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Case 19: Anatomy (Meningitis) - Coggle Diagram
Case 19: Anatomy (Meningitis)
Meninges
Define the term Meninges
Meninges are the membranous covering of the brain and spinal cord
There are three types of Meninges:
Dura mater
Dura Mater is the outer most membranous covering
Dura Mater has potential spaces known as the Epidural Space and Subdural Space
These spaces are not usually present unless there is an abnormal accumulation of CSF
Arachnoid Mater
Arachnoid Mater is the middle membranous covering
Between the Arachnoid Mater and the Pia Mater is the Sub-Arachnoid Space which contains Cerebrospinal Fluid
Pia Mater
Pia Mater is the inner most membranous covering
Together, Arachnoid Mater and the Pia Mater are known as the Leptomeninges
Dura Mater
Describe the characteristics of the Dura Mater
Dura Mater is also known as the Pachymeninx (Thick Membrane)
Pachy means thick
Meninx means membrane
Dura Mater is a tough membrane
Dura Mater is made up of two layers:
Fibrous or Endosteal layer = Periosteal Dura mater
Meningeal layer = Meningeal Dura Mater
Dural Venous Sinuses are formed in the Meningeal Layer of the Dura Mater
Dura Mater has 5 Reflections:
Falx Cerebri
Tentorium Cerebelli
Falx Cerebelli
Diaphragma Sella (Fossa of the Hypophyseos)
Dural Sinuses
Dural Reflections
Describe the features of the Dural Reflections of the Dura Mater
Falx Cerebri
Falx Cerebri is located between the Cerebral Hemispheres in the Longitudinal Cerebral Fissure
Falx Cerebri contains the Superior and Inferior Sagittal Sinuses between its layers
Tentorium Cerebelli
Tentorium Cerebelli separates the Middle Cranial Fossa and the Posterior Cranial Fossa
Tentorium Cerebelli separates the Temporal Lobe and the Occipital Lobe from the Brainstem and the Cerebellum
Tentorium Cerebelli contains the Tentorial Notch through which the Brainstem passes
Diaphragma Sellae
Diaphragma Sellae forms the roof of the Hypophyseal Fossa
Diaphragma Sellae contains aperture through which the Hypophyseal Stalk/Infundibulum passes
Dural Sinuses
Dural Sinuses are endothelium lined, valveless, venous blood channels
Dural Sinuses are typically found in the attached edge of the Dural Folds
Blood Supply to the Dura Mater
Explain the Blood Supply to the Dura Mater
Blood Supply to the Dura Mater is divided according to the Anterior Cranial Fossa, Middle Cranial Fossa and Posterior Cranial Fossa
Dura Mater in the Anterior Cranial Fossa supplied by the:
Meningeal Branches of the Anterior and Posterior Ethmoidal Artery
Frontal Branch of the Middle Meningeal Artery
Middle Meningeal Artery comes off the Maxillary Artery
Maxillary Artery is a branch of the External Carotid Artery
Dura Mater in the Middle Cranial Fossa is supplied by the:
Frontal and Parietal Branches of the Middle Meningeal Artery
Ascending Meningeal Artery
Direct branches of the Internal Carotid Artery
Dura Mater in the Posterior Cranial Fossa is supplied by the:
Vertebral Artery
Occipital Artery
Ascending Pharyngeal Artery
Anterior and Posterior Ethmoidal Arteries are branches of the Ophthalmic Artery which is also a Branch of the Internal Carotid Artery
Nerve Supply of the Dura Mater
Outline the Nerve Supply of the Dura Mater
Dura Mater is mostly innervated by the:
Meningeal Branches and the Anterior meningeal nerves of the Trigeminal Nerve
Meningeal Branches of the Cervical Nerves (C1, C2, and C3)
Arachnoid Mater
Describe the features of the Arachnoid Mater
Arachnoid Mater is a thin avascular membrane
Arachnoid Mater attached to the Dura matter by several layers of flattened cells
Arachnoid Mater conforms to the general shape of the brain
Arachnoid Mater does NOT dip into the Cerebral Sulci
Arachnoid Mater is separated from the Dura Mater by the Potential Space known as the Subdural Space
Arachnoid Mater is separated from the Pia Mater by the Subarachnoid Space, and Arachnoid Trabeculae
Arachnoid Specializations
List the structures which make up the Arachnoid Specializations
Arachnoid Specializations include:
Arachnoid Trabeculae
Arachnoid Villi
Arachnoid Barrier
Describe the structures which make up the Arachnoid Specializations
Arachnoid Trabeculae
Arachnoid Trabeculae are strands of collagenous tissue which extend from the Arachnoid mater to the Pia Mater
Arachnoid Villi
Arachnoid Villi are also known as Arachnoid Granulations
Arachnoid Villi are evaginations of the Arachnoid which project through the Dura into the Sinuses
Arachnoid Villi are involved in the reabsorption of CSF
Arachnoid Barrier
Arachnoid Barrier is the outermost Arachnoid Layer which contains cells that have Tight Junctions
Arachnoid Barrier prevents the spread of an infection from the Dura Mater to the Subarachnoid Space
Pia Mater
Outline the features of the Pia Mater
Pia Mater is a delicate membrane that is 2-3 cells thick
Pia Mater attaches to the End Feet of the Arachnoid Trabeculae
Pia Mater invests into the surface of the Brain
Pia Mater closely follows all the Sulci and Gyri of the Brain
Arteries and Veins penetrate the Pia Mater when they enter or leave the brain substance
This results in the formation of the Perivascular Space
Perivascular Space is a fluid-filled space in the Pia Mater
Spinal Meninges
List and Outline the Spinal Meninges
Spinal Meninges are devoid of the Fibrous/Endosteal layer of the Dura Mater known as the Periosteal Dura Mater
Periosteal Dura Mater ends at the margin of the Foramen Magnum
Therefore, the Spinal Cord has the follows meninges:
Meningeal Dura Mater
Arachnoid Mater
Pia Mater
There is not much difference between the Arachnoid Mater in the Brain and the Arachnoid Mater in the Spinal Cord
Pia Mater in the spinal cord forms multiple specializations:
21 Pairs of Denticulate Ligaments
Filum Terminale
21 Pairs of Denticulate Ligaments attach the meningeal Dura Mater to the Pia Mater in the Spinal Cord
Spinal Cord ends at L1/L2
Spinal Cord ends at the structure called the Conus Medullaris
Extending from the tip of the Conus Medullaris is a thin layer of the Pia Mater known as the Filum Terminale
Filum Terminale ends where the Meningeal Dura Mater ends
After that, the Pia Mater continues as the Coccygeal Ligament
Meningeal Spaces
List and Outline the Types of Meningeal Spaces in the Spinal Cord
Spinal Cord has one Meningeal Space:
Spinal Epidural Space
Spinal Epidural Space is located between the Spinal Dura mater and the Vertebral Periosteum
Spinal Epidural Space contains loose areolar connective tissue, venous plexuses and lymphatic
Spinal Epidural Space can be injected with local anaesthetics in Trunk Blocks
Spinal Epidural Space can also be used for the removal of CSF in a Lumbar Puncture
Meningeal Spaces of the Brain
List the Types of Meningeal Spaces of the Brain
Meningeal Spaces of the Brain include:
Cranial Epidural Space
Cranial Subdural Space
Subarachnoid Space
Outline the Types of Meningeal Spaces of the Brain
Cranial Epidural Space
Cranial Epidural Space is a potential space between the Bones of the Cranial Vault and the Dura Mater
Cranial Epidural Space contains Meningeal Arteries and Veins
Cranial Subdural Space
Cranial Subdural Space is a potential space between the Dura Mater and the Arachnoid Mater
Cranial Subdural Space transmits Cerebral Veins to the Venous Lacunae of the Superior Sagittal Sinus
Cerebral Veins are also known as Bridging Veins
Subarachnoid Space
Subarachnoid Space is located below the Arachnoid Mater between the Arachnoid Mater and the Pia Mater
Subarachnoid Space contains CSF
Subarachnoid Space is the ONLY True Space
Ventricles
Outline and Label the types of Ventricles
There are three main types of Ventricles:
Lateral Ventricles
3rd Ventricle
4th Ventricle
Lateral Ventricle is divided as follows:
Anterior (Frontal) Horn of the Lateral Ventricle
Body of the Lateral Ventricle
Posterior (Occipital) Horn of the Lateral Ventricle
Inferior (Temporal) Horn of the Lateral Ventricle
Lateral Ventricle connect to the 3rd Ventricle via the Interventricular Foramen
3rd Ventricle communicates with the 4th Ventricle via the Cerebral Aqueduct
4th Ventricle has a Lateral recess
4th Ventricles then continues as the Central Canal
Cerebrospinal Fluid Formation Formation
Outline the formation of CSF
CSF is mainly produced in the Choroid Plexus in the Floor of the Lateral Ventricle and the Roof of the 3rd and 4th Ventricle
CSF is manufactured at a rate of 0.35 ml/min
500 ml of total CSF is made per day and replaced every 4-6 hours
Function of CSF
List the Functions of CSF
CSF has the following function:
CSF supports and cushions the brain and the spinal against trauma (acts a shock absorber)
CSF acts as a Bouyant Fluid
Brain weighs 1500g in air, in CSF the Brain weight 50g
CSF maintain a uniform pressure
CSF provides Nutrition
Choroid plexus produces a protein-rich CSF for neural tissue
CSF removes waste product of neuronal metabolism
Circulation of CSF
Describe the circulation pathway of CSF
CSF is produced by the Choroid Plexus in the floor of the Lateral Ventricles
CSF from the Lateral Ventricles is then transported to the 3rd Ventricle via the Interventricular Foramen (Forman Monroe)
In the 3rd Ventricle, more CSF is produced by the Choroid Plexuses in the Roof of the 3rd Ventricle
CSF from the 3rd Ventricle is then transported to the 4tf Ventricle via the Cerebral Aqueduct
In the 4th Ventricle, more CSF is produced by the Choroid Plexus in the roof of the 4th Ventricle
From the 4th Ventricle the CSF has two paths it can follow:
CSF can move from the 4th Ventricle to the Central Canal of the Spinal Cord
This allows for the CSF to provide Nutrition to the Spinal Cord Tissue
CSF can move from the 4th Ventricle to the Median and Lateral Apertures (Foramen Magendie and Foramen Luschka)
From the Median and Lateral Apertures the CSF flows into the Subarachnoid Space
NOTE: 90% of the CSF goes into the Sub-arachnoid Space
NOTE: 10% of the CSF is pushed by pressure into the Spinal Central Canal
Cerebrospinal Cisterns
List the types of the Cerebrospinal Cisterns
Cerebrospinal Cisterns are sites of dilation of the subarachnoid space with pooling of CSF
There are three Cerebrospinal Cisterns:
Cisterna magna (Cerebellomedullary Cistern)
Pontine Cistern (Cerebellopontine Cistern)
Interpeduncular Cistern
Describe the Cerebrospinal Cisterns
Cisterna magna (Cerebellomedullary Cistern)
Cisterna magna is the largest Cerebrospinal Cistern
Cisterna magna receives CSF via the Median Aperture
Cisterna Magna is usually used for a Sub-Occipital Tap
Pontine Cistern (Cerebellopontine Cistern)
Pontine Cistern receives CSF via the Lateral Aperture
Pontine Cistern contains the Basil Artery, CN 7 (Facial nerve) and CN 8 (Vestibulocochlear Nerve)
Interpeduncular Cistern
Interpeduncular Cistern contains the arterial Circle of Willis
Absorption of CSF
Outline the absorption of CSF
CSF is absorbed into the Dural Venous Sinuses through the Arachnoid Villi/ Arachnoid Granulations
CSF Pressure is generally higher than the Venous Blood Pressure
Therefore, CSF is able to move via a process of diffusion (passive process) from the Subarachnoid Space through the Arachnoid Villi into he Dural venous Sinuses
Arachnoid Villi are considered One-way Valves
They collapse to prevent venous blood from entering the Subarachnoid Space
They allow a One-Way flow of CSF from the Subarachnoid Space into he Venous Circulation
When things go wrong...
Haematoma
Describe the types of Haematoma
There are two types of Haematoma:
Epidural Haematoma
Epidural Haematoma refers to the accumulation of blood in the Cranial Epidural Space
Rupture of the meningeal Arteries results in a rapid bleed
Epidural Haematoma occurs when Skull Fractures lacerate the meningeal arteries to produce space-occupying epidural Haematoma
Epidural Haematoma has a Lenticulate-like Shape
Subdural Haematoma
Subdural Haematoma occurs as a result of the rupture of the Cerebral veins (Bridging Veins) crossing the potential Subdural Space
Rupture of cerebral Veins results in a slow bleed
Subdural Haematoma can heal naturally or surgical intervention if too large/serious
Subdural Haematoma has a Crescentic Shape
Meningioma
Outline the features of a Meningioma
Meningioma is a benign, slow-growing, well demarcated tumour arising from the meningothelial arachnoid cells
Meningioma comprises of 20% of intracranial tumours and 25% of spinal tumours
Meningiomas are mostly found in the Anterior Cranial Fossa
Meningioma occurs in adults between 20-60 years, it is found mostly in women (60%)
Hydrocephalus
Outline the features of Hydrocephalus
Hydrocephalus refers to the dilation of cerebral ventricles caused by the blockage of the CSF flow
Hydrocephalus is characterised by an excessive accumulation of CSF in the Ventricles or the Subarachnoid Space
There are 4 Types of Hydrocephalus:
Non-communicating Hydrocephalus
Communicating Hydrocephalus
Normal Pressure Hydrocephalus
Hydrocephalus ex vacuo
Types of Hydrocephalus
Outline the types of Hydrocephalus
Non-communicating Hydrocephalus
Non-communicating Hydrocephalus results from an obstruction within the ventricles
Eg: Congenital aqueductal stenosis
Communicating Hydrocephalus
Communicating Hydrocephalus results from a blockage with the subarachnoid space
Normal Pressure Hydrocephalus
Normal Pressure Hydrocephalus occurs when the CSF is not absorbed by the Arachnoid Villi
Hydrocephalus ex vacuo
Hydrocephalus ex vacuo results from the loss of cells in the caudate Nucleus
Eg: Huntington Disease
Meningitis
Describe the features of Meningitis
Meningitis refers to the inflammation of the leptomeninges (Arachnoid Mater and the Pia mater) in the Brain and/or Spinal Cord
There are various types of Meningitis:
Bacterial Meningitis
Viral meningitis
