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Anatomy of IOM
Posterior fontanel
Sagittal suture
Coronal sutures
Anterior fontanel
Fig. 2.8 Superior view of the infant skull showing the
anterior and posterior fontanelles along with the development of the sagittal and coronal sutures
into this space as a result of trauma or the spontaneous rupture of a blood vessel can enlarge
this space causing compression on the brain.
This is known as a subarachnoid hemorrhage
and requires surgical intervention to decompress
the neural tissue. The dura and arachnoid are
normally attached closely. Occasionally bleeding resulting from trauma or disease will occur
opening up a space between the dura and arachnoid that does not normally exist. This potential
space is called the subdural space, and the
resulting bleed or clot would be known as a subdural hemorrhage or subdural hematoma,
The Ventricles
mater, and the pia mater. The term dura mater is
from the Latin literally meaning “tough mother,”
while pia mater means “soft mother.” The word
arachnoid implies a spider weblike quality. The
function of the meninges is to protect the brain
and contain cerebrospinal fluid (Fig. 2.9).
The dura mater is the fibrous outermost layer
of the meningeal membranes. This layer contains
larger blood vessels as well as sensory nerve
fibers. Among the blood vessels present in the
dura mater are large venous sinuses that return
blood and cerebrospinal fluid from the brain back
to the heart. There are two dural extensions that
you should be familiar with. The falx cerebri
separates the cerebral hemispheres and the tentorium cerebelli separates the occipital lobe from
the cerebellum (Fig. 2.10).
The arachnoid mater is thinner than the dura
and resembles a loose fitting sac for the brain.
Thin filaments known as arachnoid trabeculae
extend from the arachnoid to the pia mater.
The pia mater is the thinnest layer of the
meninges and closely adheres to the surface of
the brain and spinal cord following each gyrus
and sulcus. The pia has an extensive capillary
network that nourishes the surface of the brain
and spinal cord.
There is a normally occurring space between
the arachnoid and pia mater. This subarachnoid
space is filled with cerebrospinal fluid. Bleeding
There are a series of canals within the brain
whose function is to circulate cerebrospinal fluid.
These are known as the cerebral ventricles
(Fig. 2.11). There are two paired (left and right)
lateral ventricles, a third ventricle, and a fourth
ventricle. The ventricles communicate with each
other via foraminal openings and are continuous
with the central canal of the spinal cord. The left
and right ventricles communicate with the third
ventricle through the intraventricular foramina
(of Monro). The third ventricle communicates
with the fourth through the cerebral aqueduct
(also known as the aqueduct of Sylvius).
Cerebrospinal fluid returns to the subarachnoid
space and venous circulation from the fourth ventricle via the midline foramen of Magendie and
two paired foramina of Luschka.
The cerebrospinal fluid (CSF) bathes and
cushions the brain and spinal cord and is contained within the dura mater. The CSF is produced by tufts of tiny capillaries called choroid
plexus that are found within the ventricles
(Fig. 2.12). CSF is simply filtrated blood plasma.
CSF comes from the blood and must eventually
return to the blood. The presence of microorganisms or white blood cells in CSF indicates
infection within the central nervous system. CSF
can be sampled for diagnostic purposes by lumbar puncture.