Arachnoid mater

  • Superficial layer of leptomeninx
  • Between the dura mater and the pia mater
  • From the inner surface of the dura mater and its reflections to the lower end of the lumbar cistern (S2-S3)
  • Arachnoid trabeculae: fibrous tracts extending from the deep arachnoid mater to the pia mater

Cranial arachnoid

  • Covers the inner surface of the dura mater
  • Subarachnoid cisterns
    • Cisterna of lateral fossa of cerebrum (1)
    • Chiasmatic cistern (2): between the corpus callosum and the optic chiasm
    • Interpeduncular cistern (3): between the optic chiasm, the cerebral peduncles and the temporal lobes, lodged within the transverse cerebral fissure
    • Cisterna magna(4): largest subarachnoid cistern, between cerebellum and medulla oblongata
  • Arachnoid granulations
    • Along the superior edge of each cerebral hemisphere
    • Function : reabsorption and drainage of cerebrospinal fluid from the subarachnoid space towards the superior sagittal sinus
    • Specific imprints on the inner surface of the cranial vault, on both sides of the sulcus of the superior sagittal sinus

Spinal arachnoid

  • Covers the inner surface of the spinal dura mater
  • Lumbar cistern: contains the cauda equina