Spine update lumbar foraminal stenosis

Spine 2000;25:389–394

Title: Spine Update, Lumbar Foraminal Stenosis

1. Introduction

About Lateral nerve root canal

             >> Tubular-Shaped Region

             >> Passing Nerve Root from thecal sac to intervertebral foramen

Previous definitions of Foramen

1) Lee et al (19): 3 distinct areas in figure 1A

             >> Entrance or Lateral recess zone

             >> Midzone

             >> Exit zone

2) Crock (6): Single sagittal slice or "window" in figure 1B

3) Current: Vertical interpedicular zone incorporating portions of lateral recess and exit zone (19) in figure 1C

Figure 1

>> A: Diagram of lumbar spine, depicting region of the lateral nerve root canal

>> B: Depicting the foramen or "window"

>> C: Depicting the intervertebral foramen or vertical interpedicular zone

What is the Lateral spinal canal stenosis?

             >> common etiology of lumbar radicular symptomatology

             >> 8~11% incidence of lateral root entrapment (18, 26, 31)

             >> sometimes, associated with failed back surgery syndrome (3, 22)

Why did the authors do this research?

       >> to review anatomy, clinical presentation, neuroradiographic evaluation, treatment of pathology located in the intervertebral foramen

2. Anatomy

Foramen

>> oval, round, or inverted teardrop-shaped "window" in lumbar spine

>> different aspects between upper lumbar spine and lower lumbar spine

Dorsal Root Ganglion (DRG) in foramen

>> associated with symptomatology

>> potential mediator of low back pain

>> exiting nerve root compression in foramen -- radicular symptoms

3. Pathoanatomy

Why does the foraminal stenosis develop? (Incidence)

1) related to the process of lumbar spondylosis

             *normal Foraminal height: 20~23 mm

             *normal width of superior foramen: 8~10 mm, 40~160 ㎟

             *references: 8, 30

>> compressed nerve root: 15mm (FH) or less, 4 mm (posterior DH) or less

             ┗might be indicators of foraminal stenosis

>> subluxation of superior facet ▶ alteration of biomechanical forces ▶ development of hypertrophic ligamentum flavum and bony spurs ▶ diminishing foramen volume

2) cranio-caudal compression (vertical stenosis)

>> posterolateral osteophytes from vertebral endplates

  >> protrude into foramen along with laterally bulging anulus fibrosis or herniated disc

    >> compress nerve root against the superior pedicle

3) according to the positions (13)

>> 21% in neutral position

>> 15.4% in flexion position

>> 33.3% in extended position

4) according to the parts of lumbar spine (1)

>> 75% in 5th lumbar root

>> 15% in 4th lumbar root

>> 5.3% in 3rd lumbar root

>> 4.0% in 2nd lumbar root

4. Imaging studies

>> Plain radiographic lateral view: depict intervertebral foramen

       * caution for misleading because of oblique direction of foramen in lumbar spine

>> Myelography: documentation of central canal stenosis

>> CT and MRI: evaluating and quantifying the degree of foraminal stenosis

       1) CT: detection of bony encroachment of the zone

              *better detection of the space available for nerve root in parasagittal image

       2) MRI: Central and lateral spinal canal pathology

        *better detection of foramina along the length of lumbar spine in parasagittal image

5. Treatment

   1) conservative treatment

   2) Epidural steroid injection/selective nerve root blocks

   3) Limited decompressive procedures

                   >> laminotomy or laminectomy

                   >> medial facetectomy

                   >> medial foraminotomy

                   >> muscle splitting Wiltse or lateral approach to foramen with foraminotomy

   4) Direct decompressive procedure alone: most patients with Foraminal stenosis

   5) Concomitant indirect foraminal "enlargement", fusion or both: subset of patients

                   >> in fusion: increasing the foramen size and maintaining or restoring lordosis

6. Summary

>> Although no pathognomonic clinical findings, High index of suspicion for any patients with exacerbation of leg pain from lumbar extension

>> Surgical considerations: location of compression of exiting nerve root/ presence of concomitant areas requiring decompression

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