Anorectal Malformations - Radiology

1. Anorectal Malformations: Finding
the Pathway out of the Labyrinth
Dr. Mohit Goel
JR II
14/11/13

2. Anorectal malformations (ARMs) are a complex group of congenital
anomalies involving the distal anus and rectum, as well as the urinary and
genital tracts in a significant percentage of cases.
Urogenital abnormalities are the most frequently observed and appear in
up to 60% of patients, with vesicoureteral reflux and hydronephrosis the
most common findings.
The spine and spinal cord are also often involved, with agenesis and
dysplasia of the sacrum, vertebral dysplasia, and tethered cord syndrome
the most frequently detected problems.
ARMs are also present in a great number of syndromes and associations of
multisystemic congenital anomalies

5. Embryology
allantois
cloacal
membrane
cloaca
urorectal septum

6. allantois
Rathke
fold
Tourneux
fold
urorectal
septum

7. primitive urogenital
sinus
perineal area
anus
rectum
urorectal septum

8. Embryologically, ARMs can thus be subdivided into two main groups
according to when the disturbances occur:
Those manifesting as an ectopic anal orifice or fistula are due to early
abnormal development of the dorsal part of the cloaca and the cloacal
membrane (at weeks 4–7),
whereas those manifesting as an abnormal anus in a normal position are
due to later defective recanalization of the secondary occluded anal orifice
(at weeks 7 and 8).

9. Classification of ARMs
Possible locations of fistulas in males with ARMs according to the Krickenbeck
classification.
(a) Low-type ARMs have an external anocutaneous opening in the scrotum (1) or
perineum (2, 3).

10. (b) Intermediate- and high-type ARMs extend anteriorly to the base of the penis (1),
the bulbar (2) or prostatic (3) urethra, or the urinary bladder (4).

11. Possible locations of fistulas in females with ARMs according to the Krickenbeck
classification.
(a) Low-type ARMs have an external opening in the perineum (1) or vestibular area
(2).

12. (b) Cloacal anomaly is a complex anatomic disorder that manifests as a unique
external perineal opening with a short (1) or long (2) common canal for the genital,
urinary, and digestive systems. Isolated rectovaginal fistulas are extremely rare and
are considered a variant of cloacal anomaly.

13. ARMs involving a rectal pouch located below the level of the
puborectalis muscle, regardless of whether they are
associated with a fistula—perineal or vestibular—are
considered low-type ARMs.
They may be managed early with a perineal approach involving
opening of the rectal pouch and ligature of the fistula, if present.
A rectal pouch lying at or above the level of the puborectal
sling is considered an intermediate or high type of ARM;
it is treated with colostomy in the first days of life and with
posterior sagittal anorectoplasty alone or combined with
laparoscopic abdominoperineal rectoplasty in a second intervention

14. Role of Imaging in Initial Evaluation of
ARMs
Cloacal anomaly in a female fetus.

16. Imaging studies in the first 2 days of life should include radiography
of the thorax, spine, and pelvis along with cardiac, perineal,
abdominal, pelvic, and spine US to detect possible associated
anomalies.
In cases of vertebral or sacral anomalies, spinal MR imaging should be
performed.

19. Perineal US is an excellent method for evaluating the location of the distal
rectal pouch and the anatomy and location of any rectourogenital fistulas.
It is usually performed with a 10–12-MHz high-resolution linear-array
transducer by using the transperineal approach, with the child in a supine
position and the pelvis and legs elevated.
The bowel-skin distance between the rectal pouch and the anus is then
measured in the midline sagittal plane through the perineum.
A distance of greater than 15 mm indicates a high type of ARM, whereas a
distance of less than 15 mm suggests a low type of malformation.
However, any straining or crying by the patient during the examination can
increase the intraabdominal pressure, displacing the distal rectal pouch to the
perineum and shortening this distance. Fistulas may be identified as linear tracts
connecting the rectal pouch to the bladder, urethra, or posterior wall of the vagina.

20. US evaluation of the urinary tract is limited in the first 24 hours after
birth, as upper tract dilatation may be initially absent because of the
physiologic dehydration and reduced urinary output of the newborn.
Detection of any genitourinary anomalies will require complementary
voiding cystourethrography (VCUG)
Spinal US is currently accepted as a safe and inexpensive screening test
for detection of spinal dysraphism. The method provides accurate
information about the morphology and integrity of the os sacrum and
distal vertebral column and allows identification of the level of the
medullary cone and demonstration of a presacral mass.

21. Pelvic Muscle Anatomy: MR Imaging Correlation
The transverse pubococcygeal
plane connects the upper border of
the symphysis pubis (P) with the os
coccyx (C) and is the most
important reference in evaluation of
the pelvic musculature.
Axial images should be obtained
parallel to this plane (horizontal
red line); coronal images should be
obtained perpendicular to it
(vertical red line).

23. Normal anatomy of the pelvic floor musculature.
(a) Axial T2-weighted MR image in the pubococcygeal plane shows the rectum
surrounded by the puborectalis muscle (arrows), which appears as a triangle with the
apex directed posteriorly.

24. (b) Axial T2W MR image in the ischial plane shows the oval EAS (External anal
sphincter) (black arrows). Caudally, the rectum and anal canal should lie in the center
of the EAS. The superficial transverse perineal muscles (white arrows) are shown at
the anterior border of the EAS and extend laterally to the ischial rami (I).

25. d) Midsagittal T2-weighted MR image shows the sphincteric muscles (white
arrows) as a posterior curved bandlike structure, with the rectal ampulla (*)
resting over the curved structure of the levator ani muscle (black arrow)

26. (c) Coronal T2-weighted MR image shows the levator ani muscle (arrowheads)
supporting the pelvic floor and the rectal ampulla resting on the levator hammock,
whereas the rectum and anal canal penetrate the EAS (arrows).

27. Pelvic MR Imaging in Boys with ARMs
Low ARM with a perineal fistula in a boy. (a) Photograph shows normal position of the
imperforate anus (arrowhead) and the external opening of a fistula (arrow). (b)
Midsagittal T2-weighted MR image shows the rectoperineal fistula (arrowhead). The
anteriorly displaced anorectum (arrow) is seen below the level of the levator ani muscle.

28. Intermediate or high ARM with a recto–urethral bulbar fistula in a boy. (a) Image from
colostography shows a rectourethral fistula (arrows) at the level of the bulbar urethra.
(b) Sagittal T2-weighted MR image shows the rectal pouch (white arrow) ending at the
level of the levator ani muscle and the fistula (black arrow) extending anteriorly to the
bulbar urethra

29. (c) Axial T2-weighted MR image at the pubococcygeal level shows an anteriorly located
anorectum (white arrow) with an asymmetric and underdeveloped puborectalis muscle
(black arrows).

30. High ARM with a rectovesical fistula in a boy. (a) Image from colostography at 11
months shows the proximally located rectal pouch and a communication with the
posterior wall of the urinary bladder (arrow). (b) Midsagittal T2-weighted MR image
shows the high position of the rectal pouch and the trajectory of the fistula (arrow) into
the posterior bladder wall. Partial agenesis of the sacrum is also seen.

31. (c, d) Axial T2-weighted MR images show an atrophic puborectalis
muscle (arrows in c) and a diminutive EAS complex (arrowheads in d).

32. Pelvic MR Imaging in Girls with ARMs
Low ARM with a rectovestibular fistula in a girl. (a) Photograph shows the external
vestibular opening (arrow) of a rectovestibular fistula. (b) Image from colostography after
catheterization of the fistula shows the position of the rectal pouch, which is located below
the pubococcygeal line. * = fecaloma, arrow = normal position of the anus.

33. Cloacal anomaly in a girl. (a) VCUG image after placement of a catheter at the unique
external opening of the cloacal anomaly shows opacification of the bladder and genital
duplication (arrows), but the rectal pouch is not opacified.

34. (b) Midsagittal T2-weighted MR image shows the rectal pouch above the level of the
puborectalis muscle (arrow). Note the dysplastic morphology of the sacrum.
(c) Caudal axial image shows only one external opening and hypotrophic EAS fibers
(arrows).

35. Caudal regression syndrome
(cloacal anomaly with genital duplication, partial sacral agenesis, spinal cord
anomalies, horseshoe kidney, and vesicoureteral reflux) in a girl.
(a) VCUG image shows bilateral grade 3 vesicoureteral reflux and almost
complete sacral agenesis (arrow). (b) Axial T2-weighted MR image shows a
horseshoe kidney (*).

36. (c) Sagittal MR image shows a tethered spinal cord with typical rounded morphology of
the conus medullaris (arrow).
(d) Axial T2-weighted MR image shows the rectal pouch (R) between duplicate genitalia
(arrows).

37. Currarino triad
(high ARM with recto–urethral prostatic fistula confirmed at surgery, partial sacral
agenesis, tethered cord, and anterior lipomyelomeningocele) in a boy
. (a) VCUG image shows a normal urethra without demonstration of the fistula. Note the large
fecaloma (*) and partial sacral agenesis (arrow).
(b) Sagittal T2-weighted MR image of the spine shows a tethered cord (arrowhead), the partial
sacral agenesis (white arrow), and an associated presacral mass (black arrow), which corresponds
to an anterior lipomyelomeningocele.

38. Coronal (c) and axial (d) T2-weighted MR images show the heterogeneous
presacral mass, which extends between the fibers of the highly atrophic
puborectalis muscle (white arrows).

39. Conclusion
ARMs are a complex group of congenital anomalies involving the distal
anus and rectum.
They result from abnormal development of the urorectal septum in prenatal
life. Imaging plays a key role in evaluation of ARMs.
In the first days of life, clinical and imaging findings facilitate early
classification of ARMs and allow a decision about whether to perform an
immediate colostomy.
In children with intermediate and high types of ARMs, preoperative pelvic
MR imaging after the neonatal period allows accurate evaluation of the
morphology and grade of development of the sphincteric muscle complex.

40. THANK YOU