Brain surgery has been carried out on a baby inside the womb. The world first was to fix potentially deadly damage to vessels and saved the infant from suffering heart failure and a stroke after birth.
The rare pre-natal condition is known as Vein of Galen malformation (VOGM).
Arteries carrying high-pressure blood connect to one of the main veins deep at the base of the brain.
In normal foetal development, they should link to smaller capillaries - slowing flow and delivering oxygen to surrounding tissue.
The US team used ultrasound to carry out the successful procedure at 34 weeks and two days gestational age.
Due to rupture of membranes the unnamed child was delivered by induction of vaginal birth two days later. It is now at home.
Lead author Professor Darren Orbach, of Boston Children's Hospital in the United States, said: "In our ongoing clinical trial, we are using ultrasound-guided transuterine embolisation to address the vein of Galen malformation before birth.
"In our first treated case, we were thrilled to see that the aggressive decline usually seen after birth simply did not appear."
Repeated echocardiograms after birth displayed marked improvement in cardiac output. Scans showed normal heart and brain function.
Prof Orbach said: "We are pleased to report that at six weeks, the infant is progressing remarkably well, on no medications, eating normally, gaining weight and is back home.
"There are no signs of any negative effects on the brain."
Experts described the study in the journal Stroke as "pioneering". The premature newborn did not require any cardiovascular support or surgery following the treatment.
It was kept in the neonatal intensive care unit for several weeks. During that time, the newborn had a normal neurological exam and showed no strokes, fluid buildup or haemorrhage on brain MRI.
Prof Orbach said: "This is only our first treated patient. It is vital that we continue the trial to assess the safety and efficacy in other patients.
"This approach has the potential to mark a paradigm shift in managing Vein of Galen malformation where we repair the malformation prior to birth and head off the heart failure before it occurs, rather than trying to reverse it after birth.
"This may markedly reduce the risk of long-term brain damage, disability or death among these infants."
The high flow in the malformation has an even more serious effect on the heart and brain after birth - putting enormous pressure on the newborn's heart and lungs.
This may lead to pulmonary hypertension, heart failure or other life-threatening conditions.
VOGM is most often first seen on a pre-natal ultrasound scan - then diagnosed by MRI (magnetic resonance imaging) during the late second or third trimester of pregnancy.
It is estimated that VOGM, the most common congenital vascular brain malformation, occurs in as many as one in every 60,000 births.
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Current standard of care is treatment after birth with embolisation, a catheter-based procedure to close off the direct artery-to-vein connections and block excess blood flow to the brain and heart.
However, embolisation itself is high risk and is not always successful at reversing heart failure.
Additionally, severe brain damage may have already occurred, which may lead to life-long cognitive disabilities and life-threatening conditions for the infant, or even to death.
Professor Gary Satou, a foetal cardiologist at the University of California, Los Angeles, said the intervention may be "very impactful" in a specific group of patients.
He said: "As always, a number of these foetal cases will need to be performed and followed in order to establish a clear pattern of improvement in both neurologic and cardiovascular outcomes.
"Thus, the national clinical trial will be crucial in order to achieve adequate data and, hopefully, successful outcomes."
Prof Colin Derdeyn, a neuro-interventional radiologist at the University of Iowa who performs VOGM embolisations on neonates, also cautiously welcomed the breakthrough.
He said: "The key advance here is to intervene before the physiologic events of birth can cause life-threatening heart failure.
"There are caveats; one successful case is not enough experience for us to conclude that the risks of this procedure are worth the benefits.
"Safety issues may crop up in future procedures, and this approach through the veins may not be consistently successful in preventing heart failure.
"The procedure described here is designed to reduce the flow through the malformation and not to cure it.
"However, the positive heamodynamic changes that they observed in utero and after birth - reduction in flow, reduction in size of the draining vein, reversal of the abnormal reversed flow in the aorta - are really encouraging.
"These are some of the most exciting and surprising aspects of this case report. This is pioneering work being done in a very careful and responsible way."
