17. Degenerative and Demyelinating brain diseases

Question 1

Imaging modality:

Answer 1

MRI: method of choice for brain parenchyma (superior soft tissue differentiation)

Question 2

Classification of diseases:

Answer 2

Demyelinating: MS
Degenerative: atrophy, Parkinsons, Alzheimer, Huntington

Question 3

Cerebral atrophy:

Answer 3

Description: progressive loss of brain cells over time + elderly (–> cognitive dysfunction + acute confusion) + enlargement of subarachnoid space (reduced brain parenchyma) + incidental finding on imaging

Focal atrophy: age-related + alcohol-abuse

Generalized: post-ischemic + post-traumatic + parkinson/alzheimer/huntington

Diagnosis: MRI + CT
MRI: sensitive to focal atrophy in nuclei

Signs: prominent sulci, narrowed gyri, enlarged ventricles, increased subarachnoid space

Question 4

Parkinson’s disease:

Answer 4

Description: progressive degeneration of dopaminergic neurons in substantia nigra

Symptoms: resting tremors, rigidity, hypokinesia

Imaging:
Initial: small, only seen on MRI
Advanced: non-specific generalized cerebral volume loss

Normal: hyperintense swallow tail sign (nigrosome-1 in substantia nigra return high signal surrounded by low signal intensity resembling split tail of swallow)
Parkinson: NO swallow tail sign (hypointense) in substantia nigra

Question 5

Alzheimer’s disease:

Answer 5

Description: most common cause of dementia (60-80%), accumulation of amyloid-beta plaques

Imaging: CT/MRI
MRI: more sensitive to changes + better exclude other causes of dementia

Signs: enlarged ventricles, narrowed gyri, prominent sulci

Question 6

Huntington’s disease:

Answer 6

Description: loss of GABAergic neurons in basal ganglia (especially atrophy of caudate nucleus+ putamen)
Diagnosed between 30-50y

Imaging:
MRI: caudate nucleus head atrophy –> enlargement of frontal horns of lateral ventricles –> “box-like” shape

Question 7

Demyelinating disorder - MS/ADEM:

Answer 7

ADEM: acute inflammation of white matter, following viral infection or vaccination

T2w: hyperintense regions with surrounding edema
Compared to MS, involvement of corpus callosum is unusual + can involve grey matter and brainstem

HAND: HIV-associated neurocognitive disorder
Dilated ventricles, white matter lesions

Imaging:
MRS (early detection of HIV encephalitis) - low NAA, increased MI (myo-inositol)