Age effects on urethral striated muscle II. Anatomic location of muscle loss

OBJECTIVE: The purpose of the study was to measure the thickness and cross-sectional area of urethral muscle layers to identify localized striated muscle loss. STUDY DESIGN: The urethra and surrounding tissues from 25 female cadavers (mean age, 52 ± 18 [SD] years; range, 15-80 years) were used for this study. Axial and median sagittal histologic sections were prepared. Median sagittal muscle layer thickness was measured every 10% of urethral length (each decile) in the dorsal wall (adjacent to the vagina) and ventral wall, beginning at the caudal margin of the detrusor muscle (0%) and ending at the caudal margin of the striated muscle (100%). In the midurethral cross-section, the thickness of each layer was measured along radial lines placed every 45 degrees with 0 degrees at the ventral midline and 180 degrees at the dorsal midline. RESULTS: In the median sagittal sections, striated muscle layers of urethras were thinner at the vesical neck in older women. In the ventral wall, it decreased by a mean of 18 to 23 μm (3.4%-4.3%; P < .001) per year at 10% to 30% of urethral wall length. Dorsal striated muscle layers were thinner at every decile by 11 to 16 μm (3.2%-4.3%; P < .05); their total cross-sectional areas decreased by 0.19 mm 2 (3.8%) per year short ( P < .001). In the midurethral cross-sections, the muscle was thinner by 16 to 25 μm (1.5% and 4.6%; P < .05) at 90, 135, and 180 degrees. CONCLUSION: Striated muscle was lost at the bladder neck and along the dorsal wall of the urethra as women aged. (Am J Obstet Gynecol 2002;186:356-60.)