Cerebellar Degeneration MRI

A 41 yo female with slow progressive ataxia, slurred speech since last 15 years. Truncal ataxia on neurological examination. Family history of similar complains was present. 

MRI sagittal T1 and T2w images show:
Marked atrophy of the cerebellum.

Normal brain stem (midbrain, pons and medulla are spared)

Cerebellar Degeneration: 
Atrophy of the cerebellum is associated with many genetic conditions.
Non genetic causes include chronic severe alcohol intake, paraneoplastic syndromes, drugs like Phenytoin.
The nomenclature of genetic disorders associated with cerebellar atrophy is complex. Most are classified by the chromosomal location and pattern of inheritance. In many, a specific gene mutation or defective protein has been found. In the past, these disorders were referred to as cerebellar degeneration, spinocerebellar degeneration and olivopontocerebellar atrophy (OPCA) depending on whether the cerebellum, spinal cord, brainstem or a combination of any of the above affected.

Spino Cerebellar Degeneration MRI

A 28 yo male, C/o slow progressive ataxia and slurred speech. On neurological examination nystagmus, altered cognition. Family history significant.

MRI sagittal T1 and T2w images show:

Marked atrophy of the cerebellum and Brain stem, compensatory enlargement of adjacent Cp angle cisterns and fourth ventricle.

Imaging findings and history is consistent with a clinical diagnosis of Spinocerebellar Degeneration - Spino Cerebellar Ataxia.


Spino Cerebellar Ataxia (SCA)
Atrophy confined to cerebellum and Pons is an imaging wise diagnostic clue.
These neurodegenerative disorders, once termed Olivo Ponto Cerebellar Atrophy (OPCA), comprise a large group of inherited disorders characterized by progressive ataxia and brainstem signs.
DNA analysis in this patient demonstrated SCA Type 2; typically manifests with progressive gait and limb ataxia, dysarthria and slow saccadic eye movements.
The SCA-2 mutation is an expansion of an unstable CAG repeat located in the ataxin-2 gene on chromosome 12q24.1.

Huntington's Disease MRI

A 51 yo male under psychiatric treatment over several years. Relative complaining of his dementia. On neurological examination noticed Chorea. Family history was significant; father had a milder but similar illness.

Coronal MRI T1w image show:
Marked atrophy of caudate nuclei with ex vacuo dilatation of frontal horns. 
An associated diffuse cerebral cortical Atrophy.  

Imaging findings and history is consistent with Huntington's Disease.

Syn: Huntington Chorea.
An autosomal dominant neuro degenerative disorder with loss of GABAergic neurons of basal ganglia.
Clinically characterized by triad of Dementia, Choro athetosis and Psychosis.
Imaging wise diagnostic clue is caudate nuclei atrophy.
Age: Adult onset : 35 - 45years, Juvenile onset : < 20 years; M=F

Corticobasal Ganglionic Degeneration

A 75 yo male ataxia. On neurological examination marked apraxia and cortical sensory loss like astereognosis). Increased tone in lower limbs.

MRI Axial T1 image show atrophy with marked widening of cortical sulci in parietal region. No signal abnormality in brain parenchyma on T2w images suggestive of cerebral cortical atrophy confined to parietal lobes.

Imaging finding of bilateral parietal lobe atrophy with history is consistent with a clinical diagnosis of Corticobasal Ganglionic Degeneration.


Corticobasal ganglionic degeneration (CBGD)
A rare Neurodegenerative disorder.
Imaging wise cerebral cortical atrophy prominently involving parietal lobes along with basal ganglia.
Clinically characterised by prominent cortical sensory loss and Apraxia. Alien hand syndrome, whereby pt complaints that he feels that his hands are disconnected from the rest of their body.
Dysfunction of the basal ganglia results in features of Parkinsonism, including increased tone, bradykinesia and gait disturbance. However, in contrast to Parkinson's Disease, Levodopa and other similar drugs are ineffective in this condition.
CBGD has significant overlap with other rare neurodegenerative disorders, including frontotemporal dementia, primary progressive aphasia (PPA), Pick's disease and progressive supranuclear palsy (PSP).

Wallerian degeneration MRI Brain

A contiguous T2 hyperintense track of Gliosis along the topographic distribution of pyramidal tract.

WaD is seen along the ipsilateral descending white matter tracts traversing through internal capsule, midbrain, pons, medulla.

An associated primary lesion may be cortical or subcortical is often found, may be an infarction, haemorrhage, neoplasm, demyelination, trauma; even reported in patients with movement disorder.

MRI diffusion T2 and Flair are must to pick up the finding, seen as a contiguous T2 hyperintense track of Gliosis, an associated asymmetry of brain stem due to atrophy in chronic stages. Being a chronic and degenerative process restricted diffusion on dw images and contrast enhancement on post contrast study not expected. CT is completely non sensitive.

WaD is usually unilateral, always asymmetrical if it is bilateral. If bilateral and symmetrical think of ALS which is a neurodegenerative / motor neurone disease characterised by bilateral symmetrical contiguous T2 hyperintensity along CST extending from corona radiata down to brain stem and cord.

MRI Axial Flair Brain shows  a focal csf signal intensity Gliotic cavity with hemosiderin staining on T2*GRE in left corona radiata is a chronic resolved hematoma is a primary lesion with an associated distal wallerian degeneration seen as contiguous T2 hyperintensity in the region of posterior limb of ipsilateral internal capsule, mid brain , pons and medulla.

Hypertrophic Olivary Degeneration

A rare type of secondary degeneration of Inferior Olivary Nucleus (ION), usually caused by primary lesion in Dento Rubro Olivary pathway (Anatomical Triangle of Guillain and Mollaret)

Triangle of Guillain and Mollaret defined by three anatomical structures.
Dentate nucleus (DN) of Cerebellum.
Contra lateral Red Nucleus (RN).
Inferior Olivary Nucleus (ION), ipsilateral to RN.


Imagingwise Hypertrophic Olivary Degeneration seen as unilateral or bilateral enlargement of ventro medial portion of Medulla with T2 hyperintensity which corresponds to ION.

There patterns of HOD in relation to location of primary lesion.
Ipsilateal HOD, when primary lesion is in brain stem – central tegmental tract.
Contralateral HOD, when primary lesion is in DN of cerebellum.
Bilateral HOD, when primary lesion involves both central tegmental tract and superior cerebellar peduncle.

Case : A 60 yo male complaining of mild ataxia.

Findings:
Gliosis confined to right half of mid brain, Pons and cerebellar peduncle. A Gliotic lesion in the region of dentate nucleus of right cerebellar hemisphere. Ventromedial portions of both half of Medulla show enlargement with T2 hyper intensity implies to Bilateral Hypertrophic Olivary Degeneration explained by involvement of central tegmental tract, cerebellar peduncle and dentate nucleus of cerebellum.
Clinically patient has no palatal myoclonus.

Histologically olivary enlargement is a vacuolar cytoplasmic degeneration.  Hypertrophy is related to local increase in astrocyte proliferation. Associated brain stem lesions are usually a focal Gliosis, may result from ischemia, bleed, demyelination, trauma including surgery.
Clinically characterised rhythmic palatal myoclonus, may affect any age group and gender.
Usually develop after 10 to 11 month after primary lesion.
Virtually all patient with clinically palatal myoclonus will show HOD on imaging but not necessary that all patient of HOD on imaging will show palatal myoclonus clinically.

Bilateral HOD

Multiple System Atrophy MRI

Axial T2 images at the level of Pons show a cruciform hyperintensity so called "hot cross bun" sign. An associated atrophy confined to brain stem and cerebellum. 

Diagnostic criterias for multiple system atrophy (MSA) includes : 

1st Autonomic failure/urinary dysfunction, 2nd Parkinsonism 3rd Cerebellar ataxia and 4th corticospinal dysfunction. 

Definitive diagnosis of MSA requires pathological confirmation.

The so-called "hot cross bun sign" is specific for MSA but not pathognomonic for MSA.