Nearly all babies in each group had ventriculomegaly, a condition in which the fluid-filled spaces in the brain, are enlarged
A report released yesterday shows in graphic detail the kind of damage Zika infections can do to the developing brain - damage that goes well beyond the devastating birth defect known as microcephaly, in which the baby's head is smaller than normal.
The current Zika outbreak was first detected last year in Brazil, where the virus has been linked to more than 1,800 cases of microcephaly, which can cause severe developmental problems.
Prior research has shown the Zika virus attacks neural progenitor cells - a type of stem cell that develops into different types of nerve or brain cells.
The latest research, published in the journal Radiology, draws from imaging and autopsy findings linked with confirmed Zika infections done on 17 infants and fetuses cared for at the Instituto de Pesquisa, in Campina Grande in the state of Paraiba in northeastern Brazil, where the infection has been especially severe.
The study also included reports on 28 fetuses or newborns with brain anomalies whose mothers were suspected of having Zika during pregnancy.
Nearly all babies in each group had ventriculomegaly, a condition in which the ventricles, or fluid-filled spaces in the brain, are enlarged.
While most of the fetuses had at least one exam showing abnormally small head circumference, suggesting they had microcephaly, three of the fetuses with ventriculomegaly had normal head circumference, but severe ventriculomegaly.
Nearly all of the fetuses or babies in the confirmed Zika group and nearly 80 per cent of those in the presumed Zika group also had abnormalities of the corpus callosum - a large bundle of nerves that facilitates communication between the left and right hemispheres of the brain.
In all but one of the cases studied, the researchers found instances in which developing neurons did not travel to their proper destination in the brain.
In many cases, the babies' skulls seemed to have collapsed on themselves, with overlapping tissues and abnormal skin folds suggestive of a brain that had stopped growing.
"From an imaging standpoint, the abnormalities in the brain are very severe when compared to other congenital infections,” said study co-author Dr. Deborah Levine of Beth Israel Deaconess Medical Center and a radiology professor at Harvard Medical School.
As with other reports, the paper suggests that Zika does the most harm in the first trimester of pregnancy. The researchers plan to keep following the cases to see what impact prenatal Zika infections have on future brain development.
There is no vaccine or treatment for Zika, which is a close cousin of dengue and chikungunya and causes mild fever, rash and red eyes. An estimated 80 per cent of people infected have no symptoms, making it difficult for pregnant women to know whether they have been infected.
Zika is carried by mosquitoes, which transmit the virus to humans. A small number of cases of sexual transmission have been reported in the United States and elsewhere.