Images of fetuses infected with the Zika virus while still in the womb reveal neurological damage far more extensive than doctors previously thought possible, with abnormalities that range from massive calcifications in the brain to normal head sizes but very little brain tissue, researchers have found.

The images are part of an analysis by doctors in Brazil who also performed autopsies on infants who died and studied the CT scans, MRIs and sonograms of infant survivors of prenatal infection. The research, conducted in collaboration with doctors in Boston, was published as a special report in the current issue of the journal Radiology.

Doctors on Long Island said the analysis gives a heart-wrenching window into the ways the pathogen can affect a developing brain.

“I think it’s still very early and we are just beginning to see the full ramifications of the viral infection,” said Dr. Paul Wright, who chairs the Department of Neurology at Northwell Health’s campuses in Manhasset and New Hyde Park. He was not connected with the new research.

Medical investigators in Brazil found severe calcifications in the brain tissue of autopsied cases, the report said. In other instances, the head developed to a normal size but there was barely any brain tissue. Other babies had collapsed skulls, resulting in thick folds of skin on the top of their heads.

The researchers also found less gray matter, the dark tissue that makes up the brain and spinal cord, and correspondingly less white matter, tissue typified by protective fatty insulation.

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For months, reports by doctors in Brazil and the United States have focused on microcephaly — small head and brain size — as the leading form of fetal brain damage caused by the Zika virus. Microcephaly causes mental retardation, and affected children never are able to function independently.

“There were many reports about microcephaly, so that’s what everyone focused on. But there are more abnormalities to the brain tissue itself, so it’s more than just a small brain,” Wright said.

The broader understanding of Zika’s effects on fetal brain development comes about a month after the first case of microcephaly in New York City was announced by local public health officials. The mother had become infected while traveling, officials said.

In recent weeks, Zika infections independent of foreign travel were detected in Florida, with cases found in portions of Miami Beach and Palm Beach. Earlier this week, Zika-carrying mosquitoes were identified in St. Petersburg, on Florida’s Gulf Coast.

The virus — which can be transmitted by mosquitoes or through sexual intercourse — belongs to the group of pathogens known as flaviviruses, the same family to which the yellow fever and West Nile viruses belong. Zika first was identified in Brazil in mid-2013.

Whether the pathogen spreads rapidly to other states in patterns similar to those seen with the movement of West Nile has yet to be determined, some scientists have said.

However, tropical disease experts at the World Health Organization have emphasized the speed with which mosquitoes spread the Zika infection across large swaths of South and Central America, and have warned that mosquitoes in the United States can spread it widely too.

The cases studied for the new report stemmed from 438 pregnancies involving women who were seen by doctors at Instituto de Pesquisa in northeastern Brazil, the region struck hardest by the infection.

The women were institute patients from June 2015 to May, according to the report. They were referred to the facility for one of three reasons: a rash consistent with a Zika infection, suspected fetal neurological damage, or tests confirming the virus in the mother’s blood.

An infant with microcephaly -- a small head and brain -- who was born to a 34-year-old mother in Brazil who tested positive for the Zika virus. Photo Credit: Radiological Society of North America

In adults, most cases of Zika are so mild that people are unaware of the infection, medical experts said. For others, the most obvious symptoms can include rash, fever, headache and joint pain. Some adults have developed Guillain-Barré syndrome, a rare condition typified by weakness and tingling in the extremities.

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Dr. Fernanda Tovar-Moll, lead scientist of the Brazilian imaging research and a professor at the Federal University of Rio de Janeiro, wrote that it’s important for doctors to understand the fetal impact of a Zika infection. And it’s also important that doctors recognize possible virus-caused brain damage when they see malformations via medical imaging, she said.

“Imaging is essential for identifying the presence and severity of structural changes induced by the infection, especially in the central nervous system,” Tovar-Moll said.

More than 3,000 babies have been born with brain damage in Brazil since 2013, according to estimates from WHO.

“We are asking women to delay pregnancy if they are considering travel to areas where Zika is active,” said Dr. Jill Rabin, co-chief of ambulatory care and women’s health programs at Northwell Health in New Hyde Park. She said the first trimester of pregnancy is the period when the virus poses its greatest risks.

Cells attacked by the virus are those involved in the brain’s “scaffolding,” Rabin said, referring to the radial glial cells that are involved in forming the fetal spinal cord and the underlying structure of the brain itself.