The brain’s cortex normally appears very wrinkled, with ridges of tissue (called gyri) separated by “valley” called sulci. In individuals with cortical atrophy, the progressive loss of neurons causes the ridges to become thinner and the sulci to grow wider. As brain cells die, the ventricles expand to fill the available space, becoming much larger than normal.
Fig. 1: MRI of a healthy brain (on the right) compared to one with Alzheimer’s Disease (AD) (on the left).
AD spreads through the brain, causing a progressive loss of the connections between neurons (synapses) and then neurons themselves. In the later stages of the condition, the brain is noticeably shrunken: the cerebral cortex appears shriveled and the fluid-filled ventricles are expanded.
Brain MRI is often the first step in evaluation of dementia. Fig. 2
In Patient suspected of having a cognitive disorder is important to score: global atrophy, focal atrophy and vascular disease. We distinguish:
• GCA-scale for Global Cortical Atrophy
• MTA-scale for Medial Temporal lobe Atrophy
• Koedam score for parietal atrophy
• Fazekas scale for white matter lesions (WMLs)
• Looking for strategic infarcts
GCA-scale for Global Cortical Atrophy
Rated on FLAIR images, score for cortical atrophy throughout the complete cerebrum.
Fig. 3: GCA: scale for Global Cortical Atrophy
MTA-scale for Medial Temporal lobe Atrophy
Scored on T1-weighted images; present in the vast majority of patients with AD.
Fig. 4: MTA: scale for Medial Temporal lobe Atrophy
Koedam score for Parietal Atrophy
The Koedam scale rates parietal atrophy - assessed in sagittal, coronal and axial planes.
Fig. 5: Koedam score for parietal atrophy.
Fig. 6: Koedam score for parietal atrophy.
Fazekas scale for WM lesions
It is best scored on transverse FLAIR or T2-weighted images.
Fig. 7: Fazekas scale for white matter lesions.
Strategic infarctions
Strategic infarctions are infarctions in areas that are crucial for normal cognitive functioning of the brain.
Fig. 8: Strategic infarctions in different brain areas.
Fig. 9: Defect post bleeding on the left posterior basal ganglia. The “basal ganglia” refers to a group of subcortical nuclei responsible primarily for motor control, as well as other roles such as motor learning, executive functions and behaviors, and emotions.
Fig. 10: Axial MR showing a Cerebellar Ischemia. Cerebellum controls some aspects of memory, learning, and cognition.
CT in Dementia
CT identifies brain atrophy, strokes and ischemia, changes to the blood vessels and other problems such as hydrocephalus and subdural hematomas. Fig. 11
Fig. 12: CT Scan axial and coronar: note the atrophy of the temporal lobe, the thin giry and dilated sulci and ventricles.
Usually used when MRI is contraindicated.
Vascular Dementia (VaD)
Patients with small vessel disease.
Fig. 13: The images show a patient with a posterior inferior cerebellar artery (PICA) infarction involving the hippocampus.
This type of infarct can result in sudden dementia if located in the dominant hemisphere.
Frontotemporal dementia (FTDs)
FTDs encompass six types of dementia involving the frontal or temporal lobes.
Symptoms: drastic personality changes and language difficulties.
Finding:
selective atrophy of the frontal and/or temporal cortices with frontoinsular atrophy
Wernicke encephalopathy (WE)
WE is an acute neurological condition characterized by a clinical triad of ophthalmoparesis with nystagmus, ataxia and confusion due to thiamine usually with severe alcohol use disorder.
Fig. 14: Wernicke encephalopathy: Global brain involution. Periaqueductal T2 hyperintensities, in the mammillary bodies, in thalamus at the level of the third ventricle.
Normal-pressure hydrocephalus (NPH)
It is characterized by enlarged widening of the Sylvian fissures and cisterns with crowding of the gyri at the vertex.
Fig. 15: Normal pressure hydrocephalus (NPH).
Dementia with Lewy bodies
It is characterized by the presence of Lewy bodies in various regions of the hippocampal complex, subcortical nuclei and neocortex with a variable number of diffuse amyloid plaques.
Patients have one of three symptoms complexes: detailed visual hallucinations, Parkinson-like symptoms and fluctuations in alertness and attention.
MR usually normal, including the hippocampus.
Progressive supranuclear palsy (PSP)
Also known as the Steele-Richardson-Olszewski syndrome. It is a pronounced atrophy of the midbrain (mesencephalon), which accounts for the typical upward gaze paralysis.
Symptoms: decreased cognition, abnormal eye movements , postural instability and falls, parkinsonian features and speech disturbances.
Radiographic features in MRI
Midbrain atrophy
1- midbrain to pons area ratio: reduced area ratio on the midline sagittal plane to approximately 0.12 (normal ~ 0.24)
2- hummingbird sign (or penguin sign):
midbrain tegmental atrophy without pontine atrophy, associated with widening of interpeduncular cistern giving the impression of head and body of a humming bird.
3- mickey mouse appearance:
selective atrophy of the midbrain tegmentum with relative preservation of tectum and cerebral peduncles resembling the head of Mickey Mouse
4- morning glory sign:
increased lateral concavity of the midbrain tegmentum resembling morning glory.
T2: diffuse high-signal lesions in
• pontine tegmentum
• tectum of the midbrain
• inferior olivary nucleus
Fig. 16: PSP Imaging: hummingbird sign versus mickey mouse appearance versus morning glory sign.
Multi System Atrophy (MSA)
MSA presents a pronounced cerebellar atrophy and severe atrophy of the pons. -> 'hot cross bun sign', which is a result of pontine hyperintensity.
Fig. 17: Hot Cross Bun Sign. Head T2W MRI though the pons showing a hyperintense pontine cross, which is classically associated with multisystem atrophy.
Creutzfeldt-Jakob disease (CJD)
CJD is a very rare neurodegenerative disease caused by a unique type of infectious agent called a prion.
Symptoms: rapidly progressive dementia with memory loss, personality changes and hallucinations.
Imaging:
Changes in the cortical and subcortical gray matter, with loss of neurons and replacement by gliosis.
Fig. 18: CJD: MRI axial section showing generalized brain atrophy with dilated ventricles and cortex atrophy such as hyperintense signals in putamen.
Huntington Disease
Hereditary autosomal dominant disease (often de novo mutations).
Symptoms: early onset dementia, choreoathetosis and psychosis.
Imaging:
Atrophy of the caudate nucleus and subsequent enlargement of the frontal horns of the lateral ventricles.
ADEM
Acute disseminated encephalomyelitis or acute demyelinating encephalomyelitis, is a rare autoimmune disease characterized by a sudden, widespread attack of inflammation in the brain and spinal cord that damages myelin.
Symptoms: fever, fatigue, headache, nausea and vomiting, and in the most severe cases, seizures and coma.
Fig. 19: ADEM: Several small-spot lesions on the frontal lobe both sides, on the right of the temporal lobe and corpus callosus.
Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencehalopathy (CADASIL)
CADASIL occurs when the thickening of blood vessel walls blocks the flow of blood to the brain and affects small blood vessels in the white matter of the brain.
Fig. 20: CARASIL (Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy): confluent white matter hyperintensities with lacunar infarcts.
Symptoms: migraines, multiple strokes progressing and behavioral disturbances. It affects the small vessels of the brain.
Imaging: Confluent white matter hyperintesities in the frontal and especially anterior temporal lobes in combination with (lacunar) infarcts and microbleeds. Fig. 21
SUSAC Syndrome (SS)
SS is a relatively rare disorder characterized by encephalopathy, partial or complete occlusion of the small arteries and capillaries that supply blood to the retina (branch retinal artery occlusion) and inner ear disease (often hearing loss).
Fig. 21: SS: MRI of the brain typically reveals “snowball” lesions in the corpus callosum.
Traumatic Brain Injury (TBI)
TBI includes cerebral contusions and diffuse axonal injury (DAI).
Fig. 22: Condition after computer-aided design and manufacturing (CAD/CAM) on the right frontotemporoparietal lobe.
It shows parenchymal defects right parietooccipital.
Abscess
Fig. 23: Abscess: On the left axial contrast-enhanced T1-weighted image shows a ring-enhancing lesion in the right hippocampus with perifocal edema.
Note on the right image the ventriculitis.
Anorexia nervosa
Fig. 24: CT Scan a 20 years old patient affected by anorexia nervosa. Note how deep are the orbit on the right image and how they descended after 3 months on the left image due to progressive loss of intraorbital fat.
SPECT and PET
SPECT includes cerebral single-photon emission computer tomography (SPECT) with dopamine transporter (DAT) ligands.
DAT-SPECT detects or excludes nigrostriatal degeneration in neurodegenerative Parkinson's syndromes and symptomatic Parkinson's syndromes and other differential diagnoses.
Fig. 26: Typical DAT-SPECT findings in idiopathic Parkinson's syndrome with reduced striatal availability of DAT compared to normal findings.
The (posterior) putamen is almost always the most affected.
References: Nuklearmedizinische Diagnostik bei Parkinson-Syndromen Ralph Buchert, Carsten Buhmann, Ivayla Apostolova, Philipp T. Meyer, Jürgen Gallinat Dtsch Arztebl Int 2019; 116: 747–54. DOI: 10.3238/arztebl.2019.0747
PET (positron emission tomography) detects disease-specific patterns of neuronal dysfunction / degeneration; glucose analogue [18F] fluorodeoxyglucose (FDG) can be used.
PET shows changes in glucose metabolism, presence of amyloid proteins, oxygen metabolism and blood flow, all of which can reveal abnormalities of brain function.
Fig. 25: Lewy body spectrum, often (in IPS) shows hypometabolism in posterior brain regions, putamen, motor cortex and cerebellum.
MSA: reduction in FDG uptake in putamen and / or cerebellum.
PSB: hypometabolism medial frontal, nucleus caudatus, thalamus.
CBD: hypometabolism in the frontoparietal cortex, striatum and thalamus.
References: Nuklearmedizinische Diagnostik bei Parkinson-Syndromen Ralph Buchert, Carsten Buhmann, Ivayla Apostolova, Philipp T. Meyer, Jürgen Gallinat Dtsch Arztebl Int 2019; 116: 747–54. DOI: 10.3238/arztebl.2019.0747