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Spine

Disc Nomenclature: Say What the Surgeon Hears

Fellowship-level neuroradiology teaching by E. Brooke Schrickel, MD. Open this topic in the interactive reading room →

Watch · concise explainerVisual summary

Core clinical idea

Nomenclature exists so your report means the same thing to the surgeon as to you, and so you don't over-call. Two jobs: use consensus terms by measurement (bulge is not a herniation; protrusion vs extrusion is a neck-vs-dome measurement) and state location precisely, because location predicts which root is hit.

Bottom line

Use the consensus terms by measurement and state location-to-root — don't upgrade a bulge and don't blame ubiquitous degeneration for pain.

Core workstation questions

  • Is this a bulge (don't call it a herniation) or a true focal herniation?
  • Protrusion or extrusion — is the dome wider than the neck in any plane? Is there a detached (sequestered) fragment?
  • What's the axial location, and therefore which root — traversing (central/subarticular) or exiting (foraminal/far lateral)?
  • In the neck: is the central lesion soft disc (bright on GRE) or osteophyte (dark, CT correlate)?
  • Am I implying pain causation from degeneration that's probably incidental?

What changes reporting / management

  • Herniation = localized displacement beyond the disc space and includes protrusion and extrusion but NOT bulge; do not upgrade a bulge.
  • Protrusion = base wider than the displaced dome; extrusion = displaced portion wider than its neck in any plane; sequestration = detached fragment (say so, it changes surgical planning).
  • State axial location AND expected root: central/subarticular hits the traversing root; foraminal/extraforaminal hits the exiting root at that level.
  • Spondylosis deformans = annular aging (anterior/lateral osteophytes, height preserved); intervertebral osteochondrosis = nucleus/endplate process (disc narrowing hallmark, posterior osteophytes pathologic) — 'pathologic' does not mean symptomatic.
  • Don't report a high-intensity zone as proof of discogenic pain; provocation discography is a controversial, technique-dependent reference standard.
  • Cervical: distinguish soft disc (bright on GRE/T2*) from osteophyte (dark, CT correlate); reserve 'disc-osteophyte complex' for indeterminate central-canal lesions and never use it in the lumbar spine.

Practical traps

  • Calling a broad-based bulge a herniation/protrusion (inflates the report).
  • Calling an extrusion a 'protrusion' and underselling a fragment the surgeon must plan for.
  • Implying ubiquitous degenerative change is the pain source despite poor specificity.
  • Applying the lumbar internal-disc-disruption pain model to cervical discs, where uncovertebral fissuring is normal with age.

Teaching pearls

  • Bulge is not a herniation — don't upgrade it.
  • Protrusion vs extrusion is a neck-vs-dome measurement, not an impression.
  • Central/subarticular hits the traversing root; foraminal/far-lateral hits the exiting root — say which.
  • 'Pathologic' degeneration isn't 'symptomatic' — degeneration is nearly universal and poorly specific for pain.
  • Soft disc lights up on GRE/T2*; an osteophyte stays dark and matches CT.

Teaching visuals

Lumbar disc herniation zones · where the disc goes decides which rootAxial · medial→lateral: central → subarticular → foraminal → extraforaminalanterior (disc)posterior1234medial → lateralZONE → ROOTmedial to lateral1Centralthecal sac — traversingroot(s)2Subarticularlateral recess — TRAVERSINGroot3Foraminalin the foramen — EXITING root4Extraforaminalfar-lateral — EXITING rootMedial 2 → traversing. Lateral 2 → exiting.The clinical hingeName the zone, name the root. SUBARTICULAR (lateral-recess) herniation — the commonest — hits the TRAVERSING root: anL4–L5 disc here takes out the L5 root (descending to exit at L5–S1). FORAMINAL / EXTRAFORAMINAL herniation hits theEXITING root: an L4–L5 foraminal disc takes out the L4 root instead.Caveat: “lateral recess” is a LUMBAR-canal concept only. There is no cervical lateral recess — in the cervical spinethe analogous compression is at the foramen / uncovertebral region, not a recess.
Disc Nomenclature & Why the Cervical Spine Has No Lateral Recess

Source lectures

  • Intervertebral Disc Nomenclature

Educational material for radiology residents and neuroradiology fellows. Nothing here drives individual patient care, and it contains no patient data.