CM- Neuroradiology Flashcards
In a CT through the posterior fossa and middle cranial fossa, what is anterior to the forth ventricle?
What is posterolateral?
The pons is anterior to the fourth ventricle and the cerebellar hemispheres are posterolateral to the forth ventricle.
What cisterns surround the pons at the level of the posterior foss and middle cranial fossa?
What vessel can be visualized at this level?
Anterior = prepontine cistern [with the basilar trunk in it] Laterally = perimesencephalic cistern
In a CT at the level of the midbrain, what is seen anterior to the midbrain?
What is posterior?
What vessels can be seen at this level?
Anterior to the midbrain is the suprasellar cistern[with the optic chiasm visible]
Posterior to the midbrain is the quadrigeminal plate and the quadrigeminal plate cistern.
At this level, the MCA can be visualized in the sylvian fissure
What does the interpeduncular cistern merge with anteriorly?
the suprasellar cistern
What does the most cephalad aspect of the quadrigeminal plate cistern merge with anteriorly? Laterally?
What is posterior to the quadrigeminal plate cistern?
Anteriorly- aqueduct of sylvius
Laterally- ambien cistern
Posterior - superior vermian cistern
In a CT image at the level of the third ventricle and the foramina of Monro. What lies on either side of the 3rd ventricle?
What darker grey is seen even further lateral?
The thalamus flanks the third ventricle
Further laterally lie the posterior limbs of the internal capsule
What is cupped in the concavity of the frontal horns of the lateral ventricles?
caudate heads
At the level of the third ventricle, what cistern can be seen posteriorly?
cistern of Galen
What cisterns are seen behind the pulvinars of the thalami at the level where the calcified pineal gland is visible?
retrothalamic cisterns
What cisterns are located laterally to the putamen and globus pallidus [lentiform nuclei] ?
insular cistern
What can be visualized in the ventricular trigones of CT?
calcified glomus of the choroid plexus
At the level of CT where calcified choroid plexus is visible, and the corpus callosum spans the midline, what is the white matter referred to as?
Corona radiata
What is anterosuperior to the 3rd ventricle?
What is inferior?
It receives CSF from the lateral ventricles via the foramen of Monro.
Inferiorly, it opens up to the fourth ventricle via the aqueduct of sylvius.
What does the fourth ventricle open up to inferiorly?
foramina of Luschka and Madendie
What are the components of the lateral ventricles?
Which parts make up the trigone?
Which parts are most frequently asymmetric?
- frontal horns
- bodies
- temporal horns
- occipital horns
Temporal + occipital = trigones (atria) with calcified choroid plexus
Most frequently asymmetric = temporal [followed by occipital]
What are cisterns?
counterpart of the sulci- they are located around the base of the brain rather than over the convexities. They are in continuitiy with each other
What cistern is at the level of the internal auditory canals?
cerebello-pontine angle cistern
What cistern is most important for the early detection of small amounts of subarachnoid blood?
interpeducular cistern
What are the forebrain components of the basal ganglia?
- lentiform nucleus [globus pallidus, putamen]
2. caudate nucleus
White is the white matter tract at the level of the the lateral ventricles?
What is the white matter above the lateral ventricles?
At lateral ventricles- corona radiata
Above = centrum semiovale
What is the 4 step approach to Cranial CT?
- Evaluate the CSF spaces [ventricles, sulci, cisterns]
- Are there areas of asymmetry? [increased white, diminished dark]
- Contrast enhancement?
- Describe lesion characteristics if discovered
What is increased size of ventricles at the expense of sulci and cisterns?
Hydrocephalus
What pathology is associated with increased size of ventricles, sulci and cistern?
atrophy [volume loss of parenchyma]
What pathology is associated with decreased size of ventricles, sulci and cisterns?
Diffuse edema
What pathology is associated with focal attenuation of sulci or ventricles?
focal mass or mass-like lesion
What will happen to the brain if there is:
- volume loss in a given hemisphere
- volume increase in a given hemisphere
- Loss= ipsilateral shift of the midline [chronic infarct]
2. Gain = mass effect–>contralateral shift
What 4 situations would increase density on a CT? [bright white]
- recent hemorrhage
- calcium
- bone
- contrast agent
What 5 situations would decrease density on a CT?
- vasogenic edema - white matter w/masses
- cytotoxic edema- white and gray w/ ischemia
- encephalomalacia [atrophy of brain parenchyma]
- gliosis- fibrotic brain parenchyma
- chronic hematoma
What 5 things will be positive for contrast enhancement on CT?
- neoplasm [primary benign, primary malignant, secondary]
- infections [absesses]
- vascular lesions [AVMs]
- Ischemia- subacute
- active demyelination
What 4 things will be negative for contrast enhancement on CT?
- chronic ischemia
- low grade neoplasm
- quiescent demyelination
- progressive multifocal leukoencephalopathy
You have discovered a lesion on CT. What 5 characteristics should be evaluated?
- parenchymal vs. extraparenchymal
- margination [well circumscribed = benign]
- density
- contrast enhancement, nodular [lymphoma], ring-like [abscess] , patchy [ischemia]
- effect on adjacent structures
What are the 4 types of intracranial hematomas?
- parenchymal
- subarachnoid
- subdural
- epidural
Describe the effect of acute hematomas on midline.
Are they hyper or hypodense?
What can they be surrounded by?
They have mass effect and shift the midline to the contralateral direction [or focally attenuate the CSF space]
They are hyperdense [Bright white] and gradually progress to hypodense [black] over the course of several weeks.
They can sometimes be surrounded by a zone of hypodense edema
A hyperdense lesion is caused by what 4 things?
What could give you clues that it is an acute bleed?
- acute bleed= irregular smooth border, edema surrounding it, asymmetry, loss of CSF space
- calcium
- bone
- contrast
How does subarachnoid hemorrhage appear on CT?
How does the midline shift?
Where is it best appreciated?
high density fluid occupying a normally low dense CSF space.
The midline does NOT shift with subarachnoid hemorrhage.
It is best appreciated in the basal cisterns [esp. interpeducular cistern and lamina terminalis]
Subarachnoid hemorrhage often presents with what 2 accompanying phenomenon?
- intraventricular blood
2. hydrocephalus [due to meningitis obstruction of extraventricular CSF or intraventricular obstruction by blood clot]
What are the 2 most common causes of subarachnoid hemorrhage?
- aneurysm- in circle of willis [ant comm artery, posterior comm artery, MCA bifurcation, ICA bifurcation, basilar apex, PICA]
- trauma
Describe a subarachnoid lesion of the MCA region.
Hyperdense round lesion
Surrounding edema
Hyperdense material tracking into multiple cisterns
Describe the CSF spaces, asymmetry, and lesion associated with a giant basilar apex aneurysm.
CSF: dilated lateral ventricles at the expense of sulci
Assymetry: because the lesion is in the center, the overall picure is symmetric
Lesion: round density in the prepontine cistern [sellar region] displacing the pons posteriorly
You are examining a CT and note that a lesion extends across suture lines and occupy a large surface area. The lesion is not able to cross the midline.
There is blood of varying density within the collection. The contralateral lateral ventricle is dilated.
What does this presentation make you suspicious of?
Subdural hematoma:
-crosses midline not center because of double reflection of the dura [falx cerebri]
What is a reliable factor for distinguishing subdural from epidural collections of blood?
Subdural extends across the coronal suture
When examining a CT, you note an elliptoid lesion exerting mass effect with attenuation of sulci and ventricles, and a contra-lateral midline shift. The lesion does NOT extend across suture lines.
What type of hemorrhage is this likely to be?
Epidural
What brain bleed is most associated with skull fractures?
Epidural has a closer correlation than subdurals
What are the 3 “mechanisms” of infarct?
- thrombosis
- embolism
- hypoperfusion
Describe the effects of an acute infarct on the brain.
- mass effect - effacement of sulci and ventricles with contralateral midline shift
- density mildly decreased [darker]
- cytotoxic edema is present
- contrast enhancement is absent
Describe a subacute infarct on CT.
Vascular, leptomeningeal, parenchymal enhancement seen 3 days to 3 wks from the event
How can you differentiate an acute and subacute infarction?
subacute infarcts will enhance
Acute will not
Describe a chronic infarct on CT.
- marked hypodensity
- volume loss –> ipsilateral midline shift
- NO contrast enhancement
- enlargement of ipsilateral lateral ventricle
What is an example of a benign extra-parenchymal mass?
Where will it be localized on a CT?
Meningioma -localized to the periphery on a CT exerting mass effect on adjacent sulci.
Increased density, areas of calcification
You are examining a CT and see a well-circumscribed hyperdense mass with a focus of globular calcification. It is right near the surface of the skull. The patient history is that of gradual neurological decline. What is the likely diagnosis?
Meningioma - abutting the surface of the skull is a clue that the lesion is extra-parenchymal
On CT you note mass effect with attenuation of adjacent sulci and ventricles. There are patchy areas of increased density surrounded by zones of hypodense edema. Contrast enhancement is nodular and peripheral.
What is the likely diagnosis?
Mets or primary CNS cancer
A ring-enhancing lesion on CT suggests what 2 things?
- abscess
2. neoplasm
What 2 things cause hydrocephalus?
- obstruction to CSF pathways
2. overproduction of CSF
What is the difference between communicating and non-communicating hydrocephalus?
Communicating = obstruction is distal to the fourth ventricle outlets [luschka and magendie]
Non-communicating = proximal to the foramina of luschka and magendie
On CT you note a lesion that is exerting mass effect with attenuation of sulci and ventricles with a contralateral midline shift.
The lesion has a hypodense center and the peripheral wall is slightly more dense.
After contrast enhancement, there is marked enhancement of the wall [which is less developed along the ventricle margin.
What is the most likely diagnosis?
Abscess
How does cysticercosis present on CT?
- One or more small cystic areas
- some may have a scolex seen as a focus of density in the lesion
