The intracranial membranes and
sinuses
The skull
contains delicate membranous structure which is liable to damage during
delivery especially if subjected to abnormal molding. Structures include:
1.
Folds of Dura matter and
2.
Venous sinuses associated with them.
The
membrane is in two layers, an outer periosteal layer which is adherent to the
skull bones and the inner meningeal layer which covers the outer surface of the
brain. The membrane does not only cover the brain but send fibrous partition to
divide the brain into compartments.
1.
The Falx
Cerebri: It is a sickle-shaped fold of membranewhich dip down between the two
cerebral hemispheres. It runs beneath the frontal and sagittal sutures – (Fr om
root of the nose to the internal occipital protuberance).
2.
Tentorium
Cerebelli: This is a horizontal fold of duramatter situated at
the posterior part of the cranial cavity. It lies at right angle to the falx
cerebri. It has a horse – shoe shape and forms a tent-like layer between the
cerebrum and the cerebellum. It contains large blood vessels or sinus which
drains blood from the brain on their way to become the jugular vein of the
neck.
3.
The
superior Longitudinal(Sagittal) Sinus: it runs alongthe upper part of
the falx corebri from front to the back (from root of the nose to the internal
occipital protuberance)
4.
Inferior
Longitudinal (sagittal) Sinus: Runs along thelower part in the
same direction.
5.
The straight
sinus: Is a continuation of the inferior sagittalsinus and drains blood from
the great cerebral vain and the inferior sagittal sinus along the junction of
falx and the tentorium. The point where it reaches the skull and receives blood
from the superior sagittal sinus is known as the confluence of sinus.
6.
The Great
Cerebral vein of Galen: meet the inferiorSagittal Sinus at the inner end of
the junction and where the falx joins the tentorium.
7.
Lateral
Sinuses: These are two in number they pass from theconfluence of the sinuses
along the outer edge of the tentorum cerebelli and carries blood to the
internal jugular veins.
During monlding the falx and the tentorium are stretched. The tentorium is most vulnerable to tear near its attachment to the falx – (Tentorial Tears), this leads to bleeding from th e great cerebral vain giving rise to intracranial hemorrhage.
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