Ultrasound has a long tradition in the diagnosis of many diseases. It has been used in gynecology and obstetrics for many years. Recently, it has been noted by an increasing number of urogynecologists that the possibilities of ultrasound in urogynecological diagnostics are underused both in daily clinical practice and research(1, 2).
Experts agree that urethral length determined using ultrasound is one of the basic parameters that should be assessed in patients presenting symptoms of stress urinary incontinence (SUI)(1–3). The introduction of any type of diagnostic test for a wider use in research and clinical practice should always be preceded by repeatability and reproducibility evaluation(3). So far, the literature has lacked clear, standardized techniques and conditions for urogynecologic ultrasound examination. The diagnosis of stress urinary incontinence uses functional tests such as cough stress test or urethral pressure profile as a part of urodynamic testing. Each of these tests requires the patient to have their bladder filled up to approx. 250 mL(4). It seems that a similar degree of filling of the bladder should be required for diagnostic ultrasonography in SUI women, which is used for, e.g. determining the urethral length.
The aim of the study was to assess the repeatability and reproducibility of urethral length measurements during sonographic urethrocystography in females with a full bladder in the introital approach, using real-time two-dimensional transvaginal ultrasound.
Materials and methods
Ultrasound findings in females referred to the Department of Operative Gynecology and Gynecologic Oncology in Lodz for urogynecological diagnostics were analyzed. The study was approved by the ethics committee. All participants gave their consent to take part in the study.
The volume of urine in the bladder was evaluated during transabdominal ultrasound, by performing three-plane measurements of the bladder and interpreting its content of urine, which was calculated by the ultrasound system.
The sonographic urethrocystography was performed using the introital approach, in accordance with a standardized technique developed by Kociszewski, in female patients with a bladder filling of 200–300 mL. A high-frequency transvaginal probe (6.5 MHz, beam angle160°) was used for the evaluation. The test was performed in a patient in a gynecological chair in a semi-sitting position. The probe was placed near the external urethral ostium, with minimal probe compression on the investigated surface, in line with the axis of the patient. One of the images showed the pubic symphysis, which was the only constant reference point, the urethra and the bladder neck; the urethral length was measured (Fig. 1). The ultrasonographic measurement of the urethral length was performed along its long axis in the hypoechoic area of the urethra. The distance between points A and B was measured (Fig. 1). An ultrasound image of the internal urethral orifice into the bladder was selected as point A, while the point B was set in the most peripheral part inside the hypoechoic area of the urethra.
The technique of urethral length measurements during introital sonographic urethrocystography using a transvaginal probe(17)
Each of the two physicians participating in the study performed at least 100 ultrasound examinations in order to thoroughly learn the technique before performing sonographic urethrocystography for clinical and research assessments. This was followed by ultrasound measurements to estimate the repeatability of the individual urogynecologic parameters. Ultrasound measurements of the urethral length were carried out by two different physicians. The measurements were performed using BK Medical Pro Focus 2202 in the following configurations:
The analyses of repeatability and reproducibility of outcomes from the same day used data from 92 patients referred to the Department of Operative Gynecology and Gynecologic Oncology in Lodz for urogynecological diagnostics.
Data from 106 patients receiving an initial urogynecological diagnosis prior to tension-free vaginal tape procedure (TVT) and undergoing follow-up examination 3–6 months after the procedure were included in statistical analyses for the reproducibility of ultrasonographic urethral length measurements, which were performed at an interval of several months.
The Altman's coefficient (the intraclass correlation coefficient) was used in the statistical assessment of the compatibility of the ultrasonographic urethral length measurement repeatability. The r-correlation coefficient approximated by a second-degree polynomial between two sets of measurements was chosen from among the many definitions of the ICC. As in accordance with Altman, the following ICC ranges were used: ICC < 0.40 indicated poor; 0.41–0.60 indicated moderate; 0.61–0.80 indicated good agreement. ICC > 0.80 was considered a very good agreement (high repeatability) (5).
The repeatability (ICC value) of the urethral length in sonographic urethrocystography ranged between 0.9597 and 0.9873 (p = 0.0000) for the measurements taken by the same physician on the same ultrasound image.
An accuracy in the range of 0.9217 to 0.9344 (p = 0.0000) was achieved in the measurements performed by the same physician but on two different images.
High ICC consistency, i.e. 0.9280; p = 0.0000 (Fig. 2), was shown for reproducibility of measurements taken by two physicians on two different ultrasound images.
Reproducibility of ultrasound urethral length measurements assessed by two physicians on two different ultrasound images
Statistical analyses for the reproducibility of ultrasound urethral length measurements performed by two different physicians at the stage of diagnosis qualifying for TVT surgery as well as at the stage of postsurgical follow-up 3–6 months after TVT procedure confirmed high consistency of the performed measurements (ICC = 0.81 at p = 0.000).
The analysis of statistical findings confirmed a very high repeatability of ultrasound urethral length measurements taken during sonographic urethrocystography, which was performed in accordance with the standardized technique developed by Kociszewski (Fig. 2).
Diagnostic urogynecology uses many tools whose clinical and scientific usefulness has not yet been fully established(6–11). The introduction of certain diagnostic methods into research and daily clinical practice requires standardized assays as well as technical and professional methodology used in all patients. It was noted during analyses of accuracy and the causes of ultrasound measurement errors that factors such as, e.g. an appropriate cross-section, are also significant(12, 13). An assessment of repeatability and reproducibility is one of the basic conditions for standardization of measurements(3, 5). Various data on the accuracy of measurements taken during urogynecological ultrasound examination can be found in the literature(3, 5, 14, 15).
Currently, 2D, 3D and 4D ultrasounds using different probes (transabdominal, introital, transvaginal or transrectal) are used for the assessment of pelvic floor as a part of urogynecological diagnostic process(16). So far, no consensus on by whom and in what way should the procedure be performed, has been reached.
During 3D and 4D ultrasound imaging, the urethral length measurement is performed in patients with an empty bladder, from the bladder urethral orifice to the external urethral orifice(3, 14, 16).
Analyses of the urethral anatomical structure show that no muscles are present near the external urethral orifice (Fig. 1)(17).
Therefore, this region is highly susceptible to compression, which, according to the authors, may account for measurement inaccuracy. For these reasons Kociszewski suggested that the measurement be performed in the hypoechoic urethral region. Visualization of this region also confirms that an adequate urethral cross-section was achieved. Experts agree that cough stress test and urodynamic testing, which are used to assess SUI symptoms, should be performed in patients with a well-filled bladder. Kociszewski believes that this is the reason why diagnostic ultrasonography should not be performed in SUI patients with an empty bladder(4, 18, 19).
The urethra is clearly visible in the transvestibular ultrasound image using a transvaginal probe, and the image is static, which is likely to increase the probability of taking more precise measurements. The performed analyses of ultrasound urethral length measurements on the same ultrasound image as well as on different images confirmed the high repeatability and reproducibility of this measurement, which were assessed by the same physician and by two different physicians.
Further analyses should be performed to establish the position of real-time, introital sonographic urethrocystography using transvaginal probe in the diagnostic process in patients with urogynecological symptoms. This is supported by high repeatability of the performed urethral length measurements.
Very high repeatability and reproducibility of urethral length findings during sonographic urethrocystography performed in accordance with the presented technique support the possible use of this type of examination in both clinical practice and research.
Conflict of interest
The authors do not report any financial or personal links with other persons or organizations, which might affect negatively the content of this publication or claim authorship rights to this publication.