Neurology - BRAIN ANATMY 1

Ahmed Ghanem M.D

PGMD,PRB,JRB,ARB

Head of Radiology Dep. NNUH

Ahmed.ghanem@najah.edu
 Hounsfield unit:

CT images of the brain are conventionally

viewed from below, as if looking up into the top
of the head.

This means that the right side of the brain is on

the left side of the viewer.

The anterior part of the head is at the top of the

image.
 Skull bones and sutures
The brain is located inside the cranial vault, a space formed
by bones of the skull and skull base.

Everything inside the cranial vault is 'intra-cranial' and

everything outside is 'extra-cranial'.

Pathologies related to Brain parenchyma is termed Intra-axial

but the pathologies arise from other origins like meninges or
ventricles are called extra-axial.

Pathologies seen within the ventricles are called

intraventricular.
Skull bones

Bones of the skull and skull base are :

frontal, parietal, occipital, ethmoid, sphenoid and

temporal bones.

all ossify separately and gradually become united at the

skull sutures.

The skull has inner and outer tables of cortical bone with
central cancellous bone called 'diploe'
Note the appearance of the skull sutures which are
jagged (irregular) - not to be confused with fractures
which are typically straight
•Bones of the skull are
assessed viewing the 'bone
window' CT images

•Note that no detail of brain

structure is provided on these
window settings
Sutures
The main sutures of the skull are the coronal, sagittal, lambdoid
and squamosal sutures.

The metopic suture (or frontal suture) is variably present in adults.

Coronal suture - unites the frontal bone with the parietal bones

Sagittal suture - unites the 2 parietal bones in the midline

Lambdoid suture - unites the parietal bones with the occipital

bone

Squamosal suture - unites the squamous portion of the temporal

bone with the parietal bones

Metopic suture - (if present) unites the 2 fontal bones

Pterion

•The frontal, parietal, temporal and sphenoid bones

unite at the 'pterion' - the thinnest part of the skull

•The middle meningeal artery runs in a groove on the

inner table of the skull in this area

•Fractures to the pterion area can be complicated by

injury to the middle meningeal artery and formation of
an extradural hematoma (epidural hematoma)
Cranial fossae

At the skull base the bones of the cranial vault form the cranial
fossae which accommodate and support the brain.

•Anterior cranial fossa - accommodates the anterior part of the

frontal lobes

•Middle cranial fossae - accommodate the temporal lobes

•Posterior cranial fossa - accommodates the cerebellum and

brain stem

•Pituitary fossa (PF) - accommodates the pituitary gland

 Sinuses
The skull contains air sinuses which are highly variable in
appearance between different individuals.

•Maxillary sinuses (antra), ethmoid air cells, sphenoid sinus

and frontal sinuses.

•The sphenoid sinus and ethmoid air cells are continuous with the
nasal airways.

•The mastoid air cells are continuous with the middle ear

•The frontal sinuses are highly variable in appearance.

•Many people have no frontal sinuses

The sphenoid sinus and ethmoid air cells are continuous with the nasal airways.

•The mastoid air cells are continuous with the middle ear
•The frontal sinuses are highly variable in appearance.

•Many people have no frontal sinuses

•Mucosal thickening is a very common incidental finding.

•When there is air-fluid level with air bubble it means

there is acute sinusitis.

•But if there is air-fluid level in case of trauma it means

there is skull vault fracture.
Meninges
The meninges are thin layers of tissue found between the brain
and the inner table of the skull.

The meninges comprise the dura mater, the arachnoid, and

the pia mater.

The dura mater and arachnoid are an anatomical unit, only

separated by pathological processes.

The falx cerebri and the tentorium cerebelli are thick infoldings
of the meninges which are visible on CT imaging.

Elsewhere the meningeal layers are not visible on CT as they are

closely applied to the inner table of the skull.
•Knowledge of anatomy of the meninges is essential for
understanding the CT appearances of intracranial bleeding

•Dura mater = tough outermost layer, closely applied to the inner

table of the skull.

•arachnoid = thin layer closely applied to the dura mater.

* The dura mater and arachnoid are an anatomical unit, only separated by pathological processes.

•Subarachnoid space = space between the arachnoid mater and

the pia mater which contains delicate trabeculated connective
tissue and CSF.

•Pia mater = very thin layer applied to the surface of the brain
Tentorium cerebelli

•On axial slice CT images of the brain the tentorium is faintly

visible passing over the cerebellum

•in the context of subarachnoid hemorrhage or subdural

hematoma the tent may become more dense due to layering
of blood
Falx cerebri

•The falx is an infolding of the meninges which lies in the

midline and separates the left and right cerebral hemispheres

•Pathological processes may cause 'mass effect' with

deviation of the falx towards one side.

•tentorium cerebelli is continuous with the falx cerebri.

•Meningiomas are benign intracranial tumours which may

arise from any part of the meninges, including the falx or
tentorium
tentorium cerebelli is continuous with the falx cerebri
CSF spaces
The brain is surrounded by cerebrospinal fluid (CSF) within the
sulci, fissures and basal cisterns.

CSF is also found centrally within the ventricles.

The sulci, fissures, basal cisterns and ventricles together form the
'CSF spaces', also known as the 'extra-axial spaces'.

CSF is of lower density than the grey or white matter of the brain,
and therefore appears darker on CT images.

An appreciation of the normal appearances of the CSF spaces is

required to allow assessment of brain volume.
The brain surface is formed by folds of the cerebral cortex known
as gyri

Between these gyri there are furrows, known as sulci, which

contain CSF.

•Gyrus = a fold of the brain surface (plural = gyri)

•Sulcus = furrow between the gyri which contains CSF (plural

= sulci)
Fissures
•The interhemispheric fissure separates the
cerebral hemispheres
•The interhemispheric - the
fissure two halves
separates of the brain.
the cerebral
hemispheres - the two halves of the brain.

•The Sylvian fissures separate the frontal and temporal lobes

•The Sylvian fissures separate the frontal and
temporal lobes
Ventricles

The ventricles are spaces located deep inside the brain which
contain CSF.

Lateral ventricles
The paired lateral ventricles are located on either side of the brain
The lateral ventricles contain the choroid plexus which produces
CSF.
Note : The choroid plexus is almost always calcified in adults.

Third ventricle
The third ventricle is located centrally.
The lateral ventricles communicate with the third ventricle via
small holes (foramina of Monro).
Fourth ventricle

•The fourth ventricle is located in the posterior fossa between the

brain stem and cerebellum.

•It communicates with the third ventricle above via a very narrow
canal, the aqueduct of Sylvius.

Basal cisterns
•CSF in the basal cisterns surrounds the brain stem structures
Brain parenchyma and lobes
The brain consists of grey and white matter structures which are
differentiated on CT by differences in density.

White matter has a high content of myelinated axons.

Grey matter contains relatively few axons and a higher number
of cell bodies.
As myelin is a fatty substance it is of relatively low density
compared to the cellular grey matter.

White matter, therefore, appears blacker than grey matter.

Grey matter appears grey

White matter appears blacker
•White matter is located centrally and appears blacker than
grey matter due to its relatively low density.

•Pathological processes may increase or decrease the

differentiation in density between grey and white matter
Brain lobes

The brain has paired, bilateral anatomical areas or 'lobes'. These

do not exactly correlate with the overlying bones of the same
names.
•On both sides the frontal lobes are separated from the parietal
lobes by the central sulcus .

**The most anterior parts of the frontal lobes occupy the anterior
cranial fossae.

**The temporal lobes occupy the middle cranial fossae.

**The cerebellum and brain stem occupy the posterior fossa

imaging does not clearly show the anatomical borders of
the lobes of the brain.

For this reason we often refer to 'regions', such as the

'parietal region' or 'temporal region', rather than lobes.

If more than one adjacent region needs to be described

then conjoined terms can be used such as 'temporo-
parietal region' or 'parieto-occipital region'
Grey matter structures

Important grey matter structures visible on imaging of the brain

include the cortex, insula, basal ganglia, and thalamus

Cerebral cortex

The cerebral cortex is a layer of grey matter formed in gyri (folds)

over the entire brain surface.

Note that the cortex appears whiter (denser) than the underlying
white matter on CT-scan and differs on MRI regarding the used
sequance.
Cerebral cortex differs on MRI
regarding the used sequance
Insula

**The insula forms an inner surface of the cerebral

cortex found deep to the Sylvian fissure.

Loss of definition of the insular cortex may be an

early sign of an acute infarct involving the middle
cerebral artery territory
Basal ganglia and thalamus

The basal ganglia and the thalamus are important

grey matter structures which are located deep to the
insula.
putamen + globus pallidus

Basal ganglia = lentiform nucleus + caudate nucleus

White matter structures
White matter of the brain lies deep to the cortical grey matter.

The internal capsules are white matter tracts which connect with
the corona radiata and white matter of the cerebral hemispheres
superiorly, and with the brain stem inferiorly.
* Each internal capsule has an anterior limb and a posterior limb connected at the 'genu'

The corpus callosum is a white matter tract located in the

midline.
It arches over the lateral ventricles and connects white matter of
the left and right cerebral hemispheres.

•Each internal capsule has an anterior limb and a posterior

limb connected at the 'genu'
Posterior fossa
The posterior fossa accommodates the cerebellum and brain
stem.
Superiorly the cerebellum is separated from the cerebral
hemispheres by the tentorium cerebelli.

**The brain stem and cerebellum occupy the posterior fossa.

The sagittal plane can be useful to show the anatomy of the

brain stem.

**Note: MRI may be required if there is specific concern

regarding brainstem pathology
The sagittal plane can be useful to show the anatomy of the brain stem.
Calcified structures
There are several structures in the brain which are considered
normal if calcified. : choroid plexus, the pineal gland, the basal ganglia, and the falx.

Knowledge of these structures helps avoid confusion,

especially when considering if there is intracranial
hemorrhage present.

The commonly calcified structures include the choroid plexus,

the pineal gland, the basal ganglia, and the falx.
•In adults the choroid plexus of the lateral ventricles is almost always
calcified
•The pineal gland is located immediately posterior to the third ventricle
•It is very commonly partly or fully calcified in adults
•Calcification of the basal ganglia is common in elderly patients
•The falx is commonly
calcified in adults.

•If viewed on brain windows

only, calcification of the falx
can be mistaken for acute
intracranial blood.

•Use of CT 'bone windows'

show calcification of the
falx more clearly