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Spinal dura mater

The spinal dura mater is the tough outermost covering of the spinal cord, forming the protective sheath of the spinal meninges. It extends from the foramen magnum, where it is continuous with the cranial dura, down to the level of S2 vertebra, where it tapers to enclose the filum terminale externum. The spinal dura surrounds the spinal cord and cauda equina, forming the thecal sac.

It provides mechanical protection, contains the cerebrospinal fluid (CSF) within the subarachnoid space, and forms an outer boundary for the epidural space. The spinal dura is of great clinical importance in procedures such as lumbar puncture, spinal anesthesia, and in conditions such as meningitis, epidural abscess, and dural tears.

Synonyms

  • Dural sac

  • Thecal sac

  • Spinal meningeal dura

Origin, Course, and Extent

  • Origin: Continuation of the cranial dura mater at the foramen magnum

  • Course: Descends vertically within the vertebral canal, loosely attached to the vertebrae via epidural fat and venous plexus

  • Extent: Terminates at S2 vertebral level, where it merges with filum terminale externum and periosteum of the coccyx

Layers

  • Unlike cranial dura, the spinal dura consists of a single meningeal layer (no periosteal layer)

  • External surface separated from vertebrae by the epidural space filled with fat and venous plexus

  • Internal surface lined by arachnoid mater with subarachnoid space filled with CSF

Relations

  • Anteriorly: Posterior longitudinal ligament and vertebral bodies

  • Posteriorly: Ligamentum flavum and vertebral laminae

  • Laterally: Nerve root sleeves and intervertebral foramina

  • Superiorly: Continuous with cranial dura at foramen magnum

  • Inferiorly: Terminates at S2 level

Function

  • Provides strong protective covering for spinal cord, nerve roots, and cauda equina

  • Encloses and maintains the CSF-filled subarachnoid space

  • Forms a barrier against spread of infection or trauma

  • Serves as the structural boundary for epidural anesthesia and lumbar puncture

Clinical Significance

  • Lumbar puncture and anesthesia: Thecal sac is the target for CSF aspiration and spinal anesthesia

  • Dural tears/CSF leaks: Cause postural headaches and require repair

  • Meningitis: Infection involves dura and subarachnoid space

  • Spinal tumors or abscesses: May cause compression, displacement, or thickening of the dura

  • Dural ectasia: Seen in connective tissue disorders (e.g., Marfan, Ehlers-Danlos)

MRI Appearance

T1-weighted images:

  • Dura appears as a thin low-signal intensity line outlining the thecal sac

  • Surrounded externally by epidural fat (bright) and internally by CSF (dark)

T2-weighted images:

  • Dura remains as a low-signal intensity line against bright CSF

  • Thickening or enhancement may be seen in pathology (inflammation, tumor, fibrosis)

STIR (Short Tau Inversion Recovery):

  • Normal dura: low signal intensity

  • Inflamed or pathologic dura: may appear brighter, though STIR mainly highlights peridural edema/fat stranding

T1 Fat-Sat Post-Contrast:

  • Normal dura: enhances faintly and thinly, if at all

  • Pathological dura: intense or irregular enhancement (infective, inflammatory, neoplastic)

3D T2 SPACE / CISS:

  • Dura appears as a thin low-signal line with excellent contrast against very bright CSF

  • Provides exquisite visualization of dura, arachnoid space, and nerve roots

  • Useful for detecting dural tears, meningeal cysts, or arachnoid adhesions

CT Appearance

Non-Contrast CT:

  • Dura not directly visible; the thecal sac appears as soft tissue density

  • Calcification of dura may be seen as high-density linear foci

  • Epidural fat provides contrast around the thecal sac

Post-Contrast CT:

  • Normal dura shows minimal enhancement

  • Pathological dura may show thick, nodular, or linear enhancement (meningitis, carcinomatosis, metastasis)

  • Epidural abscess or hematoma can be seen as compressive collections displacing the dural sac

MRI image

Spinal dura mater MRI axial anatomy image-img-00000-00000

MRI image

Spinal dura mater MRI sagittal anatomy image-img-00000-00000