QS Study

Subarachnoid space:

It is a wide space between the pia and the arachnoid, filled with cerebrospinal fluid (CSF). It is occupied by delicate connective tissue trabeculae and intercommunicating channels containing CSF.


It surrounds the brain & spinal cord and ends below at the lower border of the second sacral vertebra. At certain points, the pia mater and arachnoid membrane are separated by wide intervals which communicate freely with each other known as subarachnoid cisterns, in which the subarachnoid tissue is less abundant.

Contents – It is the space between the arachnoid membrane and pia mater that is filled with cerebrospinal fluid and contains the large blood vessels that supply the brain and spinal cord.

  • CSF.
  • Large vessels of the brain.
  • Cranial nerves.

subarachnoid space 1

Fig: Subarachnoid Space


At the base of the brain and around the brain stem, the subarachnoid space forms intercommunicating pools, called cisterns. The subarachnoid cisterns are as follows:

  1. The cerebellomedullary cistern.
  2. The pontine cistern.
  3. The interpeduncular cistern.
  4. The cistern of the lateral sulcus.
  5. The cistern of the great cerebral vein.
  6. The cisterna chiasmatic.

Communications –

Space communicates with the ventricular system of the brain at –

  1. A median foramen (of Magendie),
  2. Two lateral foramina (of Luschka), situated in the roof of the fourth ventricle.
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