ct & mri of central nervous system

CT&MRI of Central nervous system

Dept. Radiology, the 2nd affiliated hospital, Sun Yat-Sen University

Huang Sui Qiao

CT Scanning

• Plain CT

• Contrast CT

CT scanner

CT characteristics of pictures

• CT value ： depending on different organ and tissues to X ray.

call HU （ Hounsfield Unit ） .

Bone

Soft tissue

Water

Fat

Air

Magnetic Resonance Imaging

MRI----conventional sequences

• SE sequence （ spin echo ）– T1-weighted,T1-WI

TR: 200-800ms TE:15-30ms– T2-weighted,T2-WI

TR:1500-2000ms TE:60-150ms– Proton Density,N(H) ） TR:1500-2500ms TE:15-30ms

• IR sequence （ inversion recovery sequence ） TR （ short ） TE （ short ） TI （ short ）

MR signal characteristics

• SE sequences ：– T1-WI: highist signal on fat tissue ,better for showing

anatomical structures– T2-WI: highist signal in liquid, better for detecting lesio

ns– N （ H ） Density,N(H): for characteristics of lesions

• GRE sequence ： flip angle ， fast scan• IR sequence ： separation between of fat and liq

uid

T2WI T1WI

MR signal charateristics

Fat supression Liquid supression

MR signal charateristics

Normal anatomical structure of head on CT

Brain stem; cerebellum;suprasellar cistern; lateral sulcus; quadrigeminal cistern; lateral ventricle; basilar ganglion

Normal anatomical structure of head on CT

Gray matter; white matter; cortex; frontal lobe; occipital lobe; parietal lobe; temporal lobe; internal capsule ; thalamus; falx

Normal anatomical structure of head on MRI

Flair sequence

T2WI(coronal section ）

T1WI （ sagittal section ）

Corpus callosum; optic chiasm; pituitary gland; medulla oblongata

Intracranial tumors

,primary (80%) :originating from cranial bone ٭

cranial meninges, brain tissues,

vessels, cranial nerves, pituitary

gland, etc.

glioma(50%) , mingioma(14%) , pituitary

tumor (11%) , acoustic neuroma(7%)

secondary (20%) : metastasis , involved by tumor٭

from near structures.

The types of intracranial tumors

• Intraaxial brain tumors ： 1.glioma(astrocytoma and oligodendrogliom

a)

2.ependymoma

3.medulloblastoma

4.hemangioblastoma

5.papilloma choroideum

6.metastases


• Extraaxial brain tumors 1.meningioma 2.craniopharyngioma 3.pituitary tumor 4.nerve sheath tumors-acoustic schwannoma 5.epidermorid cyst, dermoid cyst and hamartomas

The rule for diagnosis of intracranial tumors

• There are or not a tumor

• The position of a tumor ： intraaxial or

extraaxial

• The type of a tumor

一、 Direct signs 1. tumor or occupying lesion. 2. abnormal density or signal. 3. enhancement in different degree on enhanced scan.

CT and MRI Signs for diagnosis of intracranial tumors

、、

二、 indirect signs

1. shift of near structures 2. edema in brain tissue near tumor 3. intratumoral bleed 4. intratumoral calcification 5. bone changes

astrocytoma

lower grading of astrocytoma ， grading I or II ．

• Often in adult （２０～４０years ） -- more occult in cerebral hemisphere ， grading II ， solid

• child– less see ， more in cerebellum ， grading I, cyst

astrocytoma

CT ： low or slightly low density lesion ， no or slight occupying effect , no or slight enhancement. MR ： Isointensity on T1WI ， unclear border , high or slightly high signal intensity on T2WI no or slight occupying effect , no or slight enhancement.

Grading I astrocytoma

Plain CT


T1WI T2WI


T2W Gd+ Gd+

MR:39547

astrocytomahigh grading （ grading III or IV)

• Fast growing

• Occur in any age

Imaging appearances of high grading astrocytoma

• Obvious occupying effects ,infiltrating growing with unclear margin , growing across lobe and hemisphere.

• Necrosis, cyst , bleed. • Obvious brain edema around tumor.• Obvious uneven or ring-like enhancement.

Grading IV astrocytoma

MR:39985

T2W T1W Gd+


MR:39985

T2W Gd+

T2W Gd+

MR ： 53847


Brain metastasis

• Old age• Single or multiple • Multiple appearances on CT or MR, but oft

en shown in nodule • Heterogeneous density or signal, central n

ecrosis with lower density or signal on T1WI.

• Ring-like or even enhancement• Obviously finger-like peritumoral edema

Multiple metastases

Metastasis from lung cancer

uncontrast contrast

Lung cancer and brain metastases

MR:39491


• Extraaxial brain tumors 1.meningioma 2.craniopharyngioma 3.pituitary tumor 4.nerve sheath tumors-acoustic schwannoma 5.epidermorid cyst, dermoid cyst and hamartomas

meningioma

• Most common nanglial intracranial tumor.• Mostly affect 40-70 adults.• Extraaxial mass attaching dura matter,about 9

0% occult on suppratentorium of cerebellum, few of them can occult in ventricles

Imaging of meningioma

• Round or hemishere mass occur mostly in convexity of brain , especially sagittal sinus.

• Mass with clear margin which was encysted with cerebral spinal fluid and/or vessels.

• Iso- or slightly high density on plain CT and low signal on T1WI, iso- or slightly high signal on T2WI, which was enhanced obviously and evenly.

• A broad thickened dural-based margin which was called “tail sign” .

• Edema may be not or obvious.• Local bone changes including destruction, thin or th

ickness.

Left parietal meningioma

Plain CT

Contrast CT

Round high density mass

Obviously and evenly enhanced

Right parietal meningioma

Plain T1WI

Contrast T1WI

T2WI AND contrast T1WI

meningioma

T2WI

T1WI

Gd-T1W

Acoustic schwannoma

• Benign tumor, occur mostly at middle age people, approximately 7 ~8 of all primary intracranial neoplasms.﹪ ﹪

• Ovoid or tubular tumors may occur in the internal auditory canal and cerebellopontine angle cistern .

• Tumor may be part of solid and cystic . • On Plain CT, solid part of tumor was iso-density ,and cysti

c part was low density.• Iso-intensity or low signal intensity were seen in solid or cy

stic part of tumor on T1WI, but high or very high signal intensity on T2WI,.

• Obvious enhancement was seen on solid tumor.• Enlargement of internal auditory canal.

Left acoustic schwannoma


T2WI T1WI Contrast T1WI

Right acoustic schwannoma

T1WI Contrast T1WI

Right acoustic schwannoma

Contrast T1WI

CT and MRI diagnosis of brain vascular diseases

• Bleed in high pressure patients

• Intracranial aneurysm

• Cerebral infarction

Brain bleed (hemorrhage)

• Causes ： high blood pressure, vascular malformation and tumor

• Stage ： acute, subacute, chronic

CT&MRI appearances of hemorrhage at different stage

• CT was more sensitive for acute hemorrhage CT － high density, CT value about 60 － 80Hu MRI － iso-intensity on T1WI, slightly low or low intensity on T2WI.• Subacute hemorrhage CT － iso- or slightly high density. MRI － iso- or high signal intensity on T1WI, iso- or slightly high signal intensity on T2WI.• chronic hemorrhage CT － iso- or low density MRI － high signal intensity both on T1WI/T2WI.

Acute hemorrhage （ high density on CT ）

Subacute hemorrhage

Density lower than acute stage with unclear margin

acute/subacute hemorrhage

acute

subacute T2WI T1WI

Change from acute to subacute stage （ CT low density hemorrhage ）

CT after bleed CT 2W latter MRI 2W latter

Chronic intracranial hemorrhage

Intracranial aneurysm

• causes ： congenital ； acquired (often high blood pressure )

• type ： according to morphology (saccular ,fusiform), size and location etc .

Aneurysm

●Incidence ： 0.2~1%. ● Distribution of age: mid-old age(30~60years),seldon

in youth. ● morphology : saccular （ 95% ） ,fusiform . ●size ： <0.5cm small; 0.5~1.5cm middle;1.5~2.5 larg

e ; >2.5 huge ●position ： internal carotid A--41.3%; anterior commu

nicating A--24.4%; middle cerebral A—20.8%; anterior cerebral A—9%; vertebral-basilar A--4.5% 。

CT appearances

• Showing aneurysm directly, filing defect in large one （ thrombus ）

• Subarachnoid hemorrhage in ruptured aneurysm.

MR appearance

1. aneurysm without thrombus: round or oval homogeneous very low signal lesion both on T1 and T2WI. 2. aneurysm with thrombus ： heterogeneous both on T1 and T2WI ， high signal in some area. 3. enhanced scan ： may be heterogeneously enhanced

Aneurysm at left internal carotid A

T1WI-contrast T1WI-contrast

Aneurysm at left internal carotid A

Aneurysm at left middle cerebral A

CT&MRI diagnosis of cerebral infarction

CT appearances of cerebral infarction

• Acute stage－ onset within 4－ 6h. normal/slightly low density and narrowing of sul

cus on infarction area because of edema; low density after 12－ 24h， but no any abnormal finding within 24h.

• Subacute stage－ within 1 week， typical CT appearance. Low density on infarction area with mass effect. After 2－ 3 weeks , iso- or slightly low density

with unclear margin, enhancement at border area in contrast scan.

• Chronic stage － even low density with clear margin. Atrophy of local brain.

MR appearances of cerebral infarction

• High signal intensity at Acute , subacute and chronic stage on T2WI because of increment of fluid at infarction.

• Iso-intensity at acute stage , iso- or slightly low intensity at subacte stage, low intensity at chronic stage on T1WI.

• Flair and DWI sequences are more sensitive for detecting acute infarction.

MR:44396

Within 24h

After 3 days

After 2 weeks

Acute cerebral infarction

MR:44396

MR&CT appearances of acute MR&CT appearances of acute cerebral infarctioncerebral infarction

Within 24h after 3 days after 2 weeks

MR:44396

MR&CT appearances of acute cerebrMR&CT appearances of acute cerebral infarctional infarction

T2WI T1WI Flair

MR:44396

MR&CT appearances of acute cerebrMR&CT appearances of acute cerebral infarctional infarction

Flair T1WIT2WI

Acute infarction

MR ： 66335 CT ： 122740

M 39 ， CT（－）

Acute infarction

MR ： 66335 CT ： 122740

Acute infarction DWI

MR ： 66335 CT ： 122740

Subacute/chronic infarction—T2WI

T2WI--Cor

Chronic infarction at brain stem and cerebellum—T2WI

Chronic infarction at brain stem and cerebellum—T1WI

CT&MRI diagnosis of head trauma

The types of head trauma

一、 Skull fracture 二、 traumatic cerebral swelling 三、 brain contusions 四、 Intracranial bleed of trauma ( 一 ) Epidural hematoma ( 二 ) Subdural hematoma ( 三 ) Subarachnoid hemorrhage ( 四 ) intracerebral hematoma

CT&MR diagnosis of cranial trauma

Epidural hematoma：direct violence on skull ٭

skull fracture and deformation٭

direct laceration or tearing of meningeal arteries٭

local hematoma ,not across cranial suture ٭

shape of duple convex mirror٭

CT appearances

local duple convex mirror with high density, CT v ٭ alue at 40~100Hu.

there are or not mass effect according the size o ٭f hematoma which compress gyri , ventricles. Midline is shifted to contralateral side.

the density of hematoma decrease during the tim٭e, become isodesity at about 2 weeks (subacute stage) and low density at about 1 month (chronic stage) .

acute epidural hematoma at leftfrontal lobe

acute epidural hematoma at rightfrontal lobe

Acute epidural hematoma at temporal-parietal lobe

MR appearances

shape of hematoma is seen like CT ٭signal intensity of hematoma varies greatly depend ٭

ing on times. at acute stage ٭ （ 0~2 days ）， iso-intensity on T1

WI ， low intensity on T2WI.at subacute stage٭ （ 3~14 days ）， becoming hig

h signal intensity from rim to center on T1WI, still low signal intensity at 6~8 days and high signal intensity after 8 day on T2WI.

at chronic stage (14 days later) , high signal intensi ٭ty on both T1WI and T2WI for quite long times (may be several months)

Subacute hematoma at left frontal lobe

Subdural hematoma.location: supratentorial convexity٭caused by stretching and tearing of bridging vein ٭

s. hematoma is located between dura mater and ar ٭

achnoid. Often quite large extent , across cranial suture.

CT appearances ٭ ： crescentic high density. Dividing into acute, subacte and chronic stages . Density changes of hematoma at different stages similar to epidural hematoma.

MR appearances ٭ ： shape of hematoma seen as CT ， signal changes of hematoma similar to epidural hematoma at different stages.

Acute subdural hematoma at right frontal-temporal area

Subacute subdural hematoma at left frontal-temporal area

Chronic subdural hematoma at left frontal lobe

CT&MR diagnosis of brain contusion

Often involve the temporal and frontal lobe. Temporal l ٭ obe lesions tend to lie just above the petrous bone or posterior to the greater sphenoid wing. Frontal lobe lesions occur just above the cribriform plate, orbit, planum sphnoidale, and lesser sphenoid wing.

CT appearances ٭ ： high density of hemorrhagic foci (vary in size ) scattered throughout the larger nonhemorrhagic

zone or lower density area (edema). May be or may not be mass effect.

Contusion at frontal lobe

Contusion at both sides of frontal base

Contusion at temporal lobe

MR appearances

MR is more sensitive than CT to find small contu ٭ sion because of easy to find edema caused by contusion.

hemorrhagic foci appear petechia or multiple confl٭uent regions with high signal intensity.

.easy to find contusion at brain stem ٭

Contusion and epidural hemorrhage at both temporal lobe and frontal lobe

Multiple contusions at both sides of frontal and temporal lobes

ct & mri of central nervous system

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