Neuroradiology (CT, MRI) interpretation skills

Question 1

Although MRI is superior for imaging brain + sc, when is CT indicated?

Answer 1

CT is used if there are contraindications for MRI (eg metals, pregnancy…), or if the pt is unstable and quickly deteriorating neurologically. In the latter case, a significant brain hemorrhage or midline shift should probably be detectable on CT scan.

Question 2

How does acute hemorrhage appear on CT?

T2?

Answer 2

• CT: Appears bright whether in the brain or outside (subarachnoid, subdural).
• T2 weighted MRI: the center of an acute hemorrhage is brighter, w/ a darker periphery, which changes as the hematoma ages.

Question 3

What is the quickest way to see acute infarction?

How do very early infarcts appear on CT?

Answer 3

Acute infarction is seen sooner with MRI (DWI earlier than T2 weighted or other images) than CT.

Very early infarcts on CT may only appear as subtle effacement of the gray-white matter junction or sulci, or not appear until hours later.

Question 4

How does acute infarction appear on MRI?

CT?

Answer 4

Bright lesion on MRI (DWI, T2 weighted or FLAIR)

Darker lesion on CT that occurs within a vascular territory.

Question 5

How does local mass effect or edema appear on CT?

T2/FLAIR?
- What may help delineate the lesion w/in the surrounding edema?

Answer 5

CT: surrounding darkness

T2/FLAIR: bright signal around the lesion itself.
- Contrast may help delineate the lesion within the surrounding edema. [Greater mass effect may produce lateral shifts of cerebral hemispheres beneath the falx (across the midline) or down the foramen magnum]

Question 6

What is the name of enlarged ventricles due to brain atrophy?

Answer 6

Hydrocephalus ex vacuo

Question 7

Give some eg’s of CNS infections.

Answer 7

• Abscesses (mass lesions with surrounding edema)
• Encephalitis
• Myelitis (inflammation, often viral, of the brain or spinal cord)
• Meningitis

Question 8

How does myelitis appear on T2/FLAIR?

Answer 8

Appears bright on T2 weighted or FLAIR series MRI

Question 9

What should you order if you suspect menigitis, for imaging? (?)

Answer 9

May be noted as contrast enhancement of leptomeninges on MRI (so order contrast) (?)

Question 10

Where are metastatic tumors normally localized in the brain?

Answer 10

Gray-white matter jcn

Question 11

Where do epidural sc metastases often arise from?

Answer 11

Vertebral bone (expands up towards sc)

Question 12

What is the imaging used to look for MS lesions?

What may these lesions be indistinguishable from?

Answer 12

MS plaques occur in the white matter of the cerebral hemispheres, brain stem and spinal cord, seen as bright lesions on T2 weighted or FLAIR series MRI. Acute lesions may enhance.

The bright MRI lesions of MS may be impossible to distinguish from subcortical infarctions, so clinical knowledge of pt is crucial.

Question 13

What are some eg’s of degenerative spine diseases?

Answer 13

Spondylosis, disc herniation, central canal stenosis

Question 14

Degenerative spine disease is best seen w/what imaging modality?

If using CT, what may be necessary

Answer 14

MRI

W/CT, may require intrathecal contrast (CT myelography).