Byline: Fadi. Housami, Marcus. Drake, Paul. Abrams
Objectives: Measurement of bladder weight using ultrasound estimates of bladder wall thickness and bladder volume is an emerging clinical measurement technique that may have a role in the diagnosis of lower urinary tract dysfunction. We have reviewed available literature on this technique to assess current clinical status. Methods: A systematic literature search was carried out within PubMed and MedLine to identify relevant publications. These were then screened for relevance. Preliminary results from our clinical experiments using the technique are also included. Results: We identified 17 published papers concerning the technique which covered clinical studies relating ultrasound-estimated bladder wall thickness to urodynamic diagnosis in men, women, and children together with change in response to treatment of bladder outlet obstruction. The original manual technique has been challenged by a commercially available automated technique. Conclusion: Ultrasound-estimated bladder weight is a promising non-invasive technique for the categorization of storage and voiding disorders in both men and women. Further studies are needed to validate the technique and assess accuracy of diagnosis.
Lower urinary tract symptoms (LUTS) have an increasing prevalence in ageing men and women. Men who present with LUTS are investigated for benign prostatic enlargement (BPE) and bladder outlet obstruction (BOO), both of which are usually the result of benign prostatic hyperplasia (BPH).[sup]  However, LUTS alone are not sufficient in diagnosing BPE or BOO and other investigations are usually required.[sup] 
Uroflowmetry is a cheap test which provides some information on the voiding function and is easy to perform in the clinic setting. However, it lacks the required specificity as it is unable to differentiate between bladder outlet obstruction and detrusor underactivity. Conversely, pressure-flow studies remain the reference test in diagnosing BOO as they are able to provide valuable information on the detrusor contractility as well as the presence or absence of obstruction. This, unfortunately, does not come cheaply as urodynamics are invasive tests and require specialist equipment and training to perform the tests and interpret the results.[sup] 
Bladder Wall Thickness and Bladder Weight
The quest for a non-invasive test diagnostic of BOO has been ongoing for many years. Many parameters were investigated including free uroflowmetry, post-void residual volume and quantification of prostate volume.[sup]  Over the past decade or so, interest into bladder wall thickness and consequently bladder wall weight has grown rapidly. This was based on the rationale that bladder outlet obstruction is associated with detrusor hypertrophy and an increase in bladder wall thickness. In fact, morphological studies showed that the increase in bladder wall thickness was the result of smooth muscle hypertrophy as well as increased collagen deposition in the bladder wall.[sup] 
Ultrasound emerged as the easiest and least invasive option in measuring bladder wall thickness. The bladder wall appears on ultrasound as a three layer structure with the detrusor muscle represented by a hypoechogenic layer between two hyperechogenic layers representing the serosa and mucosa [Figure 1].[sup]  Some investigators measured the thickness of the three layers together,[sup]  whilst...