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 1 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 2 Cranial cavity Cranial cavity: mesaticephalic dog calvarium external occipital protuberance frontal sinus tentorium osseum cerebelli foramen magnum sphenoidal sinus containing turbinates presphenoid bone basisphenoid bone basioccipital bone Cranial cavity: cat • sphenoidal sinus is air-filled • prominent tentorium osseum 3 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 4 Cranial cavity: mesaticephalic dog orbital fissure Cr NN III, IV, VI and V (ophth) presphenoid bone Cranial cavity: mesaticephalic dog basisphenoid bone Cranial cavity: mesaticephalic dog basioccipital bone 5 Cerebral hemispheres Cerebral hemispheres: major lobes 1 2 3 4 6 5 1 = ethmoturbinates and cribriform plate; 2 = olfactory bulb of frontal lobe; 3 = frontal lobe; 4 = parietal lobe; 5 = occipital lobe; 6 = temporal lobe Cerebral hemispheres: major lobes 4 5 3 2 1 1 = ethmoturbinates and cribriform plate; 2 = olfactory bulb; 3 = frontal lobe; 4 = parietal lobe; 5 = occipital lobe 6 Cerebral hemispheres: major lobes a common site for post-seizure changes piriform lobe (a massive surface bulge, lateral to the hypothalamus) Cerebral hemispheres: falx cerebri (lined by dura mater) falx Cerebral hemispheres: falx cerebri (lined by dura mater) bone small plaques of bone may be seen between the frontal lobes in large dogs (do not mistake for meningioma): most obvious in T1W scans 7 Cerebral hemispheres: cortex (surface grey matter) normal dog gyri and sulci enlarged sulci and subarachnoid space of unknown cause: hydrocephalus ex vacuo Cerebral hemispheres: fibre tracts (white matter) corpus callosum (links the two hemispheres) Cerebral hemispheres: fibre tracts (white matter) 3 1 2 1 = corpus callosum (links the two hemispheres); 2 = internal capsule; 3 = corona radiata 8 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) c p a g caudate nucleus putamen ) lentiform globus pallidus ) nucleus claustrum amygdala 9 Cerebral hemispheres: hippocampus (deep grey matter) Cerebral hemispheres: hippocampus (deep grey matter) Diencephalon 10 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 tuberculum sellae hypophyseal (pituitary) fossa dorsum sellae sella turcica (“Turkish saddle”) 11 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 third ventricle middle cerebral artery 12 Pituitary gland contrast enhancement on T1W T1W T1/C central hyperintensity = vasopressin? Pituitary gland contrast enhancement on T1W Normal pituitary gland dimensions on MRI: dog: 6.4mm TS, 5.1mm DV cat: 5.0mm TS, 3.4mm DV, 5.4mm RCd with fat suppression Pituitary gland contrast enhancement on T1W pituitary tumours may or may not enhance 13 Cerebellum Cerebellum 1 2 3 1 2 3 vermis and two hemispheres folia and sulci Cerebellum 1 1 2 3 2 3 vermis and two hemispheres folia and sulci 14 Cerebellar peduncles R M M fibres from brain stem to cerebellum: rostral, middle and caudal Cerebellum: variants - cat Persian Brain stem 15 Brain stem Diencephalon, mesencephalon, pons and medulla oblongata 1 = diencephalon (anatomically) 2 = mesencephalon 1 3 = pons 2 4 = medulla oblongata 3 4 Brain stem Diencephalon, mesencephalon, pons and medulla oblongata 1 1 = tectum of mesencephalon 2 = mesencephalic aqueduct 2 3 = tegmentum of mesencephalon 3 Brain stem: colliculi – form the tectum of the mesencephalon Rostral colliculi – visual reflex pathways 16 Brain stem: colliculi – form the tectum of the mesencephalon Caudal colliculi – hearing reflex pathways Brain stem 1 2 1 2 pons and mesencephalic aqueduct medulla oblongata Ventricular system 17 Ventricular system, choroid plexuses and subarachnoid space viewed from the side viewed from above Miller’s Anatomy of the Dog, 3rd edition Ventricular system, choroid plexuses and subarachnoid space Ventricular system, choroid plexuses and subarachnoid space 18 Choroid plexus contrast enhancement on T1W lateral recess and aperture lateral and third ventricles useful to confirm that contrast medium has entered the patient! Ventricular system variants no septum pellucidum Labrador Boston terrier larger ventricles in dome-headed breeds Bulldog 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) 19 Ventricular system variants dilation within the olfactory bulb is sometimes seen in cats, even in the absence of obstructive hydrocephalus Inner ear Inner ear little duck! endolymph in the cochlear duct and semicircular canals is hyperintense on T2W 20 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 21 Cranial nerve II (optic) optic chiasm sagittal oblique Cranial nerve V (trigeminal) 1 2 3 1 2 3 maxillary and ophthalmic branches in cavernous sinus mandibular branch exiting oval foramen exiting brainstem Cranial nerve V (trigeminal) 22 Cranial nerve VII (facial) in facial canal of petrous temporal bone, dorsal to cochlea Cranial nerve VIII (vestibulocochlear) 70 ‘The Lord Gilleyne’ statue at the Animal Health Trust Frosty morning at the Animal Health Trust 23 .