Patofisiologi

Embriogenensis dari malformasi ini masih belum jelas. Rectum dan anus dipercayai

berkembang berasal dari bagian dorsal hindgut atau cloacal cavity. Selanjutnya akan

terbentuk septum urorectal di tengah. Septum ini akan memisahkan rectum dan anal kanal

terpisah dari vesika urinaria dan uretra. Duktus cloaca adalah penghubung antara dua porsio

hindgut. Pertumbuhan septum kea rah bawah yang bertujuan untuk menutup ductus tersebut

terjadi pada minggu ketujuh masa kehamilan. Selama masa tersebut berlangsung, porsio

urogenital ventral akan membuat jalur ke luar tubuh (external opening): bagian dorsal dari

anal akan menyusul kemudian. Anus akan berkembang dengan cara fusi pada anal tuberkel

dan external invaginasi, yang dikenal sebagai proktodeum, yang berada didekat rectum tapi

dipisahkan dengan adanya anal membrane. Perpisahan ini semestinya bergabung pada

minggu ke 8 masa kehamilan.

Adanya gangguan pada stuktur anorektal pada saat perkembangan dapat membuat anomaly

ini menjadi bervariasi, mulai dari anal stenosis, ruptur inkomplit pada membrane anal. Atau

anal agenesis sampai kegagalan kompit upper portion dari cloaca untuk turun dan gagalnya

proctodeum unutk invaginasi. Adanya penempelan pada traktus urogenitalia dan porsio rectal

pada cloacal plate menyebabkan rectourethral fistulas atau rectovestibular fistulas.

Sphincter anal eksternal, berasal dari mesoderm, biasanya terdapat pada imperforate anus tapi

memiliki derajat pembentukan yang bervariasi, mulai dari robust muscle (perineal or

vestibular fistula) sampai dengan tidak terdapatanya otot yangterlihat (complex long–

common-channel cloaca, prostatic atau bladder-neck fistula).

Epidemiologi

Frekuensi.

Di Amerika Serikat anorektal malformasi terjadi pada 1 kelahiran per 5000 bayi lahir.

Mortalitas/morbiditas.

Anorektal dan urogenital malformasi jarang mengakibatkan sesutau yang fatal, walaupun

anomali ini yang ada hubungan dengan anomali organ lain seperti jantung dan ginjal dapat

mengancam jiwa. Intestinal perforasi atau postoperative septik dapat terjadi sebagai

komplikasi pada bayi yang lahir dengan kondisi anus imperforate dapat mengakibatkan

kematian dan morbiditas yang berat.

Morbiditas biasanya terjadi karena dua sumber berikut :

Malformation-related morbidity

Malformation-related morbidity berhubungan terhadap malformasi terhadap motilitas rectal,

inervasi anorektal dan muskulatur dari sphincter. Morbiditas yang paling sering adalah

konstipasi. Anak-anak dengan malformasi ringan biasanya sering mengalami konstipasi tanpa

alasan yang jelas. Jika tidak segera ditangani, kronik konstipasi dapat menyebabkan rectal

dilatasi yang akan memperparah konstipasi dan akan terjadi impaksi feses dan overflow

pseudoincontinence, yang disebut sebagai encopresis.

Morbiditas yang paling parah adalah adnya inkontinensia urin dan feses.

Surgery-related morbidity

Dapat terjadi infeksi dan pneumonia. Adanya infeksi pada luka atau anastomosis breakdowns

dapat terjadi pada seluruh operasi yang melibatkan intestinal.

Usia

Kebanyakan anak dengan anorektal malformasi teridentifikasi pada saat pemeriksaan fisik

ruitn bayi baru lahir. Subtle malformations, speperti pada anak dengan perineal fistula dapat

terlihat normal, dan dapat saja terdeteksi dalam hitungan bulan atau tahun setelah kelahiran

saat pasien dibawa kedokter dengan keluhan konstipasi atau adanya infeksi saluran kemih,

dan ditemukan adanya perineal body yang kecil saat dilakukan pemeriksaan fisik.

Riwayat

Pemeriksaan prenatal ultrasonography sering menunjukkan temuan yang normal, walaupun

adanya polyhydramnios atau intraabdominal cysts dapat menjadi pertanda adanya

imperforate anus yang ada hubungannya dengan hydrocolpos atau hydronephrosis.

Neonatus dengna anal imperforate biasanya teridentifikasi pada pemeriksaan fisik rutin

pascakelahiran.

Pemeriksaan Fisik

Selama pemeriksaan fisik, perhatian harus difokuskan pada abdomen, genitalia, rectum, dan

lower spine.

Abdomen sebaiknya dipalpasi untuk mengetahui apakah ada masa, yang bisa berasal dari

ginjal yang dilatasi, kandung kemih, hydrocolpos, ectopic kidney.

Pada lak-laki, testis harus di palpasi di skrotum. Dan perineum harus diperiksa. Perineal

fistula di diagnosis saat perineum dibuka, keluar mekonium atau mukosa dalam jumlah kecil.

Pada perempuan, perineal fistula dapat langsung diidentifikasi sebagai small opening di

perineum. Jika tidak terdapat labia dipisahkan untuk mencari adnaya vestibular fistula.

Fourchette fistula adalah tipe vestibular fistula adalah salah satu malformasi antara perineal

dan vestibular; kondisi ini dikarakteristikan dengan adnaya mukosa yang basah pada

vestibula bagian anterior dan anoderm kering di bagian posterior pada junction antara

vestibula dan perineum.

Fourchette fistula. Malformasi ini berada pada pertengahan antara perineal fistula dan

vestibular fistula. Fistula memiliki garis vestibular mucosal yang basah pada sebagian

anterior, tetapi sebagian posterior terdiri dari kulit kering.

Jika anak memiliki uretra yang normal dan tidak memiliki vestibular fistula, kemungkinan

dia mengalami imperforate anus tanpa fistula.

Distal colostogram, gambaran posteroanterior. Initial fase dari augmented-pressure distal

colostography bertujuan untuk menentukan dimana colostomy dilakukan pada colon.

Distal colostogram, gambaran lateral. Gambar menunjukan fase kedua dari distal

colostography, dan posisi pasien berada pada posisi lateral. Tanda radioopak terlihat jelas di

bagian bawah kanan, tanda adanya muscle complex pada kulit. Gambaran ini menunjukkan

adnaya rectal pouch bergabung pada traktus urinarius pada tingkatan bulbar urethra, biasanya

sering terjadi pada laki-laki.

The remainder of physical examination is focused associated malformations. Cardiovascular

malformations occur in 12-22% of patients. The most common lesions are tetralogy of Fallot

and ventricular septal defects. Transposition of the great arteries and hypoplastic left heart

syndrome have been reported but are rare.

Many GI malformations have been described in association with imperforate anus. As many

as 10% of patients have tracheoesophageal abnormalities. Duodenal obstruction due to

annular pancreas or duodenal atresia occurs in a small percentage of patients. Malrotation

with Ladd bands that causes obstruction has also been described. Hirschsprung disease has

been well described in association with imperforate anus, although the incidence of this

combined condition is unknown. Constipation is common.

The association of imperforate anus and vertebral anomalies has been recognized for many

years. Patients with high lesions have an increased risk of this association. Lumbosacral

anomalies predominate and occur in approximately one third of patients with imperforate

anus.[3]

The frequency of spinal dysraphism (evaluated with ultrasonography or MRI) had been

thought to increase with the severity of the lesion, with higher malformations having greater

frequency than lower malformations. Several studies have disputed this and have even shown

higher incidence of spinal malformations in children with low malformations. The most

common type of dysraphism is tethered spinal cord, which is present in as many as 35% of

patients. The normal spinal cord terminates between the first and second lumbar vertebral

bodies. In patients with a tethered spinal cord, the cord ends lower in the lumbar spine. Cord

lipomas and syringohydromyelia are also common. All lumbosacral spinal malformations

negatively affect the child's prognosis with respect to urinary and fecal incontinence.

Currarino described a triad of sacral defect, presacral mass, and imperforate anus.[4] All

patients with an anorectal malformation must be screened for these vertebral abnormalities in

the newborn period using sacral radiography and lumbosacral spinal ultrasonography. As

many as one half of patients with anorectal malformations have urologic abnormalities.

Urinary anomalies are more common in patients with more complex lesions. Improved

imaging studies have provided the ability to document an increased range of abnormalities.

Mild hydronephrosis is the most common abnormal ultrasonography finding. Vesicoureteric

reflux is also a frequent finding, followed by renal agenesis and dysplasia. Cryptorchidism

reportedly occurs in 3-19% of males.

Vaginal and uterine abnormalities are common. Bicornate uterus and uterus didelphys occur

in 35% of female patients with imperforate anus. A vaginal septum is the most common

vaginal abnormality and is seen in as many as one half of girls born with a cloacal

malformation. Vaginal duplication and agenesis have also been reported. Vaginal agenesis

may be associated with ipsilateral absent ovary

Anus imperforate atau anus ektopik merupakan penyebab tersring obstruksi saluran cerna pada neonatus. Defisit anatomis dapat bervariasi mulai dari simple membranous anal atresia sampai arrest of the colon as it descends through the puborectalis sling, dengan pembentukan fistula formation from the blind-ending rectal pouch to some part of the genital or urinary tract (Fig. 52.22). In girls, the fistula may empty into the bladder, uterus, or vagina. In boys, it tends to enter into the urethra or bladder. In both sexes it can enter the perineum. Sacral and urinary tract anomalies, hydrometrocolpos, and persistent cloaca are associated. When sacral abnormalities are present, the spinal cord and canal should be screened with US for abnormalities such as tethering or masses (32). Virtually all of these patients have neurogenic bladder dysfunction (33).All associated anomalies should be demonstrated, along with the location of the fistula. US can demonstrate the distal end of the pouch. The fistula may be injected directly or it may opacify during retrograde voiding cystourethrography. In girls, flush retrograde vaginography may be required. If the fistula empties above the puborectalis sling, it can be presumed that the puborectalis muscle is hypoplastic and that continence will be difficult to accomplish with any surgical procedure. If the fistula empties below the puborectalis sling, the puborectalis muscle is usually better developed, and achievement of continence is more likely. The “M†line of Cremin has been utilized to determine the level at which the blind pouch �ends (Fig. 52.23). This line is drawn perpendicular to the long axis of the ischia on lateral view and passes through the junction between the middle and lower third of the ischia. If the blind pouch and fistula end above the line, the fistula is considered high. If they end below the line, it is considered low, and if they end at the line, it is considered intermediate. Intermediate fistulae usually pose the same problems as high fistulae

Editors: Brant, William E.; Helms, Clyde A.Title: Fundamentals of Diagnostic Radiology, 3rd EditionCopyright ©2007 Lippincott Williams & Wilkins> Table of Contents > Section XI - Pediatric Radiology > Chapter 52 - Pediatric Abdomen and Pelvis

Anus Imperforata

Anus imperforata adalah suatu defek yang terjadi pada bayi selama masih didalam

kandungan. Defek ini terjadi biasanya pada usia kehamilan minggu ke lima sampai ke tujuh.

Pada defek ini, anus dan rectum tidak berkembang secara baik.

Incidence of Imperforate Anus

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Imperforate anus affects 1 in 5,000 babies and is a little more common in males.

No one knows the exact reason some baby’s have imperforate anus. The exact cause of imperforate

anus is unknown. In some cases, environmental factors or drug use during pregnancy may play a

role, but no one is completely sure.

During a bowel movement, stool passes from the large intestine to the rectum and then to the anus.

Nerves in the anus help us feel the need for a bowel movement and start muscle activity. Muscles in

this area help control when we have a bowel movement.

With an imperforate anus, any of the following can happen:

The anal opening may be narrow or misplaced in front of where it should be located

A membrane (covering) may be present over the anal opening

The rectum may not connect to the anus

The rectum may connect to part of the urinary tract or the reproductive system though an opening

called a fistula, and an anal opening is not present

Risk Factors for Imperforate Anus

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Although most babies who have imperforate anus are the only ones in their family to have it, there

are some cases where other family members have had it as well.

Associated Disorders

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Almost 50% of babies with imperforate anus have other abnormal defects along with the

imperforate anus. These commonly include:

Spinal abnormalities, such as hemivertebra, absent vertebra and tethered spinal cord

Kidney and urinary tract malformations, such as horseshoe kidney and duplication of parts of the

urinary tract

Congenital heart defects

Tracheal and esophageal defects and disorders

Limb (particularly forearm) defects

Down syndrome, Hirschsprung's disease and duodenal atresia can also happen with an imperforate

anus.

Diagnosis of Imperforate Anus

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When a baby is born, the doctor will check the baby for any problems. While the doctor is checking

the baby, he or she will check to make sure the baby’s anus is open and in the correct position. If an

imperforate anus is found, a number of tests may be done to better understand the problem and to

see if any other problems are present.

X-rays of the stomach will give the doctor a picture showing the general location of the imperforate

anus. X-rays also let doctors know if there are problems with the spine and sacrum (a triangle-

shaped bone just below the lumbar vertebrae).

Abdominal ultrasound and spinal ultrasound -- These tests are used to look at the urinary tract and

spinal column. They also help doctors decide if a tethered spinal cord (an abnormality where the end

of the spinal cord is abnormally anchored) is present.

A tethered spinal cord may cause neurological problems, such as incontinence (toileting without

control) and leg weakness as the child grows.

Echocardiogram -- This test is done to find heart defects.

Magnetic resonance imaging / MRI --Magnetic resonance imaging / MRI -- In some cases, this test is

needed to make a definite diagnosis of tethered cord or other spinal problems.

Treatment and Repair of Imperforate Anus

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Treatment recommendations will depend on the type of imperforate anus, the presence and type of

associated abnormalities and the child's overall health. However, most infants with an imperforate

anus will need surgery

Rectoperineal Malformation

Infants with a rectoperineal malformation will need an operation called an anoplasty, which involves

moving the anus to an appropriate place within the muscles that control continence (controlled

toileting, in this case bowel movements)

Colostomy for Infants with Imperforate Anus Without a Fistula

Newborn boys and girls who have an imperforate anus without a fistula will need one or more

operations to correct it. An operation to make a colostomy is usually done early.

With a colostomy, the large intestine is divided into two sections, and the ends of intestine are

brought through small openings in the abdominal wall (small opening will be on your child’s belly).

The upper section allows stool to pass through the opening, called a stoma, and into a collection bag.

Mucus from the intestine exits through the opening of the lower section of intestine.

By performing this surgery, digestion will not be harmed and growth can continue to happen before

the next operation is needed. By changing the original route of the stool, the risk of infection will be

smaller when the next operation is done.

Nurses and other health care workers who work with your child's doctor will help you learn how to

take care of the colostomy, and they will help you, as you prepare to take care of your child at home.

Local and national support groups may also be very helpful during this time.

The next operation creates a connection between the rectum and the newly created anal opening.

This procedure is usually performed from the child’s bottom.

In some cases where the rectum ends within the abdomen (high lesions), laparoscopic surgery

(surgery through small holes, usually without an incision) or traditional open surgery (surgery with

an incision or cut opening) can be used to bring the rectum down to the anal opening.

After the rectum is brought down to the anal opening the colostomy will stay in place for six to eight

weeks. Stool will continue to leave the body through the colostomy until it is closed with surgery.

The colostomy will have to stay in place to let the new anal opening heal without being infected by

stool and let the child undergo the dilation process (schedule that includes slowly stretching the

anus to the correct size for the child’s age).

Imperforate Anus After Surgery

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A few weeks after surgery, parents are taught to perform anal dilatations to make sure the anal

opening is large enough to allow normal passage of stool.

The colostomy is closed in another operation at least six to eight weeks later. Several days after

surgery, the child will begin passing stools through the rectum (anal opening). Shortly after surgery,

stools may be loose and happen more often than usual. Diaper rash and skin irritation can also be a

problem. Your doctor and nurse will help you with the care needed to keep the diaper area healthy.

Within a few weeks after surgery, stools will happen less often and become firmer. Anal dilatations

should continue for several weeks or months.

Some infants may become constipated. To avoid this, we encourage following a high-fiber diet.

Laxatives may be required prior to the age of potty training.

In cases of severe constipation, a bowel management program may be developed according to the

specific needs of the child. The program may include child and parent education in the use of

laxatives, stool softeners, enemas, bowel training technique.

Toilet Training Children with Imperforate Anus

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Toilet training should be started at the usual age, usually when the child is around 3 years old.

Children who have had imperforate anus generally gain bowel control more slowly, and depending

on the type of malformation and the operations done to repair it, some children may not be able to

gain good bowel control. Each child’s situation will be slightly different and will be determined with

the help of your doctor.

Long-term Outlook

Hide

Children who have had an imperforate anus that have a rectoperineal fistula are usually able to gain

good control over their bowel movements after surgical repair.

However, those with more difficult types of anorectal malformation may need to participate in a

bowel management program to help them achieve control over their bowel movements and prevent

constipation.

Nurses and other health care professionals who work with your child's doctors can outline a program

made for your child's individual needs.

http://www.cincinnatichildrens.org/health/i/imperforate-anus/

Imperforate Anus: US Determination of the Type with Infracoccygeal Approach

Tae Il Han, MD, In-One Kim, MD and Woo Sun Kim, MD

1From the Department of Radiology, Eulji University School of Medicine, 24-14 Mok-Dong, Jung-Gu,

Taejon 301-726, South Korea (T.I.H.); and Department of Radiology, Seoul National University

College of Medicine, South Korea (I.O.K., W.S.K.). From the 2000 RSNA scientific assembly. Received

November 26, 2001; revision requested February 5, 2002; revision received September 23; accepted

November 18. T.I.H. supported by Korea Research Foundation grant KRF-2000-003-F00215. Address

correspondence to T.I.H. (e-mail: tihan31@hanmail.net).

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Abstract

PURPOSE: To assess the usefulness of infracoccygeal transperineal ultrasonography (US) in

differentiation between high- and low-type imperforate anus.

MATERIALS AND METHODS: Infracoccygeal US was prospectively performed with a 7–10-MHz linear-

array transducer prior to corrective surgery in 14 neonates with imperforate anus. The approach site

was just inferior to the coccyx and posterior to the anus. Transverse images of the anorectal area

were obtained. The puborectalis muscle was identified, and the relationship between the

puborectalis muscle and the distal rectal pouch was evaluated. US findings were compared with

surgical findings.

RESULTS: In 10 neonates, a low-type imperforate anus was correctly diagnosed at infracoccygeal US.

In those with low-type imperforate anus, the puborectalis muscle was seen as a hypoechoic U-

shaped band (n = 10), and the distal rectal pouch passed through the puborectalis muscle (n = 10). In

four neonates with high-type imperforate anus, the puborectalis muscle was not identified (n = 4).

CONCLUSION: Infracoccygeal transperineal US enables the determination of the type of imperforate

anus.

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© RSNA, 2003

In the diagnostic evaluation of neonates with imperforate anus, the primary goal is to distinguish

between high-type (supralevator) and low-type (infralevator) imperforate anus to determine the

correct type of surgery. The relationship between the distal rectal pouch and the puborectalis

muscle is a critical factor in the estimation of whether an imperforate anus is high or low type.

The distinction between high- and low-type imperforate anus can usually be made on the basis of

clinical data regarding the presence or absence of a visible perineal opening or passage of meconium

through the vagina or urethra (1). Many reports are available in the literature about the level of the

distal rectal pouch in patients with imperforate anus. However, preoperative imaging modalities

have been limited in the ability to reveal the relationship between the puborectalis muscle and the

distal rectal pouch (2–4).

Infracoccygeal ultrasonography (US) is an excellent diagnostic modality for demonstration of the

puborectalis muscle and anal sphincter complex in normal neonates (5). To our knowledge, US has

not been previously used to identify the puborectalis muscle preoperatively in neonates with

imperforate anus. The purpose of our study was to assess the usefulness of infracoccygeal

transperineal US in differentiation of low-type imperforate anus from high-type imperforate anus.

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MATERIALS AND METHODS

Patients

Fourteen consecutive neonates (10 male and four female; age range, 1–24 days; mean age, 6 days)

with imperforate anus identified from two participating institutions were prospectively examined

preoperatively with infracoccygeal US to distinguish between high- and low-type imperforate anus

(Table). Our institutional review board approved the study protocol, and informed consent was

obtained from the parents of the neonates. Gestational ages ranged from 36 to 41 weeks, with a

mean age of 39 weeks. Body weights ranged from 2,670 to 3,500 g (mean, 3,080 g). On the basis of

surgical results, 10 cases were classified as low- and four as high-type imperforate anus. The type of

lesion was determined on the basis of the international classification, which is determined by the

relationship of the level of the distal rectal pouch to the puborectalis portion of the levator ani

muscle (6,7).

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Patient Characteristics

Imaging

The study was performed by one of two radiologists (T.I.H. or I.O.K.) with expertise in infracoccygeal

US, and the radiographic findings were evaluated by both of the radiologists with consensus without

knowledge of the type of lesion or clinical symptoms. Infracoccygeal US was performed with a 7-

MHz linear-array transducer (model 128 XP10; Acuson, Mountain View, Calif) or a 5–10-MHz

multifrequency linear-array transducer (HDI 3000; Advanced Technology Laboratory, Bothell, Wash).

The neonates were placed in the supine position, and both legs were drawn up to the chest. The

approach site for infracoccygeal US was just inferior to the coccyx and posterior to the anus (5).

Scanning was performed to obtain transverse images of the anorectal area. Standard gray-scale

settings for the evaluation of small anatomic parts were used. Infracoccygeal US was easily

performed in all neonates without sedation, and each examination required 3–5 minutes. A thick

layer of gel was applied between the transducer and the perineum to prevent artifacts from

intervening air. US images were rotated vertically to correspond to the usual orientation on

computed tomographic (CT) or magnetic resonance (MR) images.

We identified the puborectalis muscle and evaluated the relationship between the distal rectal

pouch and the puborectalis muscle on the transverse image obtained with an infracoccygeal

approach (Fig 1). Additionally, midline sagittal scanning was performed to measure the distance from

the end of the distal rectal pouch to the perineum. US findings were compared with surgical findings.

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Figure 1. Lateral schematic of the pelvis shows the transverse scanning level to evaluate the

relationship between the puborectalis muscle and the distal rectal pouch. Scanning site (arrow) is

just inferior to the coccyx.

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RESULTS

In 10 neonates, a low-type imperforate anus was correctly diagnosed with infracoccygeal US. In

those with low-type imperforate anus, infracoccygeal US revealed the puborectalis muscle (n = 10).

On the transverse image obtained through the upper part of the anal canal, the puborectalis muscle

was seen as a hypoechoic U-shaped band (n = 10), and the distal rectal pouch passed through the

puborectalis muscle (n = 10) (Figs 2, 3).

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Figure 2.Patient 6. Transverse infracoccygeal sonogram shows the distal rectal pouch (R), which

passes through the puborectalis muscle (arrows), indicating low-type imperforate anus. U = urethra.

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Figure 3.Patient 10. Transverse infracoccygeal sonogram shows distal rectal pouch (R), which passes

through the puborectalis muscle (arrows), indicating low-type imperforate anus. U = urethra.

In four neonates with high-type imperforate anus, the puborectalis muscle and anal sphincters were

not identified on the transverse image obtained through the anal canal (Fig 4).

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Figure 4.Patient 2. Transverse infracoccygeal sonogram shows the distal rectal pouch (R). The

puborectalis muscle cannot be identified.

On the midline sagittal scan, the distance between the end of the distal rectal pouch and the

perineum was 6.3–13.0 mm (mean, 11.4 mm) in low-type imperforate anus and 11.5–14.0 mm

(mean, 12.5 mm) in high-type imperforate anus. A distance of 10–15 mm between the pouch and

the perineum was present in 12 of the 14 neonates, in eight of 10 neonates with low-type

imperforate anus, and in all neonates with high-type imperforate anus.

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DISCUSSION

The radiologic modalities used in imaging of imperforate anus include inverted lateral radiography

(invertography) (8,9), distal colostography (loopography), US (2–4), CT (10,11), and MR imaging (12–

14). They have been used to determine the level of the distal rectal pouch (2–4), to identify the

presence of fistulas (15,16), and to diagnose any associated anomalies (17,18). To distinguish

between high- and low-type imperforate anus is critical in the determination of the surgical

approach. A low-type imperforate anus is treated with a perineal anoplasty or dilatation of an

ectopic perineal orifice, whereas all cases of high-type imperforate anus require an initial colostomy

followed by a definitive repair pull-through operation (19–21).

The puborectalis muscle is a landmark used to distinguish low- and high-type imperforate anus.

However, invertography, loopograhy, and US are limited because of the inability to display directly

the puborectalis muscle. Although CT and MR imaging can demonstrate the presence of the

puborectalis muscle and external anal sphincter prior to surgery (10–14), they are limited in the

ability to reveal the relationship of the distal rectal pouch to the puborectalis muscle.

Infracoccygeal US can directly demonstrate the puborectalis muscle in neonates with imperforate

anus (5). The puborectalis muscle was identified as a hypoechoic U-shaped band at the level of the

anorectal flexure. US finding of the distal rectal pouch passing through the puborectalis muscle

suggests a low-type imperforate anus. The puborectalis muscle is the innermost portion of the

levator ani muscle and is considered to have an important role in the control of bowel function. Sato

et al (13) reported that all patients with low-type imperforate anus showed good development of

the puborectalis muscle, whereas 12 of 15 patients with high-type imperforate anus showed poor

development of the puborectalis muscle. In high-type imperforate anus, the puborectalis muscle is

small and tightly applied to the urethra or vagina (22,23). In our study, the puborectalis muscle could

not be identified on an infracoccygeal US image of high-type imperforate anus.

In contrast, conventional transperineal US cannot depict the puborectalis muscle. The differentiation

of low- from high-type imperforate anus has been indirectly performed with the measurement of

the distance from the distal rectal pouch to the perineum, which is now used routinely (2–4). A

distance of 1.0 cm or less between the pouch and the perineum suggests a low-type imperforate

anus, a distance of 1.0–1.5 cm indicates an intermediate-type imperforate anus, and a distance of

1.5 cm or greater implies a high-type imperforate anus (4). The limitation of this method is the

overlap in the measurements between high- and low-type imperforate anus. A high-type

imperforate anus can be mistaken for a low-type imperforate anus if US is performed when the

infant is crying, because this displaces the pouch caudally. In our study, there is some overlapping in

the measurements between high- and low-type imperforate anus.

In pediatric surgery, the physical examination is the most helpful method in the estimation of

whether an imperforate anus is of the high or the low type (24). In male patients, if meconium

appears anywhere in the perineum, either through an anocutaneous fistula or in the median raphe

of the scrotum, the lesion is a low type. However, if meconium is passed in urine but is not visible

elsewhere in the perineum, the lesion is almost certainly a high type. In female patients, an

anocutaneous or anovestibular fistula to the posterior fourchette of the vagina is almost always

visible in low-type lesions. If the opening of the bowel cannot be seen, it is likely that there is a high

rectovaginal fistula, which requires a temporary diverting colostomy and formal reconstruction at a

later date. However, the type of imperforate anus is not clear in a case without fistula, as observed

at clinical examination. In some cases, external fistulas may not become apparent until the neonate

is 12–24 hours of age, at which time the meconium moves distally into the rectum (25). Hence,

physical examination does not provide enough information about the level of the distal rectal pouch;

it must be defined radiographically.

In conclusion, infracoccygeal US in neonates with imperforate anus can help in the evaluation of the

relationship between the puborectalis muscle and the distal rectal pouch and is an excellent

diagnostic modality for determination of the type of imperforate anus.

Published online before print May 8, 2003, doi:

10.1148/radiol.2281011900

July 2003 Radiology, 228, 226-229.

http://radiology.rsna.org/content/228/1/226.long