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Spinal epidural space

The spinal epidural space is the anatomic space between the dura mater and the walls of the vertebral canal. It extends from the foramen magnum superiorly to the sacral hiatus inferiorly. It is filled with fat, connective tissue, and a venous plexus, serving as a cushioning layer for the spinal cord and providing a route for the spread of anesthesia and pathological processes.

The epidural space is of major clinical importance in anesthesia (epidural block), pain management, and in diagnosing or treating conditions such as epidural hematoma, abscess, or tumors.

Synonyms

  • Epidural space

  • Extradural space

  • Peridural space

Location and Boundaries

  • Anterior boundary: Posterior longitudinal ligament and vertebral bodies/discs

  • Posterior boundary: Ligamentum flavum and vertebral laminae

  • Lateral boundary: Pedicles and intervertebral foramina (where nerves exit)

  • Superior limit: Foramen magnum, where dura fuses with periosteum

  • Inferior limit: Sacral hiatus

Contents

  • Epidural fat (loose areolar and adipose tissue)

  • Internal vertebral venous plexus (Batson’s plexus)

  • Spinal nerve roots and their dural sheaths as they exit foramina

  • Lymphatics and connective tissue

Relations

  • Lies external to the dura mater (subdural space is internal to dura)

  • Continuous with paravertebral fat and venous plexus through intervertebral foramina

  • Closely related to spinal cord and meninges within the vertebral canal

Function

  • Provides cushioning and protection for the spinal cord

  • Accommodates venous drainage via epidural venous plexus

  • Facilitates spread of injected anesthetic agents during epidural block

  • Serves as a potential space for pathological collections (blood, pus, tumor cells)

Clinical Significance

  • Epidural anesthesia: Commonly used for labor and surgical procedures

  • Epidural hematoma: Hemorrhage into epidural space may compress spinal cord, causing neurological deficits

  • Epidural abscess: Infection may spread here, leading to pain, fever, and spinal cord compression

  • Tumor spread: Metastatic disease may infiltrate epidural fat and venous plexus

  • Imaging relevance: Key in evaluating back pain, infection, trauma, or suspected cord compression

MRI Appearance

T1-weighted images:

  • Epidural fat appears bright

  • Dura appears as a thin dark line separating epidural space from CSF

  • Hematomas appear variable: often iso- to hyperintense in subacute stages

T2-weighted images:

  • Epidural fat shows  bright signal

  • Fluid collections (hematoma, abscess) appear bright

  • Dura remains a thin dark line

STIR (Short Tau Inversion Recovery):

  • Fat signal is suppressed (dark)

  • Pathological collections (fluid, edema, infection) appear bright hyperintense

  • Enhances visibility of abscess or hematoma against suppressed fat

T1 Fat-Sat Post-Contrast:

  • Normal epidural fat suppressed (dark)

  • Epidural abscess or tumor shows enhancing soft tissue

  • Rim enhancement may be seen around abscess collections

3D T2 SPACE / CISS:

  • Epidural space is outlined by intermediate to mildly hyperintense fat signal relative to muscle

  • CSF appears very bright, dura as thin dark line

  • Excellent contrast for detecting small compressive lesions or nerve root involvement

CT Appearance

Non-Contrast CT:

  • Epidural fat appears as low attenuation (dark)

  • Hematoma appears as hyperdense mass compressing thecal sac

  • Abscess appears as soft tissue density displacing fat

Post-Contrast CT:

  • Epidural fat remains low attenuation

  • Abscess shows rim enhancement

  • Tumors show enhancing soft tissue replacing epidural fat

  • Venous plexus may enhance, appearing as small vascular channels

MRI image

Spinal epidural space MRI axial anatomy image-img-00000-00000

MRI image

Spinal epidural space MRI sagittal anatomy image-img-00000-00000