Neuro Submodule - Pattern Recognition in Common Neurologic Diseases (CT&MRI)

8/23/2019 Neuro Submodule - Pattern Recognition in Common Neurologic Diseases (CT&MRI)

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NEURO Submodule on Disorders of Nervous System [RADIOLOGY] 1 February 2011YL6

Pattern Recognition in Common Neurologic Diseases on CT and MRI Dr. Catherine Lazaro

Team 6 LianDetteDenisePiaRonDArnelPBGSandyPatseeTJ Page 1 of 8

OUTLINE

I. CT Scan

A. History

B. Basic principles

C. Hounsfield Unit Values of Various Substances

II. MRI

A. History

B. Types of Scanners

C. Terminologies

III. HYPERDENSE LESIONS

A. Acute Hemorrhage

B. Acute Epidural Hematoma

C. Acute Subdural Hematoma

D. Physiologic Calcifications in the Globus Pallidum

E. Focal Falcine Calcification

F. Herniation

IV. HYPODENSE LESIONS

A. Acute Infarct

B. Chronic Strokes

V. MRI LESIONS

VI. TRAUMA

A. Extra- axial

B. Intra- axial

VII. NEOPLASMS

VIII. BRAIN ABSCESSIX. PATTERNS OF EDEMA

A. Cytotoxic Edema

B. Vasogenic Edema

X. SPINAL CORD LESIONS

A. End Plate Damage

B. Disc Herniations

1. Disc Bulge

2. Disc Protrusion

3. Disc Extrusion

4. Sequestered Disc

I. Computerized Tomography Scan (CT Scan)

A. History

First introduced by British engineer Godfrey Hounsfield in

April of 1972

Hounsfield together with physicist Alan Cormack received

the Nobel prize for physiology and medicine in 1982

B. Basic Principles in CT Scan

Figure 1. Basic Principles of CT Scan

NOTE: CT is 2D but computers can manipulate it to reconstruct a 3D

image.

C. Hounsfield Unit Values of Various Substances

Numerical Value Substance

-1000 Air

-10 to -30 Fat

0 Water

average of +30 Soft tissues/muscle

+35 to +50 Acute blood /proteinaceou s material

+80 to +500 Calcium

+1000 Metal

Table 1. Hounsfield Unit Values

Hounsfield Unit degree of lightness and darkness on CT

Hounsfield Artifact dirt in a CT image

NOTE:

o Negati ve units appear black on CT

o Positive units appear white on CT

o Units only range from -1000 to +1000 units.

D. Terminologies

Hyperdense or high attenuation bright/white

Hypodense or low attenuation dark/black

Isodense degree of grayness similar to tissue being

referred to or examined (i.e., isodense to surrounding brain

parenchyma; isodense to muscular tissue)

II. Magnetic Resonance Imaging (MRI)

Used to be calledNuclear Magnetic Resonance

Contraindications: patients with metallic splinter in the eye

or those with pacemakers

It uses magnetic energy, not radiat ion.

A. History

1936 Dutch physicist, C.J. Gorter introduced the conceptof Nuclear Magnetic Resonance (NMR)

1973 Paul Lauterbur suggested the medical applications of

NMR

2003 Lauterbur and Mansfield won the Nobel prize for

physiology and medicine

B. Types of MRI Scanners

Open-type non-permanent magnet

o used mainly for claustrophobic patients

o image is not as clear as one rendered from closed-type

Closed-type permanent magnet

C. Terminologies

Hyperintense or high intensity bright/white Hypointense or low intensity dark/black

Isointense degree of grayness compared to tissue being

referred to or studied

T1-weighted (T1W) water/CSF appears black/hypo

T2-weighted (T2W) water/CSF appears white/hyper

(Remember: WW2 water is white on T2)

o Calcifications appear bright

o Infarcts appear as hypodense lesions

NOTE: Some T1W images with contrast may look like T2W images.

Technique is to look at CSF, which will always be black on T1W.


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Pattern Recognition in Common Neurologic Diseases on CT and MRI RADIOLOG


III. HYPERDENSE LESIONS

Can be caused by bone, hemorrhage, or calcifications

Do not just ident ify the lesion. Also describe what it does tosurrounding structures (e.g., herniation)

A. Acute Hemorrhage

Figure 2. CT Scan

showing an intracerebral

hemorrhage due to high

blood pressure (*) with

different densities of

layering blood (yellow

arrows).

B. Acute Epidural Hematoma

Figure 3. CT Scan

showing epidural

hematoma of the left

temporoparietal

(arrows).

NOTE: It assumes a

lentiform shape

because it is limited by

the dura.

C. Acute Subdural Hematoma

Figure 4. CT Scan showing

an acute subdural

hematoma (arrows).

NOTE: Compared to

epidural hematoma,

subdural hematomas

assume a convexity of the

lobe because it is not

limited by the dura.

NOTE:As blood ages, the color of hematoma on CT images gets

darker and may assume the color of CSF.

D. Physiologic Calcifications in the Globus Pallidum

Figure 5. Physiologic

calcifications in

globus pallidi

(bilateral).

E. Pineal Gland Calcification

Figure 6. Pineal Gland Calcification

F. Focal Falcine Calcification

Figure 7. Calcified

meningiomas from the

parietal convexity

G. Herniation

Figure 8. Subdural

hematoma resulting

to subfalcineherniation (arrows).

NOTE: Measure the

distance between the

midline and the

lesions. If it impedes

that much, it needs

surgery


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IV. HYPODENSE LESIONS

A. Acute Infarct

Figure 9. Non-contrast

CT brain of patient with

right MCA infarct. Early

ischemic changes

evident at 4 h after

onset are sulcal

effacement (green

arrows/arrows on left) ,

and parenchymal

hypoattenuation (pink

arrow/arrow on right)

due to edema.

Figure 10. After 24

hours, more

pronounced

parenchymal

hypodensity due to

swelling (yellow

arrow/arrow on left) and

petechial hemorrhagic

transformation (red

arrow/arrow on right).

Hypodense lesions are diffi cult to ident ify because almost

everything is hypodense.

Infarcts are the most common lesions seen in ER or in general

practice.

Infarcts can be hyperacu te (


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MRI is the best screening choice for rapid detection of lesions.

However, CT remains the most commonly used because MRI is

very expensive (CT: P2000; MRI: P8000)

CASE 2:

T2 FLAIR T1

Figure 12. Comparison of T2W, FLAIR, and T1W MRI

T2W image reveals hyperintensity in lentiform nucleus which

is hardly perceptible using T1.

Hyperintensi ty is seen more using Fluid Attenua tion Inversion

Recovery (FLAIR)

DWI ADC

Figure 13. Infarct seen using DWI

MRI is considered a better test than CT for identifying acute

ischemic changes with diffusion MR being highly specific test

for early detection of infarct.

o Infarct is very hyperin tense using Diffusion WeightedImaging (DWI)

However, after 12 hours, the sensitivity o f CT scan is almost

the same as MRI.

Apparent Diffusion Coefficient (ADC) is used with DWI.

o Will determine if infarct is acute, hyperacute, or chronic

o If an infarct were 4 days old, medications would not work

anymore.

Figure 14. Matched Diffusion-Perfusion

Perfusion Scan shows how much blood flows into a particular

area of the brain.

o Match/superimpose diffu sion sequence (the lesion as seen

on T1W or T2W) with perfusion sequence.

o If they are completely superimposab le (no penumbra), it

means that theres no more salvageable brain in the

lesion.

o If there is a penumbra, the salvageable parenchyma must

be reperfused within 3 hours of onset (not at detection of

infarct).

Penumbra defined as an area of markedly reduced

perfusion with loss of function of still viable neurons.

Timely perfusion of this tissue may prevent cell death and

help reestablish normal function.

Figure 15. Penumbra in an Infarction

VI. Trauma

Figure 16. Schematic CT Scan of the

most common skull and brain injuries

at trauma

1 Linear fracture

2 Depressed fracture

3 Foreign body of metal density

4 Pneumocranium and

pneumocephalus

5 Contusion hematoma with edema

6 Acute subdural hematoma

7 Chronic subdural hematoma with

re-bleeding

8 Extradural hematoma formation

A. Extra-axial Injuries

Injuries outsid e the brain parenchyma

o Epidural hemorrhageo Subdural hemorrhage

o Subarachnoid hemorrhage

1. Epidural Hematoma

Blood collection between the inner table of skull and dura

matter

Fracture across the middle menigeal artery groove

Does not cross sutures

Lentiform shape

Can cross falx and tentorium


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Figure 17. T2W MRI

image of an epidural

hematoma.

NOTE: Dura is seen as a

hyposignal line.

Epidura l hematoma shows mixed hyperdense and isodense

(intermediate intensity). This indicates that it is actively

bleeding.

2. Subdural Hematoma

Hemorrhagic collection in the subdural space

Stretching or tearing of bridging cortical veins

Crescent shaped; concave border

May cross sutures, not dural attachments

Figure 18. An axial T1W

MRI demonstrates

bilateral subacute

subdural hematomas

with increased signal

intensity. Areas of

intermediate intensity

represent more acute

hemorrhage into the

subacute collections.

3. Subarachnoid Hemorrhage

Collect around the sulci

Figure 19. MRI shows subarachnoid hemorrhage, which

appears hyperintense on T2W and FLAIR images and

isointense to hypointense on the T1W image. Findings in

the right parietal region extend into cortical sulci and

suggest hyperacute or acute hemorrhage.

B. Intra-axial Injuries

Injuries inside the brain parenchyma or spinal cord

1. Cerebral Contusion

Injury to brain surfaces involving superficial gray matter

Characteristic locations are adjacent to bonyprotruberanceor dural fold

Patchy superficial hemorrhages within edematous

background

Figure 20. Cerebral

contusion.

NOTE: These are

more shallow than

DAIs.

2. Diffuse Axonal Injury (DAI)

Traumatic axonal stretch injury

High velocity motor vehicle accident

Tends to occur in three fundamental anatomic areas (lobar

white mater, corpus callosuium and the dorsolateral

aspect of the upper brainstem involved)

Involvement becoming sequentially deeper with increased

severity of trauma

Figure 21. An axial, non-

enhanced CT image of the

brain demonstrates

multiple small petechial

hemorrhages at the gary-

white matter junction, the

caudate nucleus and the

corpus callosum,

characteristic of diffuse

axonal injury in this male

who was in a motor vehicle

accident.

MRI is the best imaging modality for cerebral contusions

Figure 22. Coup and Contrecoup Injuries


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VII. Neoplasms

A. Astrocytoma

o Primary brain neoplasm

o Has different configurations so difficult to diagnose solely on

using imaging

o The primary tumor is difficult to diagnose from the

edematous parenchyma

On T1W hypo intense On T2W hyperintense

Figure 23. MRI of astrocytoma

B. Glioblastoma Multiforme

A high grade astrocytoma

On T1W hypointense

On T2W hyperintense

o Perimetric edema

Hypointense on T1W

Hyperintense on T2W

Figure 24. MRI of Glioblastom Multiforme

VIII. Brain Abscess (Mature)

Rim enhancing lesions on IV contrast- enhanced sequences

Enhancement is secondary to collagenous capsule

surrounding the liquefied necrotic material

Pathognomonic of brain abscess: inner necrotic tissue

surrounded by enhancing rim

Figure 25. MRI of a pyogenic brain abscess

IX. Patterns of Edema

A. CYTOTOXIC EDEMA

Due to cell death and injury

Disruption of Na-K pump and autoregulation ofinflow/outflow of fluid at the cellular level

Cell bursts when too much fluid is accumulated resulting in

fluid collection around the lesion or at its perimetry thus a

perimetric configuration

Figure 26. Cytotoxic

edema may appear

as hypodensities

surrounding the

lesion. This is

common in infarcts

B. VASOGENIC EDEMA

Disruption of normal blood brain barrier

Third space loss

Fluid extravasates into the area of least resistance and less

cellularity (white matter)

frond-like or finger-like configuration, which are

project ions affect ing mainly white matter

Figure 27. Vasogenic

edema interdigitates

into the spaces

producing finger-like

appearance. Due to the

breakdown of the blood

brain barrier, fluid

extravasates into the

white matter.


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X. Overview of Spine Pathology

Imaging deals with the relationship between

o Vertebral bodies

o Intervertebral discs

o Posterior elements

o Spinal cord/column

MRI deals with soft tissues, cartilage, disc diseases, endplate

changes and cord disease

o MRI modalit y of choice for spinal cord

CT deals with the osseous structures and images anatomy as

well as fractures better than MRI

o CT Scan modality of choice for spinal column

A. End Plate Change

Seen in degenerative diseases. These have to be typed to

distinguish them from neoplasm

Figure 28. End Plate Change on MRI

Modic Type Changes T1W T2W

1 Fibrovascular

changes

Hypointense Hyperintense

2 Fatty marrow

changes

Hyperintense Hyperintense

3 Sclerotic changes Hypointense Hypointense

Table 4. Comparisons of Modic Types of End Plate Changes

B. Disc Herniations

Most common cause of complaints of back pains aside from

kidney stones

Classified into four categories because the management and

picture for each would differ although they are very similar

1. Disc bulge

Diffusely bulging discs extending symmetrically and

circumferentially

>2 mm beyond margins of adjacent vertebral body

Disc bulges outside the rim of the vertebral body

o If you see the bulge posteriorly, cords may be

compressed and therefore manifests as back pain.

o If it bulges laterally not significant in that it

doesnt compress anything; no back pain

Figure 29. Disc Bulge

2. Disc protrusion

Focal asymmetric extension of disc tissue beyond vertebral

body margin in to spinal canal or neural foramina

Mediolateral dimension broader than any other dimension

Some outer annular fibers intact

Does not extend in the cranial or caudal direction

T1W & T2W low signal

Width of the protruding disc is wider than its AP diameter

(Width > AP diameter)

Significant when it compresses the nerve roots as this

produces pain

Annular fibers are intact, keeping the nucleus pulposus in

place

There could also be spinal canal stenosis

Nucleus pulpo sus protrudes into canal

Figure 30. Disc Protrusion


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3. Disc extrusion

More pronounced than protrusion

Disruption of outer annular fibers

Greater AP dimension than base (neck area/ mediolateral

dimension)

Migrates up or down behind adjacent vertebral body but

maintains continuity with the parent disc

Same signal as parent disc on all pulse sequences

AP diameter of the extruding disc is greater than its width

(AP > width)

Causes significant narrowing of spinal canal

Can migrate up or down, but still bounded by annular

fibers

If there is migration going up or down, it will produce more

symptoms depending on level involved

Figure 18. Disc Extrusion

4. Sequestered Disc

Low signal similar to parent disc

Peripheral or diffuse high signal on T2W and T1C+

Annular fibers are torn

Can produce symptoms far away from the level where it

pinched off from (Sequestered disc may originally come

from level X but the symptoms manifested are characteristic

of level Y)

Figure 19. Sequestered Disc

QUIZ!!

Modified T/F. If false, correct the statement.

1. 24h after a CVA, an MRI becomes only as sensitive as a CT scan.

2. The penumbra is the salvageable part of an ischemic lesion and

has markedly reduced perfusion with loss of function.

3. You must act within 3h after diagnosing a patient with CVA.

4. An epidural hematoma forms a crescent shape, while a subdural

hematoma forms a lentiform shape.

5. On T2W, a hemorrhage gradually decreases from bright to dark

when shifting from hyperacute to old.

6. On T1W, a hemorrhage is hyperacutely to acutely intermediate,

subacutely bright, and dark when old.

7. Cytotoxic cerebral edema has flooding of the cells forming frond

or finger-like forms on imaging.

8. A sequestered disc is a protruded disc that may migrate up or

down while maintaining continuity with adjoining discs.

9. Most supratentorial astrocytomas are hyperintense on T1 and

slightly hypointense on T2.

10. In a patient with subdural hematoma, when the b lood has been

around for a few days, it appears hypodense on CT.

Answers:

1. 12h after a CVA, an MRI becomes only as sensitive as a CT scan.

2. TRUE (Its markedly reduced, BUT the neurons are still viable.)

3. You must act within 3h after the CVA.

4. An epidural hematoma forms a lentiform shape, while a subdural

hematoma forms a crescent shape.

5. On T2W, a hemorrhage alternates between bright and dark

when shifting from hyperacute to acute to subacute to old.

6. TRUE (Intermediate to bright to dark.)

7. Vasogenic cerebral edema has flooding of the brain parenchyma

forming frond or finger-like forms on imaging.

8. A sequestered disc is an extruded disc that may migrate up or

down and does not maintain continuity with adjoining discs.

9. Most supratentorial astrocytomas are slightly hypointense on T1

and hyperintense on T2.

10. In a patient with subdural hematoma, when the b lood has been

around for a few days, it appears isodense on CT.

Neuro Submodule - Pattern Recognition in Common Neurologic Diseases (CT&MRI)

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