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Ventricles, meninges, dural folds and dural venous sinuses
Cranial meninges
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Cranial meninges are membranous coverings of the brain
o Lie immediately internal to the cranium
Function
o Protect the brain
o Form supporting framework for arteries, veins, venous sinuses
o Enclose the subarachnoid space (fluid-filled cavity)
Composed of three membranous connective tissue layers
o Dura mater – tough, thick, external fibrous layer
o Arachnoid mater – thin intermediate layer
o Pia mater – delicate, internal, vasculated layer
Arachnoid and pia are continuous membranes; make up the leptomeninx
Subarachnoid (leptomeningeal) space in-between the arachnoid and pia
contains cerebrospinal fluid (CSF)
CSF
o Formed by the choroid plexuses of the four ventricles of the brain
o CSF leaves the ventricular system and enters the subarachnoid space,
where its function is to cushion and nourish the brain
o CSF is a clear liquid that provides nutrients to the brain; less protein and
different iron concentration to blood
o Have 150 mL in circulation at any one time; but is turned over 3-4 times
a day, so a total of ~600 mL/day

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Dura mater
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Thick, dense, bilaminar membrane
Adheres to the internal surface (table) of the calvaria
Formed of two layers
o External periosteal layer
 Periosteum covering the internal surface of the calvaria
 At the cranial foramina, it is continuous with the periosteum of
the external surface of the calvaria
 Not continuous with the spinal dura of the spinal cord (spinal
dura only has a meningeal layer)
o Internal meningeal layer
 Strong fibrous membrane
 At foramen magnum, it is continuous with the spinal dura
(covers spinal cord)
The two layers of the dura mater are fused, apart from where dural sinuses
and infoldings occur
The dura mater is fused to the bones at the cranial base

Dural infoldings/reflections
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Internal meningeal layer of the dura mater reflects away from the periosteal
layer to form dural infoldings
These infoldings divide the cranial cavity into compartments separated by
dural septa
Dural infoldings include
o Cerebral falx (falx cerebri)
o Cerebellar tentorium (tentorium cerebelli)
o Cerebellar falx (falx cerebelli)
o Sellar diaphragm (diaphragm sellae)

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Tentorium cerebelli
 Second largest dural infolding
 Separates occipital lobes from the cerebellum; divides the cranial cavity into
supratentorial and infratentorial compartments
 Attaches anteriorly to the clinoid process of the sphenoid, anterolaterally to
the petrous part of the temporal bone, and posterolaterally to the occipital
and part of the parietal bone

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Anteromedial border is free (tentorial notch), through which the midbrain
extends from the posterior to the middle cranial fossa

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Diaphragma sellae
 Smallest dural fold
 Circular sheet of dura suspended between the clinoid processes, forming a
partial roof over the hypophysial fossa and the sphenoid
 Covers pituitary, with aperture to allow passage of the infundibulum and
hypophyseal veins

Taken from Drake et al, Grey’s Anatomy for Students, Second Edition

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Dural venous sinuses
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Inferior sagittal sinus
 Smaller than superior sagittal sinus
 Runs in the inferior border of the falx cerebri, and ends in the straight sinus
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Transverse sinuses
Passes laterally from the confluence of sinuses
Forms grooves on the occipital and parietal bones
Course along the tentorium cerebelli and become the sigmoid sinuses as
they approach the posterior aspect of the petrous part of the temporal bone
Blood received by confluence of sinuses usually drained by transverse sinuses
Left sinus is usually dominant (larger)

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Occipital sinus
 Lies in attached border of the falx cerebelli and ends superiorly in the
confluence of sinuses
 Communicates inferiorly with the internal vertebral venous plexus

Taken from studyblue
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studyblue
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Cavernous sinuses
 Large venous plexus of thin-walled veins, located either side of the sella
turcica on upper surface of the sphenoid body
 Extends from the superior orbital fissure anteriorly to the petrous part of the
temporal bone posteriorly
 Receives blood from
o Superior and inferior ophthalmic veins
o Superficial middle cerebral vein
o Sphenoparietal sinus
 The cavernous sinuses communicate with each other via intercavernous
sinuses, located anterior and posterior to the stalk of the pituitary gland
 Drain posteroinferiorly into the superior and inferior petrosal sinuses and
emissary veins to the basilar and pterygoid plexuses
 Inside or embedded in the wall of each cavernous plexus are
o Internal carotid artery plus small branches
o Carotid plexus of sympathetic nerves
o Abducent nerve (CN VI)
o Oculomotor nerve (CN III)
o Trochlear nerve (CN IV)
o Trigeminal nerve (CN V) divisions – ophthalmic (V1) and maxillary (V2)
 Pulsations of the internal carotid may promote propulsion of the venous blood
from the sinus along with gravity; may also allow for heat exchange between
the warm arterial blood and cooler venous blood

Taken from bestofpicture
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com/cavernous-sinus-internal-carotid-artery
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Superior petrosal sinuses
 Run from posterior end of the cavernous sinus to the transverse sinus at the
point where they curve to become the sigmoid sinuses
 Lie in the anterolateral attached margin of the tentorium cerebelli (where it
attaches to the petrous part of the temporal bone)
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pink, Confluence Sinuses, available at http://america
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html

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Emissary veins
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These connect the dural venous sinuses with veins outside the cranium
Blood usually flows away from the brain (however, they are valveless and
blood may flow in either direction)
Varied size and number
o Children and some adults have a frontal emissary vein – passes via
foramen cecum connecting the superior sagittal sinus with the veins of
the frontal sinus and nasal cavities
o Parietal emissary vein (may be paired bilaterally) passes through
parietal foramen, connecting the superior sagittal sinus to external
veins, in particular those in the scalp
o Mastoid emissary vein passes via mastoid foramen to connect each
sigmoid sinus with the occipital or posterior auricular vein
o Posterior condylar emissary vein passes via condylar canal to connect
sigmoid sinus with sub-occupital venous plexus

Vasculature of the dura mater
Arteries
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Mostly supply blood to the calvaria rather than the dura
Middle meningeal artery is the largest (branch of the maxillary artery)
o Enters floor of middle cranial fossa via foramen spinosum
o Runs laterally in the fossa and divides into anterior and posterior
branches at the superior wing of the sphenoid

Frontal branch runs superiorly to the pterion then curves posteriorly
toward the vertex of the cranium
o Parietal branch runs posterosuperiorly and branches
Small areas of dura supplied by branches from the
o Ophthalmic arteries
o Occipital arteries
o Vertebral arteries
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Taken from Drake et al, Grey’s Anatomy for Students, Second Edition

Veins
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Accompany the arteries, often in pairs
Middle meningeal veins leave cranial cavity via foramen spinosum or ovale,
draining into pterygoid venous plexus

Nerve supply of the dura mater
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Dura covering floor of anterior and middle cranial fossa and roof of posterior
cranial fossa innervated by meningeal branches of trigeminal nerve (CN V)
Anterior and middle cranial fossa supplied by meningeal branches of
o Ethmoidal nerve (CN V1) – anterior cranial fossa
o Maxillary nerve (CN V2) – anterior and middle cranial fossa
o Mandibular nerve (CN V3) – anterior and middle cranial fossa
Dura on roof of posterior cranial fossa is innervated by the tentorial nerve
(recurrent meningeal branch of ophthalmic nerve, CN V1)
Anterior falx cerebri supplied by anterior meningeal branch of ethmoidal
nerve, CN V1
Dura on the floor of the posterior cranial fossa receive fibres from
o C2 and C3
o C2 and C3 via hypoglossal (CN XII)
o C2 via vagus (CN X)

Taken from Drake et al, Grey’s Anatomy for Students, Second Edition

Arachnoid mater and pia mater
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Arachnoid and pia develop from single layer of mesenchyme surrounding
the embryonic brain, becoming parietal (arachnoid) and visceral (pia) parts
Numerous arachnoid trebeculae pass between the arachnoid and pia
o Flattened, irregularly shaped fibroblasts
o Bridge the subarachnoid space
Continuous immediately proximal to the exit of each CN from the dura
Arachnoid mater
o Contains fibroblasts, collagen fibres, elastic fibres
o Avascular
o Closely adjacent, but not attached to the dura
Pia mater
o Thinner than the arachnoid
o Highly vascularised
o Adheres to surface of brain and follows contours
o Forms pial coat and peri-arterial spaces where cerebral arteries
penetrate the cerebral cortex

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Meningeal spaces
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Brain suspended in CSF-filled subarachnoid space via arachnoid trebeculae
A number of meningeal spaces; not all exist in the absence of pathology
Natural spaces
o Spinal epidural space
 Occupied by epidural fat and venous plexus
 Internal to the periosteum, covering the vertebrae
o Subarachnoid space
 Between arachnoid and pia
 Contains CSF, trabecular cells, arteries, veins
Not natural spaces
o Extradural space
 Pathological space between the dura-cranial interface
 E
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torn meningeal vessels push periosteum away from cranium
 External to the periosteum lining the cranium
o Dura-arachnoid interface
 Space may develop in dural border cell layer from trauma

Medical application
Pterion fracture
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Overlies the frontal branch of middle meningeal artery
Hard blow can fracture the thin bones forming the pterion
Extradural haematoma – blood builds up in between dura and skull
Exerts pressure on the cerebral cortex, and can result in death

Thrombophlebitis of facial vein
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Facial vein connects with cavernous sinus via the superior ophthalmic vein, and
pterygoid venous plexus via the inferior ophthalmic and deep facial veins
Infection of the face can spread to these sinuses
Facial vein receives blood from medial eye, nose and lips; no valves, so blood
can flow backward into sinuses
Thrombophlebitis of the facial vein is inflammation, resulting in clot formation –
infected clot may enter sinuses
Danger triangle of the face – lacerations here can lead to this

Blunt trauma to head
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Can detach periosteal layer of dura from calvaria without fracturing the bones
Can result in leakage of CSF into the potential space

Tentorial herniation
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Tentorial notch is where the tentorium cerebelli opens for the brainstem; it is
slightly larger than required
Space occupying lesions (e
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tumours) in the supratentorial compartment
increase intercranial pressure, and can cause herniation of the temporal lobe
through the tentorial notch
This can result in laceration of the temporal lobe by tentorium cerebelli; CN III
may be stretched/compressed – can lead to paralysis of extrinsic eye muscles

Bulging of diaphragm sellae
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Pituitary tumours may extend into the diaphragm sellae, or make it bulge –
pressure on the optic nerve, causing visual disturbances
Endocrine dysfunction may occur before or after visual disturbances

Occlusion of cerebral veins and dural venous sinuses
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Can occur via thrombi, thrombophlebitis, tumours e
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meningiomas
Septic thrombosis of a sinus can lead to acute meningitis

Tumour metastasis to dural venous sinuses
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Venous plexuses are valveless, so compression of the thorax abdomen or
pelvis (e
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heavy coughing/straining) may force venous blood into the
vertebral venous system
Pus in abscesses and tumour cells may spread to these regions

Fractures of cranial base
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Can cause internal carotid tear – arteriovenous fistula in the cavernous sinus
Arterial blood will enter the cavernous sinus, causing enlargement, blood
forced backward into the veins, including ophthalmic veins
Get eyeball protrusion (exophthalmos); may pulsate in time with the radial
pulse (pulsating opthalmos)
Also get engorged conjunctiva (chemosis)
CN III, IV, V1, V2 and VI may be affected, as lie in close proximity

Dural origin of headaches
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Sensitive to pain, especially related to the dural venous sinuses and
meningeal arteries
Distension of scalp or meningeal vessels will cause headache
Most headaches seem to be dural in origin, thought to be due to
stimulation of nerves in the dura

Leptomeningitis
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Inflammation of the leptomeninges due to infection
Infection and inflammation usually confined to the subarachnoid space
and arachnoid-pia
Bacteria may enter subarachnoid space via blood, infection of another
organ (heart, lungs etc
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Moore et al
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Seventh Edition



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