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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.
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