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Intervertebral Disc Extrusion, Foraminal


KEY FACTS

Terminology

  • Extruded disc material within neural foramen

  • Far lateral is disc material lateral to neural foramen

Imaging

  • Obliterated perineural fat in neural foramen on sagittal images

  • Soft tissue mass contiguous with parent disc

  • T1WI isointense to parent disc

  • T2WI iso-, hypo-, or hyperintense to parent disc

  • May enhance peripherally

  • Often missed on myelography

Top Differential Diagnoses

  • Schwannoma

  • Spinal nerve root diverticulum

  • Large facet osteophyte

Clinical Issues

  • 5-10% of all disc herniations

  • Severe radicular pain

    • Mass effect on exiting nerve root in narrow confines of neural foramen

    • More symptomatic compared with central disc herniations

    • Lumbar: 25% sciatic and 75% femoral distribution

  • Lateral bending, sitting, and increased intraabdominal pressure worsen pain

  • Pain relieved by rest with hip and knee in flexion

  • May stabilize or resolve spontaneously

  • Surgery

    • Failed conservative therapy after 6-8 weeks; progressive deficits

    • Interlaminal approach with partial medial facetectomy

    • Endoscopic lateral approaches more commonly used, but no change in outcome relative to open procedures

Axial T1WI MR shows large right lateral and intraforaminal disc herniation
at L4-L5. The disc herniation involves the lateral aspect of the neural foramen.

Axial T2WI MR in the same patient shows that the large right lateral and intraforaminal disc herniation
is almost isointense in signal to the adjacent paravertebral soft tissue. There is slight lateral displacement of the psoas muscle
(compared with the opposite side
).

Sagittal T2WI through a normal lower lumbosacral spine shows the “keyhole-shaped” neural foramina
at L3-4 and L4-5. Bright fat
surrounds the dorsal root ganglia (DRG)
and fills the neural foramina. Note that the exiting DRGs lie slightly above the level of the intervertebral discs
. The L5 nerve root
is seen exiting the L5-S1 neural foramen.

Sagittal T2WI shows an L4-5 foraminal/far lateral disc herniation
filling the neural foramen. Contrast with the normal “keyhole-shaped” L3-4 neural foramen above
.

TERMINOLOGY

Synonyms

  • Lateral/far lateral herniation

  • Nonstandard: Lateral or foraminal herniated nucleus pulposus (HNP)

Definitions

  • Extruded disc material within neural foramen

  • Far lateral is disc material lateral to neural foramen

IMAGING

General Features

  • Best diagnostic clue

    • Obscured perineural fat in neural foramen on sagittal images

      • –

        Soft tissue mass contiguous with parent intervertebral disc

  • Location

    • Lumbar: L3-L4 and L4-L5 most common

    • Cervical: C5-C6 and C6-C7 most common

    • Thoracic: Rare

      • –

        Herniation: 3 in 1,000 incidence

  • Size

    • Restricted by neural foramen

  • Morphology

    • Typical “mushroom” appearance of central or subarticular disc extrusion absent

      • –

        Conforms to neural foramen on sagittal images

Radiographic Findings

  • Radiography

    • Nonspecific degenerative changes

      • –

        Disc height loss, endplate sclerosis, facet arthropathy

      • –

        Disc material not directly visualized

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