Thursday, January 25, 2007

Fetal MRI - More Accurate Prenatal Diagnosis

I work in the Level III Neonatal ICU of a community hospital. We care for some really some sick kids, but we transport out most infants with complex congenital anomalies which need immediate surgical intervention.

Neonatal transport is really not the best way to deal with these babies. In a perfect world, you want them delivered in the same hospital where care will be given -- or at least very close to that hospital. To accomplish this, you need prenatal diagnosis. That's not always possible for a variety of reasons, but when there is reason to suspect an anomaly, there are some excellent diagnostic modalities available.

Ultrasound is still the first-line tool for screening in pregnancy and probably will be for a very long time. It is quick, cost-effective, and visualizes the baby in real time. It is still the best way to visualize cardiac anatomy. It does have some limitations, though. For example, it's difficult to see what's going on inside the skull. Also, if the mom is very large, there may be some limitations to its usefulness.

I received a newsletter from Children's National Medical Center in the mail this week with an article about fetal MRI. I couldn't find a link to their article, although it may be online next month. I did find this one in Radiology Today, though. Both articles outline the advantages of prenatal diagnosis for planning interventions in the immediate neonatal period -- including changes in location of delivery, if that is indicated. Anomalies which typically aren't repaired at birth, and which can be managed in a community hospital NICU wouldn't require a change of venue. For more complicated anomalies, especially those requiring immediate intervention, families can plan the birth at or near the hospital where treatment will occur. In addition to being better for the baby, this is less stressful for the family as it minimizes separation at birth.

MRI provides better definition of neural tube defects, thoracic structures and craniofacial anomalies than is possible with ultrasound. This makes it helpful in planning intrauterine interventions as well as initial post-delivery treatment. There are diagnostic advantages for craniofacial anomalies, neural tube defects, diaphragmatic hernias, and an assortment of mass lesions in the head, chest, and abdomen.

There is no evidence of adverse effects from MRI, so it is considered safe throughout pregnancy. Ccontrast is not used because it crosses the placenta. I think there is a typo in the Radiology Today article. It states "Since ionizing radiation is involved" -- I believe the word "no" was left out as that doesn't match what I know of MRI or the statement that "risk for any delayed sequelae is extremely small or nonexistent."

With older equipment, maternal sedation was sometimes used. Occasionally the fetus was paralyzed by injecting pavulon via the umbilical cord when it was necessary to suppress fetal motion. This is no longer necessary, although some moms fast for several hours prior to the procedure to decrease fetal movement. The latest generation of ultra-fast MRI scanners can acquire an image in under a second. Researchers believe that the next generation of scanners will be even faster. Other research in progress when the article was published last year included studies of fetal oxygenation and pre-eclampsia. It is fascinating to see where the research will lead.

No comments: