British Journal of Uro1og.v (1976), 41, 805-814 0
Ultrasound Assessment of Residual Urine in Children N.
w.
HARRISON,
c. PARKS and
T. SHERWOOD
St Peter’s Hospitals and the Institiire of Urology, London
The bladder of a healthy child probably retains no more than a few millilitres of urine after voiding under normal circumstances. Residual urine predisposes to urinary infection, may be evidence of neuropathic bladder dysfunction, and can be a significant factor in producing incontinence and upper urinary tract dilatation. There are many situations in paediatric urology where it is essential to measure residual urine and many other occasions when this information would be useful. A method of assessing residual urine which is simple, accurate, non-invasive and harmless would be of considerable value in clinical practice. None of the currently available methods meets all these requirements ; each has its advantages and limitations which are briefly considered : (1) Clinical Examination. It is routine practice to palpate and percuss for a distended bladder. If a bladder remains palpable after an adequate opportunity to void there is clearly a significant residue. Clinical assessment has obvious limitations: an enlarged bladder may be difficult to appreciate in children who are obese, nervous or unco-operative, or who have abdominal tenderness due to recent surgery or peritonitis, or in children with large floppy bladders such as in the prune belly syndrome. (2) Catheterisation. This is the most usual method of establishing a residual volume and certainly whenever a
catheter has to be passed, for example in performing a cystogram or cystometrogram, the opportunity should be taken to measure residual urine. Repeated catheterisations are undesirable because the procedure causes discomfort, especially in boys, and carries the risk of introducing infection or traumatising the urethra. A catheter usually gives an accurate measurement of residual urine but we have found that with the small size catheters used in children (6 to 10 French gauge) the volume obtained can be misleading. (3) Radiology. Post-micturition films in the course of intravenous urography and micturating cystography are useful methods of assessing the completeness of bladder emptying, but clearly radiation exposure imposes limitations on their use. (4) Dye Excretion (Phenol Red) and (5) Radioactive Labelling. (Iodine-131, Technetium-99). Both techniques avoid the use of a catheter and can give accurate quantitative results. Both inquire intravenous or suprapubic injections and have other technical difficulties which make them unsuitable for routine use.
Ultrasound Ultrasound is now an established diagnostic tool which can make a valuable contribution to the investigation of the urinary tract, particularly in the diagnosis of space-occupying renal lesions. Much of the work in this field has been done in Glasgow, where Professor Donald pioneered the development of ultrasound in obstetrics, and has been the subject of 2 papers to this Association in recent years (Kyle et af., 1971; McLaughlin et al., 1975). The basic principles of ultrasound have been well described elsewhere (Barnett and Morley, 1972). Briefly, the apparatus consists of a mobile probe containing a transducer which emits short pulses of ultrasonic energy which travel through the tissues. Echoes are reflected back from interfaces and the transducer functions also as a receiver. As the transducer is moved across a selected plane the returning echoes are displayed on an oscilloscope as a series of dots, thus building up a cross-sectional picture. This type of display is referred to as a “brightnessmodulated”, or B-mode scan. In the A-mode scan (“amplitude modulated”) the echo information is displayed as a vertical deflection whose amplitude is related to the intensity of the echo. A 805
806
BRITISH JOURNAL OF UROLOGY
Fig. 1. Midline sagittal scan of a full and empty bladder in a girl, age 10 years, ( a ) bladder full, (b) bladder empty.
more recent development is the Grey Scale Ultrasound where amplitude is reflected by differing shades of grey. Ultrasound is particularly good at identifying fluid-filled structures as fluid readily transmits ultrasound, which is reflected from the solid-fluid interface leaving an echo-free space. A full bladder can readily be identified (Fig. 1).
Procedure The apparatus we have used is a standard commercial unit (“Picker Echoview”), operating at 2.5 MHz, with the information displayed as a B-mode scan. The child is examined supine with no special preparation. Contact between the transducer and the skin is improved by the use of a coupling agent such as electrode jelly and the probe is moved back and forth across the abdominal wall in the selected plane. The picture can be seen on the
ULTRASOUND ASSESSMENT OF RESIDUAL URINE IN CHILDREN
9
I
I*
!
807
Vertical section
W Fig. 2. The technique of bladder ultrasound (see text.)
oscilloscope as it is built up and a permanent record secured by a Polaroid camera attached to the apparatus. We have made measurements both in the vertical (or sagittal) and transverse planes. In the sagittal plane it can be difficult to define the base of the bladder as it lies in the shadow of the symphysis (Fig. 2) but nevertheless we have found this the most useful plane. Patients Ultrasound bladder films and residual volumes have been measured in 17 children most of whom have neuropathic bladders. There were 9 boys and 8 girls whose ages ranged from 4 to 15 years. In 6 children calibration measurements were performed during bladder filling for micturating cystography; a series of ultrasound pictures being obtained at known filling volumes and again after voiding. In other children we have assessed residual by ultrasound at follow-up appointments, establishing the volume by catheterisation whenever possible. Findings (1) A filled bladder and an empty bladder could be readily appreciated by ultrasound (Fig. 1).
(2) With incremental filling of the bladder, changes in bladder size could be appreciated in sagittal sections but much less change was generally apparent in the transverse plane (Fig. 3). In the transverse plane there was also the difficulty of defining the level of section and for these reasons we decided to concentrate on the sagittal plane with the midline as a ready reference point. Even then the information obtained could be misleading if the bladder enlarges asymmetrically (Figs. 4 and 5). (3) To test the correlation between the ultrasound picture and bladder volume we measured bladder size in 2 planes at right angles directly from the photographs and plotted the product against volume. The results show a good straight line relationship for individual patients and for the mean values overall (correlation coefficient 0.99) (Fig. 6). However, the standard errors and standard deviations have a wide scatter which means it is not feasible to make an accurate quantitative calculation of residual volume from a single ultrasound reading. Discussion Estimating the volume of an organ of variable shape from a single-plane picture is fraught with difficulties. The area of the bladder shadow seen in post-micturition radiographs is known t o 47/7--~
808
BRITISH JOURNAL OF UROLOGY
C 01 M
m
9
ULTRASOUND ASSESSMENT OF RESIDUAL URINE IN CHILDREN
809
5 .3
0 *
5
c 3
810
BRITISH JOURNAL OF UROLOGY
T
k
b
s40 a, Fig. 5. Intravenous urogram in same patient as Fig. 4 showing asymmetrical bladder enlargement.
Fig. 6. Bladder size measured from ultrasound pictures plotted against bladder volume. Correlation coefficient on means = 0.99.
-- 30 N v,
5
0
100
200
300
Volume (ml)
correlate poorly with residual volume, showing an error of up to 50% (Bretland, 1958). Extrapolating residual volume from ultrasound picture is likely to be subject to similar difficulties. Indeed, this has been the experience reported by others who have used ultrasound to assess residual urine in adults, even when more complex mathematical analysis was applied (Holmes, 1967; Alfthan and Mattsson, 1969). However, this does not mean that ultrasound is of no value in assessing residual urine but rather that it is important to appreciate its limitations. In many clinical situations a semi-quantitative assessment is sufficient. For example, we have used the technique in children with neuropathic bladder disorders to follow the response to treatment with alpha-adrenergic blocking drugs (Figs. 7 and 8). In this kind of situation when repeated examinations are required the advantages of ultrasound are considerable. The procedure is simple, non-invasive, takes only a few minutes to perform and requires minimal patient cooperation. Children may show some initial apprehension but it is readily overcome and they will happily undergo repeated examinations on subsequent visits. This is in marked contrast to
ULTRASOUND ASSESSMENT OF RESIDUAL URINE IN CHILDREN
811
Fig. 7. Ultrasound residuals in a girl, age 4 years, with a neuropathic bladder (a),before and (b) after treatment with phenoxybenzamine. There has been a fall in residual volume together with symptomatic improvement.
the distress which catheterisation causes to nearly all children. As no special preparation is necessary for ultrasound examination the technique is very suitable for out-patients. Often, all that is required of the investigation is to establish the presence or absence of residual urine and this ultrasound can do with certainty (Fig. 9). Taking measurements from the ultrasound pictures will rarely be necessary as with practice the eye can judge changes in area quite well. If quantitative values are required it would be better to construct a calibration graph for that particular patient at an initial examination, such as at the time of a cystogram, as described earlier. For more accurate quantitative measurement of residual urine a catheter remains the method of choice. Alternatively if catheterisation is contra-indicated a radioactive labelling technique can give extremely accurate measurements of residual volume. At one time there was concern that ultrasound might carry a risk of causing cell damage or chromosomal changes, as had been shown in animal experiments but there is no evidence that this occurs at diagnostic intensities and ultrasound has been safely used in obstetrics for 13 years (Donald, 1962). Ultrasound equipment is expensive and no one would suggest acquiring the apparatus solely for assessing residual urine. However, if an ultrasound machine is already available-and its
BRITISH JOURNAL OF UROLOGY
812
Fig. 8. Ultrasound residuals in a boy, age 6 years, with a neuropathic bladder,treated with phenoxybenzamine. There was no reduction in residual and no symptomatic improvement (a) before treatment, (b) after treatment.
value in obstetrics and in the diagnosis of renal masses is sufficiently established to justify its provision in District Hospitals-then here is a further use for which it can be recommended. Conclusions
I . Ultrasound can be used for assessing residual urine semi-quantitatively. 2. Midline sagittal scans are recommended. 3. Ultrasound has the following advantages: (i) It is simple, quick and requires no preparation. (ii) It is non-invasive and free from harm. (iii) It can be performed repeatedly, and is acceptable to children. Summary
Ultrasound has been used to assess residual urine in children and found to have considerable advantages over other methods. Using a B-mode scan in the sagittal plane the presence or absence
ULTRASOUND ASSESSMENT OF RESIDUAL URINE IN CHILDREN
81 3
Fig. 9. Ultrasound appearance of a bladder with no residual urine (girl, age 10 years) (a) Longitudinal, (b) Transverse.
of residual urine can be confidently determined. Quantitative measurements of volume are subject to considerable error but semi-quantitative information in individual cases can be obtained by comparison of records made at subsequent examinations. More accurate quantitative values might be achieved by constructing an individual calibration curve. The advantages of ultrasound for assessing residual urine are that it is simple, quick, harmless and non-invasive. Because of these features the examination can be readily repeated, is suitable for out-patient use and is acceptable to children. We are grateful to Mr D. Innes Williams for allowing us to study children under his care and for his advice and encouragement. D r D. Werry carried out some of the ultrasound examinations, and the illustrations were prepared by the Department of Medical Art and Photography at the Institute of Urology.
814
BRITISH JOURNAL OF UROLOGY
References ALFTHAN,0. and MATTSSON, T. (1969). Ultrasonic method of measuring residual urine. Annales Chirurgiae et Gynaecologiae Fenniae, 58, 300-303. BARNETT, E. and MORLEY, P. (1972). Diagnostic ultrasound in renal disease. British Medical Bulletin, 28, 196-199. BRETLAND, P. M. (1958). Relationship of bladder shadow to bladder volume on excretion urography. Journal of’ the Faculty of Radiologists, 9, 152-153. DONALD, I. (1962). “Sonar”: a new diagnostic echo-sounding technique in obstetrics and gynaecology. Proceedings ofthe Royal Society of Medicine, 55, 637-640. HOLMES, J. H . (1967). Ultrasonic studies of the bladder. Journal of Urology, 97, 654-663. KYLE,K . F., DEANE, R. F., MORLEY, P. and BARNETT, E. (1971). Ultrasonography of the urinary tract. British Journal of Urology, 43, 709-711. MCLAUGHLIN, 1. S., MORLEY, P.. DEANE, R. F., BARNETT, E., GRAHAM, A. G. and KYLE.K . F. (1975). Ultrasound in the staging of bladder tumours. British Journal of Urology, 47, 51-56.
The Authors N. W. Harrison, MD, FRCS, Senior Registrar. C. Parks, DMRD, Senior Registrar. T. Sherwood, MRCP, FRCR, Consultant Radiologist.
Ultrasound Assessment of Residual Urine in Children N.
w.
HARRISON,
c. PARKS and
T. SHERWOOD
St Peter’s Hospitals and the Institiire of Urology, London
The bladder of a healthy child probably retains no more than a few millilitres of urine after voiding under normal circumstances. Residual urine predisposes to urinary infection, may be evidence of neuropathic bladder dysfunction, and can be a significant factor in producing incontinence and upper urinary tract dilatation. There are many situations in paediatric urology where it is essential to measure residual urine and many other occasions when this information would be useful. A method of assessing residual urine which is simple, accurate, non-invasive and harmless would be of considerable value in clinical practice. None of the currently available methods meets all these requirements ; each has its advantages and limitations which are briefly considered : (1) Clinical Examination. It is routine practice to palpate and percuss for a distended bladder. If a bladder remains palpable after an adequate opportunity to void there is clearly a significant residue. Clinical assessment has obvious limitations: an enlarged bladder may be difficult to appreciate in children who are obese, nervous or unco-operative, or who have abdominal tenderness due to recent surgery or peritonitis, or in children with large floppy bladders such as in the prune belly syndrome. (2) Catheterisation. This is the most usual method of establishing a residual volume and certainly whenever a
catheter has to be passed, for example in performing a cystogram or cystometrogram, the opportunity should be taken to measure residual urine. Repeated catheterisations are undesirable because the procedure causes discomfort, especially in boys, and carries the risk of introducing infection or traumatising the urethra. A catheter usually gives an accurate measurement of residual urine but we have found that with the small size catheters used in children (6 to 10 French gauge) the volume obtained can be misleading. (3) Radiology. Post-micturition films in the course of intravenous urography and micturating cystography are useful methods of assessing the completeness of bladder emptying, but clearly radiation exposure imposes limitations on their use. (4) Dye Excretion (Phenol Red) and (5) Radioactive Labelling. (Iodine-131, Technetium-99). Both techniques avoid the use of a catheter and can give accurate quantitative results. Both inquire intravenous or suprapubic injections and have other technical difficulties which make them unsuitable for routine use.
Ultrasound Ultrasound is now an established diagnostic tool which can make a valuable contribution to the investigation of the urinary tract, particularly in the diagnosis of space-occupying renal lesions. Much of the work in this field has been done in Glasgow, where Professor Donald pioneered the development of ultrasound in obstetrics, and has been the subject of 2 papers to this Association in recent years (Kyle et af., 1971; McLaughlin et al., 1975). The basic principles of ultrasound have been well described elsewhere (Barnett and Morley, 1972). Briefly, the apparatus consists of a mobile probe containing a transducer which emits short pulses of ultrasonic energy which travel through the tissues. Echoes are reflected back from interfaces and the transducer functions also as a receiver. As the transducer is moved across a selected plane the returning echoes are displayed on an oscilloscope as a series of dots, thus building up a cross-sectional picture. This type of display is referred to as a “brightnessmodulated”, or B-mode scan. In the A-mode scan (“amplitude modulated”) the echo information is displayed as a vertical deflection whose amplitude is related to the intensity of the echo. A 805
806
BRITISH JOURNAL OF UROLOGY
Fig. 1. Midline sagittal scan of a full and empty bladder in a girl, age 10 years, ( a ) bladder full, (b) bladder empty.
more recent development is the Grey Scale Ultrasound where amplitude is reflected by differing shades of grey. Ultrasound is particularly good at identifying fluid-filled structures as fluid readily transmits ultrasound, which is reflected from the solid-fluid interface leaving an echo-free space. A full bladder can readily be identified (Fig. 1).
Procedure The apparatus we have used is a standard commercial unit (“Picker Echoview”), operating at 2.5 MHz, with the information displayed as a B-mode scan. The child is examined supine with no special preparation. Contact between the transducer and the skin is improved by the use of a coupling agent such as electrode jelly and the probe is moved back and forth across the abdominal wall in the selected plane. The picture can be seen on the
ULTRASOUND ASSESSMENT OF RESIDUAL URINE IN CHILDREN
9
I
I*
!
807
Vertical section
W Fig. 2. The technique of bladder ultrasound (see text.)
oscilloscope as it is built up and a permanent record secured by a Polaroid camera attached to the apparatus. We have made measurements both in the vertical (or sagittal) and transverse planes. In the sagittal plane it can be difficult to define the base of the bladder as it lies in the shadow of the symphysis (Fig. 2) but nevertheless we have found this the most useful plane. Patients Ultrasound bladder films and residual volumes have been measured in 17 children most of whom have neuropathic bladders. There were 9 boys and 8 girls whose ages ranged from 4 to 15 years. In 6 children calibration measurements were performed during bladder filling for micturating cystography; a series of ultrasound pictures being obtained at known filling volumes and again after voiding. In other children we have assessed residual by ultrasound at follow-up appointments, establishing the volume by catheterisation whenever possible. Findings (1) A filled bladder and an empty bladder could be readily appreciated by ultrasound (Fig. 1).
(2) With incremental filling of the bladder, changes in bladder size could be appreciated in sagittal sections but much less change was generally apparent in the transverse plane (Fig. 3). In the transverse plane there was also the difficulty of defining the level of section and for these reasons we decided to concentrate on the sagittal plane with the midline as a ready reference point. Even then the information obtained could be misleading if the bladder enlarges asymmetrically (Figs. 4 and 5). (3) To test the correlation between the ultrasound picture and bladder volume we measured bladder size in 2 planes at right angles directly from the photographs and plotted the product against volume. The results show a good straight line relationship for individual patients and for the mean values overall (correlation coefficient 0.99) (Fig. 6). However, the standard errors and standard deviations have a wide scatter which means it is not feasible to make an accurate quantitative calculation of residual volume from a single ultrasound reading. Discussion Estimating the volume of an organ of variable shape from a single-plane picture is fraught with difficulties. The area of the bladder shadow seen in post-micturition radiographs is known t o 47/7--~
808
BRITISH JOURNAL OF UROLOGY
C 01 M
m
9
ULTRASOUND ASSESSMENT OF RESIDUAL URINE IN CHILDREN
809
5 .3
0 *
5
c 3
810
BRITISH JOURNAL OF UROLOGY
T
k
b
s40 a, Fig. 5. Intravenous urogram in same patient as Fig. 4 showing asymmetrical bladder enlargement.
Fig. 6. Bladder size measured from ultrasound pictures plotted against bladder volume. Correlation coefficient on means = 0.99.
-- 30 N v,
5
0
100
200
300
Volume (ml)
correlate poorly with residual volume, showing an error of up to 50% (Bretland, 1958). Extrapolating residual volume from ultrasound picture is likely to be subject to similar difficulties. Indeed, this has been the experience reported by others who have used ultrasound to assess residual urine in adults, even when more complex mathematical analysis was applied (Holmes, 1967; Alfthan and Mattsson, 1969). However, this does not mean that ultrasound is of no value in assessing residual urine but rather that it is important to appreciate its limitations. In many clinical situations a semi-quantitative assessment is sufficient. For example, we have used the technique in children with neuropathic bladder disorders to follow the response to treatment with alpha-adrenergic blocking drugs (Figs. 7 and 8). In this kind of situation when repeated examinations are required the advantages of ultrasound are considerable. The procedure is simple, non-invasive, takes only a few minutes to perform and requires minimal patient cooperation. Children may show some initial apprehension but it is readily overcome and they will happily undergo repeated examinations on subsequent visits. This is in marked contrast to
ULTRASOUND ASSESSMENT OF RESIDUAL URINE IN CHILDREN
811
Fig. 7. Ultrasound residuals in a girl, age 4 years, with a neuropathic bladder (a),before and (b) after treatment with phenoxybenzamine. There has been a fall in residual volume together with symptomatic improvement.
the distress which catheterisation causes to nearly all children. As no special preparation is necessary for ultrasound examination the technique is very suitable for out-patients. Often, all that is required of the investigation is to establish the presence or absence of residual urine and this ultrasound can do with certainty (Fig. 9). Taking measurements from the ultrasound pictures will rarely be necessary as with practice the eye can judge changes in area quite well. If quantitative values are required it would be better to construct a calibration graph for that particular patient at an initial examination, such as at the time of a cystogram, as described earlier. For more accurate quantitative measurement of residual urine a catheter remains the method of choice. Alternatively if catheterisation is contra-indicated a radioactive labelling technique can give extremely accurate measurements of residual volume. At one time there was concern that ultrasound might carry a risk of causing cell damage or chromosomal changes, as had been shown in animal experiments but there is no evidence that this occurs at diagnostic intensities and ultrasound has been safely used in obstetrics for 13 years (Donald, 1962). Ultrasound equipment is expensive and no one would suggest acquiring the apparatus solely for assessing residual urine. However, if an ultrasound machine is already available-and its
BRITISH JOURNAL OF UROLOGY
812
Fig. 8. Ultrasound residuals in a boy, age 6 years, with a neuropathic bladder,treated with phenoxybenzamine. There was no reduction in residual and no symptomatic improvement (a) before treatment, (b) after treatment.
value in obstetrics and in the diagnosis of renal masses is sufficiently established to justify its provision in District Hospitals-then here is a further use for which it can be recommended. Conclusions
I . Ultrasound can be used for assessing residual urine semi-quantitatively. 2. Midline sagittal scans are recommended. 3. Ultrasound has the following advantages: (i) It is simple, quick and requires no preparation. (ii) It is non-invasive and free from harm. (iii) It can be performed repeatedly, and is acceptable to children. Summary
Ultrasound has been used to assess residual urine in children and found to have considerable advantages over other methods. Using a B-mode scan in the sagittal plane the presence or absence
ULTRASOUND ASSESSMENT OF RESIDUAL URINE IN CHILDREN
81 3
Fig. 9. Ultrasound appearance of a bladder with no residual urine (girl, age 10 years) (a) Longitudinal, (b) Transverse.
of residual urine can be confidently determined. Quantitative measurements of volume are subject to considerable error but semi-quantitative information in individual cases can be obtained by comparison of records made at subsequent examinations. More accurate quantitative values might be achieved by constructing an individual calibration curve. The advantages of ultrasound for assessing residual urine are that it is simple, quick, harmless and non-invasive. Because of these features the examination can be readily repeated, is suitable for out-patient use and is acceptable to children. We are grateful to Mr D. Innes Williams for allowing us to study children under his care and for his advice and encouragement. D r D. Werry carried out some of the ultrasound examinations, and the illustrations were prepared by the Department of Medical Art and Photography at the Institute of Urology.
814
BRITISH JOURNAL OF UROLOGY
References ALFTHAN,0. and MATTSSON, T. (1969). Ultrasonic method of measuring residual urine. Annales Chirurgiae et Gynaecologiae Fenniae, 58, 300-303. BARNETT, E. and MORLEY, P. (1972). Diagnostic ultrasound in renal disease. British Medical Bulletin, 28, 196-199. BRETLAND, P. M. (1958). Relationship of bladder shadow to bladder volume on excretion urography. Journal of’ the Faculty of Radiologists, 9, 152-153. DONALD, I. (1962). “Sonar”: a new diagnostic echo-sounding technique in obstetrics and gynaecology. Proceedings ofthe Royal Society of Medicine, 55, 637-640. HOLMES, J. H . (1967). Ultrasonic studies of the bladder. Journal of Urology, 97, 654-663. KYLE,K . F., DEANE, R. F., MORLEY, P. and BARNETT, E. (1971). Ultrasonography of the urinary tract. British Journal of Urology, 43, 709-711. MCLAUGHLIN, 1. S., MORLEY, P.. DEANE, R. F., BARNETT, E., GRAHAM, A. G. and KYLE.K . F. (1975). Ultrasound in the staging of bladder tumours. British Journal of Urology, 47, 51-56.
The Authors N. W. Harrison, MD, FRCS, Senior Registrar. C. Parks, DMRD, Senior Registrar. T. Sherwood, MRCP, FRCR, Consultant Radiologist.
