Doctors told her parents she wasn’t expected to survive past the age of four, but a Nebraska, USA, woman born without cerebral hemispheres celebrated her 20th birthday last week, reports Medpage Today.
Alex Simpson was diagnosed with hydranencephaly, a rare congenital malformation, when 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,” her father, Shawn Simpson, told KETV in Omaha.
While babies born with hydranencephaly may seem normal at birth, with a typical head size and reflexes, signs of irritability, increased muscle tone, and symptoms such as seizures and hydrocephalus (a build-up of cerebrospinal fluid in and around the brain) can emerge. This may explain why doctors took two months to detect Simpson’s condition.
This means her vision and hearing are impaired, though her cerebellum maintains some awareness of her surroundings. Her family say they nevertheless have a strong relationship 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,” her father said in an interview for her 10th birthday.
The cerebral hemispheres – which are responsible for higher cognitive functions, voluntary movement, and sensory processing – are completely or almost completely absent in people with hydranencephaly.
Instead of brain matter, the cranial cavity is filled with membranous sacs of cerebrospinal fluid. Basal ganglia, brainstem, and meninges are preserved.
Why hydranencephaly occurs is unclear. “While we are still learning, hydranencephaly is presumed to be a destructive process impacting the brain due to a variety of causes,” Sumit Parikh, MD, a paediatric neurologist with the Cleveland Clinic, told MedPage Today.
Studies suggest that the damage is related to bilateral internal carotid artery occlusion. Either occlusion or severe hypoperfusion of the supraclinoid segments of both internal carotid arteries in the first trimester in pregnancy could lead to hydranencephaly, Parikh added.
Hydranencephaly could also be caused by an in utero infection with necrotising vasculitis, severe foetal hypoxia, or from a toxin exposure like cocaine.
“Less commonly, genetic disorders impacting cerebral blood vessel formation have been identified,” Parikh noted. “Considering we have not had comprehensive testing like whole-genome sequencing until relatively recently, it is possible that genetic causes have been under-estimated.”
Prenatal ultrasound can help make a preliminary diagnosis of hydranencephaly, but the gold standard for diagnosis is brain MRI. Some patients with hydranencephaly may appear normal after birth but start developing signs, like an increased head circumference, a few weeks later.
The prognosis is poor and patients often die in their first year of life. In those who survive, preserved brainstem regions can maintain vital functions.
“The treatment of hydranencephaly is primarily supportive,” Parikh said.
One of the longest hydranencephaly survivors was a woman in Italy who could walk with a spastic gait after intensive therapy, but never developed any form of speech. She died at age 32 due to pneumonia from Covid-19.