Fig. 6.1
3-D rendering of anal sphincter complex performed 1 week after vaginal delivery with image display on the axial (a) and sagittal (b) plane: arrows point to a hypoechoic defect of the external anal sphincter located at the 11 o’clock position
Fig. 6.2
Tomographic ultrasound imaging (TUI) of anatomic defect (arrow) seen on multiple midsagittal planes
6.2.1.2 Standard Measurements
The following measurements, performed at rest or during functional tests (Kegel and Valsalva maneuver), are taken in the midsagittal plane:
Bladder wall thickness with no more than 20 mL residue (n.v., 5 mm).
Bladder–symphysis distance, defined as the vertical distance between the bladder neck and the horizontal line tangent to the lower margin of the symphysis pubis (n.v., no more than 1 cm above at rest and no more than 1 cm below on straining).
The γ angle, defined as the angle between the inferior edge of the symphysis pubis and the anterior margin of the urethrovesical junction.
The retrovesical (β) angle, defined as the angle between the proximal urethra and the trigonal surface of the bladder.
Diameters and area of the levator hiatus in the axial plane after identification of the so-called plane of minimal hiatal dimension which extend from the posterior margin of the symphysis to the posterior anorectal junction. According to Dietz, a hiatal area exceeding 25 cm2 is considered indicative of abnormal hiatal distensibility.
6.2.1.3 Abnormal Findings
Most common changes seen in the early post vaginal delivery period include the following:
Gaping of the genital hiatus
Absent or reduced ability to perform Kegel or Valsalva maneuver
Asymmetry of the genital area
Unilateral discontinuity of levator limb from tear or avulsion (see Fig. 5.1)
Anal sphincter defect
Fascial detachment
Medium-term (within 6 months) and long-term (after the fourth decade) changes include the following:
Cysto-urethrocele
Rectocele
Enterocele
Funneling of the bladder neck
Vaginal vault prolapse
Sliding of anterior or posterior vaginal wall
Focal scarring of anterior anal canal
6.2.2 Magnetic Resonance Imaging
Thanks to the advances in technology registered during the last two decades which permit rapid image acquisition and display on any plane and to the inherent superior contrast resolution of the technique, MRI is an unsurpassed imaging modality providing unique details of postdelivery pelvic anatomy in a safe and noninvasive manner. Through this, exquisite depiction of all pelvic structures directly involved in parturition can routinely be obtained in a resting state, including the vaginal canal, levator ani muscles, anal sphincters, perineal body, endopelvic fascia, and ligaments. In addition, a dynamic series can also be acquired in the three orthogonal planes while the patient performs a Valsalva maneuver and even during emptying her bladder and/or rectal ampulla [17].
6.2.2.1 Imaging Technique
Postpartum MR scans of the pelvis are usually taken early (within 2 weeks) and late (within 6 months) after delivery with the patient supine using a 1.5-T superconducting conventional (horizontal) magnet system (Philips Medical System, Achieva model, The Netherlands) equipped with high-speed gradients and a surface phased-array coil (Body SENSE XL Torso) wrapped around the patient’s pelvis. A soft rubber catheter, 3 mm in diameter, is gently inserted within the anal canal to act as a luminal marker (early study) and for subsequent contrast administration (late study). Images are obtained in all three planes (sagittal, axial, and coronal) as different, useful information is derived from each. The typical examination is usually conducted on the following lines:
Early Study (Static Examination)
T2-weighted images are obtained first in the sagittal plane to provide a complete evaluation of pelvic floor anatomy using fast recovery spin echo pulse sequence (TR/TE, 3,704/90 ms; FA, 90°; FOV, 320 cm; BW, 253.0; slice thickness, 4 mm; interslice gap, 1 mm; matrix size, 444 × 310; ETL, 18 and 4 excitations; scan time, 2.24 min). Then, following exact localization of the intra-anal catheter, oblique axial and coronal images are taken with the same pulse sequence in a plane perpendicular and parallel to the catheter, respectively, so as to obtain true orthogonal views of the anal sphincter complex (Fig. 6.3) and contemporary differentiation of the various components of the levator ani muscle, i.e., the iliococcygeal, the pubococcygeal, and the coccygeal muscles. Occasionally, a proton density (PD) and a short tau inversion recovery (STIR) pulse sequences are also obtained for better evidence of ligaments anatomy and rule out anovaginal fistula.
Fig. 6.3
Coronal oblique T2-weighted image of the anal sphincter complex allowing clear depiction of the internal and external anal sphincter muscle (1, 2) and iliococcygeal and puborectalis muscle (3, 4), respectively
Late Study (Static + Dynamic Examination)
Following the study described in 3.1.1, intrarectal injection of up to 200 mL of acoustic gel is administered and a BFFE pulse sequence (TR/TE, 2.8/1.39 ms; FA, 90°; BW, 1255.5; slice thickness, 15 mm; matrix size, 160 × 160; image update acquisition, 1/0.891 s; scan time, 48 s and two excitations) is obtained with the patient at rest and during active contraction of pelvic floor musculature (Kegel maneuver). Then, after patient coaching to start the rectal emptying at will and just make notice of it by intercom, contemporary acquisition of images is obtained by the examiner. Using the same pulse sequence, images are also acquired in the oblique coronal plane centered at the anorectal junction (ARJ) during continuous rectal emptying for evidence of any outlet obstruction and excessive rectal floor descent. Finally, the levator ani hiatus is imaged in the horizontal axial plane using a multislice technique (TR/TE, 3.1/1.5 ms; FA, 45; slice thickness, 10 mm; BW, 1041.7; matrix, 160 × 160; NEX, 2 excitations; N° of slices, 3–4; scan time, 14.9 s) with section planes located at the superior margin of the symphysis pubis (upper level), at its inferior margin (central level), and at the perineal body (lower level) while the patient is asked to strain maximally (Valsalva maneuver) in a steady state. A complete summary of the standard imaging protocol described above is presented in Table 6.1.
Table 6.1
Protocol for pelvic floor MRI after vaginal delivery by Philips Achieva scanner (1.5 T) and SENSE XL TORSO coil
Parameter | Series 1 | Series 2 | Series 3 | Series 4 | Series 5 | Series 6 | |
|---|---|---|---|---|---|---|---|
Study type | Static | Static | Static | Dynamic | Dynamic | Dynamic | |
Plane | Sagittal | Coronal oblique | Axial oblique | Mid sagittal | Mid coronal | Axial multislice | |
TR (ms) | 4,435 | 3,649 | 4,656 | 2.8 | 2.8 | 3.1 | |
TE (ms) | 100 | 100 | 100 | 1.3 | 1.3 | 1.5 | |
BW | 253.0 | 172.6 | 252.4 | 1225.5 | 1225.5 | 1041.7 | |
ETL | 18 | 18 | 18 | 17 | 17 | 17 | |
NEX | 4 | 4 | 4 | 2 | 2 | 2 | |
FOV (FH-RL-AP) | 250*250*177 | 250*250*138 | 250*250*173 | 260*260*134 | 250*250*-112 | 250*250*112 | |
Matrix | 560 (256*246) | 560 (264*270) | 560 (264*270) | 336 (192*181) | 320 (160*153) | 336 (160*153) | |
Slice/gap (mm) | 3.70–0.13 | 3.5–0.35 | 3.5–0.35 | 10 | 10 | 10 | |
Flip angle (°) | 90 | 90 | 90 | 45 | |||
Scan time (sec) | 148 | 148 | 174 | 48 | 48 | 14.9 | |
Slices (n°) | 20 | 20 | 20 | 50 | 50 | 3 | |
Pulse sequence | FSE T2-W | FSE T2-W | FSE T2-W | BFFE | BFFE | BFFE | |
Fold over direction | F → H | R → L | R → L | R → L | R → L | A → P | |
Notes: F foot, H head, R right, L left, A anterior, P posterior, FSE fast spin echo, BFFE balance fast field echo, T2-W T2-weighted
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