2 Applied and Radiological Anatomy of the Epidural Space for Spinal Endoscopy The epidural space forms an interface between the thecal sac and the bony canal. Most spine pathologies involve some alteration or distortion of this space. All spinal endoscopic interventions are either launched or conducted in this space. This space offers safe passage to endoscopic instruments. It is thus clear that precise knowledge of epidural anatomy is critical not only to understand spine pathology but also for the safe and efficient performance of spinal endoscopy. Magnetic resonance imagings (MRIs) are used to describe anatomy. In this chapter, MRI and computed tomography have been shown to correlate well with anatomical dissections.1 The epidural space can be divided into three compartments: the posterior epidural space, the lateral epidural space, and the anterior epidural space.2 • The posterior epidural space is a triangular space that is most spacious in the midsagittal interlaminar area ( • The ligamentum flavum (LF) courses from the ventral part of the superior edge of lamina to the top of the lamina below, and thus forms the posterior and posterolateral boundary of the epidural space ( • The posterior epidural space is filled with fat globules that form a semifluid cushion for the thecal sac and provide elasticity for spinal motion ( • Laterally, the space becomes obscured (potential space) as the dura mater approaches the LF ( • The anterior boundary of the posterior epidural space is formed by the dura mater, which is at its thickest point in this area ( • The posterior epidural space is very commonly accessed for epidural analgesia as well as for therapeutic interventions such as an epidural steroid injection ( • LF hypertrophy is a common cause of lumbar spinal stenosis. Endoscopic laminectomy and flavectomy require intricate knowledge of the posterior epidural space. • The lateral epidural space lies in the region of the intervertebral foramen, freely communicating with the posterior and the anterior epidural space ( • The dura mater forms the medial boundary of the epidural space ( • The dura mater is in close proximity to the pedicles, and hence the lateral epidural space above and below the intervertebral foramen is restricted (potential space; Fig. 2.1 Lateral view: The area of the epidural space (midsagittal) and the dural sac (midsagittal) is drawn, as these represent the most posterior boundaries. Given the circular nature of the epidural space, these structures will be more anterior as the sagittal plane moves laterally. The posterior epidural space is compartmentalized, as the dura mater is in close proximity to the canal at the superior edge of the lamina. The large space is visible only in the midline and is obscured paracentrally as the dura mater and the LF come together. The dura mater is adherent at the disk level, and the anterior epidural space is seen between the disks. It is much less prominent than the anterior epidural space and joins to the lateral epidural space. Note that inferiorly the thecal sac becomes smaller and more posteriorly oriented. • The lateral margin of the foramen is unrestricted and is formed by the fascia and the psoas muscle. By convention, the epidural space ends at the narrowest part of the foramen, usually midforamen. • The contents of the lateral epidural space include the sensory and motor root, the dorsal root ganglia (DRG), venous and arterial blood vessels, and fat. • The DRG is extradural, usually lying below the pedicle above the level of the disk.3 • Understanding the anatomy of the lateral epidural space is critical for spine endoscopy. • Lateral epidural space is traversed during discography and intradiskal procedures. • The neural foramen is the site for docking instruments and carrying out extradiscal interventions, such as removal of sequestrated disk, foraminoplasty, and lateral recess decompression. • Epiduroscopy may be carried out by the transforaminal approach. • The posterior longitudinal ligament (PLL) is adherent to the dura mater and the disk annulus ( • Above and below the disk, the PLL is in close proximity to the dura mater and reflects away from the vertebral body, creating the epidural space ( • This potential space is seen mostly below L4–L5, as the thecal sac tends to translate posteriorly.1 • The fascial membrane extending laterally from the PLL isolates the anterior epidural space from the rest of the epidural space and also contains disk displacement. • The anterior epidural space is a neurovascular space containing basivertebral veins and nerves.1 • It also harbors several pain generators including the PLL and the sensitized annulus. • This is a common site for disk herniation. • Intricate knowledge of anatomy is a must when accessing this area for the removal of herniated disk. • The anatomy of the caudal space is important to understand, as this is a common method of accessing the epidural space. • Below L5, the dural sac is located more medially and posteriorly. It progressively becomes smaller as it descends inferiorly.
2.1 Introduction
2.2 Compartments of the Epidural Space
2.2.1 Posterior Epidural Space
Fig. 2.1, 
Fig. 2.2, 
Fig. 2.3). It is restricted superiorly and inferiorly by the proximity of the dura mater to the superior edge of the lamina (
Fig. 2.1, 
Fig. 2.2, 
Fig. 2.4).
Fig. 2.2, 
Fig. 2.3). The two LFs meet and generally fuse in the midline.
Fig. 2.2, 
Fig. 2.3).
Fig. 2.2, 
Fig. 2.3) and then becomes the lateral epidural space.
Fig. 2.3).
Relevance of Posterior Epidural Space to Spine Pathology and Spine Endoscopy
Fig. 2.5).
2.2.2 Lateral Epidural Space
Fig. 2.2, 
Fig. 2.4, 
Fig. 2.6).
Fig. 2.7). It also forms the dural nerve sheath for the exiting nerve root. The dural sleeve lies within the medial half of the foramen (
Fig. 2.4, 
Fig. 2.8).
Fig. 2.2, 
Fig. 2.4, 
Fig. 2.8).
Relevance of Lateral Epidural Space to Spine Pathology and Spine Endoscopy
2.2.3 Anterior Epidural Space
Fig. 2.3, 
Fig. 2.9).
Fig. 2.1, 
Fig. 2.2).
Relevance of Anterior Epidural Space to Spine Pathology and Spine Endoscopy
2.2.4 Caudal Epidural Space
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