Although the pia mater adheres to the surface of the brain, closely following the contours of its
gyri and
sulci, the arachnoid mater only covers its superficial surface, bridging across the gyri. This leaves wider spaces between the pia and arachnoid and the cavities are known as the subarachnoid cisterns.
Although they are often described as distinct compartments, the subarachnoid cisterns are not truly anatomically distinct. Rather, these subarachnoid cisterns are separated from each other by a
trabeculated porous wall with various-sized openings.
Cisterns
There are many cisterns in the brain with several large ones noted with their own name. At the base of the spinal cord is another subarachnoid cistern: the lumbar cistern which is the site for a
lumbar puncture.
Some major subarachnoid cisterns:
The third (III) cranial nerve, which passes between the posterior cerebral and superior cerebellar arteries
Cerebellopontine angle cistern. It is situated at the cerebellopontine angle – the lateral angle between the cerebellum and the pons. It contains:
The seventh (VII) and eighth (VIII) cranial nerves
The anteroinferior cerebellar artery (AICA)
The fifth (V) cranial nerve and the petrosal vein
Quadrigeminal cistern - It is situated dorsal to the midbrain. Thin, sheet-like extensions of the superior cistern that extend laterally about the midbrain, connecting it to the interpeduncular cistern. Ambient cistern may also refer to the combination of these extensions and the superior cistern. It is composed of a supratentorial and an infratentorial compartment. It contains:
The anterior cerebral arteries (A1 and proximal A2)
The anterior communicating artery
Heubner's artery
The hypothalamic arteries
The origin of the fronto-orbital arteries
Lumbar cistern. It extends from the conus medullaris (L1-L2) to about the level of the second sacral vertebra. It contains the filum terminale and the nerve roots of the
cauda equina. It is from the lumbar cistern that CSF is withdrawn during a
lumbar puncture.
Clinical significance
It is clinically significant that cerebral arteries, veins, and cranial nerves traverse through the subarachnoid space, maintaining their meningeal covering until they exit the skull.