KEY FACTS Terminology Posterior cortical atrophy (PCA) Rare neurodegenerative disorder of posterior cerebral cortex/connecting white matter (WM) Considered subtype of Alzheimer disease (AD) Results in impairment of ventral, dorsal visual perception pathways Typically precedes memory, executive impairment Imaging Sagittal T1WI, axial FLAIR show posterior > frontal, temporal volume loss Cortical thinning Left typically > right ↓ fractional anisotropy in inferior/superior longitudinal fasciculi FDG-PET Hypometabolism/hypoperfusion of posterior…

KEY FACTS Terminology Adult-onset fatal neurodegenerative disease Multiple system atrophy (MSA) has 3 clinical subtypes Cerebellar (MSA-C) Sporadic olivopontocerebellar (OPCA) atrophy Extrapyramidal (MSA-P) Parkinson subtype Striatonigral degeneration Autonomic (MSA-A) Shy-Drager syndrome Imaging General findings ↓ (“flat”) pons/medulla Cerebellar vermis/hemispheres atrophic MSA-C Selective atrophy of lower pons, medulla, middle cerebellar peduncles (MCPs), cerebellar hemispheres – ↑ T2 signal in pons, MCPs, cerebellar WM – Cruciform pontine hyperintensity…

KEY FACTS Terminology Parkinson disease (PD) Progressive neurodegenerative disease Primarily affects pars compacta of substantia nigra (SNpc) Imaging MR SNpc narrowed/inapparent (T2WI) SNpc progressively loses normal hyperintensity (from lateral to medial) Border between SNpc, red nucleus blurred in PD ↑ R2' relaxation at 3T in SNpc, caudal putamen (reflects ↑ iron content) DWI may differentiate PD from progressive supranuclear palsy, parkinsonian variant of multiple system atrophy…

KEY FACTS Terminology Important clinicopathologic Creutzfeldt-Jakob disease (CJD) variants Heidenhain variant CJD – Visual variant of CJD – Early isolated visual symptoms Brownell-Oppenheimer variant (rare) – Pure cerebellar syndrome Imaging FLAIR Subtle cortical hyperintensity in occipital lobes (“cortical ribbon”) Basal ganglia usually normal DWI Most sensitive for early detection (look for restriction in “cortical ribbon”) Occipital cortex hyperintensity T1 C+: No enhancement FDG-PET occipital hypometabolism Top…

KEY FACTS Terminology Creutzfeldt-Jakob disease (CJD): Rapidly progressing, fatal, potentially transmissible dementia caused by prion Imaging Best imaging clue: Progressive T2 hyperintensity of basal ganglia, thalamus, and cerebral cortex Predominantly gray matter: Caudate and putamen > globus pallidus Thalamus: Common in variant CJD (vCJD) Cerebral cortex: Frontal, parietal, and temporal Heidenhain variant: Occipital lobe 2 signs seen in 90% of vCJD but can also occur in…

KEY FACTS Terminology Progressive neurodegenerative dementia caused by pathologic aggregation of α-synuclein protein in neurites (Lewy bodies) Imaging MR may differentiate Alzheimer disease (AD) from dementia with Lewy bodies (DLB) Voxel-based morphometry Relatively preserved hippocampal/medial temporal lobe volume in DLB compared with AD Reduced volume of hypothalamus, substantia innominata, and putamen in DLB compared with AD fMRI may show loss of inhibition in visual system PET,…

KEY FACTS Terminology Clinical subtypes Behavioral-variant frontotemporal dementia (bvFTD) Primary progressive aphasia syndromes (PPA) – Semantic variant (sv-PPA) □ Previously known as semantic dementia – Nonfluent/agrammatic variant (nfv-PPA) □ Previously known as progressive nonfluent aphasia – Logopenic variant (lv-PPA) Frontotemporal dementia with motor symptoms Imaging Early PET shows frontotemporal ↓ glucose metabolism Late Frontotemporal atrophy with knife-like gyri on MR Subtypes have characteristic cortical atrophy patterns…

KEY FACTS Terminology Vascular dementia (VaD), multiinfarct dementia (MID) Stepwise progressive ↓ in cognitive function Heterogeneous group of disorders with varying etiologies, pathologic subtypes VaD often mixed etiology Can occur alone or in association with Alzheimer disease (AD) MID secondary to repeated cerebral infarctions Imaging General features Multifocal infarcts [cortical gray matter, subcortical white matter (WM)] Basal ganglia, pons Territorial as well as lacunar lesions Coexisting…

KEY FACTS Terminology Alzheimer disease (AD) Slowly progressive neurodegenerative disease Imaging Current role of imaging in AD Exclude other causes of dementia Identify region-specific patterns of brain volume loss Identify imaging markers of coexistent disease such as amyloid angiopathy Identify early AD for possible innovative therapy Best imaging = volumetric MR, FDG-18 PET Thinned gyri, widened sulci, and enlarged ventricles Medial temporal lobe particularly hippocampus and…

KEY FACTS Terminology ↓ overall brain volume with advancing age Reflected in relative ↑ cerebrospinal fluid spaces Imaging Broad spectrum of “normal” on imaging in elderly patients “Successfully aging brain” Smooth, thin, periventricular, high signal rim on FLAIR is normal White matter hyperintensities (WMHs) absent/few Decreased total brain volume Selective atrophy of white matter (not gray matter) predominates WMHs ↑ In number/size after 50 years Approximately…

KEY FACTS Terminology Sudden memory loss without other signs of cognitive or neurologic impairment; usually resolves within 24 h Imaging NECT, CECT almost invariably normal MR T2/FLAIR usually normal DWI: Focal dot-like area of diffusion restriction in hippocampus – Single (55%) – Multiple (45%) – Unilateral (50-55%) – Bilateral (45-50%) DWI abnormalities increase with time – From 35% at 0-6 h to 65-70% by 12-24 h…

KEY FACTS Terminology Status epilepticus: > 30 minutes of continuous seizures (SZs) or ≥ 2 SZs without full recovery of consciousness between seizures Synonyms: Transient seizure-related MR changes, reversible postictal cerebral edema Imaging Best diagnostic clue: T2 hyperintensity in gray matter &/or subcortical white matter (WM) with mild mass effect Supratentorial, related to epileptogenic focus Typically cortex &/or subcortical WM May involve hippocampus, corpus callosum, thalamus…

KEY FACTS Terminology Seizure-associated neuronal loss and gliosis in hippocampus and adjacent structures Imaging Primary features: Abnormal T2 hyperintensity, hippocampal volume loss/atrophy, obscuration of internal architecture Secondary signs: Ipsilateral fornix and mammillary body atrophy, enlarged ipsilateral temporal horn, and choroidal fissure ↑ hyperintensity on DWI (T2 shine through) ↓ NAA in hippocampus, temporal lobe Top Differential Diagnoses Status epilepticus Low-grade astrocytoma Choroidal fissure cyst Hippocampal sulcus…

KEY FACTS Terminology Osmotic demyelination syndrome (ODS) Formerly called central pontine myelinolysis (CPM) &/or extrapontine myelinolysis (EPM) Acute demyelination from rapid shifts in serum osmolality Classic setting: Rapid correction of hyponatremia ODS may occur in normonatremic patients Imaging Central pons T2 hyperintensity with sparing of periphery 50% in pons (CPM); 50% in extrapontine sites (EPM) Central fibers involved; peripheral fibers spared Basal ganglia Cerebral white matter…

KEY FACTS Terminology Many drugs (prescription, illicit, or street) have adverse CNS effects Illicit drug use often causes cerebrovascular disease Amphetamines, cocaine > opioids, cannabis Polydrug abuse (including EtOH) is common Nitrous oxide (NO₂) abuse → vitamin B12 inactivation → subacute combined degeneration Imaging Best imaging clue: Young/middle-aged adult with ischemic or hemorrhagic stroke after recent drug administration Hemorrhage: Intracranial, subarachnoid, intraventricular Nonhemorrhagic ischemic stroke: Middle…

KEY FACTS Terminology Anoxic-ischemic encephalopathy, usually with bilateral lesions, caused by inhalation of carbon monoxide (CO) gas Imaging Best diagnostic clue: Globi pallidi (GP) T2/FLAIR hyperintensity T1 MR: Both hypointensity in GP (likely necrosis) and hyperintensity in GP (likely hemorrhage) reported T2 MR: Ischemia/infarct of GP Cerebral hemispheric white matter (WM): Bilateral confluent hyperintense WM (periventricular, centrum semiovale) Cortical hyperintensity (commonly temporal lobe) Medial temporal lobe…

KEY FACTS Terminology Idiopathic intracranial hypertension (IIH) Pseudotumor cerebri “Benign intracranial hypertension” ↑ intracranial pressure (ICP) without identifiable cause Imaging Empty or partially empty sella Posterior globe flattening Intraocular protrusion of optic nerve head Optic nerve sheath enlargement: Widened ring of cerebrospinal fluid around optic nerve Optic nerve tortuosity Slit-like ventricles, rare: Poor neuroimaging sign of IIH MRV: Often shows transverse sinus stenosis and “flow gaps”…

KEY FACTS Terminology Subcortical arteriosclerotic encephalopathy Imaging General features Lacunae (lenticular nuclei, pons, thalamus, internal capsule, caudate) Cerebral hemorrhage (basal ganglia/external capsule, thalamus) Confluent white matter (WM) disease (centrum semiovale, corona radiata) CT Diffuse WM hypodensity on CT Lacunar infarcts [basal ganglia (BG), thalamus/brainstem] MR Hyperintense lesions within corona radiata, centrum semiovale, BG Multiple microhemorrhages (GRE, SWI) – Predilection for BG/thalami, brainstem, cerebellum Acute WM lesions…

KEY FACTS Terminology Cerebrovascular autoregulatory disorder Many etiologies with HTN as common component Preeclampsia, eclampsia Drug toxicity (e.g., chemotherapy) Uremic encephalopathies Imaging General Patchy parietooccipital cortical/subcortical edema in patient with severe acute/subacute HTN CT Bilateral nonconfluent hypodense foci ± symmetric lesions in basal ganglia MR Parietooccipital T2/FLAIR hyperintensities in 95% ± basal ganglia, pontine, cerebellar involvement 3 patterns of hemorrhage: Focal parenchymal hemorrhage, microhemorrhages, convexity SAH…

KEY FACTS Terminology Functional, potentially reversible clinical syndrome Acute hepatic encephalopathy (AHE) Chronic hepatic encephalopathy (CHE) Characterized by psychiatric, cognitive, and motor components Imaging AHE (hyperammonemia) High T2 signal in most of cerebral cortex (preferential insular cortex and cingulate gyri) with diffusion restriction Perirolandic/occipital regions relatively spared ↓ mI/Cr and Cho/Cr ratios and ↑ Glx/Cr ratios CHE Bilateral T1WI hyperintensity in basal ganglia (BG), particularly globus…