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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
Cranial cavity: mesaticephalic dog
presphenoid bone
orbital fissure
Cr NN III, IV, VI and V (ophth)
Cranial cavity: mesaticephalic dog
basisphenoid bone
Cranial cavity: mesaticephalic dog
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
Cerebral hemispheres: major lobes
1 = ethmoturbinates and cribriform plate; 2 = olfactory bulb; 3 = frontal lobe;
4 = parietal lobe; 5 = occipital lobe
2
3
1
4 5
7
Cerebral hemispheres: major lobes
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
Cerebral hemispheres: basal nuclei (deep grey matter)
caudate nucleus
putamen ) lentiform
globus pallidus ) nucleus
claustrum
amygdala
Cerebral hemispheres: basal nuclei (deep grey matter)
caudate nucleus
putamen ) lentiform
globus pallidus ) nucleus
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
Pituitary gland and middle cranial fossa
hypophyseal (pituitary) fossa tuberculum sellae dorsum sellae
sella turcica (“Turkish saddle”)
12
Pituitary gland and middle cranial fossa
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
Pituitary gland and middle cranial fossa
middle cerebral artery third ventricle
13
Pituitary gland contrast enhancement on T1W
T1W T1/C
central hyperintensity = vasopressin?
Pituitary gland contrast enhancement on T1W
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 gland contrast enhancement on T1W
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
Ventricular system, choroid plexuses and subarachnoid space
Ventricular system, choroid plexuses and subarachnoid space
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
Ventricular system variants
West Highland white terrier Pug
asymmetry of the lateral ventricles occurs in about 10% dogs
and occasionally in cats (usually L>R)
20
Ventricular system variants
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
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