Meninges and dural folds

Summary

  • Meninges
    • Dural folds
    • Potential spaces

Meninges

 

Layers of the scalp, skull, and meninges.  Note the order of dura, arachnoid, subarachnoid space, and pia mater. From Moore & Dalley.

 

  • 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

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
Image displaying all four of the key dural folds. From http://operativeneurosurgery.com/lib/exe/fetch.php?tok=6cd63b&media=http%3A%2F%2Fmedicine.academic.ru%2Fpictures%2Fmedicine%2F573.jpg.
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)
From https://upload.wikimedia.org/wikipedia/commons/b/b7/Illu_tentorium.jpg.
  • 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


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

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