Bulge vs. Herniation

Term	Definition	Notes
Bulging disc	>25% of circumference (>90°); usually <3 mm beyond apophysis	NOT a form of herniation; may be symmetric or asymmetric; causes include normal variant (especially L5–S1), degeneration, vertebral remodeling
Herniated disc	<25% (<90°) of circumference	Preferred term; avoid: HNP, ruptured disc, prolapsed disc

Herniation Subtypes

Subtype	Definition
Protrusion	Base wider than any dimension of the displaced portion (base > cap in all planes)
Extrusion	Displaced disc wider than its base in at least one plane, OR no continuity with disc of origin (cap ≥ base in any plane)
Sequestration	Subtype of extrusion; displaced material completely lost continuity with parent disc — use "free fragment" for the isolated piece
Migration	Extruded disc material displaced away from the extrusion site — NOT synonymous with sequestration
Intravertebral herniation	Disc herniates through vertebral end plate into vertebral body — synonym: Schmorl node

Contained vs. Uncontained

Term	Definition	MRI Appearance
Contained	Displaced disc wholly within intact outer annulus and/or PLL	Smooth posterior disc margin
Uncontained	No intact annular or PLL covering	Irregular posterior disc margin

Annular Fissures

Preferred term is annular fissure — avoid "annular tear" or "torn annulus."

Type	Description
Radial	Extends from nucleus outward toward periphery; most clinically relevant — may allow nuclear material to track outward
Concentric	Separation of annular fibers parallel to disc periphery (delamination)
Transverse	Horizontally oriented; peripheral separation from apophyseal bone; gas on XR/CT = early spondylosis deformans
HIZ (High Intensity Zone)	T2-bright focus in outer annulus; represents fluid/granulation tissue in a fissure; does NOT imply trauma or that the disc is painful

Anatomic Zones — Axial Plane

Zone	Location	Nerve Root Affected
Central canal	Between sagittal planes through medial edges of each facet; use "right/left central" when side known, "paracentral" when unspecified	Thecal sac / descending roots
Subarticular (lateral recess)	Between medial edge of pedicle and medial edge of facet	Traversing nerve root; lateral recess stenosis affects this root
Foraminal	Between medial and lateral edges of the pedicles	Exiting nerve root (e.g., L4 root at L4–5)
Extraforaminal	Beyond lateral edge of pedicle	Exiting root at same level; far lateral herniations

Canal and Foraminal Compromise Grading

Grade	Canal / Foraminal Involvement
Mild	<1/3 of canal or foramen
Moderate	1/3 to 2/3 of canal or foramen
Severe	>2/3 of canal or foramen

Same grading applied for foraminal involvement.

Modic Classification — Vertebral End Plate Changes

Type	T1 Signal	T2 Signal	Pathology
Type I	↓	↑	Fibrovascular tissue; active inflammation/edema; may mimic infection
Type II	↑	Iso or ↑	Fatty marrow replacement; stable/chronic; most common
Type III	↓	↓	Reactive osteosclerosis; least common

Pfirrmann Classification — Disc Degeneration (T2 MRI)

Grade	Signal	Nucleus/Annulus Distinction	Disc Height
I	Uniform high signal	Clear	Normal
II	High signal with central horizontal low signal line	Clear	Normal
III	Intermediate signal	Unclear	Normal or slightly reduced
IV	Low signal	Lost	Normal to moderately reduced
V	Homogeneous low signal	None	Collapsed

Preferred vs. Nonstandard Terms

Preferred	Avoid
Herniated disc	HNP, ruptured disc, prolapsed disc
Annular fissure	Annular tear, torn annulus
Free fragment	Sequestrum (for the isolated piece)
Degenerative disc	Degenerative disc disease (DDD)
L4–L5 disc	"L4 disc" (nonstandard level naming)

Imaging findings describe morphology only and do not establish causation of symptoms or indicate need for treatment. HIZ does not imply trauma. Modic Type I changes can mimic discitis-osteomyelitis — clinical correlation is required.

Reference

Fardon DF, Williams AL, et al. Lumbar disc nomenclature: version 2.0. Spine J. 2014;14(11):2525–2545. Endorsed by NASS, ASSR, ASNR.

Lumbar Disc Nomenclature — Fardon 2014