DOI:10.2214/AJR.07.2468
AJR 2007; 189:1525-1529
© American Roentgen Ray Society
Transperineal Sonography for Determination of the Type of Imperforate Anus
Hans P. Haber1,
Guido Seitz2,
Steven W. Warmann2 and
Jörg Fuchs2
1 Department of Pediatric Radiology, University of Tübingen,
Hoppe-Seyler-Str. 1, D-72076 Tübingen, Germany.
2 Department of Pediatric Surgery, University Children's Hospital,
Tübingen, Germany.
Received April 26, 2007;
accepted after revision June 10, 2007.
Address correspondence to H. P. Haber
(peter.haber{at}med.uni-tuebingen.de).
Abstract
OBJECTIVE. The purpose of this study was to assess whether
transperineal sonography is valid and accurate for discriminating the low
(translevator) type of imperforate anus from the intermediate and high
(supralevator) types. The distinction is critical in determination of the
surgical approach.
MATERIALS AND METHODS. Fifty-six consecutively enrolled infants
(0–90 days old) with imperforate anus underwent transperineal gray-scale
sonography with a 12-MHz linear array transducer. The distance between the
distal rectal pouch and the perineum was measured, and a cutoff distance for
differentiating types of imperforate anus was identified. The sonographic
findings were compared with the final diagnosis reached with radiographic and
surgical findings.
RESULTS. Transperineal sonography was feasible in all children
without specific preparation. The mean distance between the distal rectal
pouch and the perineum in the 22 infants with low imperforate anus was 10
± 4 (SD) mm compared with a mean of 24 ± 6 mm in the 34 infants
with intermediate or high anomalies (p < 0.001). The sensitivity
of transperineal sonography was 100%; all 34 cases of intermediate or high
imperforate anus were identified with a cutoff distance between the distal
rectal pouch and the perineum of 15 mm. The specificity of sonography was 86%
and the accuracy, 95%.
CONCLUSION. Transperineal sonography is a valid and accurate
noninvasive imaging technique for differentiating low and intermediate or high
imperforate anus.
Keywords: anorectal anomaly • imperforate anus • pediatric radiology • sonography
Introduction
Imperforate anus is a common congenital anomaly necessitating extensive
surgery in neonates [1]. The
low type of imperforate anus passes through the levator ani muscle group and
through its central puborectalis muscle, the major determinant of fecal
continence. This translevator type of imperforate anus is managed with
one-step transperineal anoplasty soon after birth
[2]. The intermediate and high
types of imperforate anus do not traverse the puborectalis sling. In the
intermediate type, the rectum ends at the level of the puborectalis sling; in
high (supralevator) imperforate anus, the rectum ends above the puborectalis
muscle. The appropriate surgical procedure for both types consists of initial
diverting colostomy followed by the posterior sagittal anorectoplasty as
described by Peña
[2].
Early assessment and accurate diagnosis of the type of imperforate anus are
essential for determining treatment. In addition to clinical indexes
[1–3],
several imaging techniques are used, including sonography
[4–7],
CT [8,
9], and MRI with the patients
under anesthesia [10,
11]. Noninvasive procedures
without ionizing radiation are desirable, particularly in the case of neonates
and infants.
Initial studies of sonography showed that measurement of the distance
between the distal rectal pouch and the perineum may be helpful in
differentiating high and low imperforate anus
[4–6].
However, the studies had only small sample sizes (fewer than 20 infants) and
were conducted with different approaches to the sonographic examination,
including the transabdominal and transperineal approaches. Reported cutoff
values to differentiate low from intermediate and high imperforate anus range
from 10 to 25 mm
[4–6].
The diagnostic criteria are not well defined, and the sensitivity and
specificity have not been calculated, to our knowledge. For the past 10 years,
we have been using transperineal sonography to determine the type of
imperforate anus in infants by measuring the distance between the distal
rectal pouch and the perineum. The purpose of our study was to assess whether
transperineal sonography is valid and accurate in discriminating low from
intermediate and high imperforate anus in neonates and infants.
View larger version (137K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2 —1-day-old boy with low imperforate anus without fistula.
Midline sagittal sonogram shows 5-mm distance (asterisks, dashed
line) between distal rectal pouch and perineum (P). Scale segment
distance, 2 mm. S = pubic symphysis, U = urethra (arrow), CS = corpus
spongiosum.
|
|
View larger version (130K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3 —6-day-old girl with intermediate imperforate anus and
rectovestibular fistula. Midline sagittal sonogram shows relation between
small fistula (arrow) and posterior wall of vagina. Distance
(asterisks, dashed line) between distal rectal pouch and perineum (P)
is 17 mm. Scale segment distance, 5 mm. S = pubic symphysis, U = urethra
(arrow), V = vestibule of vagina (arrow), P = perineum.
|
|
Materials and Methods
Patients
Between January 1996 and August 2006, 56 consecutively enrolled infants (30
boys, 26 girls; median age, 2 days; range, 0–90 days) with the diagnosis
of imperforate anus were examined with sonography as part of routine clinical
care to determine the type of imperforate anus and to evaluate associated
neural and spinal anomalies. The infants were referred to our institution for
surgical treatment. The final diagnosis, including the type of imperforate
anus, was made on the basis of radiographic and surgical findings according to
the international classification of anorectal anomalies, which is based on the
relation between the level of the distal rectal pouch and the puborectalis
sling of the levator muscle
[12]. Forty-six of the
patients were 28 days old or younger. Eleven infants had undergone colostomy
before the sonographic examination and were examined during a second
hospitalization for definitive treatment.
Imaging
All sonograms were obtained with a real-time scanner with a high-resolution
12-MHz linear array transducer (Sonoline Antares, Siemens Medical Solutions)
through the transperineal approach as described by Teele and Share
[13]. The gray-scale sonograms
were obtained by two sonologists, each with more than 15 years of experience
in diagnostic sonography. Transperineal sonography was performed before
radiographic studies and definitive surgical repair.
The infants were examined in the supine position without specific
preparation (Fig. 1).
Sonographic scans in the midsagittal plane through the perineum were used to
identify the base of the bladder, the urethra, and the vagina between the
urethra and the distal rectal pouch as previously described
[14] (Figs.
2 and
3). The distal rectal pouch was
identified on the basis of the presence of hypoechoic meconium or gas within
the rectum. The distance between the distal rectal pouch and the perineum was
measured in millimeters with electronic calipers as described by Teele and
Share [13] (Figs.
2,
3, and
4). All measurements were
performed in the resting state while the child was not crying. Care was taken
not to press or indent the skin or to diminish the distance between the distal
rectal pouch and the perineum. For each infant, the distance between the
distal rectal pouch and the perineum was recorded in the medical report.
Thereafter, the distance was compared with the type of imperforate anus
confirmed on the basis of radiographic and surgical findings.
View larger version (133K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4 —1-day-old boy with high imperforate anus and small
rectourethral fistula (arrow). Midline sagittal sonogram shows
distance (asterisks, dashed line) between distal rectal pouch and
perineum is 22 mm. Scale segment distance, 2 mm. S = pubic symphysis, U =
urethra, CS = corpus spongiosum.
|
|
View larger version (11K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5 —Scattergram shows distance (mean ± SD) between distal
rectal pouch and perineum measured on transperineal sonography in infants with
low, intermediate, and high imperforate anus. Dotted line indicates cutoff
distance of 15 mm. Black dots indicate data for infants with internal or
anocutaneous fistula; white dots, data for infants without internal or
anocutaneous fistula.
|
|
Before final repair, a distal colostomy study was performed to determine
the precise type of anatomic defect in children initially treated with
diverting colostomy. The study consisted of injection of hydrosoluble contrast
material through the distal stoma. The study was performed under fluoroscopic
guidance with the patient in the lateral position for identification of a
rectourogenital fistula. In rare cases, the internal fistula was found on
voiding cystourethrography or retrograde urethrography. Invertograms were not
used. The studies were performed by a radiologist with more than 20 years of
experience in pediatric radiology.
Statistical Analysis
A cutoff distance between the distal rectal pouch and the perineum was
identified to separate cases of high or intermediate imperforate anus from
those of low imperforate anus. The theoretic sensitivity and specificity for
each potential cutoff point were analyzed. A receiver operator characteristic
curve was used to a establish a cutoff point for obtaining the maximum
diagnostic accuracy. A Student's t test was used to test for
statistically significant differences in distance between the distal rectal
pouch and the perineum for the types of imperforate anus.
Results
The patient data and final diagnoses confirmed on the basis of radiographic
and surgical findings are summarized in
Table 1. Transperineal
sonography was feasible in all patients. The mean examination time was 11
minutes (range, 7–20 minutes). The distances between the distal rectal
pouch and the perineum are shown in Figure
5.
A final diagnosis of low imperforate anus was made for 22 patients. In 16
infants, the anocutaneous fistula was detected at inspection. At sonographic
examination, the mean distance between the distal rectal pouch and the
perineum in this group was 10 ± 4 (SD) mm (range, 5–17 mm). A
final diagnosis of intermediate or high imperforate anus was made for 34
patients (Figs. 2 and
3). At sonographic examination,
the mean distance between the distal rectal pouch and the perineum in this
group was 24 ± 6 mm (range, 16–37 mm). The difference between the
pouch-to-perineum distance in the low imperforate anus group and that in the
intermediate or high group was statistically significant (p <
0.001). The 17 infants with intermediate imperforate anus had a mean
pouch-to-perineum distance of 23 ± 6 mm (range, 16–37 mm). The 17
infants with high imperforate anus had a mean distance of 25 ± 5 mm
(range, 18–35 mm).
View larger version (120K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 6 —28-day-old girl with low mimicking high imperforate anus.
Midline sagittal sonogram shows gas-filled distal rectal pouch decompressed by
large anocutaneous fistula (arrowheads). Distal end of pouch is
difficult to delineate and pouch-to-peritoneum (P) distance
(asterisks) is more than 15 mm, fulfilling criterion for high
anomaly. In general, anocutaneous fistula indicates low anomaly, making
pouch-to-peritoneum measurements unnecessary. S = pubic symphysis, V =
vagina.
|
|
At a cutoff pouch-to-perineum distance of 15 mm, the maximum diagnostic
accuracy was estimated to be 95%. Sensitivity and specificity were estimated
to be 100% and 86%. The positive predictive value of sonography was 92% in
this series, and the negative predictive value was 100%. On the basis of the
15-mm cutoff point, 19 of 22 cases of low imperforate anus, including the six
cases without anocutaneous fistula, were correctly classified at sonographic
examination (Fig. 1). Three
infants had a pouch-to-perineum distance of 16–17 mm, and therefore the
anomaly was erroneously classified at sonographic examination as intermediate
or high imperforate anus (Fig.
6). All three of these patients had an anocutaneous fistula
detectable at physical examination. All 34 cases of intermediate or high
imperforate anus, including the four without internal fistula, were correctly
classified at sonographic examination.
Discussion
Imperforate anus occurs with a frequency of approximately one to four cases
per 5,000 neonates [1]. An
accurate diagnosis usually can be made when typical clinical features are
present
[1–3].
The presence of an anocutaneous fistula indicates the presence of the low type
of imperforate anus. Neonates with this phenotype do not need further
diagnostic procedures on the anorectum and undergo a surgical procedure in the
first days of life. The presence of perineal pearls or corrugated perineum
also indicates low imperforate anus
[3]. The absence of an
anocutaneous fistula and passage of meconium through the vagina or urethra
indicate the presence of the intermediate or high type of imperforate anus.
However, accurate determination of the type of imperforate anus on the basis
of clinical data can be difficult, especially in the 10–20% of boys and
approximately 10% of girls with imperforate anus who do not have a fistula at
clinical examination [1]. In
some cases, external fistulas may not become apparent until the neonate is
12–24 hours old, at which time the meconium moves distally into the
rectum. Peña [1]
proposed performing inverted lateral radiography (invertography) for
determining the surgical approach in the care of these infants.
The type of fistula is commonly taken into account in defining the type of
imperforate anus. In this series, however, we focused on sonographic
measurement of the distance between the distal rectal pouch and the perineum.
We report data on the sensitivity and specificity of conventional
transperineal sonographic examination in the preoperative diagnosis of
imperforate anus. Our experience has shown that unlike the transverse scans
used in the infracoccygeal approach
[7], conventional midline
sagittal sonographic scans are easy to perform without artifacts caused by
gluteal tissue. In our series, there were three false-positive findings. Three
(14%) of the 22 infants with low imperforate anus had a pouch-to-perineum
distance greater than 15 mm. All three of these patients, however, had an
anocutaneous fistula, and the diagnosis was made on clinical grounds.
Sonographic measurements may not be accurate in infants in whom the distal
pouch is decompressed by a large fistula, causing the distance to be
exaggerated (Fig. 6). The
results in these patients emphasize that sonographic findings in patients with
imperforate anus must be correlated with clinical findings. In our series,
however, imperforate anus was correctly classified in all infants who had
undergone colostomy before sonographic examination.
There were no false-negative results in our series. None of the infants
with surgically proven intermediate or high imperforate anus had a
pouch-to-perineum distance less than 15 mm, which we consider the cutoff value
for discriminating low from intermediate and high anomalies. In our
experience, it has been extremely important to perform the sonographic
examination when the child is not crying. Crying and straining increase
intraabdominal pressure, and the distal rectal pouch moves toward the
perineum, shortening the distance between the distal rectal pouch and the
perineum. Because there is no associated pain or discomfort, sedation for the
procedure is not necessary.
Our results with this series of patients indicate that in infants without
an anocutaneous fistula and with a greater than 15-mm distance between the
distal rectal pouch and the perineum, the diagnosis of intermediate or high
imperforate anus can be reliably made. If desired by the surgeon, the
sonographic findings can be elaborated with CT and MRI to show the anatomic
features of the levator ani muscles and external anal sphincter before surgery
[8–10].
However, the studies of CT and MRI had only small sample sizes, and owing to
poor development of the sphincter muscles in most cases of high imperforate
anus, both techniques are limited in depicting the relation between the distal
rectal pouch and the puborectalis muscle
[9,
10]. The best radiologic
techniques for discerning the type of imperforate anus are antegrade contrast
studies performed through the distal limb of a colostomy and cystography and
genitography in selected cases.
The limitations of our study included institutional case-selection bias and
lack of data on intraobserver and interobserver variability of measurements.
Further work with series of infants with this disorder is necessary to
overcome these shortcomings.
Transperineal sonography enables determination of the type of imperforate
anus and therefore may assist in determining the appropriate surgical
approach. This noninvasive imaging method allows the surgeon to identify low
imperforate anus, particularly when a fistula is not detected at clinical
examination, sparing some infants unnecessary colostomy.
References
- Peña A. Important basic considerations. In: Peña A,
ed. Atlas of surgical management of anorectal
malformations. New York, NY: Springer-Verlag, 1989:1
-14
- Peña A. Management of anorectal malformations during the
newborn period. World J Surg 1993;17
: 385-392[CrossRef][Medline]
- Seibert JJ, Golladay ES. Clinical evaluation of imperforate anus:
clue to type of anal–rectal anomaly. AJR1979; 133:289
-292[Medline]
- Schuster SR, Teele RL. An analysis of ultrasound scanning as a
guide in determination of "high" or "low" imperforate
anus. J Pediatr Surg 1979;14
: 798-800[Medline]
- Oppenheimer DA, Carroll BA, Shochat SJ. Sonography of imperforate
anus. Radiology 1983;148
: 127-128[Abstract/Free Full Text]
- Donaldson JS, Black CT, Reynolds M, Shermann JO, Shkolnik A.
Ultrasound of the distal pouch in infants with imperforate anus. J
Pediatr Surg 1989; 24:465
-468[CrossRef][Medline]
- Han TI, Kim IO, Kim WS. Imperforate anus: US determination of the
type with infracoccygeal approach. Radiology2003; 228:226
-229[Abstract/Free Full Text]
- Kohda E, Fujioka M, Ikawa H, Yokohama J. Congenital anorectal
anomaly: CT evaluation. Radiology 1985;157
: 349-352[Abstract/Free Full Text]
- Ikawa H, Yokohama J, Sanbonmatsu T, et al. The use of computerized
tomography to evaluate anorectal anomalies. J Pediatr
Surg 1985; 20:640
-644[CrossRef][Medline]
- Sato Y, Pringle KC, Bergmann RA, et al. Congenital anorectal
anomalies: MR imaging. Radiology 1988;168
: 157-162[Abstract/Free Full Text]
- McHugh K, Dudley NE, Tam P. Pre-operative MRI of anorectal
anomalies in the newborn period. Pediatr Radiol1995; 25:33
-36[Medline]
- Santulli TV, Kiesewetter WB, Bill AH. Anorectal anomalies: a
suggested international classification. J Pediatr Surg1970; 5:281
-287[CrossRef][Medline]
- Teele RL, Share JC. Transperineal sonography in children.
AJR 1997; 168:1263
-1267[Free Full Text]
- Kim IO, Han TI, Kim WS, Yeon KM. Transperineal ultrasonography in
imperforate anus: identification of the internal fistula. J
Ultrasound Med 2000; 19:211
-216[Abstract]
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
Top
Abstract
Introduction
