Question

Cerebellar Agenesis, or Life Without the Cerebellum? (10 pts)

Arrigoni et al (2015). Learning to live without the cerebellum. NeuroReport 26, 809-813.

Yu et al (2015). A new case of complete primary cerebellar agenesis: clinical and imaging findings in a living patient. Brain 138, 1-5.

Omair et al (2018). Primary cerebellar agenesis in a normal man. Neurology India 66, 871-873.

Below are summaries of three individuals (noted by sex and age), who by brain scans, have more-or-less complete, absence of the cerebellum:

M48. Severe delay of early developmental milestones (Table). By age 4, neurological diagnosis of cerebellar ataxia, and psychiatric description as withdrawn and autistic. Over several decades of remedial programs, steady gradual improvements in all areas. Today, moderate gait ataxia, mild dysmetria, and mild intention tremor, but walks and performs all activities of daily living. No psychiatric disorder, and only mild intellectual impairment, including fair abilities to talk, read and write. “This progress was hardly foreseeable when he was a child diagnosed with severe cognitive and motor delay.”

(A) Sagittal and (C) coronal MRI show flattened pons and posterior fossa filled with CSF. Superimposed DTI-tractography shows normal corticospinal tracts from motor and somatosensory areas, normal cranial nerve V (yellow arrow), but no corticocerebellar or spinocerebellar pathways.

F26. At age 24, admitted to hospital, complaining of nausea for ~1 month, and dizziness and inability to walk steadily of more than 20 years! CT, MRI, DTI-tractography, and MR-angiography showed complete absence of cerebellar structures. According to her mother, she did not walk unassisted until 7 y, and has never ran or jumped. Her speech was unintelligible until 6 y and she did not enter school. Today, moderate gait ataxia, and mild to moderate dysmetria in the finger-to-nose test. Normal word comprehension and expression, and no sign of aphasia, but moderate dysarthria. Now married with a small child.

M45. At age 45, admitted to ER for head trauma: CT revealed complete absence of both cerebellar hemispheres, with small remnant of midline vermis. MRI refused for claustrophobia. Neurological exam showed no motor signs of cerebellar dysfunction. No history of any difficulty in walking, but he had had mild cognitive impairment, and dropped out of school.

1) What indications do CT, MRI, DTI-tractography, and MR-angiography provide that there is no anatomical cerebellum? What are their limitations?

What are their limitations?

2) Give three explanations of why motor impairments in primary cerebellar agenesis may appear less severe than some adult-onset ataxias? How do you test between these hypotheses?

How do you test between these hypotheses?

Answer 1

Ans 1) In this case, the studies from CT, MRI, DTI-topography and the MR-angiography showed that he completely lacked the cerebellum. According to the image analysis by the DTI-tractography, this showed that there is no spinocerebellar or corticocerebellar pathway which leads to the cerebellum. According to these analysis, it shows that there is no proper cerebro-cerebellar pathways and this shows that the cerebellum is missing from the brain. There is only a small midline vermis shown by the CT result and no cerebellum. This is a condition of cerebellar agenesis and following a CT analysis, it can be seen that there is low posterior fossa density along with no traces of cerebellar tissues along with the anterior fossa being filled up with CSF.

Ans 2) Three explanation that motor impairment in primary cerebellar agenesis is less severe:-

1. It impacts the cognition and development rather than initially impacting the motor movements. The progress with severe cognition and motor delay was not seen as the disorder onset takes place gradually.
2. The cerebellum is an area that is responsible for control and balance and when a person suffers from lack of cerebellum, the abnormalities change from time to time and it can be changed through stimulaton.
3. There is no impact on the blood circulation and other activities that are directed by the brain and hence it has no impact on the motor instruction initially.