A technique to evaluate the thickness and density of nonvascular smooth muscle in the suburethral fibromuscular layer

OBJECTIVE: The suburethral fibromuscular layer (SUFML) contains nonvascular smooth muscle that may play an important role in the continence mechanism. This study was undertaken to develop a method to systematically quantify differences in the thickness and density of nonvascular smooth muscle within the SUFML and to demonstrate its use in assessing variation. STUDY DESIGN: Urethral and anterior vaginal wall sections from the urethrovesical junction of fresh cadavers were stained to define alpha actin in smooth muscle cells. The thickness of the SUFML was microscopically measured and the density of the nonvascular smooth muscle was determined with computer-aided analysis. RESULTS: The mean thickness of the SUFML was 3.04 mm (range 1.74-3.78 mm, SD +/-0.63 mm). The mean density of nonvascular smooth muscle within it was 17.94% (range 10.48%-42.84%, SD +/-9.4%). The mean age was 55 years (range 36-69 years, SD +/-10.75 years). CONCLUSION: The thickness and density of the nonvascular smooth muscle within the SUFML can be quantified and there is variation among individuals.