normal mri anatomy of the brain (and variants) · • brain stem = (diencephalon anatomically,...

1

Normal MRI anatomy of the brain

(and variants)

Ruth Dennis DipECVDI

Centre for Small Animal Studies

Animal Health Trust

Newmarket UK

EVCN Brain Camp MRI Course 9th-10th August 2014, Bologna

Brain: pulse sequences

• T2W images give best contrast between white

matter, grey matter and CSF

Brain: image planes

• 3 orthogonal planes: transverse, dorsal and sagittal

• sagittal oblique for optic nerves

2

Major anatomical areas

• forebrain

- telencephalon (cerebral hemispheres and basal nuclei)

- diencephalon (thalamus, hypothalamus)

• midbrain

- mesencephalon

• hindbrain

- pons and cerebellum (metencephalon)

- medulla oblongata (myelencephalon)

• brain stem = (diencephalon anatomically, although not

functionally), mesencephalon, pons and medulla oblongata

Major anatomical areas

Miller’s Anatomy of the Dog, 3rd edition

Areas considered

• cranial cavity

• cerebral hemispheres

• diencephalon

• pituitary gland and middle cranial fossa

• cerebellum

• brain stem

• ventricular system

• inner ear

• cranial nerves

3

Cranial cavity

Cranial cavity: mesaticephalic dog

calvarium

tentorium

osseum

cerebelli

frontal sinus

sphenoidal sinus

containing turbinates

presphenoid bone basisphenoid bone basioccipital bone

foramen magnum

external occipital

protuberance

Cranial cavity: cat

• sphenoidal sinus is air-filled

• prominent tentorium osseum

4

Cranial cavity: brachycephalic dog

• small / absent frontal sinuses

• ventrally-displaced cribriform plate and olfactory bulb

• domed calvarium

Cranial cavity: brachycephalic cat

Cranial cavity: caudal fossa asymmetry (especially boxer & GSD)

• no clinical significance

5


presphenoid bone

orbital fissure

Cr NN III, IV, VI and V (ophth)


basisphenoid bone


basioccipital bone

6

Cerebral hemispheres

Cerebral hemispheres: major lobes

1 = ethmoturbinates and cribriform plate; 2 = olfactory bulb of frontal lobe;

3 = frontal lobe; 4 = parietal lobe; 5 = occipital lobe; 6 = temporal lobe

3

2

1

4

5

6


1 = ethmoturbinates and cribriform plate; 2 = olfactory bulb; 3 = frontal lobe;

4 = parietal lobe; 5 = occipital lobe

2

3

1

4 5

7


piriform lobe (a massive surface bulge, lateral to the hypothalamus)

a common site for

post-seizure changes

Cerebral hemispheres: falx cerebri (lined by dura mater)

falx

Cerebral hemispheres: falx cerebri (lined by dura mater)

small plaques of bone may be seen between

the frontal lobes in large dogs (do not mistake

for meningioma): most obvious in T1W scans

bone

8

Cerebral hemispheres: cortex (surface grey matter)

gyri and sulci

enlarged sulci and

subarachnoid space of

unknown cause:

hydrocephalus ex vacuo

normal dog

Cerebral hemispheres: fibre tracts (white matter)

corpus callosum (links the two hemispheres)

Cerebral hemispheres: fibre tracts (white matter)

1 = corpus callosum (links the two hemispheres);

2 = internal capsule; 3 = corona radiata

1

2

3

9

Cerebral hemispheres: basal nuclei (deep grey matter)

caudate nucleus

putamen ) lentiform

globus pallidus ) nucleus

claustrum

amygdala


caudate nucleus

putamen ) lentiform


claustrum

amygdala


caudate nucleus

putamen ) lentiform


claustrum

amygdala

p g c

a

10

Cerebral hemispheres: hippocampus (deep grey matter)

Cerebral hemispheres: hippocampus (deep grey matter)

Diencephalon

11

Diencephalon: thalamus and hypothalamus (rostral brain stem)

interthalamic adhesion

surrounded by third ventricle

Pituitary gland and middle cranial fossa


hypophyseal (pituitary) fossa tuberculum sellae dorsum sellae

sella turcica (“Turkish saddle”)

12


cavernous sinuses containing venous blood; middle meningeal arteries;

a ramus of the external ophthalmic artery;

cranial nerves III, IV, VI and V (maxillary and ophthalmic branches)

Pituitary gland and cavernous sinuses

disease in the middle cranial fossa (“middle fossa syndrome”)

internal and external ophthalmoplegia, loss of facial sensation and

sympathetic nerve deficits


middle cerebral artery third ventricle

13

Pituitary gland contrast enhancement on T1W

T1W T1/C

central hyperintensity = vasopressin?


with fat suppression

Normal pituitary gland dimensions on MRI:

dog: 6.4mm TS, 5.1mm DV

cat: 5.0mm TS, 3.4mm DV, 5.4mm RCd


pituitary tumours may or

may not enhance

14

Cerebellum

Cerebellum

vermis and two hemispheres

folia and sulci

1 2 3

1

2

3

Cerebellum

vermis and two hemispheres

folia and sulci

1

2

3

1

2

3

15

Cerebellar peduncles

fibres from brain stem to cerebellum: rostral, middle and caudal

M

R M

Cerebellum: variants - cat

Persian

Brain stem

16

Brain stem

Diencephalon, mesencephalon,

pons and medulla oblongata

1 = diencephalon (anatomically)

2 = mesencephalon

3 = pons

4 = medulla oblongata

1

2

3 4

Brain stem

Diencephalon, mesencephalon,

pons and medulla oblongata

1 = tectum of mesencephalon

2 = mesencephalic aqueduct

3 = tegmentum of mesencephalon

1

3

2

Brain stem: colliculi – form the tectum of the mesencephalon

Rostral colliculi – visual reflex pathways

17

Brain stem: colliculi – form the tectum of the mesencephalon

Caudal colliculi – hearing reflex pathways

Brain stem

pons and mesencephalic aqueduct

medulla oblongata

1 2

1

2

Ventricular system

18

Ventricular system, choroid plexuses and subarachnoid space

Miller’s Anatomy of the Dog,

3rd edition

viewed from the side

viewed from above



19

Choroid plexus contrast enhancement on T1W

useful to confirm that contrast medium has entered the patient!

lateral recess and aperture

lateral and

third

ventricles

Ventricular system variants

Labrador

Boston terrier

Bulldog

no septum pellucidum

larger ventricles in dome-headed breeds


West Highland white terrier Pug

asymmetry of the lateral ventricles occurs in about 10% dogs

and occasionally in cats (usually L>R)

20


dilation within the olfactory bulb is sometimes seen in

cats, even in the absence of obstructive hydrocephalus

Inner ear

Inner ear

endolymph in the cochlear duct and semicircular canals is

hyperintense on T2W

little duck!

21

Cranial nerves

Cranial nerves

• Cranial nerves II, III, V (and its divisions) and VIII observed

consistently on 3mm and 4mm thick slices (often VII too)

• Cranial nerves IV, VII and IX-X-XI seen on 2mm thick slices

• Cranial nerves I, VI and XII not seen with certainty

Cranial nerve II (optic)

1 2

1 2

22

Cranial nerve II (optic)

sagittal oblique optic chiasm

Cranial nerve V (trigeminal)

maxillary and

ophthalmic branches in

cavernous sinus

mandibular branch

exiting oval foramen

exiting brainstem

1

2

3

1 2 3

Cranial nerve V (trigeminal)

23

Cranial nerve VII (facial)

in facial canal of petrous temporal bone, dorsal to cochlea

Cranial nerve VIII (vestibulocochlear)

70

Frosty morning at the Animal Health Trust

‘The Lord Gilleyne’ statue at the Animal Health Trust

normal mri anatomy of the brain (and variants) · • brain stem = (diencephalon anatomically,...

Documents