Nebraska woman Alex Simpson celebrates 20th birthday with hydranencephaly

Alex Simpson reaches her 20th birthday

Alex Simpson, from Nebraska, was diagnosed at two months old with a rare congenital brain condition that suggested she might not live to see her first birthday.

Against those medical expectations, Simpson and her family celebrated her 20th birthday on 4 November this year.

Her condition, hydranencephaly, leaves her cerebral hemispheres almost entirely absent. These are the two large brain lobes which normally account for most of the brain and govern cognitive ability, voluntary movement and sensory processing. Although her brainstem and certain other structures remain, cerebrospinal fluid fills the rest of her cranial cavity.

Hydranencephaly has no cure and requires intensive supportive care to manage it.

Hydranencephaly symptoms and surviving infancy

Babies with hydranencephaly can appear typical at birth, with a usual head size and normal reflexes. However, irritability, raised muscle tone, seizures and hydrocephalus - a build-up of cerebrospinal fluid in and around the brain - may later develop. This could be why Simpson's condition was not identified until she was two months old.

"Technically, she has about half the size of my pinky finger of her cerebellum in the back part of her brain, but that's all that's there," Alex's father, Shawn Simpson, told Omaha news station KETV earlier this month.

As a result, Simpson has impaired sight and hearing, although her cerebellum retains some awareness of what is around her. Her family nevertheless say they share a close bond with her.

"She knows her mum and her dad, her little brother. She knows when good things are going on around us, she knows when bad things are going on around her," Alex's father said in a KETV interview for Alex's 10th birthday.

Her brainstem, which carries signals between the brain and the body, is intact. Her meninges, the brain's protective membranes, and basal ganglia also remain, allowing her most essential functions to continue.

The basal ganglia normally contribute to movement, learning, cognition and emotion, although the effects of missing cerebral hemispheres on these processes are not clear.

How hydranencephaly develops

Hydranencephaly starts during the early phases of fetal development, and most babies with the condition do not live until birth. It occurs in around 1 in 10,000 births globally and in fewer than 1 in every 250,000 births in the US.

In many instances, ultrasounds reveal the early indications while a baby is still in the womb. When it is diagnosed in utero, parents may choose abortion after considering the child's quality of life, the emotional and financial consequences of the care required to control symptoms, and their own beliefs.

The cause of hydranencephaly remains unknown, although some studies indicate that it could result from vascular damage - such as a stroke or infection - that interrupts the brain's blood supply.

Symptoms generally become apparent during the second trimester, though in some cases they can be seen from as early as 12 weeks.

"While we are still learning, hydranencephaly is presumed to be a destructive process impacting the brain, commonly due to a variety of causes," paediatric neurologist Sumit Parikh of the Cleveland Clinic told Judy George at MedPage Today.

"Less commonly, genetic disorders impacting cerebral blood vessel formation have been identified," Parikh said. "Considering we have not had comprehensive testing like whole-genome sequencing until relatively recently, it is possible that genetic causes have been underestimated."

Hydranencephaly should not be confused with the similarly named hydrocephalus, where fluid accumulates in a brain that has otherwise formed fully. Hydrocephalus may be a symptom of hydranencephaly or occur independently, and increased pressure within the skull can also reduce the cerebral hemispheres.