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The subarachnoid cisterns are spaces formed by openings in the subarachnoid space, an anatomic space in the meninges of the brain. [1] The space is situated between the two meninges, the arachnoid mater and the pia mater. These cisterns are filled with cerebrospinal fluid (CSF). [1]
The lumbar cistern is part of the subarachnoid space.It is the space within the thecal sac which extends from below the end of the spinal cord (the conus medularis), typically at the level of the first to second lumbar vertebrae down to tapering of the dura at the level of the second sacral vertebra.
The cisterna magna (posterior cerebellomedullary cistern, [1] or cerebellomedullary cistern [2] [3]) is the largest of the subarachnoid cisterns.It occupies the space created by the angle between the caudal/inferior surface of the cerebellum, and the dorsal/posterior surface of the medulla oblongata (it is created by the arachnoidea that bridges this angle [3]).
The cauda equina occupies the lumbar cistern, a subarachnoid space inferior to the conus medullaris. The nerves that compose the cauda equina innervate the pelvic organs and lower limbs to include motor innervation of the hips , knees , ankles , feet , internal anal sphincter and external anal sphincter .
The space between the arachnoid and the underlying pia mater is called the subarachnoid space. The subarachnoid space contains cerebrospinal fluid, which can be sampled with a lumbar puncture, or "spinal tap" procedure. The delicate pia mater, the innermost protective layer, is tightly associated with the surface of the spinal cord.
The bases of denticulate ligaments arise in the pia mater and are firmly attached to the arachnoid mater and dura mater at the apex. [2] The denticulate ligaments extend across the subarachnoid space between anterior nerve roots and posterior nerve roots, piercing the intervening spinal arachnoid mater to reach the dura.
The filum terminale is situated centrally [2] amid the spinal nerve roots of the cauda equina [3] [2] (but is not itself a part of the cauda equina [2]).. The inferior-most spinal nerve, the coccygeal nerve, leaves the spinal cord at the level of the conus medullaris via respective vertebrae through their intervertebral foramina, superior to the filum terminale.
Rarely, the vertebral arteries enter the subarachnoid space at C1-C2 (3%) or C2-C3 (only three cases have been reported) vertebral levels instead of the atlanto-occipital level. [ 9 ] The portion of vertebral arteries located within the skull (intracranial) have diameters of 3.17 mm.