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NEUROLOGY
& FEMALE UROLOGY
Urethral
sphincter morphology and function with and without stress incontinence
Morgan DM, Umek W, Guire K, Morgan HK, Garabrant A, DeLancey JO
University of Michigan, Ann Arbor, Michigan, USA
J Urol. 2009; 182: 203-9
- Purpose:
Using magnetic resonance images we analyzed the relationship between
urethral sphincter anatomy, urethral function and pelvic floor function.
- Materials
and Methods: A total of 103 women with stress incontinence
and 108 asymptomatic continent controls underwent urethral profilometry,
urethral axis measurement with a cotton swab, vaginal closure force
measurement with an instrumented speculum and magnetic resonance imaging.
Striated urogenital sphincter length was determined and its thickness
was measured in the proximal sphincter, where its circular shape enables
estimation of striated urogenital sphincter area. A length-area index
was calculated as a proxy for volume.
- Results:
The striated urogenital sphincter in women with stress incontinence
was 12.5% smaller than that in asymptomatic continent women (mean +/-
SD length-area index 766.4 +/- 294.3 vs. 876.2 +/- 407.3 mm(3), p =
0.04). The groups did not differ significantly in striated urogenital
sphincter length (13.2 +/- 3.4 vs. 13.7 +/- 3.9 mm, p = 0.40), thickness
(2.83 +/- 0.8 vs. 3.11 +/- 1.4 mm, p = 0.09) or area (59.1 +/- 18.4
vs. 62.9 +/- 24.7 mm(2), p = 0.24). Striated urogenital sphincter length
and area, and the length-area index were associated during voluntary
pelvic muscle contraction with more urethral axis elevation and increased
vaginal closure force augmentation.
- Conclusions:
A smaller striated urogenital sphincter is associated with stress incontinence
and poorer pelvic floor muscle function.
- Editorial
Comment
The authors reviewed two populations of women, one with stress incontinence
and one without stress incontinence and had the two groups undergo urodynamic
testing, physical examination as well as magnetic resonance imaging.
Parameters evaluated included striated urethral sphincter length, thickness,
area, and volume estimates as well as the relation of the sphincter
size determined and pelvic floor metrics.
Conclusions noted included the smaller the striated urethral sphincter,
the greater association with female stress incontinence and lesser pelvic
floor muscle function.
The authors, upon review, also found that their population of stress
incontinent women had a higher body mass index than those that were
continent. In addition, other pertinent findings included that aging
was correlated with a shorter striated urethral sphincter and a longer
vesical neck and those plagued with incontinence had a smaller striated
urethral sphincter. The authors have a very interesting discussion section,
including their observation that the increase in the actual area of
the sphincter associated with maturational process is most likely secondary
to an increase in connective tissue and a decrease in the striated muscle
cells. Though larger in diameter, its’ shortness of length may
be one of the factors towards an increase in incontinence. Numerous
authors have also noted the role of striated urethral sphincter and
its effect on voiding function. Reviews on the use of terazosin on females
with voiding dysfunction have noted that perhaps when the medication
fails; it may be secondary to the striated urethral sphincter as opposed
to the bladder neck area (1). Perhaps this may explain the anecdotal
observation of women with voiding dysfunction from a pelvic floor spasms
or failure of relaxation being usually younger in age. In addition,
when one reviews the actual physics of work being defined as work equals
force times length it may make intuitive sense that the shorter striated
sphincter zone, though bulkier, may allow the bladder to expel urine
much easier in a stress situation in view that it requires less actual
work to overcome the sphincteric resistance secondary to the lesser
length.
Reference
1. Kessler
TM, Studer UE, Burkhard FC: The effect of terazosin on functional bladder
outlet obstruction in women: a pilot study. J Urol. 2006; 176: 1487-92.
Dr.
Steven P. Petrou
Professor of Urology, Associate Dean
Mayo School of Graduate Medical Education
Jacksonville, Florida, USA
E-mail: petrou.steven@mayo.edu |