Cistern (neuroanatomy)
（重定向自Subarachnoid cisternae）
In neuroanatomy, a cistern (Latin: "box") is any opening in the subarachnoid space of the brain created by a separation of the arachnoid and pia mater. These spaces are filled with cerebrospinal fluid.
Although the pia mater adheres to the surface of the brain, closely following the contours of its gyri and sulci, the arachnoid covers only its superficial surface. It follows from this that in certain areas around the brain the pia and arachnoid are separated widely; in such regions are formed cavities called the subarachnoid cisterns.