Study of female pelvic floor muscle in overactive bladder based on MRI 3D reconstruction

This study examined the three-dimensional (3D) morphological changes of the urination and urinary continence anatomical structures in overactive bladder (OAB) patients, to offer a morphological data for OAB diagnosis and treatment.

Eleven OAB patients, 9 healthy females and 22 pelvic organ prolapse (POP) patients were enrolled and underwent MRI scans. The anatomical components of urination (bladder detrusor) and the urinary continence (main part of the urethral sphincter, compressor urethrae, and levator ani muscle (LAM) were 3D reconstructed and measured with Amira software. We also analyze the relativity between pelvic floor muscle's morphological parameters among the volunteers, OAB and POP group.

Through 3D reconstruction, increased thickness and volume of the bladder detrusor were found in the OAB patients compared with volunteers (3.1 ± 0.7 mm vs. 1.9 ± 0.3 mm; P = 0.000 and 50,632.0 ± 19,724.7 mm³ vs. 23,386.6 ± 7826.3 mm³; P = 0.001). The volume of LAM showed no significant difference between the OAB patients and volunteers (27,089.4 ± 5015.0 mm³ vs. 27,294.4 ± 4461.4 mm³; P = 0.924); whereas, LAM's volume of the POP patients was significantly larger than that of the volunteers (34,130.6 ± 7968.3 mm³ vs. 27,294.4 ± 4461.4 mm³; P = 0.023). The thickness and volume of the main part of urethral sphincter were significantly lower in the OAB patients compared with volunteers (2.2 ± 0.5 mm vs. 2.7 ± 0.3 mm; P = 0.018 and 2558.6 ± 703.2 mm³ vs. 23,267.3 ± 681.9 mm³; P = 0.035). The volume of the compressor urethrae was significantly lower in the OAB patients than that in the volunteers (630.3 ± 301.2 mm³ vs. 866.1 ± 514.2 mm³; P = 0.247).

In OAB patients, the bladder detrusor has long-term tension and contraction, which thickened muscle and increased volume, and aggravate urination. The compressor urethral and main part of urethral sphincter are weaker and the anterior part of LAM hiatus is relaxed, easily resulting in leakage of urine and ultimately incontinence. The MRI 3D reconstruction and measurement can help to evaluate pelvic floor urination and continence function, and accurately diagnose.