بسم الله الرحمن الرحيم

�َها ثُم� ع�رَض�َه�ُم� عَل�ى �َل �ُم� آَد�َم� األسماَء� ُك وع�َل�ؤني بأسماَء هؤالَء� إن المالئكِة� فقاَل� أنِب

.ُم� لنا َل �ك ال ع� ِبحان �ُم صاَدقين * قالوا س� �نُت ُك�ك أنَت� الَع�َليُم� الحكيُم * �مُتنا إن � ما ع�َل إال

)سورة الِبقرة(

Diffusion weighted magnetic Diffusion weighted magnetic resonance imaging in diagnosis resonance imaging in diagnosis and characterization of brain and characterization of brain

tumors in correlation with tumors in correlation with conventional MRIconventional MRI

EssayEssay

Submitted bySubmitted byMahmoud Abdou Mohammed AbdullahMahmoud Abdou Mohammed Abdullah

M.B.B.ChM.B.B.ChFor partial fulfillment of master degree inFor partial fulfillment of master degree in

Radio diagnosisRadio diagnosis

Supervised bySupervised by

PROF. AHMED FARID YOSEFPROF. AHMED FARID YOSEFProfessor of radio diagnosisProfessor of radio diagnosis

Faculty of medicine - Banha UniversityFaculty of medicine - Banha University

DR. ISLAM MAHMOUD ELSHAZLYDR. ISLAM MAHMOUD ELSHAZLYLecturer of radio diagnosisLecturer of radio diagnosis

Faculty of medicine – Banha UniversityFaculty of medicine – Banha University

Faculty of medicineFaculty of medicineBanha UniversityBanha University

20122012

IntroductionIntroduction

The development of techniques capable of accurately depicting The development of techniques capable of accurately depicting

tumor grades in vivo is important for determination of the most tumor grades in vivo is important for determination of the most

appropriate treatment of tumors.appropriate treatment of tumors.

An unfortunate choice of biopsy site or insufficiently large An unfortunate choice of biopsy site or insufficiently large

samples may result in an incorrect histological diagnosis. The samples may result in an incorrect histological diagnosis. The

diagnosis of brain tumors by magnetic resonance imaging (MRI) is diagnosis of brain tumors by magnetic resonance imaging (MRI) is

usually based on basic unenhanced T1- and T2-weighted images usually based on basic unenhanced T1- and T2-weighted images

and post contrast T1-weighted images. Conventional MRI and post contrast T1-weighted images. Conventional MRI

techniques are not sufficient for the grading and specification of techniques are not sufficient for the grading and specification of

brain tumors. brain tumors.

In diffusion-weighted imaging (DWI), the image In diffusion-weighted imaging (DWI), the image

contrast is determined by the random translational contrast is determined by the random translational

(Brownian) motion of water molecules. The (Brownian) motion of water molecules. The

quantification of diffusion using DWI has been quantification of diffusion using DWI has been

attracting growing interest as an easy method to attracting growing interest as an easy method to

further characterize the nature of brain tumors. further characterize the nature of brain tumors.

Diffusion weighted imaging may help to distinguish Diffusion weighted imaging may help to distinguish

tumoral invasion from normal tissue or edema. This tumoral invasion from normal tissue or edema. This

distinction if possible, would be very important for distinction if possible, would be very important for

planning surgical resection, biopsies and radiation planning surgical resection, biopsies and radiation

therapy.therapy.

BRAIN ANATOMYBRAIN ANATOMY

The cerebrumThe cerebrum

They are large, oval structures that superficially They are large, oval structures that superficially

resemble the surface of a shelled walnut. The resemble the surface of a shelled walnut. The

midline longitudinal cerebral fissure, occupied in midline longitudinal cerebral fissure, occupied in

life by the life by the falx cerebrifalx cerebri, incompletely separates the , incompletely separates the

two cerebral hemispherestwo cerebral hemispheres from one another. The from one another. The

floor of the cerebral fissure is formed by the floor of the cerebral fissure is formed by the corpus corpus

callosumcallosum, a large myelinated fiber tract that forms , a large myelinated fiber tract that forms

an anatomical and functional connection between an anatomical and functional connection between

the right and left hemispheres. Each cerebral the right and left hemispheres. Each cerebral

hemisphere is subdivided into hemisphere is subdivided into five lobesfive lobes: the : the

frontal, parietal, temporal, and occipital lobes, and frontal, parietal, temporal, and occipital lobes, and

the insula. the insula.

Additionally, the cortical constituents of the limbic Additionally, the cortical constituents of the limbic

system are also considered to be a region of the cerebral system are also considered to be a region of the cerebral

hemisphere and some consider it to be hemisphere and some consider it to be the sixth lobe, the the sixth lobe, the

limbic lobelimbic lobe. The temporal lobe is separated from the . The temporal lobe is separated from the

parietal lobe by the lateral fissure parietal lobe by the lateral fissure (fissure of Sylvius)(fissure of Sylvius). .

The central sulcus The central sulcus (central sulcus of Rolando)(central sulcus of Rolando), separates , separates

the frontal lobe from the parietal lobe. The division the frontal lobe from the parietal lobe. The division

between the parietal and occipital lobes is defined on the between the parietal and occipital lobes is defined on the

lateral aspect as the imaginary line between the lateral aspect as the imaginary line between the

preoccipital notch and the parieto-occipital notch. On the preoccipital notch and the parieto-occipital notch. On the

medial aspect, they are separated by the medial aspect, they are separated by the parieto-occipital parieto-occipital

sulcussulcus and its continuation, the calcarine fissure. and its continuation, the calcarine fissure.

Lateral surface of the brain

The Posterior fossaThe Posterior fossa The posterior fossa is divided into two compartments The posterior fossa is divided into two compartments

by the by the 4th ventricle4th ventricle. Anteriorly the . Anteriorly the brain stembrain stem occupies occupies

about one third and posteriorly the about one third and posteriorly the cerebellumcerebellum

occupies the posterior two thirds of the posterior fossa. occupies the posterior two thirds of the posterior fossa.

The brain stem has three anatomically recognizable The brain stem has three anatomically recognizable

components; the components; the midbrain, pons and medullamidbrain, pons and medulla. The two . The two

cerebellar hemispheres are joined by the cerebellar hemispheres are joined by the

midline structures of the vermis.midline structures of the vermis.

The ventricular systemThe ventricular system

TheThe ventricular system is composed of ventricular system is composed of four fluid-filled four fluid-filled

cavities (ventricles)cavities (ventricles), which are located deep within the brain. , which are located deep within the brain.

The lateral ventriclesThe lateral ventricles consist of central portion called the body consist of central portion called the body

and three extensions: the anterior, occipital and temporal horns. and three extensions: the anterior, occipital and temporal horns.

The junction of the body and occipital and temporal horns form The junction of the body and occipital and temporal horns form

the triangular area termed the trigone (atria). The lateral the triangular area termed the trigone (atria). The lateral

ventricles open downward into the ventricles open downward into the third ventriclethird ventricle through the through the

paired interventricular foramen paired interventricular foramen (foramen of Monro).(foramen of Monro). The third The third

ventricle is located midline just inferior to the lateral ventricles. ventricle is located midline just inferior to the lateral ventricles.

The third ventricle communicates with the The third ventricle communicates with the fourth fourth

ventricleventricle via a narrow passage way termed the cerebral via a narrow passage way termed the cerebral

aqueduct aqueduct (aqueduct of Sylvius). (aqueduct of Sylvius). The fourth ventricle is a The fourth ventricle is a

diamond-shaped cavity located anterior to the cerebellum. diamond-shaped cavity located anterior to the cerebellum.

The lateral angles of the fourth ventricle extend to form the The lateral angles of the fourth ventricle extend to form the

lateral apertures lateral apertures (foramina of Luschka).(foramina of Luschka). The inferior angle The inferior angle

of the fourth ventricle has an opening called the median of the fourth ventricle has an opening called the median

aperture aperture (foramen of Magendie),(foramen of Magendie), which is continuous with which is continuous with

the central canal of the spinal cord. The apertures allow the central canal of the spinal cord. The apertures allow

passage of CSF between the ventricles and subarachnoid passage of CSF between the ventricles and subarachnoid

space. space.

Diagram of the ventricles of the brain and central canal of the spinal cord

Axial T2 of the brain at the level of lateral ventricles

Pathology of Brain TumorsPathology of Brain Tumors

Brain tumors may be Brain tumors may be primaryprimary (i.e. originating from brain (i.e. originating from brain

itself), or itself), or secondarysecondary (i.e. metastatic from another primary site (i.e. metastatic from another primary site

of cancer). Both primary and secondary brain tumors are of cancer). Both primary and secondary brain tumors are

capable of producing neurological impairment according to capable of producing neurological impairment according to

their site. A their site. A benign benign tumor is composed of tumor is composed of slow-growing cellsslow-growing cells, ,

but can be life threatening when located in vital areas. but can be life threatening when located in vital areas.

Primary Primary malignantmalignant tumors are usually invasive and composed tumors are usually invasive and composed

of of fast growing cellsfast growing cells. Primary tumors, whether benign or . Primary tumors, whether benign or

malignant, rarely spread outside of the central nervous system malignant, rarely spread outside of the central nervous system

(CNS). Therefore, most symptoms tend to be neurologic in (CNS). Therefore, most symptoms tend to be neurologic in

origin. origin.

WHO classification of tumors of the WHO classification of tumors of the nervous system grouped by their tissue nervous system grouped by their tissue of origin into the following major of origin into the following major

categoriescategories:: I. Tumors of neuroepithelial tissue includeI. Tumors of neuroepithelial tissue include::

Glial tumors.Glial tumors. Neuronal and mixed neuronal glial tumors.Neuronal and mixed neuronal glial tumors. Non-glial tumors.Non-glial tumors.

II. Tumors of the sellar region:II. Tumors of the sellar region: Pituitary adenoma.Pituitary adenoma. Pituitary carcinoma.Pituitary carcinoma. Craniopharyngioma.Craniopharyngioma.

III. Hematopoeitic tumors:III. Hematopoeitic tumors: Primary malignant lymphoma.Primary malignant lymphoma.

IV. Germ cell tumors:IV. Germ cell tumors: Germinoma.Germinoma. Embryonal carcinoma.Embryonal carcinoma. Yolk sac tumor.Yolk sac tumor. Choriocarcinoma.Choriocarcinoma. Teratoma.Teratoma. Mixed germ cell tumor.Mixed germ cell tumor.

V. Tumors of the meninges:V. Tumors of the meninges: Menengioma.Menengioma. Mesenchymal tumors (chondrosarcoma, Mesenchymal tumors (chondrosarcoma,

Hemangiomapericytoma.).Hemangiomapericytoma.). Primary melanocytic lesions.Primary melanocytic lesions.

VI. Tumors of uncertain histogenesis VI. Tumors of uncertain histogenesis HemangioblastomaHemangioblastoma

VII. Tumors of the peripheral nerves that VII. Tumors of the peripheral nerves that affect the CNS:affect the CNS:

Schwannoma.Schwannoma. Neurofibroma.Neurofibroma. Malignant schwannoma.Malignant schwannoma.

VIII. Local extensions from regional tumors:VIII. Local extensions from regional tumors: Paraganglioma (chemodectoma).Paraganglioma (chemodectoma). Chordoma.Chordoma. Others.Others.

IX. Metastatic tumors.IX. Metastatic tumors.

X. Cysts and tumor like lesions:X. Cysts and tumor like lesions: Arachnoid cyst.Arachnoid cyst. Epidermoid cyst.Epidermoid cyst. Dermoid cystDermoid cyst..

Tumors of neuroepithelial tissueTumors of neuroepithelial tissue: :

A- Glial tumorsA- Glial tumors::

11 - -Astrocytic tumorsAstrocytic tumors

22 - -Oligodendroglial tumorsOligodendroglial tumors

33 - -Mixed gliomasMixed gliomas

44 - -Ependymal tumorsEpendymal tumors

B- Neuronal and mixed neuronal glial tumorsB- Neuronal and mixed neuronal glial tumors::

e.g gangilioglioma and central neurocytomae.g gangilioglioma and central neurocytoma..

C- Non-glial tumorsC- Non-glial tumors::

11 - -Choroid plexus tumors (CPT)Choroid plexus tumors (CPT)::

22 - -Pineal parenchymal tumorsPineal parenchymal tumors::

33 - -Tumors with neuroblastic elements Tumors with neuroblastic elements e.g: e.g: meduloblastoma and PNETmeduloblastoma and PNET..

Physical Principles of DiffusionPhysical Principles of Diffusion––Weighted ImagingWeighted Imaging

FICK'S LAW:FICK'S LAW:

It which states that It which states that local differences in solute local differences in solute

concentration will give rise to a net flux of solute molecules concentration will give rise to a net flux of solute molecules

from high concentration regions to low concentration from high concentration regions to low concentration

regionsregions.. However, However, even with no concentration gradients even with no concentration gradients

the water molecules are still in random motionthe water molecules are still in random motion. This is . This is

because; diffusion motions are caused by the because; diffusion motions are caused by the intrinsically intrinsically

possessed kinetic energypossessed kinetic energy of the liquid medium. The of the liquid medium. The

phenomenon of diffusion was named "phenomenon of diffusion was named "Brownian motionBrownian motion" "

after the person who first described it, Robert Brown.after the person who first described it, Robert Brown.

Free and restricted diffusionFree and restricted diffusion:: In a glass of water, the motion of the water molecules is In a glass of water, the motion of the water molecules is

completely random and is limited only by the boundaries completely random and is limited only by the boundaries

of the container. In biologic systems totally free diffusion of the container. In biologic systems totally free diffusion

generally does not occur due to the presence of generally does not occur due to the presence of

restrictions such as cell membranes or molecular restrictions such as cell membranes or molecular

boundaries. The extent of translational diffusion of boundaries. The extent of translational diffusion of

molecules measured in a biologic system is therefore molecules measured in a biologic system is therefore

referred to as the apparent diffusion coefficient (ADC). referred to as the apparent diffusion coefficient (ADC).

The intra-cellular diffusion coefficient is lower than in the The intra-cellular diffusion coefficient is lower than in the

extra-cellular space extra-cellular space due to intracellular barriers as due to intracellular barriers as

organelles, membranes and macromolecules. organelles, membranes and macromolecules.

DIFFUSIONDIFFUSION––WEIGHTED IMAGING WEIGHTED IMAGING USING PULSED GRADIENTUSING PULSED GRADIENT

In their fundamental In their fundamental study Stejskal and Tanner study Stejskal and Tanner described an experimental described an experimental

method to sensitively method to sensitively measure diffusion with measure diffusion with

MRI. Stejskal and Tanner MRI. Stejskal and Tanner used a used a pair of pulsed pair of pulsed

magnetic field gradients, magnetic field gradients, symmetrically positioned symmetrically positioned

around the 180around the 180° ° refocusing spin echo pulse refocusing spin echo pulse (as shown in this figure). (as shown in this figure).

The The first gradient pulse first gradient pulse induces a induces a phase shift for all spinsphase shift for all spins. .

The The second gradient pulse second gradient pulse will will invert this phase shiftinvert this phase shift thus thus

cancelling the phase shift completely for static spinscancelling the phase shift completely for static spins. . Spins Spins

having completed a change of location due to Brownian motion having completed a change of location due to Brownian motion

will however experience will however experience different phase shiftsdifferent phase shifts by the two by the two

gradient pulses. Thus they are incompletely refocused and gradient pulses. Thus they are incompletely refocused and

consequently lead to a consequently lead to a signal losssignal loss. According to Fick. According to Fick’’s law, s law,

true diffusion is the net movement of molecules due to a true diffusion is the net movement of molecules due to a

concentration gradient. With MR imaging, molecular motion concentration gradient. With MR imaging, molecular motion

due to concentration gradients cannot be differentiated from due to concentration gradients cannot be differentiated from

molecular motion due to pressure gradients, thermal molecular motion due to pressure gradients, thermal

gradients, or ionic interactions. gradients, or ionic interactions.

Disadvantages of pulsed gradient diffusion Disadvantages of pulsed gradient diffusion

weighted imaging:weighted imaging: Measurement of diffusion properties requires an imaging Measurement of diffusion properties requires an imaging

sequence sensitive for the detection of motion. However, such a sequence sensitive for the detection of motion. However, such a

sequence will sequence will also have sensitivity to bulk motionalso have sensitivity to bulk motion as CSF as CSF

pulsations, involuntary twitches and cardiac cycling. Attempts to pulsations, involuntary twitches and cardiac cycling. Attempts to

minimize bulk motion include use of a head holder and cardiac minimize bulk motion include use of a head holder and cardiac

gating, but CSF pulsations remain problematic. gating, but CSF pulsations remain problematic. To avoid these To avoid these

non-diffusional motions, ultra-fast techniques are usednon-diffusional motions, ultra-fast techniques are used..

These ultra-fast techniques are:These ultra-fast techniques are:

I- ECHOPLANAR IMAGING (EPI).I- ECHOPLANAR IMAGING (EPI).

II- HASTE.II- HASTE.

I-I- ECHOPLANAR IMAGING (EPI)ECHOPLANAR IMAGING (EPI)

With the development of high-performance gradients, DWI With the development of high-performance gradients, DWI

can be performed with an echo-planar spin-echo T2-weighted can be performed with an echo-planar spin-echo T2-weighted

sequence. The substitution of an echo-planar spin-echo T2-sequence. The substitution of an echo-planar spin-echo T2-

weighted sequence weighted sequence markedly decreased imaging time and markedly decreased imaging time and

motion artifactsmotion artifacts and increased sensitivity to signal changes due and increased sensitivity to signal changes due

to molecular motion. As a result, the DW sequence became to molecular motion. As a result, the DW sequence became

clinically feasible to perform. clinically feasible to perform. In EPI, multiple lines of imaging In EPI, multiple lines of imaging

data are acquired after a single RF excitationdata are acquired after a single RF excitation. Like a . Like a

conventional SE sequence, a SE EPI sequence begins with 90° conventional SE sequence, a SE EPI sequence begins with 90°

and 180° RF pulses. and 180° RF pulses.

Conventional SE imaging. Within each TR period, the pulse sequence is executed and one line of imaging data is collected. The frequency-encoding gradient (Gx), phase-encoding gradient (Gy), and section-selection gradient (Gz) are shown during one TR period. RF = radio frequency.

Echo-planar imaging. Within each TR period, multiple lines of imaging data are collected. Gx = frequency-encoding gradient, Gy = phase-encoding gradient, Gz = section-selection gradient

Single-shot and multi-shot EPISingle-shot and multi-shot EPI

EPI can be performed by using single or multiple EPI can be performed by using single or multiple

excitation pulses ("shots"). The excitation pulses ("shots"). The number of shots number of shots

represents the number of TR periods represents the number of TR periods required to required to

complete the image acquisition. In single-shot (snapshot) complete the image acquisition. In single-shot (snapshot)

EPI, all of the k-space data are acquired with only one EPI, all of the k-space data are acquired with only one

shot. Distortions and signal loss occur predominantly at shot. Distortions and signal loss occur predominantly at

boundaries between tissue and air, due to the local boundaries between tissue and air, due to the local

change of magnetic field strength. change of magnetic field strength. To achieve higher To achieve higher

resolution and reduce the image distortion and signal resolution and reduce the image distortion and signal

loss, multishot EPI can be performed.loss, multishot EPI can be performed.

Comparison between single-shot and multishot echo-planar imaging. Axial images were obtained with 1 shot (a), 8 shots (b), 16 shots (c), and 32 shots (d). The geometric distortion of the anterior aspect of the brain (arrow) is reduced as the number of shots increases.

II- HASTEII- HASTE::

Another non-EPI fast technique is diffusion weighted Another non-EPI fast technique is diffusion weighted

hahalf-Fourier lf-Fourier ssingle-shotingle-shot t turbo spin urbo spin eecho, cho, in which only in which only

half of the k-space is traversed and the other half half of the k-space is traversed and the other half

constructed by mirroringconstructed by mirroring, with the advantage of , with the advantage of

reducing susceptibility artifactsreducing susceptibility artifacts. Images covering the . Images covering the

whole brain can be obtained in one minute whole brain can be obtained in one minute and it takes and it takes

minutes to acquire data for calculation of the diffusion minutes to acquire data for calculation of the diffusion

coefficient. This technique can be implemented on most coefficient. This technique can be implemented on most

conventional MRI systems conventional MRI systems

ISOTROPIC AND ANISOTROPIC ISOTROPIC AND ANISOTROPIC DIFFUSIONDIFFUSION

In isotropic diffusionIn isotropic diffusion, there, there is is no preferred directionno preferred direction of of

water motion.water motion. However, for However, for white matterwhite matter, consisting of dense , consisting of dense

fiber bundles,fiber bundles, water moves more easily parallel to the fibers water moves more easily parallel to the fibers

than across themthan across them.. The anisotropic nature of diffusion in the The anisotropic nature of diffusion in the

brainbrain can be appreciated by comparing images obtained with can be appreciated by comparing images obtained with

DW gradientsDW gradients applied in three orthogonal directions. applied in three orthogonal directions. The The

signal intensity decreases when the white matter tracts run signal intensity decreases when the white matter tracts run

in the same direction as the DW gradientin the same direction as the DW gradient because water because water

protons move preferentially in this direction. protons move preferentially in this direction.

Anisotropic nature of diffusion in the brain. Transverse DWI with the diffusion gradients applied along the x (Gx, left), y (Gy, middle), and z (Gz, right) axes demonstrate anisotropy.

Note that the corpus callosum (arrow on left image) is hypointense when the gradient is applied in the x (right-to-left) direction, the frontal and posterior white matter (arrowheads) are hypointense when the gradient is applied in the y (anterior-to-posterior) direction, and the corticospinal tracts (arrow on right image) are hypointense when the gradient is applied in the z (superior-to-inferior) direction.

CREATION OF ISOTROPIC DW IMAGE

DW gradient pulses are applied in one direction at a time. The

resultant image has information about both the direction and the

magnitude of the ADC. To create an image that is related only to

the magnitude of the ADC, at least three of these images must be

combined. The simplest method is to multiply the three images

created with the DW gradient pulses applied in three orthogonal

directions. The cube root of this product is the DW image.

b value The magnitude of the diffusion weighting is referred

to as the b value. The b value increases with the strength of diffusion gradient used, the duration of each gradient lobes, and the time between the gradient lobes. At small b values, there is minimal sensitivity to diffusional motions and T2 weighted dominates. At high b-values the contrast is largely due to diffusion properties. Unfortunately even with the maximal currently applied b values, T2 component is still present in all diffusion weighted images. As result of this,T2 shine through effect occur. Increasing b values result in a progressive decrease in the gray to white matter signal intensity ratio. Iso intensity between gray and white matter results at b values between 1000 and 2000 sec/mm2 (Typical b values in clinical use are 300-1000sec/mm2 ). At b values greater than 2000, the gray- white pattern reverses relative to the usual b value 1000.

CREATION OF AN ADC MAP

An ADC map is an image whose signal intensity is equal

to the magnitude of the ADC. The ADC is calculated for each

pixel of the image and is displayed as a parametric map. By

drawing regions of interests on these maps, the ADCs of

different tissues can be derived. Areas of restricted diffusion

show low ADC values compared with higher ADC values in

areas of free diffusion. Thus areas of restricted diffusion will

appear of high signal DW images, these areas will appear as

low-signal intensity areas (opposite to DW

images) on the ADC map.

Importance of ADC mapThe residual T2 component on the DW image

makes it important to view the ADC map in conjunction with the DW image. In lesions such as acute stroke, the T2- and diffusion-WI effects both cause increased signal intensity on the DW image.

The ADC maps are used to exclude "T2 shine through" as the cause of increased signal intensity on DW images. The ADC maps are useful for detecting areas of increased diffusion that may be masked by T2 effects on the DW image.

Conventional MRI findings of brain tumorsGliomas

1-Astrocytomas : The common signal characteristics of the tumors include low signal in T1 and high signal intensity T2 and appear more homogenous without central necrosis

a-Diffuse astrocytoma they appear homogeneously hypointense on T1WI

and hyper intense on T2 WI. Contrast enhancement is absent on MRI in diffuse low grade astrocytomas.

b. Glioblastoma multiforme(GBM) (WHO grade IV)

solitary deep heterogeneous ring enhancing lesion with extensive surrounding vasogenic edema and mass effect. The most common feature of the enhancing ring is irregularity, with a wide ring that varies in thickness and has a shaggy inner margin. The lesion usually extends through the corpus callosum in most cases.

c. Juvenile pilocystic astrocytomas The mural nodules appears homogenously

hyperintense to grey matter on T2 WI and hypointense on T1 WI. The associated cyst is even more hyperintense on T2 weighted images and even more hypointense on T1 WI. Edema of the adjacent white matter is usually minimal. Homogenous contrast enhancement of the tumor nodule is characteristic although a calcific focus if present does not demonstrate enhancement.

d. Pleomorphic xanthoastrocytoma (PXA) A cystic supratenitorial mass containing an enhancing

mural nodule.e. Subependymal gaint cell astrocytoma(SEGA) Occurs almost extensively in patients with tuberous

sclerosis in their late teens or 20s. Tumor appears as heterogonous sharply demarcated intraventricular mass that is mildly hyperintense on T2 WI, hypo to iso intense in T1 WI and appears as a markedly enhancing mass

GBM in the left frontal lobe. Axial

gadolinium-enhanced T1-weighted image

demonstrates a mass with thick, irregular,

enhancing walls and areas of central

necrosis .

Pleomorphic xanthoastrocytoma (a) Axial T1-WI. Soft-tissue (S) and cystic (C) components are noted. (b) Axial T2-WI shows mild low signal intensity of the soft-tissue portion of the mass, whereas the cystic portions are hyperintense. Small “fingers” of vasogenic edema surround the mass. (c) Contrast-enhanced axial T1-WI shows intense enhancement of the soft-tissue portion of the mass with rim enhancement of the cystic margin .

SEGA in a 16-year-old boy with a history of psychomotor developmental delay. (a) Axial T1-weighted MR image shows bilateral masses (arrows) near the foramen of Monro. The masses are slightly hypointense compared with the white matter. (b) On an axial T2-weighted MR image, the masses are slightly hyperintense compared with the white matter (c) Contrast enhanced axial T1-weighted MR image shows intense enhancement of both masses

2-Oligodendrogliomas

Oligodendrogliomas appear heterogenous on both T1WI and

T2 WI; on T1WI, the tumors appear predominantly hypointense

to gray matter and on T2WI, they are most often hyperintense,

with small intramural cysts, focal calcification and

heterogenicity.

3- Ependymal cell tumors:

Most ependymomas arise in the floor of the fourth ventricle.

They have tendency to extend through the foramina of

Luschka and Magendi into the basal cisterns. The tumor is

often calcified and may demonstrate a large cystic component.

Inhomogeneous enhancement is usually seen.

4 -Tumors of Choroid plexus:

Most choroid plexus tumors occur as the benign, slowly

growing choroid plexus papilloma, (WHO grade I) tumor with a

favorable overall prognosis. The other 20% of cases manifest as

a much more biologically aggressive (WHO grade III) tumor,

the choroid plexus carcinoma, which is far more common in

children than adults. Choroid plexus tumors have long been

associated with hydrocephalus secondary to an increase in the

production of CSF by the tumor. It shows intense enhancement

on contrast enhanced MRI due to the marked vascularity of

these tumors.

Choroid plexus carcinoma. (a) Axial T1-weighted MR image shows the lobulated mass with heterogeneous signal intensity. (b) On an axial T2-weighted MR image, the mass is slightly hyperintense compared with the white matter. (c) Contrast enhanced axial T1-weighted MR image shows intense but heterogeneous enhancement within the mass. At surgery, the ventricular wall was traversed by the mass, and histologic analysis confirmed choroid plexus carcinoma.

Primitive neuro ectdermal tumors :

PNET of CNS can be divided into infratentorial tumors (medulloblastoma)

and supratentorial tumors PNET.

Supratentorial PNET : Their most common location is the frontal lobes.

They are often large tumors with lesser degrees of surrounding edema,

demonstrated heterogeniety of signal intensity on both T1WI and T2WI, the

solid portion of the tumor demonstrates strong contrast enhancement.

Medulloblastomas: In children, medulloblastomas are usually at the

cerebellar vermis, but in adults they tend to be located more laterally in

the cerebellar hemispheres. The tumors are mildly hypointense to

isointense on T1WI, and isointense to hyperintense on T2WI.

Medulloblastoma (a) Axial T1-weighted MR image shows mild hyperintensity in the hemorrhagic regions; otherwise the mass is predominantly hypointense. (b) Axial T2-weighted MR image reveals marked hypointensity in the hemorrhagic zones. These features are consistent with intracellular methemoglobin. (c) Contrast-enhanced axial T1-weighted MR image demonstrates heterogeneous but intense enhancement of the nonhemorrhagic portions.

Contrast enhancement of solid portion of the tumor is

seen in more than 90% of patients; it is typically

intense and homogenous but may be irregular and

patchy.

Dysembryoplastic neuroepithelial tumors:

DNET commonly occur above the tentorium, mainly in the temporal

lobe or frontal lobe. They are lesions of long standing duration that

most frequently involve the convexity cortex and often protrude

beyond the adjacent cortical margin, eroding the overlying inner

table of the calvarium. Demonstrated as a mass centered in the

convexity cortex and bulging externally. It is hypointense to adjacent

brain on T1WI and hyperintense on T2WI with no surrounding edema.

The protruding external margin may present as (Soap bubble)

appearance, reflecting internal cystic changes. Contrast enhancement

is seen in only a minority of these lesions.

DNET: Axial T2-weighted image (a). Contrast-enhanced axial T1-weighted image (b) showing no evidence of enhancement within the mass. Note the protruding external margin.

Lymphoma Most lymphomas occur in patients who are immunocompromised (such

as patients under chemotherapy and patients of (AIDS). Lymphomas

typically appear as homogeneous slightly high signal to isointense

masses deep within the brain on T2 weighted images. They are

frequently found in close proximity to the corpus callosum and have

tendency to extend across the corpus callosum into the opposite

hemisphere. Multiple lesions are presented in 50% of cases. They are

associated with only a mild or moderate amount of peritumoral edema.

By time of presentation they can be quite large and yet produce

relatively little mass effect, most lymphomas show homogeneous contrast

enhancement.

Primary central nervous system lymphoma. Axial postcontrast T1-weighted MR image (a) demonstrates a homogeneously enhancing mass in the right frontal lobe, which is isointense on the axial fluid-attenuated inversion-recovery MR image (b), with extensive surrounding T2 hyperintensity.

Meningioma

Most commonly they are seen parasagittally (25%). Other

locations include the convexity (20%), sphenoid ridge (15-20%),

olfactory groove (5-10%), posterior fossa 10%, intraventricular

region 2% and extracranial region 1%. Meningiomas are more

common in women than men. They have predilection to occur from

the third to sixth decades of life. They are rare in patients younger

than 20 years and if present commonly are associated with

neurofibromatosis type II. The WHO classified meningiomas into the

following three basic groups: benign meningioma, atypical

meningioma and malignant meningioma. Most meningiomas are

usually isointense with cortex on T1 and T2WI. On non enhanced

MRI the majority are of homogenous appearance.

Meningioma: Axial post contrast T1 WI showing intense homogenous enhancement with tapered enhancing extension of the related dura (dural tail).

The strong, often striking, homogenous contrast

enhancement seen in most meningiomas enables

their accurate detection and location. A thickened

tapered extension of contrast enhancing dura is

commonly identified at the margin of the tumors.

Schwannoma This tumor arises from the Schwann cells of the nerve sheath of the

cranial nerves. Most common site of intracranial involvement is the

superior vestibular division of the eighth cranial nerve. On axial images,

the tumor often has a comma-like shape with a globular cisternal mass

medially and a short tapered fusiform extension laterally into the internal

auditory canal. Contrast enhancement is seen in nearly all

Schwannomas; and may be homogenous in two thirds of cases. On T1WI

it appears as homogenous mild hypointense or isointense to adjacent

brain; on T2WI, it appears mildly to markedly hyperintense and may be

obscured by the similarity in signal intensity to that of the surrounding

CSF.

Schwannoma (acoustic neuroma_ Contrast enhanced axial T1-weighted MR image shows a homogeneously enhanced, coma-shaped right cerebello-pontine lesion.

Brain metastasis Most metastasis is round well-demarcated lesions located at the

junction of gray and white matter. Leaky tumor vessels result in

an extensive zone of edema surrounding the tumor. Most intra-

cerebral metastatic lesions are hypo intense on T1WI and hyper

intense on T2WI. Signal intensity depends on cellularity of the

lesion, the extent of intratumoral necrosis, the presence and age

of hemorrhage, the presence and extent of calcification. Contrast

administration facilitate delineation of the tumor margin.

Melanoma has somewhat characteristic appearance if there has

not been previous hemorrhage, the lesion is hyperintense in

T1WI and isointense T2WI most likely because of free radical

content of melanin.

Dermoid tumors and Epidermoid tumors

Dermoid tumors are thought to arise at the site of neural tube

closue at the midline. This may explain the frequent midline location

of dermoid tumors. In contrast, epidermoid tumors are often located

lateral to the midline of the cranium. Intracranial dermoid tumors

usually present in patients up to 20 years of age. In contrast,

epidermoid tumors are most often first diagnosed in patients aged 40-

50 years. Most epidermoid cysts show a distinctive MR imaging

appearance consisting of an irregularly shaped lesion having slightly

higher signal intensity than CSF on T1, T2 and proton density

weighted images. Dermoid without fat or calcification within them

may be indistinguishable from epidermoid or arachnoid cysts.

Epidermoid cyst To the left: Axial T1-weighted MR image shows an epidermoid cyst with characteristic focal marbling in the left CPA (arrow). To the right: Axial T2-weighted MR image shows the lobulated margins of the cyst impinging on the pons (arrowhead).

Diffusion MRI and Brain Tumors

Diffusion of water molecules. ( a) Restricted diffusion: high cellularity and intact cell membranes. Note water

molecules (black circles with arrows) within extracellular space, intracellular space, and intravascular space, all of which contribute to measured MR signal. In this highly cellular environment, water diffusion is restricted because of reduced extracellular space and by cell membranes, which act as barrier to water movement. (b( Free diffusion: low cellularity and defective cell membranes. In less cellular environment, relative increase in extracellular space allows free water diffusion than more cellular environment would. Defective cell membranes also allow movement of water molecules between extracellular and intracellular spaces.

Role of Diffusion MRI in glioma Exact differentiation and grading of malignant brain tumors are

essential for proper treatment planning. Although conventional

MRI can detect the location and extent of the tumor, it is

sometimes insufficient for differentiation and grading of malignant

brain tumors. Also often some low-grade tumors may demonstrate

peritumoral edema, strong enhancement, central necrosis, or mass

effect. The enhancing pattern of a tumor is not always reliable for

distinguishing high-grade and low-grade tumors because tumoral

enhancement is mainly due to disruption of the blood brain barrier

rather than from tumoral vascular proliferation itself and these

two entities are usually independent of each other.

Furthermore, the peritumoral abnormal high signal intensity

on T2-weighted images, is not specific for the tumor because

it may reflect vasogenic edema, the tumoral infiltration, or

frequently both, and its exact nature is indistinguishable by

conventional MRI .

Diffusion criteria of gliomas: The signal intensity of

cerebral gliomas on DWI is variable (hyper, iso or

hypointense). In high grade cerebral gliomas, areas of tumors

that show significant enhancement on T1WI obtained after

injection of contrast material has lower ADC value than the

ADC of non enhancing tumor and peirtumoral edema. Cystic

or necrotic portions of tumor show the highest ADC value.

Glioblastoma multiforme. (a) Contrast-enhanced T1-, (b) diffusion-weighted images, and (c) ADC map. The necrotic components are hypo intense on DWI, while the non necrotic components are slightly hyper intense. The peritumoral vasogenic edema is isointense to the white matter because the effect of increased diffusion (dark) is compensated for by the increased T2 value of edema (bright). The peritumoral edema ,CSF, and necrotic component of the tumor are hyper intense (high diffusion) on ADC map.

Grading of gliomas

Tumor cellularity (and histologic tumor grading) is inversely

correlated with tumor ADC value in various grades of astrocytomas.

Glioblastoma multiforme had the lowest ADC; anaplastic astrocytoma

had intermediate ADC and low-grade astrocytoma had the highest

ADC. Although the ADCs of grade II astrocytoma and glioblastoma

overlapped somewhat, the combination of routine image

interpretation and ADC had a higher predictive value. The lower ADC

suggesting malignant glioma, whereas higher ADCs suggest low-

grade astrocytoma. The ADC of anaplastic astrocytoma (grade III

astrocytoma) is intermediate between those of glioblastoma and

grade II astrocytoma.

Delineation of gliomas

In malignant gliomas, peritumoral edema, which can be depicted

with either CT or conventional MR imaging, often has been reported

to have infiltrating neoplastic cells. Therefore, the tumor border is

still inaccurately depicted even with imaging techniques. Areas that

showed marked signal suppression with a higher ADC, most likely

representing areas of predominantly peritumoral edema, and areas

that showed a lesser degree of signal suppression with similar but

slightly lower ADCs than those of edema, most likely representing

areas of predominantly nonenhancing tumor. So DWI is a useful

technique to distinguish areas of predominantly nonenhancing

tumor from areas of predominantly peritumoral edema.

Role of diffusion MRI in cystic brain Role of diffusion MRI in cystic brain tumorstumors

Differentiation between Differentiation between brain abscessesbrain abscesses and and cystic brain cystic brain

tumorstumors such as high-grade gliomas and metastases is often such as high-grade gliomas and metastases is often

difficult with conventional MRI. Diffusion MRI study provides difficult with conventional MRI. Diffusion MRI study provides

tremendous contribution to differential diagnosis of these tremendous contribution to differential diagnosis of these

lesions when conventional approaches fail. The abscess cavity lesions when conventional approaches fail. The abscess cavity

viscosity is highly restricting the microscopic diffusional viscosity is highly restricting the microscopic diffusional

movements of water molecules . movements of water molecules . High signal intensity on DWI High signal intensity on DWI

and low ADCand low ADC value in brain abscesses, in contrast to value in brain abscesses, in contrast to low low

signal intensity on DWI and high ADC valuesignal intensity on DWI and high ADC value in most tumors or in most tumors or

high signal intensity on DWI for cystic or necrotic tumors is high signal intensity on DWI for cystic or necrotic tumors is

due to T2 shine-through.due to T2 shine-through.

Cerebral abscess. (a) Transverse contrast-enhanced T1WI showing rim enhancement of the abscess wall, (b) DWI showing high signal of the abscess cavity, and (c) ADC map showing low signal of the abscess cavity matching with restricted diffusion.

Glioblastoma multiforme. (a) Contrast enhanced T1WI showing rim enhancement of the solid component, (b) DWI showing low signal of the necrotic center and (c) ADC map showing high signal of the necrotic center matching with free diffusion.

Role of Diffusion MRI in Role of Diffusion MRI in meningiomameningioma

It is useful to It is useful to distinguish among benign, malignant and atypical distinguish among benign, malignant and atypical

meningiomasmeningiomas before resection, because it would aid in the surgical before resection, because it would aid in the surgical

and treatment planning. Atypical and recurrent meningiomas have and treatment planning. Atypical and recurrent meningiomas have

more tendency for recurrence. This distinction is neither easily nor more tendency for recurrence. This distinction is neither easily nor

reliably accomplished with conventional MRI. Using diffusion-reliably accomplished with conventional MRI. Using diffusion-

weighted MR imaging, weighted MR imaging, atypical and malignant meningiomasatypical and malignant meningiomas tend to tend to

be be markedly hyperintense on DWI and exhibit marked decreases in markedly hyperintense on DWI and exhibit marked decreases in

ADC valuesADC values when compared to normal brain parenchyma on routine when compared to normal brain parenchyma on routine

MRI. Although MRI. Although benign meningiomasbenign meningiomas have have variable appearances on variable appearances on

DWIDWI, they tend to have , they tend to have higher ADC valueshigher ADC values compared to the normal compared to the normal

brainbrain . .

Left frontal benign meningioma. Hypointense in T1 WIs (a), isointense in T2 WIs (b), FLAIR (c), uniform contrast enhancement in axial T1WI (d), hypointense in DWI (e), and iso to hyperintense in ADC (f)

Right parietal malignant meningioma. Isointense in T1WI (a), hyperintense in T2 WI (b), hyperintense in FLAIR (c), uniform contrast enhancement in axial T1WI (d), markedly hyperintense in DWI (e), and isointense in ADC (f).

Recurrent malignant meningioma. (a) Axial post-contrast T1WI shows intense enhancement of meningioma, (b) DWI shows hyper intense signal, and (c) ADC map shows hypo intense signal reflecting restricted diffusion due to high cellularity.

Role of Diffusion MRI in Role of Diffusion MRI in lymphomalymphoma

The rate of water diffusion in CNS lymphoma, as The rate of water diffusion in CNS lymphoma, as

represented by ADC value is significantly lower than represented by ADC value is significantly lower than

that of high grade astrocytoma. that of high grade astrocytoma. The cellularity of The cellularity of

lymphoma, as represented by nuclear to cytoplasmic lymphoma, as represented by nuclear to cytoplasmic

(N/C) ratio, is significantly higher than that of (N/C) ratio, is significantly higher than that of

astrocytomaastrocytoma. Lymphomas are generally . Lymphomas are generally hyperintense to hyperintense to

gray mater on DWI gray mater on DWI and and iso to hypointense on ADC iso to hypointense on ADC

mapsmaps, findings that are consistent with , findings that are consistent with lower diffusivitylower diffusivity. .

In contrast, high grade astrocytomas are generally In contrast, high grade astrocytomas are generally

hypo- or hyperintense to the gray matterhypo- or hyperintense to the gray matter . .

Primary CNS lymphoma. (a) Axial contrast-enhanced T1-, (b) Axial FLAIR shows perilesional edema. (c) ADC map shows low signal intensity within the enhancing tumor and high signal intensity in peritumoral edema. This is denoting restricted diffusion at the tumor and facilitated diffusion at the peri-lesional edema du to high N/C ratio.

Role of Diffusion MRI in metastasis

The signal intensity of non-necrotic component of cerebral

metastasis on DWI is variable (generally iso or hypointense,

occasionally hyper intense). The necrotic component of

metastasis shows marked signal suppression on DWI and

increased ADC values. The signal intensity of the solid

component depend on the tumor cellularity. Metastasis from

well differentiated adenocarcinomas has significantly higher

ADC values than in poorly differentiated adenocarcinomas and

lesions other than adenocarcinoma. The signal intensity of the

necrotic component is related to increased free water.

Multiple metastases. Axial contrast-enhanced T1- (a) diffusion (b) weighted images, and corresponding ADC map (c). Free diffusion of the necrotic component is noted with low signal in DWI and high signal in ADC map.

Role of Diffusion MRI in Differential diagnosis of cyst like tumor lesions

Epidermoid tumors appear sharply hyperintense on DWI relative

to the brain and CSF; however, have higher signal intensity on

ADC maps than that of the brain. Apparently, this hyperintensity

on DWI should not be attributed to a decrease in ADC, but should

be attributed to the T2 shine-through effect, meaning that the T2

properties dominated the contributions to DW signal intensity and

even overwhelmed the effect of signal attenuation resulting from

the increase in ADC. The differential diagnosis of epidermoid and

arachnoid cyst is straightforward on DWI. (The epidermoid cyst is

bright, while the arachnoid cyst is dark on DWI).

Arachnoid cyst (a) Axial T1 post contrast image, (b) Axial T2 WI, (c) DWI showing low signal and (d) ADC map showing high signal due to free diffusion.

Epidermoid cyst (a) T1 WI , (b) T2 WI , (c) FLAIR, (d) DWI showing high signal due to T2 shine through effect and (e) ADC map showing that epidermoid cyst has diffusion rate relatively more than normal brain parenchyma.

Role of Diffusion MRI in differentiation of Cerebellar Tumors in Children

ADC values and ratios are simple and readily available techniques for evaluation of pediatric cerebellar neoplasms that may accurately differentiate the 2 most common tumors, JPA and medulloblastoma. Proposed cutoff values of (>1.4 × 10−3 mm2/s) for JPA and (<0.9 × 10−3 mm2/s) for medulloblastoma seem to reliably provide the diagnosis, which may affect further diagnostic studies, treatment plan, and prognosis. Ependymomas are also significantly different from other tumor types, and in most of cases show ADC values (1.00–1.30 × 10−3 mm2/s).

Scatter diagram of average ADC tumor values for all pilocytic astrocytomas (JPA), ependymomas (Epend) and medulloblastomas (Medullo) (open circles) along with their respective mean (full circles) and standard deviation (bars) values. ADC values are expressed in 10−3 mm2/s.

Fifteen-year-old girl with cerebellar JPA. ADC map in axial plane at level of middle cerebellar peduncles shows well defined, oval mass in right paramedian location with increased diffusion

Sixteen-year-old boy with ependymoma A, Axial T2-weighted image at level of middle cerebellar peduncles shows a very heterogeneous abnormality (arrows) within the fourth ventricle .

B, Corresponding contrast-enhanced T1-weighted image demonstrates enhancement of the solid portion of this mass (arrows) .

C, ADC map at a level similar to that of A and B shows that diffusion within the solid portion of the tumor (arrows) is slightly higher compared with normal cerebellum .

22-year-old woman with desmoplastic cerebellar medulloblastoma. Axial ADC map at level of middle cerebellar peduncles reveals lesion of decreased diffusion in left cerebellar hemisphere (arrow). No significant surrounding edema is seen.