Meninges and dural folds

Summary

• Meninges
  • Dural folds
  • Potential spaces

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Meninges

 

 

• Functions:
  • Prevent ischaemia/injury
  • Provide buoyancy
  • Chemical stability
• 4 layers (from superficial to deep:
  1. Dura mater – tough, fibrous layer
     • Two layers of dura:
       1. Periosteal dura – lines the skull bone
       2. Meningeal dura – lines the arachnoid mater (there is a potential space called the subdural space between them
     • Venous sinuses run between the two layers of dura
  2. Arachnoid mater
     • Delicate membrane
     • Arachnoid granulations transfer CSF in the subarachnoid space => venous sinuses in dura
  3. Subarachnoid space
     • Contains CSF and cerebral arteries
     • Contains arachnoid trabeculae from the arachnoid => pia
     • Larger above the sulci (as more distance between pia/arachnoid)
  4. Pia mater
     • This is a delicate vascular membrane

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Dural folds (Falx)

• These are folds of the meningeal dura
  • Meningeal dura detaches from the periosteal dura
  • Then both parts of the detached meningeal durae fold and then fuse with each other to form the Falx

    

• The falx contain the venous sinuses
  • Venous drainage of the brain occurs through between dura
• There are 4 dural folds:
  1. Falx cerebri
  2. Tentorium cerebelli
  3. Falx cerebelli
  4. Diaphragma sellae

Falx Cerebri

• Reflects down the sagittal fissure of the brain
  • Between cerebral hemispheres
  • Prevents lateral movement of brain

• Contains 3 venous sinuses:
  • Superior sagittal sinus at superior margin
  • Inferior sagittal sinus at lower margin
  • Tentorial/straight sinus at border with tentorium

 

Tentorium Cerebelli

• Reflection of dura between the cerebellum and occipital lobes
  • Prevents superior/inferior movement of brain (cerebellum and cerebrum)

• Attaches to the anterior clinoid process
  • Covers everything except the brainstem
    • Opening for brainstem = tentorial notch

• Clinically very significant:
  • Volume expansion above tentorium can cause uncal herniation of brain
    • Brain goes through tentorial notch
    • This puts pressure on brainstem which compresses key basic functions (e.g. cardiorespiratory centres)
    • Tentorium may lacerate the herniating brain

Cerebellar falx

• Between cerebellar hemispheres
  • Prevents lateral movement of the cerebellum

Sellar diaphragm (Diaphragm Sellae)

• Suspended between anterior and posterior clinoid processes
  • Passes between the pituitary and hypothalamus
  • An aperture allows passage of infundibulum
  • Forms the roof of the cavernous sinus

    

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Potential spaces

• 3 key spaces to consider
  1. Subarachnoid space between arachnoid and pia mater
  2. Subdural space between dura and arachnoid
  3. Epidural space between periosteal dura and bone

• Note that the subdural and epidural spaces are usually only potential spaces
  • All can become significant with haemorrhage