Acontractile bladder (AcB)/detrusor underactivity (DU) were urodynamic-based diagnosis with similar pathologenic mechanism but different clinical presentations. They share common pathophysiology with myogenic changes related to ischemia, which lead to bladder detrusor wall fibrosis and loss of detrusor muscle contractility. The aim of this study was to determine the sensitivity of transvaginal ultrasound shear wave elastography (SWE) as a good parameter for evaluating the biomechanical characteristics of bladder to measure the posterior bladder wall pressure in women with AcB/DU.

During the period from October of 2019 to December of 2020, 18 patents were enrolled in this prospective study. According to urodynamic results, 10 women were classified as poor bladder function with AcB/DU and poor compliance of bladder, 8 women were normal bladder function with detrusor normoreflexia and normal compliance of bladder. Transvaginal ultrasound was performed by using an ultrasound machine (Aplio i-Series A800, Canon Medical System) with a transcavitary curvilinear probe (3 to 11 mHz) equipped with SWE. Detrusor wall thickness (DWT) and SWE of posterior bladder wall were acquired sequentially starting from empty bladder, different degree of bladder filling (50ml, 100ml, 150ml, 200ml), and once again empty bladder. An independent t-test was used for comparing two groups under different bladder volume. Two-tailed p value of less than 0.05 was considered statistically significant.

The mean age was 76.40± 10.28 years old for poor bladder function group, 63.13±17.12 years old for normal bladder function group. DWT decreases during the bladder filling, and no statistical difference was found between the two groups (table 1).Patients with AcB/DU and poor compliance of bladder showed significantly greater mean shear wave modulus than those with detrusor normoreflexia and normal compliance of bladder under distension (at 100cc, 150cc and 200cc).

Patients with poor bladder function (AcB/DU and poor compliance of bladder) showed significantly greater mean shear wave modulus than those with normal bladder function (normoreflexia and normal compliance of bladder) under distended bladder at 100cc. Poor bladder function group had the characteristics of urine leakage under distended bladder at 150cc and 200cc, causing mean shear wave modulus without increased significantly.

In our study, poor bladder function group had statically significant in detrusor stiffness under bladder distention at 100cc. Comparing to detrusor wall thickness, shear wave elastography has more reliable and clinical value for investigating poor bladder function with DU/AcB and poor compliance of bladder.  By measuring bladder shear wave modulus, we could also predict bladder fibrotic changes of detrusor muscle that resulted in AcB/DU. In summary, shear wave elastography is a feasible and reliable tool for bladder function survey.

Structural, biomechanical and hemodynamic assessment of the bladder wall in healthy subjects J Urol . 2017 Aug;198(2):422-429. doi: 10.1016/j.juro.2017.03.127. Epub 2017 Mar 31.