12. MRI Brain Flashcards
How does Gadolinium work?
Shortens T1 relaxation time of effected tissues -> Hyperintense
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What specific adverse reaction / disease is associated with Gad administration?
Nephrogenic Systemic Fibrosis
What are general features of Proton Density weighted images?
- Intermediate between T1 and T2
- Good for anatomic detail, particulalry grey / white matter
- Acquired during T2 dual echo sequence
What is Gradient Echo useful for?
- Identification of inhomogeneities in the field
=> CHRONIC haemorrhage (2-3 days) - presence of ferrous / ferric ions
- Susceptibility artefact -> extremely sensitive indicator of haemorrhage
=> Void typically larger due to BLOOMING
What is the most common intracranial developmental anomaly?
Hydrocephalus
=> Congenital form most common
List three mechanisms by which hydrocephalus may develop
- Obstruction to outflow
- Increased CSF production / decreased absorption
- Brain atrophy
Agenesis of the septum pellucidum is seen in which breeds most frequently? How freq is it considered intact in dogs?
- Large brachycephalics
- 25% of dogs have intact
Describe the three patterns of supracollicular fluid accumulation. What does the membrane represent?
1) Enlargement of caudodorsal recess of third ventricle -> Displacement of membrane caudodorsally
2) FLuid in caudodorsal recess and quadrigeminal cistern -> Membrane visible seperating them
3) Quadrigeminal fluid only -> Membrane displaced rostrally.
MEMBRANE = Likely Third ventricular wall. Where pia mater joins ependymal layer forming the tela choroidea of 3rd ventricle
Define differenes between hydrancephaly and porencephaly? List 3 causes of porencephaly
Hydrancephaly = extensive fluid accumulations within developing brain
Porencephaly = focal fluid accumulations
“Encephaloclastic porencephaly” broad term -> loss from e.g. ischaemia, infection, trauma
=> Usually involve lateral ventricles OR subarachnoid space
What is Dandy Walker syndrome?
- Absence of caudoventral aspect of cerebellum -> occurs to varying degress, with resultant effect on CS
- Number of manifestations -> “Dandy Walker variant” should be used
What is holoprosencephaly? Name three types. What associated malformation is described? What associated clinical signs / breed for this anomaly?
Holoprosencephaly: Failure of normal bifurcation of cerebral hemispheres
1) ALOBAR
2) SEMILOBAR
3) LOBAR (described in dogs)
* Associated corpus callosal agenesis/dysgenesis -> Mini schnauzers
Hypodipsic hypernatraemia
List 4 uncommon intracranial cystic lesions due to defects of neural tube closure
- Dermoid cyst
- Epidermoid cyst
- Rathkes cleft cyst
- Craniopharyngioma
Where are epidermoid / dermoid cysts most commonly located (x2)? MRI features?
- 4th ventricle
- Cerebellopontine angle
MR: If lipid - T1w hyper and T2w hyper; may contain hair (dermoid) hypo foci; usually do not enhance, althoigh can enhance peripherally. Do not FLAIR null if lipid
Where are Rathkes cleft cysts / craniopharyngiomas identified?
Sella turcica -> Pituitary anomalous development
Classic features of Caudal Occipital Malformation syndrome
- Crowding of caudal fossa
- Herniation of cerebellar vermis
- CKCS overrepresented (up to 95% breed demonstrate this)
- 2ry syringohydromyelia
- Some association between syndrome and formation of dorsal Atlanto-axial bands
What is lissencephaly? Which breed is over-represented?
Lack / absence of normal gyral formation
LHASA APSO
List 4 “common” storage diseases (Inborn errors of brain metabolism)
- Mucopolysaccharoidosis
- Neuronal cell Lipofuscinosis
- Cerebellar abiotrophy
- Globoid cell leuckodystrophy
Describe features of mucopolysaccharoidosis / lipofuscinosis
BOTH:
- Progressive juvenile cerebral atrophy -> hydrocephalus
- Small Corpus callosum
**LIPOFUSCINOSIS -> often SEVERE peripheral meningeal thickening and enhancement**
Describe features of cerebellar abiotrophy
- Progressive cerebellar atrophy -> Increased conspicuity of cerebellar folia
Describe features of Globoid cell leukodystrophy
- Symmetrical, white matter disease
- Mild hydrocephalus
- Symmetrical contrast enhancement of CC, internal capsule and corona radiata
List a common NUTRITIONAL brain disorder, and associated features
THIAMINE DEFICIENCY
- Bilaterally symmetric, multifocal
- Nuclei of brain and brainstem:
LATERAL GENICULATE, CAUDAL COLLICULI, VESTIBULAR NUCLEI and others
What intracranail change may be seen with PSS? What other conditions have been associated with these changes?
- T1 hyperintensity of lentiform nuclei (manganese deposition)
- IN PEOPLE ALSO: Hepatic insufficiency, parenteral nutrition
Describe features of subacute necrotizing encephalopathy
- ALASKAN HUSKY, Yorkie, Bull terrier
- Ultimately fatal neurodegen disorder
- Bilaterally symmeterical T2/FLAIR hyper centrally within Thalamus. May extend to colostrum / putamen
May also have focal T2w hyper in midbrain and medulla
What MR features may be seen with hyperNa (not associated with holoencephaly / CC anomalies)?
- Bilaterally symmetrical increase in T2 at junction of internal capsule and lateral margin of thalamus
