New Prenatal Surgery for Spina Bifida Holds Promise
Immediately after they are born, most infants with the disabling birth defect spina bifida undergo surgery in which the faulty covering of their spinal cord is closed up. Most also receive a surgically implanted shunt to drain away spinal fluid that accumulates in the brain because of defects in the spinal cord.
The surgeries provide some protection against future damage but do little to correct problems created by the defect. They are, according to Dr. Joseph P. Bruner of Vanderbilt University Medical Center, like slamming the barn door shut after the horses have already escaped.
Bruner has been one of the pioneers in a new form of prenatal surgery that, in effect, shuts the door much earlier. Vanderbilt is one of two U.S. hospitals where surgeons go into the womb during the sixth or seventh month of pregnancy to repair the spinal cord.
At least 74 children have undergone the procedure, and the results look promising. The children are much less likely to develop hydrocephalus--known colloquially as water on the brain--and to require a shunt. Preliminary results also suggest that they may be less likely to develop the paralysis and other lower-body problems common in spina bifida, and may suffer less mental impairment.
The procedure is by no means a cure for spina bifida, and some critics charge that the benefits observed so far do not outweigh the potential risks to both the infant and mother. But physicians and parents believe the procedure moderates the often disastrous outcomes of spina bifida, and that is a real benefit, they say. “If we have the chance to lessen the extent of the injury, why wouldn’t we do that?” Bruner said.
Spina bifida, in which part of the spine fails to develop properly during the fourth week of pregnancy, is one of the most common and most devastating birth defects, affecting an estimated 4,000 fetuses in the United States each year. In about half those cases, the parents choose to abort the fetus.
Those born with the most severe form of spina bifida, called myelomeningocele, are normally severely handicapped. Their legs are partially or completely paralyzed, they suffer loss of bowel and bladder function and loss of sensation, and hip and leg deformities are common. Hydrocephalus, which squeezes the brain, can produce significant brain damage.
No one knows what causes spina bifida, but one contributing factor is a low level of folic acid in the mother’s diet. The link to spina bifida is one reason the government recently began requiring fortification of flour with that vitamin.
Work by Bruner and others has shown, however, that the damage caused by spina bifida arises in two distinct steps--what he calls the “two-hit” theory. Some damage is done by the actual lesion on the spine. But the exposure of bare spinal nerves to amniotic fluid during the final weeks of the pregnancy compounds the damage and may, in fact, produce some of the most disabling problems associated with the disorder. It is these latter effects that prenatal surgery is designed to prevent.
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The road to the current spina bifida surgeries has, unfortunately, been littered with catastrophes, according to Dr. Joe Leigh Simpson of Baylor College of Medicine in Houston. Researchers first tried to implant shunts prenatally to limit the effects of hydrocephalus during pregnancy.
Tragically, surgeons did not appreciate the magnitude of other defects associated with such early hydrocephalus, he noted. Had the surgeons not intervened, the fetuses almost certainly would have miscarried naturally. With the shunts in place, the fetuses made it to birth, but were born with severely disabling defects.
Based on experiments in animals, Bruner and a colleague, Dr. Noel Tulipan, initially attempted to perform the prenatal spine-closing operation endoscopically--working though narrow tubes inserted through thin slits in the mother’s abdomen. That also was a failure, for reasons that are not yet clear. When they tried it on four expectant mothers, two fetuses died and one was born very prematurely.
Given that record, the new procedure, pioneered by Bruner and Tulipan at Vanderbilt and Dr. N. Scott Adzick and his colleagues at Children’s Hospital of Philadelphia, has been quite trouble-free.
In the procedure, they perform a so-called bikini incision on the mother’s abdomen and partially remove the uterus, resting it on the mother’s stomach. They then make a small incision in the uterus, drain most of the amniotic fluid, and position the fetus so that the lesion in the spinal cord is directly under the hole.
After sewing synthetic skin over the hole in the spinal cord, they fill the uterus with saline solution, put it back in the abdomen and sew up the initial incision.
The Vanderbilt team has so far performed the procedure on 63 fetuses and the Philadelphia team on 11, all with few problems. One fetus at Vanderbilt was stillborn and one had to be delivered during the surgery, but is now doing well. Virtually all of the others were delivered two to five weeks prematurely, but they, too, seem to have suffered no ill effects from the surgery.
And many seem to benefit. Whereas 90% of children born with spina bifida normally require surgical installation of a brain shunt after birth, less than half of those undergoing the prenatal surgery required one--and even in those cases, the hydrocephalus appeared to be mild.
Most of the infants seem to have acceptable leg and bowel function as well, but the oldest is only about 22 months, so it is still a little early to tell. “We know these babies are getting benefits,” Bruner said. “We still haven’t done enough cases and followed up long enough to know how much benefit in each individual case.”
They don’t expect to know about the effects on brain function until the children begin to enroll in kindergarten.
Bruner and Tulipan perform the surgery at about 28 weeks of gestation. Adzick and Dr. Leslie N. Sutton, in contrast, perform it at about 22 to 25 weeks. “Our research suggests that performing this surgery earlier in pregnancy . . . better prevents injury to the fetus,” Sutton said. They found, for example, that only three of their first 10 cases required a postnatal shunt.
Not all spina bifida fetuses are candidates for the procedure. Appropriate cases, Adzick said, “would be babies with a severe defect, but who have leg movement detected early in gestation by ultrasound. The fetus cannot have any other anatomical abnormalities [which would increase the risk of miscarriage]. Most importantly, the parents have to be committed to carrying the pregnancy. . . .”
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The procedure is not without risks to the mother. In addition to premature delivery, the stress can cause pre-eclampsia, gestational diabetes, uterine rupture and other problems. Future pregnancies, moreover, will most likely require Caesarean section. None of the women treated so far, however, have suffered serious problems.
The balance between risks and benefits has not yet been established, Simpson concluded, “but clearly there is enough potential benefit to proceed with further investigation.”
For further information, and to see a video of the procedure, visit: https://www.fetalsurgery.chop.edu and www.fetalsurgeons.com.
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Surgery in the Womb
Doctors at two U.S. hospitals have developed a surgical technique to help lessen the effects of the most severe form of spina bifida, called myelomeningocele. The surgery is done between weeks 22 and 28 of gestation.
BEFORE
The hindbrain protrudes into the spinal column because of a defect in the lower spine that causes accumulation of spinal fluid. Pressure on the brain can produce significant brain damage, and infants may be handicapped in many other ways, including leg paralysis and loss of bowel and bladder function.
AFTER
Synthetic skin is sewed over the defect in the spinal cord, allowing the hindbrain to move back into a more normal position. A total of 74 operations of this type have been done and babies seem to benefit, doctors say. However, the oldest is only about 22 months, so many developmental questions remain.
THE PROCEDURE
After making an incision in the mother’s abdomen and uterus to expose the back of fetus, surgeons at Children’s Hospital of Philadelphia prepare to correct a spina bifida lesion caused by abnormal development of the spinal cord.
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Source: Children’s Hospital of Philadelphia
