Original Article

Quantification of Levator Ani (LA) Hiatus enlargement and pelvic organs impingement on Valsalva maneuver in parous and nulliparous women with obstructed defecation syndrome (ODS): a biomechanical perspective

  • VITTORIO PILONI
  • VALENTINA AMBROSELLI
  • MANUELA NESTOLA
  • FRANCESCO PILONI

Pelviperineology 2016;35(1):25-31

Aim:

to standardize a method for axial MR multislice image acquisition of female levator ani hiatus on straining in the steady state.

Subjects and Method:

The clinical and imaging series of 41 symptomatic women with evacuation dysfunction, aged 22-56 yrs. (mean 43± 4.1 yrs, median, 43 yrs.) referred for static and dynamic MR imaging between July 2013-June 2014, were reviewed. Of them, 13 were nulliparous (mean age 37±2 yr), the remaining 28 were parous by either vaginal delivery (15, mean age 46±8 yr), cesarean section (8, mean age 46±3 yr), or both (5, mean age 45±5 yr). MR Imaging (Philips, Achieva, 1.5 T, horizontally oriented, the Netherland) was obtained at rest, on evacuation of acoustic gel and during Valsalva maneuver in the steady state using axial, sagittal and coronal sections. Image analysis in the midsagittal plane included (1) quantification of pelvic organs position relative to the hymen plane (mm above [-], or below [+]); and (2) measurement of levator hiatus area (cm2) at rest and on straining in the axial plane from three key images passing through the midsymphysis (level I); tangent to the inferior border of the symphysis (level II); and at the point of the maximal anterior rectal wall bulging (level III), respectively. Characterization of levator ani muscle defects, included presence of thinning, discontinuity and/or focal increase in the MR signal intensity compared to that of the obturator internus muscle. Classification of ODS at MRI into five degrees was used as described in a previous report. Statistics included, among others, the correlation coefficient between hiatus area at rest and on maximal straining in search for potential prediction of hiatus enlargement under the effect of abdominal pressure.

Results:

At rest, considerable overlap occurred in the average values of levator hiatus areas of parous and nulliparous groups (range 17.1±1.4 cm2 to 19.6±3.5 cm2, p >0.005) as opposed to the significant increase (range 108-134%) in all groups seen on Valsalva; however, despite mild difference between parous and nulliparous, a surprising overlap between subjects with vaginal and cesarean delivery (43.1±14.9 cm2 vs 44.2±9.1 cm2, p ns) was noted; in addition, values at rest did not correlate with those on Valsalva (Pearson’s correlation coefficient, Y = 0.37 + 19.27, R2=0.14), indicating that in no case was it possible to predict the actual hiatus enlargement on the basis of resting values. Finally, regardless of parity or not (8/10 nulliparous; 5/8 with cesarean delivery; and 6/15 with vaginal delivery) the levator hiatus ballooning and organs impingement involved mainly the posterior compartment and were most frequently associated with difficulty in rectal emptying and trapping of contrast; interestingly, focal anatomical defects affecting both the muscular and fascial component was seen more frequently in women who delivered vaginally compared to nulliparous and cesarean groups (10/15 [66.6%] vs 2/13 [15.3%] and 1/8 [12.5%], respectively).

Conclusions:

Regardless of parity, delivery history and the onset of symptoms, the existence of difficult evacuation in women makes it unpredictable to establish the actual levator ani hiatus deformity and pelvic organ impingement under the effect of abdominal vector forces until using static and dynamic pelvic MRI.

Keywords: Fast MR pelvic imaging; Childbirth-related defects of pelvic floor; Biomechanics of levator hiatus; Evacuation dysfunctions; Pelvic organ prolapse.