was signi¢cantly thicker than in females (1.2 mm; 25%^75% per-centiles 1.2^1.31mm; P< 0.001, Mann^Whitney test; Fig. 5).

DWTand Age

Male and female volunteers were evaluated separately inorder to avoid the in£uence of the gender on DWT. Both menand women were divided into three di¡erent age groups com-paring volunteers between 15 and 20, 21 and 30, and 31 and40 years of age. Bladder ¢lling at the time of DWTmeasure-ment was not signi¢cantly di¡erent between the age groups(389^436 ml; P ¼ 0.547, ANOVA). DWT between the di¡er-ent age groups of men (P ¼ 0.421, Kruskal^Wallis test) orwomen (P ¼ 0.98, Kruskal^Wallis test) did not show any sig-ni¢cant di¡erences (Fig. 6).

DWTand BMI

Male volunteers were signi¢cantly taller (183� 6.7 cm vs.167 � 5.3 cm, P < 0.001, t-test) and heavier (80.7 � 13.6 vs.

64 � 6.3 kg, P < 0.001, t-test) than female volunteers. Volun-teers had di¡erent body constitutions, the BMI variedbetween 18.4 and 37.1 kg/m2. BMI between the di¡erent gen-der and age groups were not signi¢cantly di¡erent (Table I).Non-parametric correlation analysis showed that there wasno signi¢cant correlation between DWT and BMI in men(P¼ 0.138) or women (P ¼ 0.37).

DISCUSSION

The bladder wall and the di¡erent layers of the bladder canbe imaged very well using ultrasound technology. Schoor et al.[1994] ¢rst demonstrated in rabbits that bladder wall thicknesscan be measured with an ultrasound device accurately. Later,other study groups used ultrasound technology in men withBPH [Kojima et al., 1996, 1997; Manieri et al., 1998; Hakenberget al., 2000; Oelke et al., 2002] and in children with non-neu-rogenic bladder dysfunction [Cvitkovic-Kuzmic et al., 2002]to prove thickening of the bladder wall due to BOO as wellas in women to discriminate between stress and urge urinaryincontinence [Khullar et al., 1994, 1996]. Until now, only ¢vestudies have investigated bladder or DWT in healthy children[Jequier and Rousseau, 1987; Cvitkovic-Kuzmic et al., 2001;Mˇller et al., 2001; Yamazaki et al., 2001] or healthy adults[Hakenberg et al., 2000]. DWT of non-obstructed BPH-patients or women with urinary incontinence might notre£ect DWT in healthy adults accurately and, therefore,should be measured in a group of healthy individuals. Becauseonly the detrusor adapts to the increased workload in patientswith BOO,Oelke et al. [2002] proposed tomeasureDWTonlyin order to receive more detailed information about the blad-der muscle and the state of muscle decompensation. This wasthe reason why we measured detrusor instead of bladder wallthickness of healthy adults in this study. Similar approacheswere made in children [Mˇller et al., 2000, 2001; Cvitkovic-Kuzmic et al., 2001, 2002].Measurements of DWT were performed at the anterior

bladder wall using a 7.5 MHz linear array. It has been reportedthat all parts of the bladder (anterior, posterior, and lateralwalls as well as the trigone and dome) have the same thicknessin one individual [Kojima et al., 1996; Cvitkovic-Kuzmic et al.,2001].Therefore, the anterior bladder wall is a reliable locationto receive information about DWT. The depth of penetrationof the ultrasound waves as well as the resolution of the ultra-sound image is frequency dependent: the higher the ultra-sound frequency, the better the resolution but, however, thelower the penetration of the ultrasound waves in the tissue[Harris et al., 1991].Ultrasound probes (2.5 or 3.5 MHz) pene-trate deeper into the tissue than a 7.5 MHz probe but give lessresolution and image quality at the anterior bladder wall.The anterior bladder wall of a full bladder in adults is locatedapproximately 4^8 cm below the skin and, thus, can beimaged with a 7.5 MHz ultrasound probe excellently. Thedistance between the skin and the anterior bladder walldepends on the thickness of the subcutaneous fatty tissue and




Fig. 3. a: DWT in relation to bladder filling in healthyadultmen.Each line represents themeasurements of

one man. During the first 250 ml of bladder filling, DWT decreases continuously but, thereafter, remains

almost stable until maximum bladder filling. No significant differences of DWT were found at a bladder

filling volume�250ml.b: DWT in relation to bladder filling in healthyadultwomen.Each line represents the

measurements of one woman. Similar to men, DWT decreases during the first 250 ml. After 250 ml of

bladder filling, DWTstays almost stable and does not show significant differences compared to DWTs at

higher bladder fillings.

312 Oelke et al.


Fig. 4. a: DWT in relation to bladder capacity in healthy adultmen. Each bladder filling volumeofmenwas

converted to percentage of bladder capacity. DWT decreases quickly at low bladder capacity but,

thereafter, remains almost stable untilmaximumbladder capacity.b: DWT in relation to bladder capacity in

healthyadult women. Similar tomen,DWTdecreasesat low bladder capacity quickly but, thereafter, stays

almost stable until maximum bladder capacity.



Fig. 5. DWT inmen and women. DWTwas significantly greater in healthy male volunteers than in female

volunteers (P< 0.001). Each box shows 50% of the measurements of one group; the black line in the box

represents the median value of the measurements. The distances from the median value to the upper or

lower edges of the box represent the 25% or 75% percentiles. The line at the top of the box reaches to the

maximum measurement and the line at the bottom of the box to the minimum measurement.

Fig. 6. DWTof male and female volunteers of different ages. Each gender group was divided into three

different age groups (15–20, 21–30, and 31–40 years). No significant differences were found between

the different life intervals (P> 0.05).

314 Oelke et al.

abdominal muscles as well as on the bladder ¢lling. DWTmea-surements of very thick or muscular individuals might be dif-¢cult but, however, was not a problem with any volunteer inthis study. Structures deeper than the anterior bladder wall(such as the dorsal parts of the lateral wall or the posteriorbladder wall) appear with less resolution and quality. Thesestructures are di⁄cult to image with a suprapubically posi-tioned 7.5 MHz ultrasound array good enough for measure-ments of DWT. This might be the reason why themeasurements of DWT at a low bladder capacity and, there-fore, at a higher distance from the ultrasound probe vary somuch. The closer the anterior bladder wall moves to the skinand ultrasound probe, the better the quality of the images andthe more precise the measurements of DWT become. At fullbladder, the di¡erence between the three measurements of oneindividual was only 0.1 mm, which corresponds to the mea-surement error of the ultrasound device (which is <0.13 mmfor a 7.5 MHz ultrasound probe).

This study demonstrated that DWT is dependent on thebladder ¢lling but only at a bladder ¢lling volume of <250 ml.At a bladder ¢lling of �250 ml, DWT remains almost stableuntil maximum bladder ¢lling. No statistical di¡erencesbetween DWT of 250 ml and DWT of 300^800 ml werefound. If DWT was measured at a time that the volunteerhad a full bladder (100% bladder capacity), bladder ¢llingwas always>250 ml. Therefore, DWTshould be determinedat a full bladder or bladder ¢lling volume of at least 250 ml.At this state of bladder ¢lling, DWT is not volume dependentanymore and measurements of di¡erent volunteers orpatient groups become comparable. To our best knowledge,this feature of DWT with increasing bladder ¢lling is the¢rst report in healthy adults. Inadequate bladder ¢lling(<250 ml) might occur in patients with an overactive blad-der. In such cases, there needs to be a di¡erent referencevalue for DWT, which however, can be estimated with thehelp of the DWT-bladder volume graphs (Fig. 3).

In accordance with our ¢ndings, Hakenberg et al. [2000]described a signi¢cant negative correlation between bladdervolume and bladder wall thickness in healthy men and womenas well as in symptomatic patients with BPH. However, thisresult was obtained in a group analysis of 488 individuals inwhom bladder wall thickness was measured in each individualat a single but varying bladder-¢lling volume. In newborns andchildren up to 13 years of age, measurements of DWT withvarying bladder volumes demonstrated a similar characteris-tic to that of our study [Mˇller et al., 2001; Yamazaki et al.,2001]. Because of the increasing bladder size with increasingage of children, DWT was correlated with bladder capacity.The feature of detrusor wall thinning with increasing bladdercapacity was very similar in children from 0^1.9, 2^ 6.9, and7^13 years of age and also similar to the ¢ndings of our study[Mˇller et al., 2001].

Our study also proved a signi¢cant di¡erence of DWTbetween healthy men and women. The di¡erence of DWTbetween the genders was 0.2 mm. Hakenberg et al. [2000] also

found a signi¢cant di¡erence between men and women butdid not correct the measurements for bladder ¢lling volume.Yamazaki et al. [2001] investigated 238 neonates and found abladder wall thickness of 1.38 mm in females and 1.63 mm inmales. Mˇller et al. [2001] also found a signi¢cant di¡erence ofDWT at the anterior bladder wall between the sexes. Thisstudy evaluated 79 boys and 71 girls between 0.04 and 13.1years of age and found a gender di¡erence of 0.2 mm. Accord-ing to the available data, it seems to be necessary to evaluateDWT in men and women separately. A thicker detrusor wallin males might re£ect the greater voiding resistance of themale urethra, which is longer and passes through the prostate.In order to evaluate the in£uence of the age on DWT, we

divided men and women in three di¡erent age groups each(15^20, 21-30, and 31^40 years). No individual older than40 years was included in this study because no employee ofour department was older than this age. Calculation of DWTwas performed in men and women separately in order toexclude gender di¡erences. No signi¢cant di¡erences ofDWTwere found between the di¡erent age groups of one gen-der. With regard to DWT, ageing does not play a signi¢cantrole in young adults. However, DWT remains to be investi-gated in healthy and asymptomatic individuals older than40 years of age. With ageing, the histological components ofthe detrusor might change which may also result in changesof DWT. In healthy children, DWT increased signi¢cantlywith increasing age [Cvitkovic-Kuzmic et al., 2001; Mˇlleret al., 2001]. Even though boys and girls were not calculatedseparately in these studies, DWT increased from 1.1 mmin children of 2 years to 1.4 mm in children of 16 years[Cvitkovic-Kuzmic et al., 2001]. Di¡erences of DWT betweendi¡erent age groups of children might re£ect the growth of theurethra and development of the prostate in young men.In young adults however, this growth is completed and nophysiological changes should appear after puberty.BMI does not have an in£uence on DWT. No analysis of

this factor has been done so far. BMI was used to investigatethe in£uence of the body constitution and to make the higherweight as well as height in men comparable with women.Thisstudy included volunteers of all body constitutions and BMI(18.4^37.1 kg/m2). The average values for BMI of di¡erent ageand gender groups as well as the correlation between BMI andDWT were not signi¢cantly di¡erent. Therefore, weight,height, BMI, or body constitutions do not have a signi¢cantimpact on DWT and can be ignored during DWT measure-ment.This study aimed to determine the normal DWT in healthy

adults. According to our results, DWTat the anterior bladderwall has to be evaluated in men and women separately andwith a full bladder or at least with a bladder ¢lling of 250 ml.Under these conditions, measurements are comparable andcan be used as reference values for patients. DWTwas 1.4 mmin healthy men and 1.2 mm in healthy women. The results ofour study are in line with those that were published earlier: inhealthy children between 0 and 19 years of age, DWT varied



between1.2 mm [Cvitkovic-Kuzmic et al., 2001], 1.3 mm [Cvit-kovic-Kuzmic et al., 2002], 1.55 mm [Jequier and Rousseau,1987], and 1.38^1.63 mm [Yamazaki et al., 2001]. In ourstudy, all measurements of DWT in healthy individuals were�1.6 mm. In a former study of 70 symptomatic BPH-patients,a regression tree analysis showed that a DWTof <2 mm indi-cated men without BOO and�2 mmmen with BOO the best[Oelke et al., 2002].Unobstructed patients of this study had anaverage DWTof 1.3 mm and patients with equivocal obstruc-tion one of 1.62 mm. Therefore, symptomatic but unob-structed men with BPH do not seem to have a di¡erent DWTcompared to healthy young adults.

Another study investigated 174 BPH-patients of which24 patients were urodynamically unobstructed [Manieriet al., 1998]. The mean bladder wall thickness of these unob-structed patients (Sch�fer grade 0 þ 1) varied between 3 and4 mm and, thus, was thicker than the DWTof healthy volun-teers in our study. Three reasons might be responsible forthese di¡erences which underline the necessity to standar-dize ultrasound measurements of the bladder wall in thefuture: di¡erences of bladder ¢lling, measurement of bladderor DWT, and di¡erent ultrasound probes. Manieri et al.inserted a transurethral catheter, ¢lled the bladder with 150ml, and measured the thickness of the anterior bladder wallwith a 3.5 MHz ultrasound probe afterwards. Due to the factthat measurements were performed at a lower bladder ¢llingthan in our study but bladder wall thickness decreases withincreasing bladder ¢lling, it becomes obvious that the valuesof this study have to be greater than those of our study. Blad-der wall thickness should be thicker than DWT because thelengths of the mucosa and adventitia have to be added tothe detrusor. On ultrasound images of the bladder wall, themucosa and adventitia appear hyperechogenic. However, theadventitia cannot always be discriminated from the perivesi-cal tissue, which is hyperechogenic as well, especially whenusing an ultrasound probe with a frequency of 3.5 MHz(which has a resolution of approximately 0.3 mm). Placementof the measurement marker in the perivesical tissue wouldindicate a thicker bladder wall. In contrast, the detrusorappears hypoechogenic and, thus, can be discriminated fromthe inner and outer hyperechogenic layers of the bladder wallaccurately [Kojima et al., 1996]. Furthermore, the thicknessof the mucosa or adventitia could be a¡ected by other factors(such as infection or cancer) which would make the measure-ment unreliable for determination of the BOO or inconti-nence. Therefore, measurements of DWT with a 7.5 MHzultrasound array seem to be more accurate and reliable thanmeasurements of bladder wall thickness with a 3.5 MHzarray.

With catheterization and retrograde ¢lling of the bladderwith a certain amount of £uid, the ultrasound measurementof DWT becomes invasive [Manieri et al., 1998]. With mea-surements at a full bladder, catheterization and ¢lling of thebladder are not necessary anymore. Our technique, therefore,provides a rationale for a non-invasive measurement, which

appears to be one of the major advantages compared to an(invasive) urodynamic evaluation.

CONCLUSIONS

Our study, for the ¢rst time, demonstrated the relationshipbetween DWT and bladder ¢lling, gender, age, and BMI inhealthy adults. DWTdecreases with increasing bladder-¢llingvolume only during the ¢rst 250 ml but remains stable at ahigher bladder ¢lling. According to our results, it is crucial tocompare measurements at the same state of bladder ¢llingand, therefore, the degree of bladder ¢lling should be indi-cated in all studies in the future. Measurements of DWT at�250 ml of bladder ¢lling should be used to show the in£u-ence of a disease on the detrusor. Healthy men have a signi¢-cantly greater DWT than women and, thus, have to beevaluated separately. The age and BMI of the volunteer haveno signi¢cant in£uence on DWT. In order to judge DWT inpatients correctly, measurements should be compared withDWTvalues of healthy individuals.

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Ultrasound measurement of detrusor wall thickness in healthy adults