ultrasound diagnosis of fatal anomalies

6 Abdomen
Anal Atresia
1
2
3
4
5
Definition: Congenital absence of the opening of
the anus.
Incidence: One in 5000 births.
Sex ratio: M:F=3:2.
Clinical history/genetics: Sporadic, rarely familial
forms with autosomal-recessive inheritance.
Embryology: Failure of division of the cloaca into
the urogenital sinus and rectum, around 9 weeks
after conception. Various lesions are recognized
in which the rectumterminates above or below
the puborectal sling. The higher the location of
anal atresia, the more frequent the associated
malformations. The level of atresia also determines
whether primary surgical therapy is indicated
after birth or whether a colostomy should
be performed first, with definitive surgical correction
at a later stage. This anomaly is commonly
accompanied by esophageal atresia.
Teratogens: Alcohol, thalidomide, diabetes mellitus.
Associated malformations: These are found in
50%. Skeletal anomalies are associated in 30%,
urogenital malformations in 38%, esophageal
atresia in 10%, and cardiac anomalies in 5%.
Associated syndromes: Over 80 syndromes have
been described in which anal atresia is found, including
VACTERL association. Various chromosomal
anomalies—e.g., partial trisomy 22q and
partial monosomy 10q.
Ultrasound findings: The anus can be seen as an
echogenic spot at the level of the genitals in
transverse section. In the case of anal atresia, the
echogenic spot is missing. Dilation of the large intestine
and calcification of meconium within it
may be an additional sign. These findings are
first evident at a later gestational age (after
30 weeks).
Clinical management: Further sonographic
screening, including fetal echocardiography.
Karyotyping. Injection of contrast medium into
the amniotic cavity followed by radiography of
the fetus (amniofetography) have been performed
in some cases historically.
Procedure after birth: Atretic anus is diagnosed
at once at the first examination of the newborn
after birth. Oral feeding is then contraindicated.
A nasogastric tube should be inserted to relieve
the secretions. In male infants, the anal fistula
joins the urethra, and in the females the vagina.
A blind ending of the rectumis an exception. An
anus praeter is often established initially, so that
definitive surgical treatment can follow at the
age of 6–12 months.
Prognosis: This depends on the associated malformations.
In the isolated form of anal atresia,
70% of cases show good functional capacity after
surgical correction.
Self-Help Organizations
Title: The Pull-Thru Network
Description: A chapter of United Ostomy Association.
Support and education of families
with children born with anorectal malformations
(including cloaca, VATER, cloacal exstrophy,
or atretic anus and Hirschsprung’s disease).
Maintains a database for personal networking.
Quarterly newsletter. Online discussion
group. Phone support and literature.
Scope: National
Number of groups: Two affiliated groups
Founded: 1988
Address: 2312 Savoy Street, Hoover, AL
35226–1528, United States
Telephone: 205–978–2930
E-mail: pullthru@bellsouth.net
Web: http://www.pullthrough.org
106