Morphometric Analysis of Smooth Muscle in the Posterior Vaginal Wall of Women with Pelvic Organ Prolapse
Drs. M. Boreham, C. Wai, J. Schaffer, R. Word
University of Texas Southwestern
Dallas, Texas

Objective: To compare the smooth muscle content of the posterior vaginal wall in normal women and women with pelvic organ prolapse. 
Material and Methods: Full-thickness specimens were taken from the apex of the posterior vaginal cuff after hysterectomy from 12 women with pelvic organ prolapse and 6 controls.  Smooth muscle cells of the posterior vaginal wall were identified by immunohistochemistry with antibodies to smooth muscle a-actin.  Morphometric analysis of histologic cross-sections of the posterior wall was used to determine the fractional area of nonvascular smooth muscle.  Statistical comparisons between two groups were conducted by a Student’s t-test.  Prolapse was staged according to pre-operative POP-Q examination results.  Comparisons between multiple groups were conducted with a one-way analysis of variance (ANOVA) followed by post-hoc Student Neuman Keuls test. 
Results: The fractional area of nonvascular vaginal smooth muscle in the muscularis of women with prolapse of the posterior vaginal wall (³Stage 2) was significantly decreased compared with that of controls (0.18 ± 0.02 vs. 0.51 ± 0.05, P £.0.02).  In women without genital prolapse, smooth muscle cells were organized in discrete, tightly packed bundles oriented in a circular or longitudinal direction.  In women with prolapse of the posterior vaginal wall, SM bundles were poorly organized with extensive deposition of extracellular matrix between bundles.  In women with isolated anterior compartment prolapse (i.e., posterior wall £ Stage 1), the fraction of smooth muscle in the posterior vagina was similar to controls (0.48 ± 0.08). 
Conclusion: The fraction of smooth muscle in the muscularis of the posterior vaginal wall is significantly decreased in women with posterior prolapse.  This alteration of smooth muscle content appears to be a focal process occurring in the prolapsed tissue as opposed to a global process involving the entire vaginal musculature.
Keywords:  prolapse, vagina, smooth muscle, microscopic anatomy, immunohistochemistry