ultrasound diagnosis of fatal anomalies

SPINA BIFIDA APERTA
Spina Bifida Aperta, (Myelo-)Meningocele
Definition: Midline defect of the vertebra combined
with a neural tube defect, leading to
herniation and exposure of neural tissue and the
meninges. This results in a considerable loss of
neurological function. The defect is located in
the lumbosacral region in 90% of cases, in the
thoracic region in 6–8%, and in the cervical
vertebrae in 2–4%. In 75%, the herniated sac
shows a myelomeningocele and in 25% a meningocele.
Incidence: Varies geographically; in Germany
one in 1000, in the USA between one in 500 and
one in 2000 births.
Sex ratio: M:F=1: 1
Clinical history/genetics: Alpha fetoprotein in
serum is elevated in 80% of mothers. The recurrence
rate after one affected child is 2–3%, and
after two affected children 10%.
Teratogens: Valproic acid, folic acid antagonists,
high doses of vitamin A, thalidomide, diabetes
mellitus, hyperthermia, folic acid deficiency.
Embryology: A defect in the posterior arch of the
vertebra, which develops up to the 6th week. The
usual location is lumbosacral, with hydrocephalus
resulting from the Arnold–Chiari malformation
present in 90% of the cases.
Associated malformations: Arnold–Chiari malformation
(“banana sign”) and hydrocephalus,
deformation of the head with overlapping of the
frontal bones (“lemon sign”), club feet, occasionally
hydronephrosis and heart defect.
Associated syndromes: Over 90 chromosomal
and nonchromosomal syndromes have been described.
Ultrasound findings: Widening of the vertebral
column in the affected region appears as a U shape
in transverse section. Frequently, a cystic elevation
is found dorsal to the vertebral column. Most
commonly located in the lumbosacral region.
(The upper edge of the iliac bone represents the
5th lumbar vertebra). Sometimes a bulge is seen
in the affected area. The vertebral column should
be viewed in the horizontal and longitudinal axis.
In small defects, Arnold–Chiari malformation
(“banana sign”) and “lemon sign” are more easily
recognized than the defect in the vertebra.
Widening of the lateral ventricles is often present,
the head circumference however may still be
small. Ninety-eight percent of the myelomeningoceles
are detected through ultrasound screening
of the head and the vertebral column. Club
feet and absence of movement in the lower extremities
predicts a poor prognosis. On the other
hand, spontaneous movement of the lower extremities
does not assure normal neurological
function postnatally or after surgery.
Clinical management: Karyotyping (chromosomal
aberrations in 10%), measurement of
amniotic fluid alpha fetoprotein and acetylcholinesterase.
Progression of hydrocephalus
should be monitored regularly. Premature
delivery after 31weeks of gestation may be advised
if hydrocephalus progresses. Recommendations
regarding the mode of delivery are inconsistent.
Recent reports have shown that primary
cesarean section prior to onset of labor allows
the greatest preservation of motor skills.
Procedure after birth: The delivery should take
place in a perinatal unit. Gentle handling of the
defect without causing trauma is essential; the
defect should be covered using aseptic measures.
Hydrocephalus may develop even after the
defect has been surgically repaired. It is often
necessary to place a ventriculoperitoneal shunt
prior to surgery. Recurrent urogenital infections
and orthopedic dysfunction are treated symptomatically.
Prognosis: This depends on the size and location
of the meningomyelocele. There is a 10% risk of
mental retardation. A certain degree of neurological
deficit in the lower extremities and urinary
bladder dysfunction are expected.
Recommendation for the mother: Intake of folic
acid (4 mg/d) prior to conception reduces the
risk of recurrence significantly.
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