imaging Flashcards
MRI and CT orientation
patient’s feet would be pointed towards the observer and the top of the head away from the observer
MRA/CTA to Dx PCOM aneurysms
Can detect 2-4 mm PCOM aneurysm
Gold standard for cerebral aneurysm detection = invasive catheter angiography
However, CTA and MRA are now capable of detecting virtually all aneurysms large enough to cause a 3rd nerve palsy.
Most false negatives = 2/2 result of human error rather than an intrinsic limitation of the MRA or CTA study.
MRI
T1 = longitudinal relaxation (fat = bright, water = dark). Best for anatomy.
T2 = fat = dark, water = bright. Maximize difference in tissue water content and state. Most sensitive to inflammation, ischemic, neoplastic alterations
outside brain= lighter
Image with neuroretinitis?
Neuroretinitis is NOT a risk factor for MS development.
Lab testing: Bartonella henselae (“cat scratch fever”), syphilis, sarcoidosis, toxoplasmosis, and Lyme disease.
Majority of cases the blood work is unrevealing and the diagnosis is idiopathic neuroretinitis.
Pseduotumor
Sagittal MRI slice =partially “empty sella sign”
non-specific but suggestive indicator of increased ICP
pituitary that looks compressed and molded to the base of the sella (with a concave appearing superior border).
Interestingly an empty sella pituitary still typically produces hormones normally.
Just to be clear, an MRI with a partially empty sella that is otherwise normal and daily HA are not enough to make a definitive diagnosis of pseudotumor cerebri. Need other clinical Si/Sx.
To confirm Dx:, there should be papilledema on examination and a lumbar puncture showing elevated opening pressure taken in the lateral decubitus position (> 25 CM H20 in adults) normal CSF (protein, glucose, cell count, etc)
patient must not be meds known to cause increased intracranial pressure (e.g. tetracycline or retinoic acid derivatives).
Only other neurological deficit permitted in pseudotumor cerebri = unilateral or bilateral abducens (CN6) palsy. (Increased ICP Idisplaced inferiorly brainstem by high pressure thereby stretching the abducens nerve(s) and causing paresis.)
very rare: CN 3, 4, or 7 palsies in association with pseudotumor. If you see one of these palsies, should raise a red flag for alternative Dx that can mimic pseudotumor such as malignant infiltration of the meninges, infectious meningitis, or inflammatory meningiopathies (e.g. sarcoid).
MS imaging
classic demyelinating white matter lesions of the deep white matter on this FLAIR (fluid-attenuated inversion recovery) sequence.
The FLAIR sequence is essentially a modified T2 sequence where the CSF bright signal is attenuated thereby making it easier to see periventricular white matter hyperintensities.
Several of the lesions on this MRI fit the classic MS “Dawson’s finger” appearance meaning that they are periventricular ovoid T2 hyperintensities arranged perpendicular to the adjacent ventricle.
T1
fat/blood bright, water/vitreous dark
better for anatomy, esp. with gado
Outside brain = darker
T2
water/vitreous bright, fat/blood dark
better for infarcts/tumor
outside brain= lighter
T1-fat-saturated
for vascular dissection
T2-FLAIR
for edema, white matter lesions
outside brain= lighter
DWI / ADC
for acute stroke
Gradient Echo / Susceptibility
for iron products (blood), calcium
