This document provides an overview of the anatomy of the epidural space. It discusses the boundaries, contents, size, and structures that must be penetrated to access the epidural space. Key points include that the epidural space lies between the spinal meninges and vertebral canal, contains connective tissue, fat, blood vessels and spinal nerves. It varies in size from 1-6mm depending on the spinal region. To access it requires penetrating the skin, ligaments and ligamentum flavum in the midline.

1. Anatomy of Epidural Space
Chairperson: Dr.Vinayak Jannu
Presenters: Dr.Niharika R & Dr. Karthavya S L

2. Epidural space or Peridural space or Extradural space is the
space that lies between the spinal meninges and the sides
of the vertebral canal.

3. History
 1885: Corning first performed epidural anesthesia with
cociane for pain relief in extremity but it was apparently
accidental.
 1895: Cathelin first used epidural in sacral region which is
now called caudal analgesia.
 1921: Fidel Pages first used epidural anaesthesia in his
surgical practice.
 Tuohy introduced the needle used in Epidural Anaesthesia
in 1945.
 1951: Crawford used epidural anesthesia for thoracic
surgery.

4.  The epidural space is the potential space between periosteum
lining the vertebral canal and the spinal dura mater.
 It extends from the foramen magnum to the sacral hiatus, and
surrounds the dura mater anteriorly, laterally, and posteriorly

5. Boundaries
 Cranially by foramen magnum.
 Caudally by sacrococcygeal ligament. (sacral hiatus)
 Anteriorly by posterior longitudinal ligament
 Laterally by vertebral pedicles & intervertebral foramina.
 Posteriorly by ligamentum flavum and the laminae.

6. Boundaries
 At foramen magnum the vertebral periosteum fuses with
the periosteal layer of the skull
This periosteal layer is the extracranial extension of the
endosteal layer of cranial dura,the spinal dura at the same
point fuses with the meningeal layer of cranial dura.
 The lower limit is the sacrococcygeal ligament.

7. Boundaries
 The space is more extensive and easily distensible
posteriorly while anteriorly the dura adheres closely to the
periosteum of vertebral bodies.
 Laterally the space accompany the spinal nerves through
the intervertebral foramina into the paravertebral tissue up
to the angle of ribs.

8. Contents
 Areolar connective tissue
 Fat
 Spinal nerve roots with their dural sleeves
 Blood vessels-spinal arteries and venous plexus (Batson’s
plexus)
 Lymphatics

9. Areolar connective tissue
 It is present in significant amounts ventrally forming
strong connections between duramater and anterior
longitudinal ligament in the vertebral canal.
 The existence of fibrous connections in the posterior
epidural space called as PLICA MEDIANA DORSALIS of
the duramater extending longitudinally in the midline
connecting the dura and ligamentum flavum is also noted.

10. PLICA MEDIANA DORSALIS
 This is in form of strands connecting flaval ligament to the
dura.
 It is present in the midline and these bands divide the
epidural space into right and left sides and narrow the
space.
 The connection is well developed in region of vertebral
arches.
 In some instances, it forms a complete membrane in a
dorsomedian sagittal plane.

11. Epidural Fat
 It is principally present in posterior and lateral space.
 It has effects on pharmacology of drugs injected
intrathecally.
 There is a linear relationship between opiod’s lipid
solubility and its terminal elimination halftime in the
epidural space.
 Increased lipid solubility leads to sequestration of drugs in
fat, thereby reducing bioavailability of drug.

13. Lymphatics
The lymphatics of the epidural space are concentrated in the
region of the dural roots where they remove foreign
materials including microorganisms from the
subarachnoid and epidural spaces.

14. Blood vessels
 The epidural arteries located in the lumbar region of the
vertebral column are branches of the ilio-lumbar arteries.
 These arteries are found in the lateral region of the space
and therefore not threatened by an advancing epidural
needle.

15. Blood vessels
 The internal vertebral venous plexus consists of four
interconnecting longitudinal vessels, two anterior and two
posterior.
 The external vertebral plexus (EVP) in contrast, lies
peripheral to the vertebrae and is made of the anterior and
posterior external vertebral plexuses.
 The EVP is situated anterior to the vertebral bodies and in
relation to the laminae, spinous processes,transverse
processes and articular processes respectively.

17. Blood vessels
 These veins communicate with the segmental veins of the neck,
the intercostal, azygos and lumbar veins. With the veins of bones
of the vertebral column, the internal and external vertebral
plexuses form Batson’s plexus.
 These veins are predominantly in the antero-lateral part of the
epidural space, and ultimately drain into the azygous system of
veins.
 As the whole system is valveless, increased intrathoracic or intra-
abdominal pressure (e.g. ascites, pregnancy) can lead to major
congestion and vessel enlargement within the spinal canal.

19. Size of epidural space
 The distance across the semi or half moon circular
epidural space varies.
 In the anterior region it is almost nonexistent while it can
be measured in posterior region, the average values are;
Cervical: 1mm-1.5mm
Upper thoracic: 2.5mm-3mm
Lower thoracic: 4mm-5mm
Lumbar: 5mm-6mm

20. How to reach?
To reach epidural space in midline these structures have to
be penetrated:
 Skin and subcutaneous tissues
 Supraspinous ligaments
 Interspinous ligaments
 Ligamentum flavum