Department of Obstetrics and Gynecology

University of Michigan Health System

Objective: Evaluate the thickness and density of smooth muscle in the sub-urethral fascia and describe its variability.

Methods: The urethra and vagina were harvested en bloc from 10 adult cadavers within 24 hours of death. They were sectioned at the level of the upper urethra, and an alpha actin stain was used to define smooth muscle cells. The fascia between the vaginal mucosa and urethra was analyzed at 5 equally spaced locations between the midline and the paraurethral sulcus along lines perpendicular to the plane of the fascia. The thickness of the layer was microscopically measured using a Vernier scale. Density of smooth muscle was determined by digitally capturing contiguous rectangular high power (400x) fields along the sampling lines. After blood vessel smooth muscle was excluded, the proportion of actin stained pixels within each microscopic field was analyzed.

Results: Smooth Muscle Thickness: The thickness of the suburethral fascia ranges from 1.74 to 3.78mm with a mean of 3.04mm (SD+/-0.63mm). The range of the mean value is 67% (Max-Min/Mean x 100). The standard deviation of the thicknesses measured at the five different sites is 0.51mm (SD+/-0.16mm) amongst all specimens. Smooth Muscle Density: The density of the nonvascular smooth muscle, measured by the percentage of actin stained pixels in the suburethral fascia, ranges from 10.48% to 42.84 with a mean of 17.94% (SD +/- 9.4%). This represents a 180% range of the mean value. The standard deviation of smooth muscle density at the five sampling sites is +/-2.2% amongst all specimens.

Conclusions: The smooth muscle in the EPF varies considerably from one individual to another with a greater variation in density than in thickness. Comment: Although 17% may seem low, the same proportion of smooth muscle is found in the

smooth muscle layers of the urethra. The reasons for the considerable variation among individuals are not known. A larger sample size will be needed to gain further insight.

Future Plans - Dr. Morgan will remain at the University of Michigan's Department of Gynecology for a fellowship in Urogynecology.

*Dr. Daniel Morgan presented this research at the 2001 University of Michigan Paper Day, May 9, 2001