The spinal dura mater is the outermost covering of the spinal cord, serving as a protective sheath within the bony spinal column. This structure, whose name translates from Latin to “tough mother,” is a dense, fibrous connective tissue membrane. It forms a cylindrical sac that encases the entire spinal cord and the surrounding fluid. The dura mater is a key part of the central nervous system’s protective mechanism, shielding delicate neural tissue from external physical forces.
The Anatomy of the Spinal Dura
The spinal dura mater is a continuation of the inner meningeal layer of the dura mater surrounding the brain, starting at the foramen magnum. Unlike the cranial dura, the spinal dura consists of a single, thick layer of inelastic collagen fibers forming a loose sheath around the spinal cord. This cylindrical structure extends down the vertebral column, tapering off and fusing with the periosteum of the coccyx, typically at the second sacral vertebra (S2).
The epidural space separates the spinal dura mater from the walls of the vertebral canal, a key anatomical distinction from the cranial region. This space contains loose connective tissue, fat, and a network of internal vertebral veins. Deep to the dura lies the potential subdural space, which separates it from the middle meningeal layer, the arachnoid mater.
The spinal dura mater wraps around the spinal nerves as they exit the vertebral column through the intervertebral foramina, blending with the epineurium (the outer covering of the nerves). The dura’s fibrous nature allows it to be a relatively non-adherent layer, facilitating gliding movements between the protective sac and the surrounding bone during spinal flexion and extension.
Essential Protective Functions
The primary role of the spinal dura mater is to provide mechanical protection for the spinal cord, acting as a strong buffer against trauma and physical stresses. Its dense, inelastic composition offers a resilient barrier that prevents delicate neural tissue from sustaining injury during sudden movements or external impacts. The dura also anchors the spinal cord within the vertebral canal, limiting excessive internal movement that could damage the nerve roots and cord itself.
A second function is the containment of the cerebrospinal fluid (CSF) within the subarachnoid space. The dura mater effectively seals this fluid-filled compartment, maintaining the necessary pressure and volume of CSF that acts as a liquid cushion for the spinal cord. This hydrostatic cushion absorbs shock and supports the spinal cord, preventing it from resting directly on the hard interior surfaces of the vertebrae.
Clinical Relevance and Injury
The spinal dura mater is relevant in medical procedures accessing the central nervous system, such as a lumbar puncture or spinal anesthesia. A dural puncture occurs when a needle is intentionally passed through the dura mater into the subarachnoid space to administer medication or collect a CSF sample. The size and type of needle used during these procedures directly influence the likelihood of complications.
The most common complication is a Post-Dural Puncture Headache (PDPH), which occurs when the puncture site fails to seal, leading to persistent leakage of cerebrospinal fluid. This loss of CSF reduces fluid pressure, causing the brain to sag slightly when the patient is upright, stretching pain-sensitive structures. PDPH is characterized by a severe headache that worsens when standing or sitting and improves when lying down, usually starting within five days of the procedure.
If leakage is severe or persistent, an epidural blood patch may be performed, involving the injection of the patient’s own blood into the epidural space to clot and seal the dural tear. Chronic leakage issues, such as a Spinal Cord Dural Fistula (SCDF), require specialized surgical repair to restore normal fluid dynamics. Prevention of dural injury is a primary focus during neuraxial procedures, as smaller, pencil-point needles result in a lower risk of PDPH compared to larger, cutting-point needles.