Wednesday, November 22, 2017
Health

Zika, a formidable enemy, attacks and destroys parts of babies' brains

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The images tell a heartbreaking story: Zika's calamitous attack on the brains of babies — as seen from the inside.

With a macabre catalog of brain scans and ultrasound pictures, a new study details the devastation done to 45 Brazilian babies whose mothers were infected with Zika during pregnancy. The study, published Tuesday in the journal Radiology, is the most comprehensive collection of such images so far, and it reveals a virus that can launch assaults beyond microcephaly, the condition of unusually small heads that has become the sinister signature of Zika.

Most of the babies in the study were born with microcephaly, but many of them also suffered other impairments, including damage to important parts of the brain: the corpus callosum, which connects the two hemispheres of the brain; the cerebellum, which plays a significant role in movement, balance and speech; the basal ganglia, which are involved in thinking and emotion.

"It's not just the small brain, it's that there's a lot more damage," said Dr. Deborah Levine, an author of the study and a professor of radiology at Harvard Medical School in Boston. "The abnormalities that we see in the brain suggest a very early disruption of the brain development process."

The findings also raised worrisome concerns about whether babies born without such obvious impairments could develop brain damage as they grow. For example, almost all the babies in the study had problems in the cortex, including clumps of calcium and neurons that did not reach the right location in the brain. Because the cortex keeps developing after birth, Levine said, "we're concerned that there might be mild cases that we haven't seen yet, and we should keep monitoring the babies after birth to see if they have cortical abnormalities."

The images studied came from 17 babies whose mothers had a confirmed Zika infection during pregnancy and from 28 without laboratory proof but with all indications of Zika. Levine worked with colleagues in Brazil, which has had more than 1,800 cases of Zika-related microcephaly, to analyze images from the Instituto de Pesquisa in Paraiba. Three of the babies died in the first three days of life, and researchers studied their autopsy reports.

The images include scans of twin girls, who both developed microcephaly. The pictures show folds of overlapping skin and a sloping forehead, indications not only that the brain is smaller, but also that the forebrain has not developed normally, Levine said.

The researchers said they are making many of the images public so doctors around the world will have a better idea of what to look for in the brains of fetuses and newborns afflicted with the virus.

The study suggests that Zika is a formidable enemy, able to strike in many ways. Levine, who is also director of obstetric and gynecologic ultrasound at Beth Israel Deaconess Medical Center, described its three-pronged attack.

The virus causes dysgenesis, in which parts of the brain do not form normally. It causes obstruction, primarily because it keeps the ventricles or cavities of the brain so full of fluid that they "blow up like a balloon," she said. And it destroys parts of the brain after they form.

"The brain that should be there," Levine said, "is not there."

A baby was one of three in the study whose head size was not small enough to meet the medical definition of microcephaly. But that, said Levine, is likely because his ventricles are filled with cerebrospinal fluid that has been unable to drain.

"The ventricles have blown up, and they've kept the skull even bigger," she said.

In the brain scans, taken at 36 weeks into pregnancy and one day after birth, fluid is so prominent, "it looks like the skull, and very little brain tissue inside it," she said. On the top of the baby's head are folds indicating that the head was once bigger or that the skin continued to grow as the head stopped.

"There's too much skin for the size of the head," Levine said.

What will happen as this baby develops is unclear. Ventricles, she said, "like a balloon, can pop." And if they do, "the brain will collapse on itself."

A video shows a series of scans of the brain of the same baby taken one day after birth. It essentially provides a tour of the brain from bottom to top, Levine said. At about 3 seconds into the video, the images reveal a head so filled with fluid-enlarged ventricles that it is difficult to see signs of other brain matter.

The twins included in the study both developed microcephaly. While in some cases, one twin will develop microcephaly and the other will not, in this case, the twins sustained a similar degree of brain damage, suggesting that in their mother's womb, "they both got infected at the same time," Levine said.

The brain scans of the twin girls show that the babies have little or no corpus callosum to help one side of the brain communicate with the other.

"The corpus callosum is very important," Levine said. "It is the largest structure that connects the two sides of the brain."

Abnormalities in the corpus callosum were found in 38 babies. "In some of them I'm sure it wasn't there," she said. "That either means it never formed or it was destroyed."

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