DOI:10.2214/AJR.07.3773
AJR 2008; 191:1469-1476
© American Roentgen Ray Society
Postoperative Pelvic MRI of Anorectal Malformations
Mohamed A. Eltomey1,
Lane F. Donnelly2,
Kathleen H. Emery2,
Marc A. Levitt3 and
Alberto Peña3
1 Department of Radiology and Imaging, Medical Compound, Faculty of Medicine,
Tanta University, Elbahr St., Tanta, Egypt 31511.
2 Department of Radiology, Cincinnati Children's Hospital Medical Center,
Cincinnati, OH.
3 Colorectal Center, Division of Pediatric Surgery, Cincinnati Children's
Hospital Medical Center, Cincinnati, OH.
Received February 5, 2008;
accepted after revision May 30, 2008.
Address correspondence to M. A. Eltomey
(meltomey{at}yahoo.com).
Abstract
OBJECTIVE. Patients operated on for anorectal malformations can
experience technical complications related to the initial corrective surgery.
Many of these complications may necessitate reoperation. Pelvic MRI is part of
the evaluation to assess the position of the pulled-through bowel, the
sphincter muscles, and the critical area of the posterior urethra. This
article reviews the various pelvic MRI findings in these patients.
CONCLUSION. Pelvic MRI is a valuable tool in the assessment of
postoperative anorectal malformations that may necessitate additional
surgery.
Keywords: anorectal malformations • pelvic MRI • postoperative complications
Introduction
Anorectal malformations encompass a diverse group of congenital
malformations of the ano rectum. They are frequently as so ci ated with other
anomalies, especially of the spinal cord, vertebrae, and urogenital system.
Anorectal malformations occur in one in 5,000 patients and have a slight
predominance among boys [1,
2]. The goals of surgical
correction are to promote anatomic reconstruction, establish socially
acceptable bowel function, and avoid undesirable sequelae such as fecal
incontinence, urinary incontinence, and sexual dysfunction
[3]. Despite advances in the
management of ano rectal malformations, some patients have technical
complications. Failed initial repairs of anorectal malformations may
necessitate additional surgical intervention. The indications for reoperation
include rectal mislocation; strictures or acquired atresia of the rectum,
vagina, or urethra; persistent, recurrent, and acquired fistulas; posterior
urethral diverticulum; rectal prolapse; persistent cloaca; and persistent
urogenital sinus in patients with persistent cloaca
[4].
Pelvic MRI is a useful a tool for assessment of anorectal malformations
before and after the initial repair
[5]. Advantages include
excellent inherent soft-tissue contrast enhancement, multiplanar imaging
capabilities, and lack of ionizing radiation. Disadvantages of MRI include
cost, the relatively frequent need for sedation, and lack of access to the
technique in some locations. Pelvic MR images obtained because of
postoperative complications are reviewed for quality and shape of the
sphincter muscle, position of the rectum, shape of the sacrum, and associated
pelvic abnormalities related to the initial operation.
Technique
Pelvic MRI of patients who have undergone surgical repair of anorectal
malformations is performed with high-resolution phased-array coils, such as
eight-channel cardiac or torso phased-array coils. The imaging protocol
includes T1- and fast or turbo spin-echo T2-weighted sequences in the axial,
sagittal, and coronal planes. To highlight the low-signal-intensity muscle and
bowel wall against the higher-signal-intensity fat and mucosa, fat saturation
is not used. The surgeon is interested in the midsagittal section because it
is the plane used for the operative approach. An optional sequence is oblique
coronal T2-weighted images angulated in line with the anal canal when further
clarification of the sphincter–bowel relation is necessary. Axial
T2-weighted images with fat suppression may be helpful for differentiating
associated anomalies of the lower genitourinary tract. Except in the uncommon
instance of postoperative anal atresia, a 24-French Foley catheter is advanced
through the anus into the rectum. For safety, the balloon is not inflated, and
a small amount of tap water (high signal intensity on T2-weighted images) is
instilled in the catheter lumen to facilitate identification of the bowel
lumen in relation to the sphincter muscle complex.
Findings
Muscle Quality and Shape
The anatomic features of the anal sphincter mechanism are complex,
including voluntary striated muscles and involuntary smooth muscle. Children
with anorectal malformations have variable degrees of striated muscle
development from near-normal muscles to complete absence of the sphincter
muscle [6]. The striated muscle
component of the sphincter mechanism is well assessed with MRI. Assessment of
muscle quality is subjective and based on internal comparison for symmetry,
comparison with pelvic MR images of healthy persons, and ease or difficulty of
visualization of the muscles in the different planes. The sphincter muscle
complex is best seen on axial images at the level of the symphysis pubis and
below [3] (Figs.
1A,
1B,
1C and
2A,
2B). Coronal and sagittal
images are necessary to verify findings on the axial images and to assist in
ascertaining the location of the bowel in relation to the muscles (Figs.
3A,
3B and
4A,
4B).
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Fig. 1A —5-year-old boy with normal sphincter and pelvic muscles.
Coronal T2-weighted MR image of pelvis shows pelvic floor muscles
(arrows) with shape of inverted umbrella and rectal ampulla resting
over it. Structure of voluntary muscles (arrowheads) surrounding anal
canal is evident.
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Fig. 1C —5-year-old boy with normal sphincter and pelvic muscles.
Axial T2-weighted MR image of pelvis at level of inferior pubic ramus shows
sphincter around anal canal (arrows) and transverse superficial
perineal muscles (arrowheads).
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Fig. 3A —3-year-old girl with poorly developed sphincter muscles after
repair of cloacal anomaly. Axial T2-weighted MR image of pelvis shows absence
of sphincter mechanism, denoting its poor development on both sides
(arrowheads). Asterisk indicates Foley catheter within lumen of
bowel.
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Fig. 3B —3-year-old girl with poorly developed sphincter muscles after
repair of cloacal anomaly. Coronal T2-weighted MR image shows bilateral poor
delineation of pelvic floor muscles (arrows) and thinning of
sphincter mechanism.
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Fig. 4A —5-month-old boy with asymmetric sphincter muscles after
repair of high anorectal anomaly (rectoprostatic fistula). Axial T1-weighted
MR image of pelvis shows fair development and asymmetry of sphincter mechanism
(arrows), which is thicker on left side compared with right. Rectum
is located centrally within sphincter.
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Fig. 4B —5-month-old boy with asymmetric sphincter muscles after
repair of high anorectal anomaly (rectoprostatic fistula). Coronal T2-weighted
MR image of pelvis shows fair development of sphincter muscles
(arrowheads).
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Location of Pulled-Through Bowel
After identification of the muscles of the sphincter mechanism, it is
important to assess the relation between the sphincter and the pulled-through
bowel. Malpositioning of the rectal pull-through can be identified on axial,
coronal, and sagittal images. Axial and coronal images best show side-to-side
displacement of the bowel. Sagittal images help in assessment of
anteroposterior displacement of the bowel in relation to the sphincter (Figs.
5A,
5B,
6A,
6B,
7A,
7B). The most commonly
reported error is anterior misplacement of the pulled-through bowel within the
sphincter [4]. In some cases,
the bowel is properly located but mesenteric fat inadvertently pulled with
bowel through the sphincter during the initial repair interferes with the
continence mechanism [5]. Axial
T1- and T2-weighted images without fat saturation show this fat as a halo of
high signal intensity surrounding the wall of the pulled-through bowel (Figs.
8 and
9).
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Fig. 5A —8-year-old boy with eccentric location of bowel after repair
of high anorectal anomaly (rectal–bladder neck fistula). Axial
T1-weighted MR image of pelvis shows irregular shape and asymmetry of
sphincter muscle (arrow). Rectum has eccentric location
(arrowhead) to left side of sphincter.
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Fig. 5B —8-year-old boy with eccentric location of bowel after repair
of high anorectal anomaly (rectal–bladder neck fistula). Coronal
T2-weighted MR image of pelvis and lower abdomen shows poorly developed
irregular and asymmetric muscles (arrow) and eccentric location
(arrowhead) of rectum.
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Fig. 6A —6-year-old boy with misplacement of bowel through sphincter
after repair of high anorectal anomaly. Axial T2-weighted MR image of pelvis
shows fairly well developed and asymmetric sphincter, which is thicker on left
side (arrow). Rectum is posterior and to right of sphincter muscle
(arrowhead) at this level.
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Fig. 6B —6-year-old boy with misplacement of bowel through sphincter
after repair of high anorectal anomaly. Axial T2-weighted MR image of pelvis
at level of inferior pubic ramus shows fairly developed sphincter
(arrow). Anal canal (arrowhead) is situated eccentrically to
right and anterior to sphincter at this level.
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Fig. 7A —33-year-old man with anteriorly and laterally misplaced bowel
after repair of high anorectal anomaly. Axial T1-weighted MR image of pelvis
shows poorly developed sphincter (arrow). Anal canal is anterior and
to left of muscle (arrowhead). Fatty infiltration of gluteal muscles
is present on both sides.
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Fig. 7B —33-year-old man with anteriorly and laterally misplaced bowel
after repair of high anorectal anomaly. Sagittal T1-weighted MR image of
pelvis shows poorly developed sphincter (arrow) and anal canal
anterior to sphincter. Catheter in bowel lumen facilitates visualization of
lumen.
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Fig. 8 —10-year-old boy with pulled-through fat after repair of high
anorectal anomaly. Axial T1-weighted MR image of pelvis shows fairly developed
and asymmetric sphincter muscles. Rectum is in central location within
sphincter with fat visible as area of high signal intensity (arrows)
around sphincter.
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Fig. 9 —2-year-old boy with pulled-through fat after repair of high
anorectal anomaly. Axial T1-weighted MR image of pelvis shows fairly developed
symmetric sphincter. Rectum is central within pelvis with fat
(arrows) circumferentially surrounding it.
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Persistent Fistula and Posterior Urethral Diverticulum
Anorectal anomalies in boys usually are associated with a fistula between
the terminal part of the bowel and the urinary tract. This fistula may not be
visualized during the initial surgical repair, leading to inadequate
resection. Lack of fistula identification is frequently due to improper
performance of preoperative distal colostography
[7,
8]. Incomplete resection of a
fistula results in a persistent fistula or, when a segment of the terminal
rectum is left attached to the urethra, posterior urethral diverticulum
[4]. Identification of such a
diverticulum on MRI depends on its size. A small diverticula can be missed,
and a large one can manifest as a masslike lesion of variable signal
intensity—depending on whether the contents are fluid, mucus, or
debris—between the urinary bladder and the rectum (Figs.
10A,
10B,
11A,
11B,
12A,
12B).
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Fig. 10A —3-year-old boy with posterior urethral diverticulum after
repair of high anorectal anomaly (rectoprostatic fistula). Sagittal
T1-weighted MR image of pelvis shows large hypointense masslike lesion
posterior to bladder and anterior to rectum. Dysplastic shape of sacrum is
evident.
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Fig. 10B —3-year-old boy with posterior urethral diverticulum after
repair of high anorectal anomaly (rectoprostatic fistula). Axial T1-weighted
MR image shows well-defined hypointense masslike lesion (arrow)
displacing rectum to right. Lesion was proved at surgery to be posterior
urethral diverticulum (former distal rectum attached to urethra) related to
inadequate initial resection. Asterisk indicates Foley catheter within bowel
lumen.
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Fig. 11A —16-year-old boy with posterior urethral diverticulum after
repair of high anorectal anomaly (rectoprostatic fistula). Sagittal
T1-weighted MR image of pelvis shows isointense masslike lesion
(arrow) posterior to bladder neck and anterior to rectum.
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Fig. 11B —16-year-old boy with posterior urethral diverticulum after
repair of high anorectal anomaly (rectoprostatic fistula). Axial T2-weighted
MR image at level of prostate shows well-defined isointense to slightly
hyperintense masslike lesion (arrow) posterior to prostate and
anterior to rectum. Mass displaces rectum laterally to left. Lesion was proven
at surgery to be posterior urethral diverticulum (former distal rectum
attached to urethra) related to inadequate initial resection.
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Fig. 12A —5-month-old boy with small posterior urethral diverticulum
manifesting as acquired atresia of anus after repair of high anorectal anomaly
(rectoprostatic fistula). Sagittal T2-weighted MR image of pelvis shows subtle
irregularity in posterior aspect of prostatic urethra (arrow).
Well-developed sphincter and absence of segments of sacrum are evident.
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Fig. 12B —5-month-old boy with small posterior urethral diverticulum
manifesting as acquired atresia of anus after repair of high anorectal anomaly
(rectoprostatic fistula). Voiding cystourethrogram shows diverticulum-shaped
area (arrow) of prostatic urethra corresponding to irregularity in
A. Surgery revealed posterior urethral diverticulum related to
inadequate initial repair.
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A fistula also can be acquired as the result of inadequate repair of a
complex anomaly such as cloacal malformation. A fistula can appear as a linear
area of high signal intensity on T2-weighted images with or without fat
saturation if filled with fluid. Fistulas can easily be missed at MRI. The
reported sensitivity of detection of fistulas with MRI in patients with
anorectal malformations is low
[5]. Fluoroscopic studies
remain the reference standard for preoperative and postoperative fistula
detection in patients with anorectal malformations
(Fig. 13).
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Fig. 13 —5-year-old girl with dribbling of urine and incontinence due
to acquired fistula after repair of cloacal anomaly. Axial T2-weighted MR
image of pelvis shows linear area of high signal intensity representing
fistula between urethra and vagina, which is filled with urine
(arrow). Asymmetry of sphincter complex and displacement of rectum to
right side (arrowhead) are evident. Surgery revealed acquired fistula
related to inadequate initial repair. Asterisk indicates Foley catheter within
bowel lumen.
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Sacrum and Presacral Masses
As many as one half of patients with anorectal malformations have sacral
abnormalities. There is an excellent correlation between the degree of
skeletal sacral anomaly and the functional prognosis for a neonate with an
anorectal malformation [9]. The
Currarino triad is an example of a specific anomaly of the sacrum. The triad
consists of scimitar sacrum, anal stenosis, and a presacral mass (e.g.,
lipoma, lipomeningocele) [10,
11]. The presacral mass
occasionally is missed during the initial repair if preoperative
investigations have been inadequate. MRI can show the presence of a presacral
mass and the degree of sacral development (Fig.
14A,
14B).
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Fig. 14A —18-month-old boy with missed presacral mass after repair of
rectal stenosis. Sagittal T1-weighted (A) and axial T2-weighted
(B) MR images show sacrum missing last segment. Oval mass
(arrow) at tip of sacrum is isointense in A and hyperintense
in B. Mass was surgically removed and proven to be teratoma. Dysplastic
shape of sacrum is evident in A.
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Fig. 14B —18-month-old boy with missed presacral mass after repair of
rectal stenosis. Sagittal T1-weighted (A) and axial T2-weighted
(B) MR images show sacrum missing last segment. Oval mass
(arrow) at tip of sacrum is isointense in A and hyperintense
in B. Mass was surgically removed and proven to be teratoma. Dysplastic
shape of sacrum is evident in A.
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Genitourinary Anomalies
MRI depicts associated urologic anomalies of primary developmental origin
or due to neurovesical dysfunction. There is a 20–54% incidence of
associated genital anomalies with anorectal malformations
[9]. This incidence increases
to 90% in cloacal malformations
[6]. Hydrocolpos is a frequent
finding in such patients and usually appears on T2-weighted images as a
fluid-distended structure between the urinary bladder and rectum. Vaginal and
uterine septation or duplication is frequently seen on MR images
(Fig. 15).
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Fig. 15 —4-year-old girl with multiple genitourinary anomalies after
repair of cloacal anomaly. Axial T2-weighted MR image of pelvis shows two
hemivaginas (arrowheads) with retained fluid (hydrocolpos).
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MRI evidence of an overdistended or thickened bladder wall can indicate
cystitis due to associated neurovesical dysfunction. Congenital anomalies of
the urinary bladder, such as duplication, although rare, also can be seen, as
can undescended testis [12].
Associated genital anomalies not managed at the initial repair should be
addressed. Knowledge of their presence is important for overall management of
these complex cases (Fig.
16).
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Fig. 16 —4-year-old boy with multiple genitourinary anomalies after
repair of high anorectal anomaly (rectal–bladder neck fistula). Axial
T2-weighted MR image of pelvis shows left hemibladder (arrow) and
right undescended testis (arrowhead). Fairly developed sphincter
mechanism and eccentric location of rectum on left side in relation to
sphincter are evident. Asterisk indicates Foley catheter within bowel
lumen.
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Conclusion
Pelvic MRI is a useful tool for assessing postoperative anorectal
malformations in patients with surgical complications. It is helpful in
assessing pelvic muscle quality, the position of the bowel, sacral
abnormalities, and associated genitourinary anomalies frequently seen in these
patients. A simple protocol including axial, sagittal, and coronal T1- and
T2-weighted MR images without fat saturation obtained with high-resolution
phased-array coils typically depicts the important anatomic structures and
aids in planning of optimal patient care.
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Abstract
Introduction
