Cerebellar Agenesis: Life without a Cerebellum

Many people are familiar with the famous patient H.M., the man who, in an attempt to control his intractable epilepsy, underwent surgical resection of both his medial temporal lobes.

There is another patient who is less famous, known the by initials H.C. He died in 1939 when H.M. was just entering adolescence. Unlike H.M., this patient did not undergo radical resection surgery. In fact, he never underwent brain surgery at all. His contribution to neurology did not begin until after his death at the age of 76.

In what was supposed to have been a routine autopsy, H.C. was discovered to have had no cerebellum (see pictured brain above). H.C. had a very rare neurological condition known as cerebellar agenesis. When I was in graduate school, I was taught that the neuroplasticity of the brain was so remarkable, that even a child born without his or her cerebellum could grow-up to have no deficits and live a normal life. As it turns out, that was only partly true. H.C. was in fact, not without deficits. His tale is recounted briefly in two articles from the March 2010 issue of Brain:

"It was clear that there were indeed clinical signs included right external strabismus (i.e., misaligned eyes), slow and slurred articulation and an unsteady gait." (1)

However, he did live a "normal life":

H.C. "had employment, that he was able to work in a manual job and that his working life was not curtailed by his cerebellar agenesis." (1)

What is interesting about H.C. compared to H.M., is that H.C.'s agenesis was discovered only after he died. Very little clinical history about his life exists, making this story a great neurological detective case. Most of what is known about H.C. comes from hospital notes during his last years of life, just before he developed dementia:

"The social history describes him as 'single.' The notes contained a record of his assessment by a neurologist, Dr. Jacobson, who described him as 'a simple man with some hearing loss and slow slurred speech; he has a fair memory for recent and remote events concerning himself, but with limited general knowledge. There is no hallucination or delusions nor emotional defect. He is clean in his habits and able to attend to his person. He is able to get around unassisted." (1)

The human brain is estimated to have approximately 85 billion neurons (2). The cerebellum, which is typically 1/4 the size of the rest of brain, contains a full 50% of all our neurons. If you pay close attention to the image above, you will notice that, in addition to not having a cerebellum, H.C. was also missing his pons, the bulbous structure that is typically adjacent to the cerebellum and is responsible for arousal and alertness.

Many of the patients I have seen with cerebellar strokes typically have severe and irreversible deficits. While H.C. did have some cognitive and functional deficits, that he lived a full and functional life is nothing less than remarkable. His case is an example of how extraordinary the human brain actually is.

I encourage you to read more about the mysterious case of H.C. here.



Boyd, C. (2009). Cerebellar agenesis revisited Brain, 133 (3), 941-944 DOI: 10.1093/brain/awp265

Lemon, R., & Edgley, S. (2010). Life without a cerebellum Brain, 133 (3), 652-654 DOI: 10.1093/brain/awq030