Spinal dura

At a glance

English

Spinal dura

Latin (TA2)

Dura spinalis

System

Nerve

Region

Trunk

Side

Single, on the midline

About the spinal dura

The spinal dura mater is the outermost and strongest of the three meninges around the spinal cord, the others being the arachnoid and the pia. It is a dense sheet of irregular fibrous tissue that forms a long tube, the dural or thecal sac. The arachnoid is pressed against its inner surface, and inside them lies the cerebrospinal fluid that cushions the cord.

Inside the skull the dura has two layers fused together, an outer periosteal layer lining the bone and an inner meningeal layer. Only the meningeal layer continues into the vertebral canal. The spinal dura is therefore a single layer and is not attached to the vertebrae, except loosely at a few points. The gap between it and the bone, the epidural space, is filled with fat and a plexus of thin-walled veins. Above, the dura is fixed firmly around the margin of the foramen magnum and to the second and third cervical vertebrae. Below, the sac narrows and closes at about the second sacral vertebra; from there a thin dural covering wraps the filum terminale and anchors it to the back of the coccyx.

Along its length the dura sends a sleeve outwards around each pair of nerve roots. The sleeve follows the roots into the intervertebral foramen and merges with the outer covering (epineurium) of the spinal nerve. Small fibrous bands also tie the dura to the posterior longitudinal ligament, and in the upper neck connective tissue links it to the small suboccipital muscles. The dura receives blood from segmental spinal arteries and is innervated by recurrent meningeal branches of the spinal nerves.

The anatomy matters in practice. Epidural anaesthesia places drug in the fat outside the dura, whereas spinal anaesthesia and lumbar puncture pass through it into the fluid; a puncture hole that leaks can cause a headache when upright. Spontaneous leaks of fluid through tears in the dura produce the same picture. The sac may widen abnormally (dural ectasia) in inherited connective tissue conditions, Marfan syndrome among them.

Course and supply

Arises from

Attached above to the margin of the foramen magnum and to the bodies of the second and third cervical vertebrae.

Ends in

Closes at about the second sacral vertebra and continues as the dural covering of the filum terminale to the back of the coccyx.

Supplies

Encloses and protects the spinal cord, nerve roots and cerebrospinal fluid, and gives each root a protective sleeve as it leaves the canal.

Nerve supply

Recurrent meningeal (sinuvertebral) branches of the spinal nerves.

Blood supply

Small branches of the segmental spinal arteries, from vertebral, intercostal, lumbar and sacral arteries.