Appearance of the levator ani muscle subdivisions in magnetic resonance images.

OBJECTIVE: Identify and describe the separate appearance of 5 levator ani muscle subdivisions seen in axial, coronal, and sagittal magnetic resonance imaging (MRI) scan planes. METHODS: Magnetic resonance scans of 80 nulliparous women with normal pelvic support were evaluated. Characteristic features of each Terminologia Anatomica-listed levator ani component were determined for each scan plane. Muscle component visibility was based on pre-established criteria in axial, coronal, and sagittal scan planes: 1) clear and consistently visible separation or 2) different origin or insertion. Visibility of each of the levator ani subdivisions in each scan plane was assessed in 25 nulliparous women. RESULTS: In the axial plane, the puborectal muscle can be seen lateral to the pubovisceral muscle and decussating dorsal to the rectum. The course of the puboperineal muscle near the perineal body is visualized in the axial plane. The coronal view is perpendicular to the fiber direction of the puborectal and pubovisceral muscles and shows them as "clusters" of muscle on either side of the vagina. The sagittal plane consistently demonstrates the puborectal muscle passing dorsal to the rectum to form a sling that can consistently be seen as a "bump." This plane is also parallel to the pubovisceral muscle fiber direction and shows the puboperineal muscle. CONCLUSION: The subdivisions of the levator ani muscle are visible in MRI scans, each with distinct morphology and characteristic features.

Can women without visible pubococcygeal muscle in MR images still increase urethral closure pressures?

OBJECTIVE: The purpose of this study was to determine if the ability to increase maximum urethral closure pressure (MUCP) with a pelvic muscle contraction is impaired in women without pubococcygeal muscle (PCM). STUDY DESIGN: This was a cross-sectional study of continent women comparing those with (n=28) and those without (n=17) PCM as identified by MR scans. A pelvic muscle contraction was performed simultaneously with recordings of urethral and bladder pressures. RESULTS: Eighty-six percent of the women with PCM compared with 41% of the women without could volitionally increase (>5 cm H(2)O) their MUCP. Those with PCM generated a mean intraurethral pressure rise of 14.0 (10.8) cm H(2)O, compared with 6.2 (8.7) cm H(2)O in those without (P=.015). Among women who could produce a visible pressure rise, there was not a statistically significant difference between groups (with PCM=17.2 [7.8] cm H(2)O; without PCM=14.7 [7.5] cm H(2)O; P=.457). CONCLUSION: Selective women without visible PCM can increase MUCP.

Quantitative analysis of uterosacral ligament origin and insertion points by magnetic resonance imaging.

OBJECTIVE: To estimate the percentage of healthy women in whom the uterosacral ligaments are identifiable on standard magnetic resonance imaging (MRI) scans and to determine origin points from the genital tract and insertion points on the pelvic sidewall. METHODS: Eighty-two asymptomatic women (mean +/- standard deviation age 53 +/- 12 years; mean parity 2.5, range 0-7) volunteered for this study. They were eligible if the most dependent vaginal wall point lay at least 1 cm above the hymenal ring remnant during a Valsalva maneuver. Axial proton density MRI of the entire pelvis was analyzed at 5-mm intervals. All results were referenced to the ischial spine. We determined the visibility of the uterosacral ligaments and located their origins from the genital tract and their insertion points on the pelvic sidewall. RESULTS: Uterosacral ligaments were visible in 61 (87%) of 70 analyzable scans. They extended over a mean craniocaudal distance of 21 +/- 8 mm (range 10-50). Three regions of origin were found: cervix alone, cervix and vagina in the same section, and vagina alone. Thirty-three percent, 63%, and 4% of 254 identified origin points were from these three areas, respectively. Of 259 uterosacral insertion points, 82% overlaid the sacrospinous ligament/coccygeus muscle complex, 7% the sacrum, and 11% the piriformis muscle, the sciatic foramen, or the ischial spine. Although uterosacral ligament morphology was similar bilaterally, its craniocaudal extent was greater on the right side. CONCLUSION: In healthy women, the uterosacral ligament origin and insertion points exhibited greater anatomic variation than their name would imply.

The axial location of structural regions in the urethra: a magnetic resonance study in nulliparous women.

OBJECTIVE: To define and quantify the appearance and location of distinct regions of the bladder neck and urethra by using axial magnetic resonance images from healthy, continent, nulliparous women. METHODS: Seventy-eight asymptomatic, healthy, nulliparous women (mean age 29.2 +/- 5.4 years) volunteered for this study. All women were proven continent on urodynamic examination. Axial proton density magnetic resonance images of the pelvic floor were analyzed at 5-mm intervals. A geometric origin was established at the internal urethral meatus. The presence or absence of each of six structural regions--the bladder base, bladder neck, striated urethral sphincter, compressor urethrae and urethrovaginal sphincter, perineal membrane, and distal urethra--was then noted in each more distal image. The proportion of women in whom a structural region was seen at each 5-mm interval was recorded. RESULTS: The striated urogenital sphincter was observed at 5-25 mm distal to the bladder base. It was observed 10 and 15 mm below the bladder base in 91% (95% confidence interval [CI] 85%, 98%) and 99% (95% CI 97%, 100%), respectively, of all women. The perineal membrane, marking the distal end of the muscular urethra, was located 20-35 mm distal to the bladder base. The length of the muscular region of the urethra ranged from 20 to 35 mm (mean 24 mm, 95% CI 24, 25 mm). CONCLUSION: Magnetic resonance images allow the normal appearance and location of urethral and bladder neck structures to be quantified in healthy, continent, nulliparous women.

The urethra during pelvic floor contraction: observations on three-dimensional ultrasound.

OBJECTIVE: To investigate with three-dimensional ultrasound how voluntary pelvic floor contractions influence the morphology of the female urethra's components. METHODS: Twenty female patients with benign gynecologic disorders (mean age: 29 years; range: 19-40) had transrectal sonography using a 7.5-MHz mechanical sector endoprobe with three-dimensional features during both pelvic floor muscle relaxation and pelvic floor muscle contraction. The multiplanar display of the scanned volumes allowed detailed morphologic assessment of the urethra and the measurement of distances and volumes of the urethral components. Statistical end points were maximum sagittal and transverse urethral diameter, maximum sphincter length and thickness, maximum smooth muscle thickness, and the volumes of the sphincter, the smooth muscle, and the entire urethra. RESULTS: All 20 rectal scans were feasible. Two patients had to be excluded from analysis because of poor image quality, leaving 18 patients for evaluation. When compared with pelvic floor relaxation, the following measures were smaller during pelvic floor contraction: sagittal urethral diameter (10.4 versus 11.5 mm; P =.004), transverse urethral diameter (14.1 versus 15.0 mm; P =.009), urethral sphincter thickness (2.4 versus 2.7 mm; P =.012), urethral sphincter volume (0.5 versus 0.6 mL; P =.003), and total urethral volumes (1.4 versus 1.5 mL; P =.007). Sphincter length and smooth muscle thickness, as well as smooth muscle volume, did not change significantly during pelvic floor contraction. CONCLUSION: On three-dimensional ultrasound, the morphologic changes of the female urethra during pelvic floor contraction suggest external compression of the urethra rather than contraction of the sphincter muscle.