Meninges around brain and spinal cord (dura matter and dura venosinusis)

🖇 I. The Meninges and Protective Layers

📌 Brain Protection:

• Protected by:
• 1. Bony skull (bone box)
  2. Three layers of meninges

📌 Three Meningeal Layers:

1. Dura mater (outermost)
2. Arachnoid mater (middle)
3. Pia mater (deepest/innermost layer)

🖇 A. Dura Mater (Pachymeninx)

📌 Characteristics:

• Tough layer
• Arabic name: "Al-Umm Al-Jāfiya" (the tough mother)
• Critical role in brain protection

🟠 Two Primary Layers:

1. Outer Endosteal layer: Lies next to the bone
2. Inner Meningeal layer (Dura Propria)

Relationship:

• Typically fused together
• Separate in specific areas to form spaces housing venous sinuses

🟣 Dural Folds and Function:

Protective Function (Exam Point):

• Prevent brain lobes from excessive movement
• Ensure brain doesn't "slosh" inside skull during running/jumping

Major Dural Folds:

• Falx Cerebri
• Tentorium Cerebelli:
• • Acts as barrier
  • Separates cerebrum (above) from cerebellum (below in posterior cranial fossa)

🖇 II. Meningeal Spaces and Associated Hemorrhages

🚨 1. Epidural Space (Extradural Space):

Location:

• Between Outer Endosteal layer (outer dura beneath bone) and bone itself

Hemorrhage:

• Blood accumulation = Extradural Hemorrhage (Exam Point)

🚨 2. Subdural Space:

Location:

• Between Dura mater and Arachnoid mater

Hemorrhage:

• Blood accumulation = Subdural Hemorrhage (Exam Point)

📌 3. Arachnoid Mater:

• Layer beneath the dura
• Arabic name: "Al-Ankabut" (the spider web)

🚨 4. Subarachnoid Space:

Location:

• Between Arachnoid mater (externally) and Pia mater (most internal layer)

Main Contents (Exam Point):

1. Cerebrospinal Fluid (CSF)
2. Blood vessels
3. Cranial Nerves
4. Fila (Filaments)

🖇 Subarachnoid Hemorrhage (SAH)

🚨 Mechanism (Exam Point):

• Occurs if bleeding happens in subarachnoid space
• Often results from rupture of congenital aneurysm (weak point in vessel wall) under high pressure

🟣 Clinical Note: Diagnosis:

Symptoms:

• Signs of increased intracranial pressure

Diagnosis:

• Confirmed by CSF puncture revealing blood (bloody tap)
• Normal CSF is clear fluid
• Doctors note CSF appearance (aspect) before chemical analysis:
• • Clear
  • Turbid
  • Containing blood

🖇 CSF Circulation and Cisterns

📌 Arachnoid Villi/Granulations:

Arachnoid Villi:

• Projections of Arachnoid mater
• Extend into dural sinuses
• Responsible for transfer of CSF into blood (Exam Point)

Arachnoid Granulations:

• Aggregates of Arachnoid Villi

🟠 Cisterns (Cisternae):

Definition:

• Areas where meningeal layers separate
• Contain CSF

Examples:

• Cisterna Pontis
• Interpeduncular Cistern (in interpeduncular fossa)

Function:

• Contain CSF
• Serve as cushion around brain and spinal cord

🖇 C. Pia Mater (Leptomeninx)

📌 Characteristics:

• Most internal meningeal layer
• Thin
• Highly delicate
• Highly vascular

🟠 Anatomical Relationship (Exam Point):

• Adheres closely to brain surface
• Follows contours of gyri
• Extends into depth of sulci

🟣 Vascular Function:

• Carries blood vessels (arterial and venous) deep into neural tissue
• Tracks along sulci to reach neurons

📌 Perivascular Spaces (Virchow-Robin Spaces):

• Pia mater forms sheath around blood vessels as they penetrate brain

🚨 Tela Choroidea and Choroid Plexus (Exam Point):

Structure:

• Pial vascular structure forms sheath around blood vessels
• Combined with lining epithelium

Forms:

• Choroid Plexus

Location:

• Within ventricles

Function:

• Secretes CSF into the brain

🖇 D. Comparison of Meninges (Brain vs. Spinal Cord) - Clinical Note

📌 Similarities:

• Meningeal layers (Dura, Arachnoid, Pia) cover both brain and spinal cord

🚨 Critical Difference:

• Dura and Arachnoid surrounding spinal cord extend down to level of second sacral vertebra (S2)

🖇 III. Dural Venous Sinuses

📌 Definition and Function:

• Collecting spaces for venous blood
• Along with veins, help regulate intracranial pressure

🖇 A. Classification of Dural Sinuses

🟠 1. Single (Unpaired) Sinuses:

• Superior Sagittal
• Inferior Sagittal
• Occipital
• Intercavernous (Anterior and Posterior)
• Basilar

🟠 2. Paired Sinuses:

• Cavernous
• Superior Petrosal
• Inferior Petrosal
• Transverse
• Sigmoid
• Sphenoparietal
• Retrosquamous

🖇 B. Cavernous Sinus (Most Important Sinus)

🚨 Importance (Exam Point):

• Most important and famous sinus
• Commonly asked about in oral examinations

📌 Location:

• In Sella Turcica
• Specifically within Hypophyseal Fossa

📌 Dimensions:

• Approximately 2 cm long
• 1 cm wide

📌 Extension:

• Anteriorly: To Superior Orbital Fissure
• Posteriorly: To petrous part of temporal bone

🟠 Boundaries:

• Floor: Formed by endosteum
• Walls, Roof, and Cover: Formed by meningeal layer (Dura Propria)

🚨 Structures Running Through Lateral Wall (Exam Point):

1. Oculomotor Nerve (CN III)
2. Trochlear Nerve (CN IV)
3. Ophthalmic division of Trigeminal Nerve (CN V1)
4. Maxillary division of Trigeminal Nerve (CN V2)

🚨 Structures Running Through the Sinus (Exam Point):

1. Internal Carotid Artery (ICA)
2. Sympathetic plexus surrounding the ICA

📌 Note on Relations (Exam Point):

• Anatomical relations of Cavernous Sinus should be OMITTED
• Not required for integrated course

🖇 C. Tributaries and Communications of Cavernous Sinus

🟠 Tributaries (Sources of Drainage) (Exam Point):

1. Orbital:

• Superior Ophthalmic Veins
• Inferior Ophthalmic Veins
• Crucial for disease spread from eye/orbit

2. Cerebral:

• Superficial Middle Cerebral Vein
• Inferior Cerebral Veins

3. Meningeal:

• Sphenoparietal Sinus

🟠 Communications (Connections) (Exam Point):

Cavernous Sinus communicates with:

• Exterior and other sinuses through various pathways:
• • Through Pterygoid Plexus (via emissary veins)
  • With Internal Jugular Vein (IJV)
  • With Transverse Sinus via Superior and Inferior Petrosal Sinuses (Petrosal sinuses act as intermediaries)
  • Via emissary veins passing through Foramen Ovale and Foramen Lacerum

🖇 D. Clinical Pathology of Cavernous Sinus

🚨 Clinical Note: Cavernous Sinus Thrombosis (CST)

Nature:

• Famous and serious condition
• Caused by infection entering skull from external sources

🟣 Sources of Infection:

• Face infections:
• • Tooth decay
  • Dental abscesses (pus in teeth/gums)
  • Complications following tooth extraction

📌 Mechanism of Infection Spread:

• Infection travels from face (outside)
• Through communicating veins (ophthalmic veins)
• Through emissary veins
• Into Cavernous Sinus
• Leads to thrombosis

🚨 DANGER WARNING (Exam Point):

• STRICTLY FORBIDDEN to squeeze any:
• • Boil
  • Abscess
  • Inflamed lesion on the face
• Squeezing can cause diffusion of inflammation into skull through communication pathways

🖇 E. Other Major Dural Venous Sinuses

📌 1. Superior Sagittal Sinus (SSS):

Location:

• Runs in midline (median sagittal plane)

Path:

• Starts: Anteriorly at Crista Galli
• Runs: Posteriorly in groove in cranial bones (frontal, parietal, occipital)
• Terminates: At Internal Occipital Protuberance

Structure:

• Contains venous spaces/lakes (Lacunae)
• Lacunae receive Arachnoid Granulations

Tributaries:

• Receives Superior Cerebral Veins

Clinical Note:

• Infection from nose can spread to SSS

📌 2. Inferior Sagittal Sinus (ISS):

Location:

• Smaller than SSS
• Situated between dural layers
• Along free lower margin of Falx Cerebri

Termination (Exam Point):

• Joins Great Cerebral Vein of Galen
• Forms Straight Sinus

📌 3. Straight Sinus:

Formation:

• Continuation of Inferior Sagittal Sinus

Termination:

• Usually drains into Left Transverse Sinus

📌 4. Transverse Sinus:

Path:

• Starts at Internal Occipital Protuberance

Continuation:

• Continues and becomes Sigmoid Sinus

📌 5. Sigmoid Sinus:

Importance:

• Direct continuation of Transverse Sinus

Termination (Exam Point):

• Drains into Internal Jugular Vein (IJV)
• IJV is considered endpoint of dural sinuses