Spinal arachnoid mater

Last revised by Henry Knipe on 6 Oct 2023

The spinal arachnoid mater is a thin, delicate and avascular connective tissue membrane which forms the middle layer of the meninges and covers the spinal cord 1.

Gross Anatomy

The spinal arachnoid mater becomes continuous with the cerebral arachnoid mater as it traverses the foramen magnum and terminates at the S2 vertebral level 2. It is in direct contact but does not adhere to the inner aspect of the dura mater, from which it is separated by a thin film of lymph. The arachnoid mater sends many wispy web-like processes or trabeculae across the cerebrospinal fluid-filled subarachnoid space to the underlying pia mater 3. These form an incomplete posterior median septum in the posterior midline of the spinal cord 1. 

Blood supply

The blood supply to the spinal arachnoid mater mirrors the other layers of the spinal meninges and comes from the one anterior and two posterior spinal arteries running the length of the spinal cord. Supply to these comes from the basilar portion of the circle of Willis and is reinforced by the segmental arteries at each level which themselves originate from a variety of sources (see spinal cord blood supply) 4

The largest of these segmental arteries and the dominant supplying artery to the thoracolumbar spinal cord is the artery of Adamkiewicz which has a variable origin 5.

The venous drainage principally follows the arterial supply. The anterior and posterior spinal veins drain into the segmental veins 4


The spinal arachnoid mater is innervated by sensory fibers of the meningeal branches of each spinal nerve. These fibers branch off from each spinal nerve near the bifurcation of the ventral and dorsal rami 4.

Related pathology

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Cases and figures

  • Figure 1: spinal meninges (Gray's illustration)
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