HNS03 Meninges And Blood Supply Flashcards
Meninges
Membranes covering Brain + Spinal cord (Dura + Arachnoid + Pia mater):
- Protection
- Support blood vessels supplying the brain
- Space for CSF flow
Layers of head
Skin of scalp —> Periosteum —> Skull bone —> ***Dura mater (Periosteal / Endosteal —> Meningeal) —> ***Arachnoid mater —> ***Pia mater (記: DAP)
Dura mater
(Dense irregular CT)
- Endosteal / Periosteal layer (outer)
- tough, lines inner surface of skull
- continuous along outside of skull (包住成個頭骨, 但剩係入面嗰層叫endosteal layer)
- tightly adhered to skull (esp. along sutures)
- ends at ***Foramen magnum
- ∴ ONLY in head, NOT in spine - Meningeal layer (inner)
- lines endosteal layer most of the time EXCEPT at dura folds
- extend into spine —> ends at ***filum terminale (S2 level)
- ∴ covers brain + spinal cord
Dural folds
Meningeal layer invaginates and separate from endosteal layer
4 Places:
- Falx cerebri
- Tentorium cerebelli
- Falx cerebelli
- Diaphragma sellae
Form compartments of brain:
- Left / Right
- Supratentorial / Infratentorial
Dura’s blood supply
Middle Meningeal artery (mostly)
- located in ***epidural space (above Dura, under skull)
- a lot of causes of intracranial haemorrhage (Epidural haemorrhage)
Dura’s nerve supply
Supratentorial: Trigeminal nerve CN5
Infratentorial: Spinal nerves C1-3
Dura / Meninges: very pain sensitive —> common source of headache (migraine / tension headache)
Tumour of meninges
Meningiomas
—> usually arise from dural folds e.g. Falx cerebri, Tentorium cerebelli
Arachnoid layer
- Loose spider-web like layer
- Trabeculae of collagen fibres (Arachnoid trabeculae) linking Arachnoid membrane + Pia mater
- CSF runs in subarachnoid space (between arachnoid and pia)
Functions:
- Space for CSF circulation
- Support ***cerebral vessels (blood supply of brain)
- Space for cranial nerves
- Cushion the brain
Arachnoid granulations
Projections from Arachnoid into Venous sinuses (in between 2 layers of Dura) for CSF circulation back to venous blood (將CSF由subarachnoid space送返入venous blood)
Pia mater
- Soft, tender, very thin, innermost membrane
- Tightly covers brain and spinal cord surface
- Follow all cerebral sulci and gyri
- Invaginates into ventricles forming Choroid plexus (珊瑚體) which produces CSF
Clinical relevance
Epidural hematoma:
- hematoma between dura (above dura) and skull
- bleeding usually from fractured skull bone (brain not injured)
- hematoma press on brain
- arterial blood (from Middle meningeal artery)
Subdural hematoma:
- deep to dura
- bleeding usually from brain / vessels supplying brain (as a result of brain injury)
- worse prognosis
- venous blood
Subarachnoid haemorrhage:
- bleeding from subarachnoid space (e.g. aneurysm in artery in subarachnoid space)
Cerebrospinal fluid
- crystal clear fluid within subarachnoid space
- produced by Choroid plexus
- ~150mL in adult (~50ml in brain, 100ml in spine)
- daily production ~450mL (imbalance / obstructive: hydrocephalus)
- Functions:
1. Cushion the brain
2. Nourish the brain
3. More Na, Cl; Less Ca, K compared to serum
4. >50% of serum glucose, trace of protein
Choroid plexus
Consists of:
- Ependymal cells (Glial cells forming epithelial lining of ventricles’ wall)
- Blood capillaries
Blood filtered into ventricle space —> CSF
(blood capillary —> Ependymal cells —> ventricle space)
CSF ventricular system
CSF secreted by choroid plexus in Right + Left Lateral ventricle
—> Interventricular foramen (Foramen of Monro)
—> Third ventricle (Choroid plexus in third ventricle adds more CSF)
—> Aqueduct
—> Fourth ventricle (Choroid plexus in fourth ventricle adds more CSF)
—> 2x Foramen of Luschka (lateral apertures), 1x Foramen of Magendie (median aperture)
—> CSF go outside of ventricle into subarachnoid space
—> fills subarachnoid space
—> bathes external surface of brain and spinal cord
—> CSF reabsorbed into venous blood of dural venous sinuses at arachnoid villi
Meningitis
Infection of meninges (Arachnoid, Pia mater)
—> Pus like CSF
Four major blood vessels going into brain
- Right / Left Internal Carotid artery
2. Right / Left Vertebral artery
Network of blood vessels at base of brain
Anterior circulation:
Internal Carotid artery (R/L)
—> Anterior cerebral artery (joined by Anterior communicating artery) + Middle cerebral artery
Posterior circulation:
Vertebral artery (R/L)
—> Basilar artery (form Vertebrobasilar complex)
—> 2x Posterior cerebral artery
Anterior and Posterior circulation joined by:
***Posterior communicating artery (between Middle + Posterior cerebral artery)
—> form Circle of Willis
Anterior circulation
From Internal carotid artery (R/L) (ICA)
Gives off:
- Anterior cerebral artery (ACA)
- Middle cerebral artery (MCA)
- Ophthalmic artery
- Perforators / Lenticulo-striate arteries (small blood vessel go to base of brain / brainstem into deep nuclei of cerebrum; great haemodynamic stress —> degeneration/blockage/rupture —> ischaemic/haemorrhagic stroke)
Posterior circulation
From Vertebral artery (R/L)
Gives off (先—>後, 下—>上):
- Posterior inferior cerebellar artery (PICA) —> Cerebellum
- Anterior inferior cerebellar artery (AICA) —> Cerebellum
- Basilar artery
- Superior cerebellar artery —> Cerebellum
- Posterior cerebral artery (PCA)
Major cerebral arteries
Anterior circulation
- Anterior cerebral artery:
- travels within interhemispheric fissure
- supplies ***front part of cerebrum - Middle cerebral artery:
- travels within lateral (Sylvian) fissure
- supplies ***side of cerebrum
Posterior circulation
- Vertebral-basilar artery complex:
- travels around
- supplies **brainstem + **cerebellum and finally ***back of cerebrum
ALL branches at last anastomose throughout the brain
ACA, MCA, PCA territories
ACA:
- Medial side of anterior brain (frontal lobe)
- affects cognition
MCA:
- Lateral brain
- affects sensori-motor cortex (contralateral body side)
PCA:
- Medial side of posterior brain
- affects visual cortex
Cerebral infarction
- Major arteries have communicating arteries (AComA, PComA) —> form collaterals within brain —> support blood supply in each other’s territory
- Collaterals have limits —> interruption in one key artery can still cause ischaemia / cerebral infarction within its own territory
- Extent of ischaemia / infarction varies between patients, depending on anatomy of the circle of Willis and “dominance” of affected artery
- Clinical signs and symptoms depend on location and extent of ischaemia / infarction
Circle of Willis
- a circle formed by AComA, PComA
- Only 25% people have complete circle
- several variants may result in poor “cross over” of circulation (e.g. Hypoplastic PComA, Hypoplastic AComA)
Cerebral venous drainage
Superficial cerebral veins (X rmb individual names)
- Superior cerebral veins
- Superficial middle cerebral vein
- Inferior cerebral veins
Deep cerebral veins
- Internal cerebral veins x2
- Basal vein of Rosenthal x2
- Great vein of Galen
- Veins of cerebellum, colliculi etc.
ALL go to **Dural venous sinuses
—> finally drains through 2x **Internal Jugular veins
Dural venous sinuses
Superficial system:
Superficial cerebral veins
—> Superior sagittal sinus
Deep system: Deep cerebral veins + Basal vein of Rosenthal —> Great vein of Galen —> Inferior sagittal sinus —> Straight sinus
Both system meet at Confluences of the sinuses
—> Transverse sinus (at edge of Tentorium cerebelli)
—> Sigmoid sinus
—> Internal jugular vein
Cerebral sinus thrombosis
Can cause:
- Venous congestion
- Cerebral ischaemia
- Bleeding due to high pressure within affected brain region
