6. Neuro (Brain - Misc, Neuro-degenerative, Metabolic, Infections)

Question 1

Monro-Kellie Doctrine (2)

Answer 1

This is the idea that the head is a clsoed shell, and that the 3 major components (brain, blood, CSF) are in a state of dynamic equillibtium.
As volume of one goes up, another must go down

Question 2

Intracranial hypotension (3)

Answer 2

Leaking CSF will decrease the overall fixed volume, the volume of venous blood will increase to maintain equilibrium.
This results in meningeal engorgement (enhancement), distension of durial venous sinuses, predominance of the intracranial vessels and engorgement of the pituitary.
Development of subdural hygroma and haematomas is also classic here.

Question 3

Idiopathic intracranial hypertension (pseudotumour cerebri). (5)

Answer 3

Classically fat, middle aged woman with headache.
Cause isn’t well understood.
Associated with hypothroid, Cushings, vit A toxicity.
Increased CSF causes slit like ventricles, shrinking pituitary (partially empty sella) and venous sinuses appear compressed.
Vertical tortuosity of the optic nerves and flattening of posterior sclera can also occur.

Question 4

Cytotoxic oedema (3)

Answer 4

Can be thought of as intracellular swelling, due to malfunction of Na/K pump.
Tends to occur in grey matter, looks like loss of grey-white differentiation.
Classically seen in stroke or trauma.

Question 5

Vasogenic oedema (4)

Answer 5

Extracellular, due to blood brain barrier disruption.
Looks like oedema tracking through the white matter, less tightly packed than grey matter.
Seen in tumour and infection.
Response to steroids is classic for vasigenit oedema.

Question 6

Communicating oedema (3)

Answer 6

Obstruction at the level of the villi/granulation, blocking reabsorption.
All ventricles dilated (25% have normal 4th ventricle).
Caused by Normal Pressure Hydrocephalus, Blood, Pus, Cancer.

Question 7

Normal pressure hydrocephalus (6)

Answer 7

Idiopathic.
“Ventricular size out of proportion to atrophy”
Frontal and temporal horns of lateral ventricles are most affected.
Upward bowing of the corpus callosum is another buzzword.
MRI: transependymal flow and or flow void in the aqueduct and 3rd ventricle.
Clinical triad of urinary incontinence, confusion and ataxia.
Rx: Surgical shunting

Question 8

Blood, pus, cancer (communicating oedema) (2)

Answer 8

Anything causing plugging of the villi, most commonly SAH, meningitis, Carcinomatous meningiits

Question 9

Non-obstructive hydrocephalus (2)

Answer 9

Anything that produces more CSF.
Choroid plexus papilloma is usually the answer.

Question 10

Transependymal flow

Answer 10

Seeen more with acute rather than chronic hydrocephalus.

Question 11

Subfalcine herniation (2)

Answer 11

aka midline shift.
ACA may be compressed, causing infarct.

Question 12

Descending transtentorial herniation (8)

Answer 12

Uncus and hippocampus herniate through the tentorial incisura.
Effacement of ipsilateral suprasellar cistern occurs first.
Perforating basilar artery branches get compressed, causing Duret Haemorrhages (classically midline at pontomesencephalic junction)
CN3 compressed between PCA and Superior Cerebellar artery, causing ipsilateral pupil dilatation and ptosis.
Kernohan’s notch/phenomenon: Midbrain on the tentoriun forming an indentation/notch.
- Clinically: Ipsilateral hemiparesis “false localising sign”

Question 13

Ascendng transtentorial herniation (4)

Answer 13

Posterior fossa mass. Vermis will herniate upward through tentoral incisura, often causing severe obstructive hydrocephalus.
“smile” of quadrigeminal cistern is flattened or reversed.
“spinning top” is buzzword for the appearance of the midbrain from bilateral compression along its posterior aspect.
Severe hydrocephalus (at the level of the aqueduct)

Question 14

Cerebellar tonsil herniation (2)

Answer 14

Can be from severe herniation after downward transtentorial herniation.
In isolation, could be Chiari malformtion (Chairi 1 = 1 tonsil 5mm or both 3mm)

Question 15

Multiple sclerosis (10)

Answer 15

Commonest demyelinating disease.
Usually women 20-40. No difference in gender in kids.
Multiple types, relapsing-remitting (85%) is comonest.
Clinical Hx of separated by time and space.
Classic T2/FLAIR oval and periventricular perpendicularly orientated lesions.
Involvement of calloso-septal interface is 98% specific in MS, helps differentiate from vascular lesions and ADEM.
In kids, posterior fossa is more commonly involved.
Acute demyelinating plaques should enhance and restric diffusion.
Brain atrophy is accellerated in MS.
Can get big MS plaque like a tumour, will ring enhance but classically incomplete (horseshoe), with leading demyelinating edge.
Solitary spinal cord involvement can be seen, but is usually in addition to brain lesions.
Cervical spine is most common spinal location. Cord lesions tend to be peripherally located.

Question 16

ADEM (5)

Answer 16

MS variant, Acute Disseminated Encephalomyelitis.
Presents in childhood or adolescents after viral illness or vaccination.
Multiple, large T2 bright lesions, enhancing in a nodular or ring pattern (open ring).
Lesions do not involve the calloso-septal interface.

Question 17

Acute haemorrhagic leukoencephalitis (3)

Answer 17

Aka Hurst Disease
Fulminant form of ADEM with massive brain swelling and death.
Haemorrhagic part only seen on autopsy.

Question 18

Devics (neuromyelitis optica) (2)

Answer 18

Transverse myelitis + optic neuritis.
Lesions in the cord and the optic nerve

Question 19

Marburg variant (2)

Answer 19

Childhood variant that is fulminant and leads to rapid death.
Usually febrile prodrome

Question 20

PRES (Posterior Reversible Encephalopathy Syndrome) (3)

Answer 20

Seen in HTN or chemotherapy.
Asymmetric cortical and subcortical white matter oedema, usually in parietal occupital regions.
Does NOT restrict diffusion, can differentiate from stroke

Question 21

Radiation induced demyelination (3)

Answer 21

Seen as T2 bright areas and atrophy corresponding to radiation portal.
Can be seen with haemosiderin deposition and mineralising microangiopathy (calcifications involving the basal ganglia and subcortical white matter)

Question 22

Osmotic demyelination syndrome (CPM) (3)

Answer 22

Seen with rapid correction of sodium.
T2 bright in the central pons, spares the periphery.
Can also have extra-pontine presentation involving the basal ganglia, external capsule, amygdala and cerebellum.

Question 23

Wernicke encephalopathy (3)

Answer 23

Caused by thiamine deficiency.
Contrast enhancement of mammillary bodies (seen more in alcoholics).
Increased T2/FLAIR signal in bilateral medial thalamus and periaqueductal grey matter.

Question 24

Carbon monoxide poisoning (2)

Answer 24

CT: hypodensity. MRI: T2 bright globus pallidus

Question 25

Alcohol poisoning

Answer 25

Brain atrophy, especially cerebellar vermis

Question 26

Marchiafava-Bignami (3)

Answer 26

Seen in drunks.
Swelling and T2 bright signal affecting the corpus callosum (typically beginning in the body, then genu, then splenium).
Involves the central fibres and spare the dorsal and ventral fibres, called sandwich sign on sagittal imaging

Question 27

Methanol poisoning (2)

Answer 27

Optic nerve atrophy, haemorrhagic putaminal and subcortical white matter necrosis.

Question 28

Post-radiation changes (5)

Answer 28

Latent period in which imaging findings don’t show up for 2 mmonths.
Whole brain radiation: T2 bright in periventricular white matter, sparing subcortical regions early on.
Peripheral extension to subcortical regions occurs later.
Localised ratiation: Usually severe focal oedema with mass effect and enhancement.
Differentiation from residual tumour can be difficult, MR perfusion is useful here

Question 29

Post chemotherapy (3)

Answer 29

T2 effects acutely in the white matter, can progress to atrophy.
Enhancement or mass effect is rare, unless very severe.
Children recieving radiation and chemo sometimes develop calcifications “mineralising microangiopathy”

Question 30

Disseminated necrotising leukoencephalopathy (3)

Answer 30

Severe white matter changes, which demonstrate ring enhancement, classically with leukaemia patients undergoing radiation and chemo.
Can be fatal.

Question 31

PET in dementia

Answer 31

On FDG PET, the motor strip is always preserved in dementia

Question 32

Alzheimer disease (3)

Answer 32

Commonest cause of dementia.
Hippocampal atrophy occurs first, and out of proportion to rest of brain atrophy.
Tempral horn atrophy (>3mm) seen in more than 65% of cases.

Question 33

Multi-infarct dementia (3)

Answer 33

Second commonest cause of dementia.
Cortical infarcts and lacunar infarcts seen on MRI.
PET-FDG shows multiple scattered areas of decreased activity.

Question 34

Crossed cerebellary diaschisis (CCD) (2)

Answer 34

Depressed blood flow and metabolism affecting the cerebellar hemisphere after a contralateral supratentorial insult (infarct, tumour resection, radiation)

Question 35

Demential with Lewy bodies (3)

Answer 35

3rd commonest cause of dementia, similar picture to Parkinsons dementia (except here the dementia comes first).
Hippocampi remain normal.
Decreased FDG uptake in the lateral occipital cortex, with sparing of the mid posterior cingulate gyrus (cingulate island sign)

Question 36

Binswanger disease (3)

Answer 36

Subcortical leukoencephalopathy affecting older people, strongly associated with HTN.
Basically small vessel vascular dementia.
Classically spares subcortical U fibers

Question 37

FDG-PET in Brain DDx (4)

Answer 37

Alzheimer: low posterior temporoparietal cortical activity, identical to Parkinsons dementia
Multi-infarct: Scattered areas of decreased activity. Lyme, HIV and vasculitis are mimics.
Dementia with Lewy bodies: Low activity in lateral occipital cortex. Preservation of mid posterior cingulate gyrus (Cingulate island sign)
Picks/frontotemoral/depression: Decreased frontal lobe activity.
Huntingtons: low activity in caudate nucleus and putamen

Question 38

Torch infections (2)

Answer 38

Only clinically important in first 2 trimesters.
Calcifications and microcephaly seen in all of them

Question 39

CMV (4)

Answer 39

Commonest torch infection.
Likes to affect germinal matrix, causing periventricular tissue necrosis.
Periventricular calcifications also seen.
Highest association with polymicrogyria among TORCH infections

Question 40

Toxoplasmosis (4)

Answer 40

Second commonest TORCH.
Associated with cat faeces.
Calcifications are more random, and affet basal ganglia.
Frequency is increased in 3rd trimester (less clinically significant here).
Associated with hydrocephalus

Question 41

Rubella (3)

Answer 41

Less commoin due to vaccination.
Calcifications are less common.
MR: focal high T2 signal in white matter, related to vasculopathy and ischaemia

Question 42

HSV (3)

Answer 42

Usually HSV-2. Unlike adults, doesn’t primarily affect the limbic system, rather the endothelial cells, resulting in thrombus and harmorrhagic infarction, causing encephalomalacia and atrophy.

Question 43

HIV (3)

Answer 43

Not a TORCH, but occurs during pregnancy, at delivery or through breast feeding.
Brain atrophy in the frontal lobes predominantly.
Faint basal ganglia enhancement on CT and MRI preceeding the appearance of basal ganglia calcifications

Question 44

Opportunistic infections (4)

Answer 44

Most common opportunistic infection with AIDS patients is toxoplasmosis.
Commoinest fungal infection in AIDS is Cryptococcus.
JC virus and CMV are also notable

Question 45

HIV encephalitis (5)

Answer 45

Affects around 50% of people with AIDS.
CD4 <200.
Symmetric increased T2/FLAIR signal in deep white matter. Normal T1.
Lesions will not enhance.
May be associated brain atrophy.
Tends to spare subcortical U fibres (PML will involve them).

Question 46

Progressive Multifocal Leukoencephalopathy (PML) (4)

Answer 46

Caused by JC virus.
CD4 <50.
Imaging shows single or multiple scattered hypodensities with corresponding T1 hypointensity and T2/FLAIR hyperintensities out of proportion to mass effect.
Predilictions for subcortical U fibres.
Asymmetry helps differentiate from HIV.

Question 47

CMV (2)

Answer 47

Brain atrophy, periventricular hypodensities (T2/FLAIR bright) and ependymal enhancement.

Question 48

Cryptococcus (5)

Answer 48

Most common fungal infection in AIDS.
Usually meningitis affecting base of brain (leoptomeningeal enhancement).
Dilated perivascular spaces filled with mucoid gelatinous material which will not enhance.
Can also be seen as lesions in the basal ganglia (cryptococcomas), which are T1 dark, T2 bright and may ring enhance.

Question 49

Toxoplasmosis (4)

Answer 49

Commonest opportunistic infection in AIDS.
T1 dark, T2 bright, ring enhancing lesions without diffision restriction.
Lots of surrounding oedema.
Toxoplasmosis is thallium cold, lymphoma is thallium hot

Question 50

Toxoplasmosis vs lymphoma (4)

Answer 50

Both demonstrate
- Ring enhancement
Haemorrhage more common after treatment vs less common
Thallium hot vs cold
PET cold vs hot
MR perfusion: decreased CBV vs increased (or decreased) CBV

Question 51

Stroke vs Tumour vs Abscess vs MS plaque (8)

Answer 51

T2: All will have oedema so will all be bright.
DWI: Classically, Abscess and stroke will restrict diffusion, however hypercellular tumours like lymphoma and demyelinating lesions with acute features can also restrict diffusion
Enhancement: Each shoud have a different enhancement pattern
- Tumour: heterogenous or homogenous if high grade.
- Abscess with RING enhance
- MS will have Incomplete ring enhancement
- Stroke will have cortical ribbon (gyriform) type enhancement in subacute perior (around 1 week)

Question 52

TB meningitis (4)

Answer 52

Looksl ike regular meningitis, except prediliction for basal cisterns and may have dystrophic calcifications.
May be enhancement of the basilar meninges with minimal nodularity.
Complications include vasculitis (May result in infarct (more common in kids).
Obstructive hydrocephalus is common.

Question 53

HSV (4)

Answer 53

HSV 1 in adults and HSV 2 in kids.
Swollen (uni or bilateral) medial temporal lobe, will be T2 bright.
Earliest sign is restricted diffusion related to vasogenic oedema.
Blooming on gradient means bleeding (more common in adult form).
Spares the basal ganglia unlike MCA stroke.

Question 54

Limbic encephalitis (3)

Answer 54

Not infection, but common mimic.
Paraneoplastic syndrome, usualy small cell lung cancer, looks similar to HSV.
Ask for lung cancer screening.

Question 55

West Nile virus (4)

Answer 55

Several viruses characteristically involve the basal ganglia (Japanese Encephalitis, Murray Valley Fever, West Nile).
West nile causes T2 bright basal ganglia and thalamus, corresponding to restricted diffision.
Haemorrhage sometimes seen.

Question 56

CJD (7)

Answer 56

3 types
- Sporadic (80-90%), variant (rare) and familial (10%)
Characteristic appearance on EEG and 14-3-3 protein assay on CSF.
Imaging is variable, can be unilateral, bilateral, symmetric or asymmetric.
3 likely appearances
- DWI showing cortical gyriform restricted diffusion (diffusion is most sensitive sign, cortex is the most common, early site of manifestation)
- Hockey stick sign/Pulvinar sign: Restricted diffusion in the dorsal medial thalamus (which looks like hockey stick) or int he pulvinar.
- Series of MR or CT showing rapidly progressive atrophy

Question 57

Neurocysticercosis (7)

Answer 57

Caused by undercooked pork. Tinea solium is the pathogen.
Common locations are subarachnoid space overlying the cerebral hemispheres, basal cisterns, brain parenchyma and ventricles (in order).
Involvement of basal cisterns carries worst prognosis.
4 stages
- Vesicular: thin walled cysts, iso on T1/T2, no oedema
- Colloidal: hyperdense cyst, bright on T1/T2 and oedema
- Granular: Cyst shrinks, wall thickens, less oedema
- Nodular: small calcified lesion, no oedema.

Question 58

Meningitis and cerebral abscess (7)

Answer 58

4 main categories of meningitis:
- Bacterial (acute pyogenic)
- Viral (lymphocytic)
- Chronic (TB or fungal)
- Non infectious (Sarcoid)
Thick, leptomeningeal enhancement in the appropriate clinical setting.
Complications include thrombosis, vasospasm (leading to stroke), empyema, ventriculitis, hydrocephalus, abscess.
Infants often get sterile reactive subdurals (less common in adults).
Abscess imaging: DWI restricts, MRS - raised lactate, PET FDG - increased metabolic

Question 59

Empyema (4)

Answer 59

Subdural or epidural. Same rules as blood for crossing dural attachments (epidurals don’t) or crossing falx (subdurals don’t).
Subdural is more common and have more complications.
Most subdurals are due to frontal sinusitis, as are most epidurals.
Often T1 bright and restrict diffusion.

Question 60

Intraaxial infections (4)

Answer 60

Cerebritis, Abscess and Ventriculitis.
Lots of causes via direct or haematogenous spread.
Left to right shunts and pulmonary AVMs are important causes.
Cerebritis is early form of intra-axial infection, which can lead to abscess if not treated.

Question 61

Ventriculitis (3)

Answer 61

Usually due to shint placement or intrathecal chemo.
Ventricle will enhance and can sometimes seen ventricular fluid-fluid levels.
If septa start to develop, can get obstructive hydrocephalus.
Intraventricular extension of abscess is serious/ominous “pre terminal” event.