Modifications of the bladder wall (organ damage) in patients with bladder outlet obstruction: ultrasound parameters.

Introduction: Progressive changes in the bladder wall are observed in men with lower urinary tract obstruction secondary to benign prostatic enlargement (BPE). The high pressure voiding causes initially an increase in the proportion of smooth muscle (hyperplasia/hypertrophy of the detrusor) that develops to major changes in the advanced stages of bladder decompensationi (fibrosis), hyperactivity and decreased functional capacity. Early identification of bladder changes by noninvasive transabdominal ultrasound can suggest therapeutic choices that can prevent further organ damage in the bladder wall. Aim of our study is to review ultrasound (US) parameters, that could be considered reliable and reproducible, in order to demonstrate the damage of the bladder wall.
Methods: We performed a literature review to detect reported US parameters according to our aims. Our clinical experience was evaluated in retrospective manner to detect feasibility and limitations of the evaluation of these parameters in men with different degrees of bladder damage secondary to BPE.
Results: Measurement of the bladder wall thickness (BWT) or detrusor wall thickness (DWT) by US is reliable, with at least 3 measurements of the anterior bladder wall taken at a filling volume of 250 ml. In particular, the DWT [thickness of the hypoechoic muscle between two hyperechoic layers corresponding to serosa and mucosa] is considered the best diagnostic tool to measure detrusor hypertrophy using cut-off value > 2.9 mm in men. US derived measurements of bladder weight (Estimated Bladder Weight, EBW) is another noninvasive tool for assessing bladder modifications in patients with bladder outlet obstruction (BOO) with a cut-off value of 35 gr. Technique for measuring the BWT and EBW relies on conventional US 7.5-4 MHz using the automatic system of computation (BVM 6500 3.7 MHz). The variability of intra-operator (4.6 to 5.1%) and interoperator measurements (12.3%) is acceptable. Also conventional US detects established signs of bladder damage: diverticulosis, trabecolations in the bladder wall (pseudo-diverticula), calculi and post-void residual urine (PVR) (> 50 cc). Furthermore the Intravescical Prostate Protrusion (IPP), easy measured by transabdominal ultrasound, is strongly correlated to obstruction in men with BPE (cut-off 12 mm). Measurement, scoring and monitoring of the cervico-urethral obstruction in men with symptomatic BPE is possible by the non-invasive US of the bladder wall. Early identification by measuring DWTand EBW in addition to established US paremeters has the advantage of suggest the adoption of therapeutic measures sufficient to prevent progression of bladder damage.
Conclusions: US derived measurements of DWT and EBW are reproducible and reliable. Transabdominal US also detect established bladder damage such as diverticula, stones and PVR, while IPP measurement seems to be correlated to BOO. US bladder parameters are considered potential noninvasive clinical tools for baseline assessment of patients with BOO. In particular noninvasive US parameters could be useful for longitudinal studies monitoring men with lower urinary tract obstruction secondary to BPE.