Urethral sphincter morphology in women with detrusor instability.

OBJECTIVE: To determine whether sonographic urethral sphincter morphology is different in patients with detrusor instability than in those with normal urodynamic testing. METHODS: Patients from a population of women presenting for evaluation of urinary incontinence or pelvic organ prolapse underwent intraurethral ultrasonography before multichannel urodynamic testing. Maximal rhabdosphincter thickness, total urethral diameter, total urethral circumference, and longitudinal smooth muscle thickness, diameter, and circumference were measured. For patients with detrusor instability, the strength of the involuntary detrusor contraction and the bladder volume at its onset were recorded. These data were compared with information from history questionnaires and urodynamic evaluations. RESULTS: The 17 patients with detrusor instability and 16 patients with normal urodynamic testing did not differ with respect to age, vaginal parity, race, weight, body mass index, prior continence surgery, or maximal total urethral closure pressure. Patients with detrusor instability, had decreased urethral longitudinal smooth muscle thickness (3.0 +/- 0.9 mm vs 4.1 +/- 0.7 mm, P =.001), total urethral diameter (18.0 +/- 1.6 mm vs 19.4 +/- 1.4 mm, P =.01), and total urethral circumference (5.65 +/- 0.5 cm vs 6.1 +/- 0.4 cm, P =.012) compared with those with normal urodynamic tests. A linear relationship between rhabdosphincter thickness and strength of involuntary detrusor contraction was observed (r =.686, P =.002). CONCLUSION: Urethral sphincter morphology is different in patients with detrusor instability compared with those who have normal urodynamic tests. These findings provide an anatomic basis for the physiologic findings in patients with "urethrogenic" detrusor instability.