Structural Failure Sites in Anterior Vaginal Wall Prolapse: Identification of a Collinear Triad.

OBJECTIVE: To test the null hypothesis that six factors representing potential fascial and muscular failure sites contribute equally to the presence and size of a cystocele: two vaginal attachment factors (apical support and paravaginal defects), two vaginal wall factors (vaginal length and width), and two levator ani factors (hiatus size and levator ani defects).
METHODS: Thirty women with anterior-predominant prolapse (women in a case group) and 30 women in a control group underwent three-dimensional stress magnetic resonance imaging. The location of the anterior vaginal wall at maximal Valsalva was identified with the modified Pelvic Inclination Coordinate System and the six factors measured. Analysis included repeated-measure analysis of variance, logistic regression, and stepwise linear regression.
RESULTS: We identified a collinear triad consisting of apical location, paravaginal location, and hiatus size that were not only the strongest predictors of cystocele size, but were also highly correlated with one another (r=0.84-0.89, P<.001) for the presence and size of the prolapse. Together they explain up to 83% of the variation in cystocele size. Among the less significant vaginal factors, vaginal length explained 19% of the variation in cystocele size, but no significant difference in vaginal width existed. Women in the case group were more likely to have abnormalities in collinear triad factors (up to 80%) than vaginal wall factors (up to 23.3%). Combining the strongest collinear triad with the vaginal factors, the model explained 92.5% of the variation in cystocele size.
CONCLUSION: Apical location, paravaginal location, and hiatus size are highly correlated and are strong predictors of cystocele presence and size.