Original research
Urethral sphincter morphology in women with detrusor instability

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Abstract

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.

Section snippets

Materials and methods

To determine the clinical utility of this new radiologic modality for women with urinary incontinence, 130 consecutive patients underwent intraurethral ultrasonography. Urethral sphincter morphology in the stress-incontinent cohort has previously been compared with women who present with a normal urodynamic test.17 Not all women who underwent urodynamic testing had symptoms of urinary incontinence. Some had prolapse of the posterior vaginal wall and underwent urodynamic testing with their

Results

All of the patients who underwent intraurethral ultrasonography had urodynamic testing. The urodynamic diagnoses of the 130 patients were as follows: 16 were normal (12.3%), 17 had detrusor instability (13.1%), 59 had genuine stress incontinence (45.4%), 18 had genuine stress incontinence with coexistent detrusor instability (13.8%), 15 had intrinsic sphincter deficiency (11.5%), three had decreased bladder compliance (2.3%), one had overflow incontinence (0.8%), and one chart was lost (0.8%).

Discussion

This study demonstrates a clear difference in urethral sphincter morphology between patients with detrusor instability and those with normal urodynamic testing. Women with detrusor instability had a smaller total urethral diameter and circumference as a result of a loss of longitudinal smooth muscle thickness. This suggests an anatomic reason for the physiologic findings in patients with “urethrogenic” detrusor instability.

In a previous study, we found a weak positive linear association between

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