The cerebellum is a portion of the brain that is responsible for fine motor movements including posture, balance, motor learning (like learning to kick a ball), and speech. Located at the base of the skull, the cerebellum contains about half of all neurons in the brain, though it represents only 10% of the volume. Losing partial function due to injury or disease isn’t completely unprecedented, though lacking a cerebellum from birth is exceedingly rare. Physicians in China discovered a 24-year-old woman who is only the ninth known case of a living person with cerebellar agenesis. Her condition was described in the journal Brain.
The woman’s condition was discovered after she sought medical attention due to nausea and vertigo. CT scans and MRI images revealed the missing cerebellum, which readily explains why those symptoms would be present. It also explains why she wasn’t able to speak until she was six and wasn’t able to walk until age seven. She had never been able to play and jump like normal kids due to this defect.
Magnetic resonance angiography image reveals that the posterior cranial fossa, where the cerebellum is missing, does not have cerebellar arteries bringing blood to the region. Image credit: Feng Yu et al.
Unsurprisingly, the woman had been unable to walk steadily without support throughout her life.
While testing revealed that she had no trouble understanding vocabulary, the missing cerebellum caused her to have difficulties with pronunciation. Her voice trembles, words are slurred, and the doctors described her voice tone as “harsh.” Even still, the doctors were amazed that her symptoms were more in line with a mild to moderate impairment, not a complete absence.
In the space where the cerebellum should have been, cerebrospinal fluid has filled the gap. The chemistry of the fluid appeared normal, though the pressure was a bit high. Initial measurements read 210 mm H2O, exceeding normal limits of 70-180 mm H20. She was treated with a dehydration treatment that removed some of the water pressure along with other techniques that were less invasive, which provided immediate and lasting improvement of her symptoms. Even at a follow-up appointment four years later, she was still doing quite well.
Neurological defects do not appear to run in her family, and she was able to get married and have a neurologically-typical daughter without pregnancy complications. The structures and tissues surrounding the missing cerebellum appear to be mostly well-formed with no signs of extreme defects. The pons appeared underdeveloped, but considering part of its job is to convey messages from the frontal cortex to the cerebellum, that’s not completely surprising.
Diffusion tensor imaging reveals a lack of pontocerebellar fibers, which function to bring signals from the pons to the cerebellum. Image credit: Feng Yu et al.
As the condition is so rare, it isn’t very well understood how it occurs. While there are about 30 mutations associated with disorganized cerebella, complete absence of the structure is a bit tougher to figure out. This woman represents a very unique opportunity to study the effects of this disorder in a living adult. It isn’t known how her condition will change as she ages, but the fact that she has made it this far is a testament to the plasticity of the brain.
[Hat tip: New Scientist]