1.A. MENINGES & DURAL SINUSES- Pituitary & Pineal glands (51slides).pptx

Learning Objectives Define Meninges Functions of Meninges Composition of Meninges To describe Dura Mater To describe the dural foldings and modifications To explain the dural venous sinuses To describe the arachnoid and the pia mater To describe the meningeal spaces Be able to describe anatomy of pituitary gland and

applied imporatace

Cranial Meninges

Composed of three membranous connective tissue layers:

Dura mater (dura): Tough, thick external fibrous layer.

Arachnoid mater (arachnoid): Thin intermediate layer.

Pia mater (pia): Delicate internal vasculated layer.

Cranial Meninges

Leptomeninx: Arachnoid and pia collectively make up the leptomeninges.

Arachnoid is separated from the pia by the subarachnoid (leptomeningeal) space, which contains cerebrospinal fluid (CSF).

CSF: Clear liquid similar to blood in

constitution Provides nutrients Act as a cushions Formed by the choroid

plexuses of the ventricles of the brain.

Leaves the ventricular system and enters the subarachnoid space between the arachnoid and the pia mater.

Meningeal SpacesThree meningeal spaces �commonly mentioned in relation to the cranial meninges.

Extradural or epidural space: the dura cranial interface.

Not a natural space between the cranium and the external periosteal layer of the dura because the dura is attached to the bones.

Subdural space: � at the dura arachnoid junction or interface

A space may develop in the dural border cell layer as the result of trauma, such as after a blow to the head.

Subarachnoid space: between the arachnoid and the pia, contains CSF, trabecular cells, arteries, and veins.

Dura Mater (Pachymeninx): Two layers of the cranial dura

mater

External periosteal layer: formed by the periosteum covering the internal surface of the calvaria

Internal meningeal layer: a strong fibrous membrane, continuous at the foramen magnum with the spinal dura mater covering the spinal cord.

External periosteal layer of the dura mater: Adheres to the internal surface of

the cranium Attach along the suture lines and in

the cranial base. Continuous at the cranial foramina

with the periosteum Not continuous with the dura

mater of the spinal cord

Internal meningeal layer: Intimately fused with the periosteal

layer and cannot be separated from it.

Dural Infoldings or Reflections Internal meningeal layer reflects

from the external periosteal layer of dura to form dural infoldings (reflections).

Dural foldings divide the cranial cavity into compartments

Forming partial partitions (dural septa) between certain parts of the brain

Provide support for the brain.

Dural infoldings include:

Cerebral falx (L. falx cerebri).

Cerebellar tentorium (L. tentorium cerebelli).

Cerebellar falx (L. falx cerebelli).

Sellar diaphragm (L. diaphragma sellae).

Cerebral Falx: Sickle-shaped structure

Lies in the longitudinal cerebral fissure that separates the right and left cerebral hemispheres.

Attachment: Anterior: frontal crest of the

frontal bone and crista galli of the ethmoid bone anteriorly

Posterior: Internal occipital protuberance posteriorly and fuses with cerebellar tentorium.

Cerebellar Tentorium: Wide crescentic septum

Separates the occipital lobes of the cerebral hemispheres from the cerebellum.

Attachment:• Rostrally : clinoid processes of

the sphenoid

• Rostrolaterally: petrous part of the temporal bone

• Posterolaterally: internal surface of the occipital bone and part of the parietal bone.

Cerebellar Tentorium: Divides the cranial cavity into

supratentorial and infratentorial compartments.

Supratentorial compartment divided into right and left halves by the cerebral falx.

Cerebral falx attaches to the cerebellar tentorium and holds it up, giving it a tent-like appearance.

Concave anteromedial border of the cerebellar tentorium is free.

Producing a gap called the tentorial notch through which the brainstem extends from the posterior into the middle cranial fossa.

Cerebellar falx: Vertical fold

Lies inferior to the cerebellar tentorium in the posterior part of the posterior cranial fossa.

Attached to the internal occipital crest

Partially separates the cerebellar hemispheres.

Sellar Diaphragm: Circular sheet

Suspended between the clinoid processes

Forming a partial roof over the hypophysial fossa in the sphenoid.

Covers the pituitary gland in this fossa

Has an aperture (opening, hole, space) for passage of the infundibulum and hypophysial veins.

Blunt Trauma to the Head

A blow to the head can detach the periosteal layer of dura mater from the calvaria

Fracture of the cranial base usually tears the dura and results in leakage of CSF.

MRI image

Tentorial Herniation Tumors in the supratentorial

compartment, produce increased intracranial pressure.

May cause part of the adjacent temporal lobe of the brain to herniate through the tentorial notch.

Temporal lobe may be lacerated by the tough cerebellar tentorium and the oculomotor nerve (CN III) may be stretched, compressed, or both.

Oculomotor lesions may produce paralysis of the extrinsic eye muscles supplied by CN III.

Cerebral MRI:The large arrow shows the tentorial herniation of the splenium of the corpus callosum and the cingular gyrus. The transtentorial herniation reaches a line drawn tangential to the frontal cranial base. The thin arrow shows the tonsillar herniation through the foramen magnum. The tip of the tonsils descends to the upper part of the arch of C1 as indicated by the lower line (drawn parallel to the upper line)

Bulging of the Sellar Diaphragm:

Pituitary tumors

May extend superiorly through the aperture in the sellar diaphragm or cause it to bulge.

Often expand the sellar diaphragm, producing disturbances in endocrine function

Superior extension of a tumor may cause visual symptoms owing to pressure on the optic chiasma

MRI Scan : Tuberculum Sellae Meningioma in a 46 year old male with Left Visual impairment.

Dural Venous Sinuses:

Endothelium-lined spaces between the periosteal and the meningeal layers of the dura.

Large veins from the surface of the brain empty into these sinuses

Venograms of dural sinuses. A and B. Radiopaque dye injected into the arterial system has circulated through the capillaries of the brain and collected in the dural venous sinuses, as shown in these radiographic studies. C, confluence of sinuses; I, internal jugular vein; S, sigmoid sinus; T, transverse sinus. In the AP view (A), notice the left-sided dominance in the drainage of the confluence of sinuses. (Courtesy of Dr. D. Armstrong, Associate Professor of Medical Imaging, University of Toronto, Toronto, Ontario, Canada.)

Superior sagittal sinus: Lies in the convex attached

border of the cerebral falx. Begins at the crista galli Ends near the internal

occipital protuberance at the confluence of sinuses, a meeting place of the superior sagittal, straight, occipital, and transverse sinuses.

Receives the superior cerebral veins

Arachnoid granulations:

Tufted prolongations of the arachnoid

Protrude through the meningeal layer of the dura mater into the dural venous sinuses

Enlarged arachnoid granulations (often called pacchionian bodies) may erode bone, forming pits called granular foveolae in the calvaria.

Structurally adapted for the transport of CSF from the subarachnoid space to the venous system.

Inferior sagittal sinus: Runs in the inferior

concave free border of the cerebral falx

Ends in the straight sinus.

Straight sinus (L. sinus rectus): Formed by the union of the inferior sagittal sinus with the great cerebral vein. Runs inferoposteriorly along the line of attachment of the cerebral falx to the

cerebellar tentorium Joins the confluence of sinuses.

Transverse sinuses: Pass laterally from the confluence

of sinuses

Forming a groove in the occipital bones and the posteroinferior angles of the parietal bones.

Course along the posterolateral attached margins of the cerebellar tentorium

Become the sigmoid sinuses as they approach the posterior aspect of the petrous temporal bones.

Usually the left sinus is dominant (larger).

Sigmoid sinuses: S-shaped courses in the

posterior cranial fossa

Forming deep grooves in the temporal and occipital bones.

Continues inferiorly as the IJV after traversing the jugular foramen.

Occipital sinus: Lies in the attached border of

the cerebellar falx

Ends superiorly in the confluence of sinuses

Communicates inferiorly with the internal vertebral venous plexus.

Cavernous sinus: Located on each side of

the sella turcica on the upper surface of the body of the sphenoid.

Thin-walled veins

Extends from the superior orbital fissure anteriorly to the apex of the petrous part of the temporal bone posteriorly.

Cavernous sinus: Receives blood from the

superior and inferior ophthalmic veins, superficial middle cerebral vein, and sphenoparietal sinus.

Communicate with each other through venous channels anterior and posterior to the stalk of the pituitary gland the intercavernous sinuses.

Drain posteroinferiorly through the superior and inferior petrosal sinuses and emissary veins to the pterygoid plexuses.

Contents of the cavernous sinus:

Internal carotid artery with its small branches, surrounded by the carotid plexus of sympathetic nerve(s),

Abducent nerve (CN VI).

Pulsations of the artery within the cavernous sinus are said to promote propulsion of venous blood from the sinus, as does gravity.

Following nerves related to the Lateral wall: Oculomotor (CN III), Trochlear (CN IV), Opthalmic Maxillary

Superior petrosal sinuses: Run from the posterior ends of the

cavernus sinus to the transverse sinuses.

Lies in the anterolateral attached margin of the cerebellar tentorium

Inferior petrosal sinuses:

Commence at the posterior end of the cavernous sinus inferiorly.

Runs in a groove between the petrous part of the temporal bone and the basilar part of the occipital bone.

Drain the veins of the lateral cavernous sinus directly into the origin of the IJVs.

Basilar plexus:

Connects the inferior petrosal sinuses

Communicates inferiorly with the internal vertebral venous plexus.

Emissary veins:Connect the dural venous sinuses with veins outside the cranium. Valveless and blood may flow in both directionsFlow in the emissary veins is usually away from the brain.

Frontal emissary vein: Present in children and some adults. Passes through the foramen cecum of the cranium Connecting the superior sagittal sinus with veins of the frontal sinus and nasal

cavities.

Mastoid emissary vein:Passes through the mastoid foramen.Connects each sigmoid sinus with the occipital or posterior auricular vein.

Parietal emissary vein:Paired bilaterallyPasses through the parietal foramen in the calvariaConnecting the superior sagittal sinus.

Posterior condylar emissary vein:Occasionally presentPassing through the condylar canalConnecting the sigmoid sinus with the suboccipital plexus of veins.

Occlusion of Cerebral Veins and Dural Venous Sinuses: Facial veins make

clinically important connections with the cavernous sinus through the superior ophthalmic veins.

Thrombophlebitis of the facial vein may extend into the cavernous sinus, producing thrombophlebitis of the cavernous sinus.

Occlusion of Cerebral Veins and Dural Venous Sinuses: Cavernous sinus thrombosis

usually results from infections in the orbit, nasal sinuses, and superior part of the face (the danger triangle).

Infection of one sinus may spread to the opposite side through the intercavernous sinuses.

Thrombophlebitis of the cavernous sinus may affect the abducent nerve as it traverses the sinus and may also effect the nerves embedded within the lateral wall of the sinus.

Metastasis of Tumor Cells to the Dural Sinuses: Basilar and Occipital sinuses

communicate with the internal vertebral venous plexuses.

Venous sinuses are valveless Compression of the thorax,

abdomen, or pelvis, as occurs during heavy coughing and straining, may force venous blood from these regions into the internal vertebral venous system and from it into the dural venous sinuses.

Pus in abscesses and tumor cells in these regions may spread to the vertebrae and brain.

Fractures of the Cranial Base Internal carotid artery may be torn Producing an arteriovenous fistula within

the sinus. Arterial blood rushes into the cavernous

sinus, and forcing retrograde blood flow into its venous tributaries, especially the ophthalmic veins.

Eyeball protrudes (exophthalmos). Eyeball pulsates in synchrony with the radial pulse,known as pulsating exophthalmos.

Conjunctiva becomes engorged (chemosis).

CN III, CN IV, CN V1, CN V2, and CN VI, may also be affected.

Vasculature of the Dura Mater Arteries of the dura: The larger supply by the middle

meningeal artery, is a branch of the maxillary artery.

Small areas of dura are supplied by

other arteries: meningeal branches of the ophthalmic arteries, branches of the occipital arteries, and small branches of the vertebral arteries.

Veins of the dura accompany the meningeal arteries, often in pairs.

Middle meningeal veins accompany the middle meningeal artery drain into the pterygoid plexus.

Leptomeningitis The infection and inflammation are

usually confined to the subarachnoid space and the arachnoid pia.

Microorganisms may enter the subarachnoid space through the blood (septicemia, or blood poisoning) or �spread from an infection of the heart, lungs, or other viscera.

Microorganisms may also enter the subarachnoid space from a compound cranial fracture or a fracture of the nasal sinuses.

Acute purulent meningitis can result from infection with almost any pathogenic bacteria (e.g., meningococcal meningitis).

Leptomeningitis purulenta

Head Injuries and Intracranial Hemorrhage Extradural or epidural hemorrhage is arterial in

origin.

Blood from torn branches of a middle meningeal artery collects between the external periosteal layer of the dura and the calvaria, and forms an extradural or epidural hematoma.

Typically, a brief concussion (loss of consciousness) occurs, followed by a lucid interval of some hours.

Later, drowsiness and coma (profound unconsciousness) occur.

Compression of the brain occurs as the blood mass increases, necessitating evacuation of the blood and occlusion of the bleeding vessels.

Head Injuries and Intracranial Hemorrhage A dural border hematoma usually

caused by extravasated blood that splits open the dural border cell layer.

The blood does not collect within a pre-existing space, but rather creates a space at the dura arachnoid junction.

Dural border hemorrhage is typically venous in origin and commonly results from tearing a superior cerebral vein as it enters the superior sagittal sinus.

Subarachnoid hemorrhage: Extravasation (escape) of blood,

usually arterial, into the subarachnoid space.

Most subarachnoid hemorrhages result from rupture of a saccular aneurysm (sac-like dilation on the side of an artery), such as an aneurysm of the internal carotid artery.

Bleeding into the subarachnoid space results in meningeal irritation, a severe headache, stiff neck, and often loss of consciousness.

Subarachnoid hemorrhage (SAH). A nonenhanced computed tomography scan of the brain

Nerve Supply of the Dura Mater Innervated by meningeal

branches arising directly or indirectly from the trigeminal nerve (CN V).

Meningeal branches of the ethmoidal nerves (CN V1), maxillary (CN V2) and mandibular (CN V3) nerves

The dura of the floor of the posterior cranial fossa receives sensory fibers from the spinal ganglia of C2 and C3 carried by those spinal nerves or by fibers transferred to and traveling centrally with the vagus (CN X) and hypoglossal (CN XII) nerves.

Pain arising from the dura is generally referred, perceived as a headache arising in cutaneous or mucosal regions supplied by the involved cervical nerve or division of the trigeminal nerve.

Pituitary Gland (Hypophysis Cerebri)

Small, oval structure

Attached to the undersurface of the brain by the infundibulum.

Located in the sella turcica of the sphenoid bone.

Hypophysis cerebri referred to as the master endocrine gland.

Pituitary gland:Divided: Anterior lobe, or adenohypophysis

Posterior lobe, or neurohypophysis.

Anterior lobe: subdivided into

Pars anterior (Pars distalis)

Pars tuberalis: a projection from the pars anterior, the, extends up along the anterior and lateral surfaces of the pituitary stalk.

Pars intermedia: may be separated by a cleft (remnant of an embryonic pouch).

RelationsAnteriorly: • sphenoid sinus

Posteriorly: • Dorsum sellae• Basilar artery• Pons

Superiorly:• Diaphragma sellae: has a central

aperture that allows the passage of the infundibulum. It separates the anterior lobe from the optic chiasma .

Inferiorly:• Body of the sphenoid and

sphenoid air sinuses

Laterally: • Cavernous sinus and its contents

Sphenoid sinus

Pons

Blood SupplyArteries: Superior and inferior

hypophyseal arteries, branches of the internal carotid artery.

Veins: Drain into the intercavernous

sinuses.

Functions of the Pituitary Gland Influences the activities of many other

endocrine glands.

Controlled by the hypothalamus

Pineal Gland Small cone-shaped

Projects posteriorly from the posterior end of the roof of the third ventricle of the brain.

Consists of groups of cells, the pinealocytes, supported by glial cells.

Has a rich blood supply

Innervated by postganglionic sympathetic nerve fibers.

Pineal gland

Functions of the Pineal Gland The secretions, produced by the pinealocytes, reach

their target organs via the bloodstream or through the cerebrospinal fluid.

Actions are mainly inhibitory and either directly inhibit the production of hormones or indirectly inhibit the secretion of releasing factors by the hypothalamus.

Influences the activities:• Pituitary gland• Islets of Langerhans of the pancreas• Parathyroids• Adrenals• Gonads

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