Overactive Bladder (OAB) is a subjective, symptom-based syndrome that impairs the quality of life of millions of individuals. Unfortunately, the diversity of phenotypes of OAB hampers the effectiveness of a single treatment, and invasive pressure-flow studies are often utilized for further investigation in refractory cases.  Recent studies emphasize the potential value of abdominal ultrasound (US) to quantify bladder shape and further define overactive bladder [1, 2]. In one study, investigators found that US-derived bladder height-to-width ratios were abnormal in women with OAB compared to BMI and age-matched controls without OAB [1]. In the present study, a bladder shape nomogram was generated using sagittal perimeter measurements from women without OAB and the ability of the algorithm to identify irregular bladder shapes in women with OAB was tested.

Data were analyzed for female participants from two prospective studies. 3D bladder US images were collected at 1-minute intervals during a urodynamics study with filling at 10% cystometric capacity per minute, and at 5-10-minute intervals during 2-4 fills of an accelerated oral hydration protocol [3] using a GE Voluson E8 US system with a 4-8MHz abdominal probe. Both studies included individuals with and without OAB based on urgency question 5a of the ICIq-OAB questionnaire (with OAB: 5a≥2, without OAB 5a<2). A trained technician manually traced the perimeter of all bladder images in six cross-sectional planes 30° apart in GE 4D-View (Fig1) and measured geometric parameters including perimeters and cross-sectional areas in transverse, sagittal and coronal planes. The present study focused on the development of a nomogram for the sagittal perimeter as a function of volume using data from participants without OAB. A power model was selected for approximating upper and lower nomogram bounds with a confidence interval of 95% (Fig2A). The nomogram was tested using sagittal perimeter values in the volume range of 100ml to 500ml from each participant with OAB (Fig2B), and a participant was classified as having an abnormal bladder shape if they had sagittal perimeter values out of the nomogram bounds for 3 or more volumes. To validate the robustness of the designed nomogram, sagittal perimeter values from participants with and without OAB were tested accordingly.

The nomogram was developed using sagittal perimeter data from 533 US images from 27 women without OAB, including 14 from urodynamic studies and 13 from hydration studies (Fig2A), and the nomogram was tested using 264 sagittal perimeter measurements from 24 women, including 16 from urodynamics studies and 8 from hydration studies (Fig2B). In the testing phase, five women with OAB and zero without OAB were found to have at least three sagittal perimeter measurements outside the nomogram bounds, and having an abnormal sagittal perimeter was significantly associated with OAB (Fig 2, Fisher’s exact test, p<0.05). Four of the five individuals with OAB identified with abnormal bladder shapes had smaller sagittal perimeter values, or relatively flat bladders as shown in the example in Fig1.

The results indicate that some women with OAB may have abnormally shaped bladders, and bladder shape nomograms may provide a non-invasive way to identify these individuals.  Larger data sets are needed to refine the nomogram and determine whether there is a clinically relevant subgroup of women with OAB that have abnormal bladder shapes during filling.

Abdominal US imaging and bladder shape nomograms provide a feasible, non-invasive means to potentially identify a subgroup of women with shape-associated OAB.

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Sheen D, Kolli H, Nagle A, Cullingsworth Z, Vinod N, Naimi H, De Wachter S, Mazzeo S, Stothers L, Speich J, Klausner A. Validation of a real-time bladder sensation meter during oral hydration in healthy adults: Repeatability and effects of fill rate and ultrasound probe pressure. LUTS. 2019;11(4):224-231.