Lower urinary tract symptoms (LUTS) include storage symptoms (frequency, urgency, nocturia, urge incontinence, etc.) and voiding symptoms (thin urine line, short distance, interrupted urination, dribbling after urination, urinary retention, etc.), which seriously affect the quality of life of patients. Forty-one percent of men >50 years of age in the United States have moderate or severe LUTS.
The storage and voiding symptoms in patients without neuropathy are usually caused by detrusor overactivity (DO) and bladder outlet obstruction (BOO), for which there is no ideal non-invasive diagnostic method. Pressure. Volume and pressure flow studies (PFS) remain the gold standard for the diagnosis of LUTS, but these tests are invasive, expensive, tedious, and time-consuming.
With recent advances in ultrasound technology and improvements in ultrasound software, the use of ultrasound to measure bladder wall thickness (BWT), detrusor wall thickness (DWT), and estimated bladder weight (UEBW) has become more common. However, these methods are not yet available in clinical practice. In this article, we review the recent advances in the use of ultrasound for the evaluation of LUTS and discuss its clinical application.
Ultrasonography has been used to evaluate LUTS, usually measuring BWT/DWT, but also measuring the blood supply to the bladder and UEBW, mostly transabdominally, transvaginally, transrectally, and also transvaginally. Although more layers are penetrated and distances are covered, with the improvement of color Doppler ultrasound equipment, transabdominal ultrasound (TAUS) has become more advantageous because of its simplicity and ease of patient acceptance.
I. BWT/DWT in healthy adults
Oelke et al. performed DWT measurements in 55 healthy volunteers and the mean DWT was 1.4 mm in men and 1.2 mm in women at bladder volumes ≥250 ml. Bright et al. reported that the mean BWT measured by TAUS at different bladder volumes was 3.33 mm in men and 3.04 mm in women.
Ultrasound measurements of BWT/DWT in healthy adults vary widely depending on the degree of bladder filling. It has been suggested that measuring DWT is superior to BWT, possibly because: (1) the thickness of the detrusor muscle is most affected by the degree of bladder filling and bladder pressure; and (2) TAUS can clearly show the 3 layers of the bladder wall. The central hyperechoic layer represents the bladder forceps muscle and is flanked by the mucosal and subplasmic layers. The forceps layer is easier to visualize and its thickness can be measured precisely. The BWT includes the mucosal layer, which is susceptible to other pathological changes such as infection and tumors.
BWT/DWT in BOO patients
The results of animal studies show that bladder wall thickening and bladder weight increase after only 2 weeks of mild BOO, with a mean bladder wall thickness of 2.04 mm and 2.77 mm in the mild and severe BOO groups compared to 1.57 mm in the no BOO control group, with a statistically significant difference between the three groups (P<0.05), the most significant difference being in the detrusor layer. Some studies have attempted to diagnose BOO by quantifying TAUS measurements of BWT/DWT.
Elizabeth et al. measured the BWT in 170 patients with urodynamics (UDS) diagnosed BOO at a bladder volume of 150 ml, and the mean value was 4 mm. 88% of these patients had a BWT ≥5 mm, which was considered the optimal threshold for the diagnosis of BOO.
Shinbo and Kurita found that as the degree of BOO increased, DWT increased with it. The mean DWT was 1.33, 1.62, 2.40, and 3.78 mm for the four groups of patients diagnosed with no, suspected, mild, and severe BOO by PFS, respectively.
The median DWT was 1.7, 1.8, and 2.7 mm in the non-BOO, suspected BOO, and BOO groups, respectively, and DWT ≥ 2.9 mm was the optimal threshold for the diagnosis of BOO with 100% sensitivity, 100% specificity, and an area under the curve of 0.88. In these two studies, the DWT in the non-BOO and BOO groups was 1.7, 1.8, and 2.7 mm, respectively. The difference in DWT between the non-BOO and BOO groups was statistically significant in both studies (p<0.01). < p="">
Li Ning et al. found that the DWT in the female BOO and non-BOO groups was (1.8±0.3) and (1.4±0.2) mm, respectively, at a bladder perfusion volume of 250 ml or 50% of the maximum bladder capacity, with a statistically significant difference (P=0.00). When the DWT was ≥1.9 mm, the specificity and positive predictive value were 100%, and the sensitivity was 38%. The negative predictive value was 62%, and the area under the curve was 0.88±0.06.
The range of reference values for confirming the diagnosis of BOO using TAUS measurement of BWT/DWT has been reported differently, which is related to the different testing conditions such as the bladder volume at the time of measurement.
III. UEBW
Color Doppler ultrasound measurement of BWT/DWT is limited in clinical use because of its susceptibility to bladder volume. Zhang Xue-Bin et al. applied TAUS to measure BWT, assuming a spherical bladder, and estimated bladder weight based on bladder contents (residual urine volume + urine volume) and BWT, and the UEBW was (98.6±54.4) g in the BOO group and (38.l±5.9) g in the control group, with a statistically significant difference between the two groups (P= 0.000). The sensitivity of UEBW was 91.8%, the specificity was 89.7%, and the accuracy was 9l.0%.
Panayi et al. examined 34 male BOO patients and 31 male non-BOO patients with a mean UEBW of 46.2 g and 29.3 g, respectively, with statistically significant differences between the two groups (P<0.05), of which 87.="" uebw="">35 g, with a working characteristic curve analysis demonstrating that the cut-off value for predicting BOO was UEBW ≥35 9.
He also investigated the relationship between UEBW and prostate size. By examining 234 patients, he found that the mean UEBW of 41.1 g in those with larger prostates was significantly higher than that of 27.1 g in those with normal prostates, and that UEBW >35 g was significantly associated with enlarged prostate and residual urine volume >100 ml.
Bright et al. studied UEBW in patients with acute urinary retention (AUR). 90% of patients with AUR had UEBW ≥ 35 g, and only 41% of patients with UEBW ≥ 35 g did not develop AUR. The incidence of AUR was 13.4 times higher in men with UEBW>35 g than in men with normal UEBW.
In the longitudinal study of 33 patients with BPH, the mean UEBW decreased from 52.9 g to 35.0 g at 4 weeks after prostatectomy compared with 26.5 g in the control group and 31.6 g at 12 weeks after surgery, with the majority of patients having a completely normal UEBW. A longitudinal study of tamsulosin for LUTS found that 48.0% of patients had UEBW ≥ 35 g before treatment and 81.7% underwent prostatectomy after 5 years, and a multifactorial analysis showed that UEBW ≥ 35 g and lPSS ≥ 20 were significant risk factors for surgical treatment.
Although UEBW is an ideal method to assess BOO, its diagnostic validity should not be exaggerated. UEBW has not yet been studied as a diagnostic parameter.
BWT /DWT in women
The anatomical features of women make them less susceptible to BOO, yet a significant number of women suffer from DO. Clinicians have long considered bladder trabeculae formation as a sign of BOO. DO causes repeated contractions of the detrusor muscle against the contracting urethral sphincter, resulting in detrusor hypertrophy. Therefore, measurement of BWT/DWT should be able to distinguish the presence of DO in women.
Kuo et al. confirmed these findings by examining 180 women, with a mean BWT of 6.3 mm in women with DO compared to 3.9 mm in normal women, patients with stress urinary incontinence (SUI), and patients with mixed incontinence. In 42 women with no DO on static USD but BWT >5 mm, D0 was diagnosed by dynamic USD in 36 (85.7%) patients.
Although transvaginal ultrasound (TVUS) is faster than USD, it is more demanding on the sonographer and patients may perceive TVUS as an invasive test. The average DWT at the top of the bladder was 4.7 mm in women with DO and 4.1 mm in the no-DO group.
DO was confirmed by USD examination in all cases, and although the difference between the two groups was statistically significant, the predictive power of transvaginal ultrasound was low, with a sensitivity of 37% and specificity of 79% at a cut-off value of 5 mm, and an area under the curve of only 0.606.
Housami et al. reported a study using TAUS to measure BWT and UEBW in women, including 12 patients with SUI and 13 patients with DO diagnosed by USD, with a mean UEBW of 36.5 g in the SUI group and 42.6 g in the DO group, and a decrease in BWT with increasing bladder volume (<400 ml). In a study with 81 women, 28 in the dry OAB group, 25 in the wet OAB group, and 28 in the control group, it was found that DWT decreased significantly with increasing bladder volume at bladder volumes <250 ml; at bladder volumes from 250 ml to maximum volume, DWT still decreased, but not significantly.
At bladder volume of 250 ml, DWT was measured by TAUS, and the difference between the groups was not statistically significant. At maximum bladder volume, the DWT was significantly higher in the wet OAB group than in the other groups, with a statistically significant difference (P<0.01), but the difference was small (0.2 - 0.4 mm), and Kuo suggested that the resolution of the 3.5 - 7.5 MHz ultrasound scan was 0.1 - 0.3 mm. The variability of DWT values and BWT values between groups was 5-10%, therefore, the differences may be due to variability and resolution.
V. BWT/DWT and bladder volume thickness index in children
The DWT of the posterior bladder wall in 150 healthy infants to school-age children was 0.4-1.9 mm and the DWT of the anterior wall was 0.4-2.3 mm, and the DWT and bladder volume increased with age, thus suggesting a reference value of 1.5 mm for the DWT of the posterior bladder wall at <2>10% of maximum bladder volume. This result also suggests that there are multiple factors that can influence DWT.
Leung et al. calculated the bladder volume and wall thickness index (BVWI) by measuring the internal diameter of the bladder and the average thickness of each part of the bladder (top, bottom, and both sides of the bladder).
Yeung et al. calculated bladder volume by measuring the internal diameter of the bladder in three sagittal planes at maximum bladder capacity, and the average of the anterior, lateral, and posterior bladder walls was used as the mean BWT, and BVWI was obtained as the maximum bladder volume/mean BWT. was significantly associated with DO.
Oelke et al. reported that 80% of 514 children with primary enuresis had a normal BVWI (70 -130) and responded well to desmopressin, and 70% of 152 children with BOO had a BVWl <70.< p="">
The difference in DWT and BWT between children with BOO and normal children has been shown to be statistically significant, although there are differences between reports. The mean DWT of 4 children with BOO was 4.4 mm, and the difference in mean BVWI between the BOO and control groups was statistically significant (P
Because there are more measurements in children and adults for reference, many publications recommend the use of TAUS to measure BWT/DWT. TAUS is non-invasive and undoubtedly the best choice for pediatric and female patients. TAUS can measure BWT and UEBW at bladder volumes of 150-400 ml, whereas conventional ultrasound requires bladder volumes of 150-250 ml at the time of measurement.
In conclusion, despite the differences in basic principles and data reported in the literature, BWT/DWT and UEBW have been shown to be useful in the diagnosis of LUTS under certain conditions. If further improved and refined, ultrasound measurement of BWT/DWT and UEBW will be the most powerful clinical tool for assessing lower urinary tract function.