Moving from the central to right lateral in the axial (horizontal) plane, location may be defined as central, right central, right subarticular, right foraminal, or right extraforaminal. The term “paracentral” is less precise than defining “right central” or “left central” but is useful in describing groups of discs that include both, or when speaking informally, when the side is not significant. For reporting of image observations of a specific disc, “right central” or “left central” should supersede the use of the term “paracentral.” The term “far lateral” is sometimes used synonymously with “extraforaminal.”
In the sagittal plane, location may be defined as discal, infrapedicular, suprapedicular, or pedicular. In the coronal plane, anterior, in relationship to the disc, means ventral to the midcoronal plane of the centrum.
Note: Some terms and definitions included in this glossary are not recommended as preferred terminology but are included to facilitate the interpretation of vernacular and, in some cases, improper use. Preferred definitions are listed first. Nonstandard definitions are placed in brackets and, by consensus of the organizational task forces, should not be used in the manner described. Some terms are also labeled as colloquial, with further designation as to whether they are considered nonpreferred or nonstandard.
Acute disc herniation: Disc herniation of a relatively recent occurrence. Note: Paradiscal inflammatory reaction and relatively bright signal of the disc material on T2-weighted images suggest relative acuteness. Such changes may persist for months, however. Thus, absent clinical correlation and/or serial studies, it is not possible to date precisely by imaging when a herniation occurred. An acutely herniated disc material may have brighter signal on T2-weighted MRI sequences than the disc from which the disc material originates.46,59,64,68 Note that a relatively acute herniation can be superimposed on a previously existing herniation. An acute disc herniation may regress spontaneously without specific treatment. See chronic disc herniation.
Aging disc: Disc demonstrating any of the various effects of aging on the disc. Loss of water content from the nucleus occurs before MRI changes, followed by the progression of MRI-manifested changes consistent with the progressive loss of water content and increase in collagen and aggregating proteoglycans. See Pfirrmann classification.
Annular fissure: Separations between annular fibers, separations of fibers from their vertebral body insertions, or separations of fibers that extend radially, transversely, or concentrically, involving 1 or many layers of the annular lamellae. Note that the terms “fissure” and “tear” have often been used synonymously in the past. The term “tear” is inappropriate for use in describing imaging findings and should not be used (tear: nonstandard). Neither term suggests injury or implies any knowledge of etiology, neither term implies any relationship to symptoms or that the disc is a likely pain generator, and neither term implies any need for treatment. Also, see annular gap, annular rupture, annular tear, concentric fissure, HIZ, radial fissure, transverse fissure.
Annular gap (nonstandard): Focal attenuation (CT) or signal (MRI) abnormality, often triangular in shape, in the posterior aspect of the disc, likely representing widening of a radially directed annular fissure, bilateral annular fissures with an avulsion of the intermediate annular fragment, or an avulsion of a focal zone of macerated annulus.
Annular rupture: Disruption of fibers of the annulus by a sudden violent injury. This is a clinical diagnosis; use of the term is inappropriate for a pure imaging description, which instead should focus on a detailed description of the findings. Ruptured annulus is not synonymous with “annular fissure” or “ruptured disc.”
Annular tear, torn annulus (nonstandard): See fissure of the annulus and rupture of annulus.
Anterior displacement: Displacement of disc tissues beyond the disc space into the anterior zone.
Anterior zone: Peridiscal zone that is anterior to the midcoronal plane of the vertebral body.
Anulus, annulus (abbreviated form of annulus fibrosus): Multilaminated fibrous tissue forming the periphery of each disc space, attaching, craniad and caudad, to endplate cartilage and a ring apophyseal bone, and blending centrally with the nucleus pulposus. Note: Either anulus or annulus is correct spelling. Nomina Anatomica uses both forms, whereas Terminologia Anatomica states “anulus fibrosus.”22 Fibrosus has no correct alternative spelling; fibrosis has a different meaning and is incorrect in this context.
Asymmetric bulge: Presence of more than 25% of the outer annulus beyond the perimeter of the adjacent vertebrae, more evident in one section of the periphery of the disc than in another but not sufficiently focal to be characterized as a protrusion. Note: Asymmetric disc bulging is a morphological observation that may have various causes and does not imply etiology or association with symptoms. See bulge.
Balloon disc (colloquial, nonstandard): Diffuse apparent enlargement of the disc in superior-inferior extent because of bowing of the vertebral endplates due to weakening of the bone as in severe osteoporosis.
Base (of displaced disc): The cross-sectional area of the disc material at the outer margin of the disc space of origin, where disc material beyond the disc space is continuous with disc material within the disc space. In the craniocaudal direction, the length of the base cannot exceed, by definition, the height of the intervertebral space. On axial imaging, base refers to the width at the outer margin of the disc space, of the origin of any disc material extending beyond the disc space.
Black disc (colloquial, nonstandard): See dark disc.
Bulging disc, bulge (noun [n]), bulge (verb [v])
- A disc in which the contour of the outer annulus extends, or appears to extend, in the horizontal (axial) plane beyond the edges of the disc space, usually greater than 25% (90°) of the circumference of the disc and usually less than 3 mm beyond the edges of the vertebral body apophysis.
- (Nonstandard) A disc in which the outer margin extends over a broad base beyond the edges of the disc space.
- (Nonstandard) Mild, diffuse, smooth displacement of disc.
- (Nonstandard) Any disc displacement at the discal level.
Note: Bulging is an observation of the contour of the outer disc and is not a specific diagnosis. Bulging has been variously ascribed to redundancy of the annulus, secondary to the loss of disc space height, ligamentous laxity, response to loading or angular motion, remodeling in response to adjacent pathology, unrecognized and atypical herniation, and illusion from volume averaging on CT axial images. Mild, symmetric, posterior disc bulging may be a normal finding at L5–S1. Bulging may or may not represent pathological change, physiological variant, or normalcy. Bulging is not a form of herniation; discs known to be herniated should be diagnosed as herniation or, when appropriate, as specific types of herniation. See herniated disc, protruded disc, and extruded disc.
Calcified disc: Calcification within the disc space, not inclusive of osteophytes at the periphery of the disc space.
Cavitation: Spaces, cysts, clefts, or cavities formed within the nucleus and inner annulus from disc degeneration. See vacuum disc.
Central zone: Zone within the vertebral canal between sagittal planes through the medial edges of each facet. Note: The center of the central zone is a sagittal plane through the center of the vertebral body. The zones to either side of the center plane are right central and left central, which are preferred terms when the side is known, as when reporting imaging results of a specific disc. When the side is unspecified, or grouped with both right and left represented, the term paracentral is appropriate.
Chronic disc herniation: A clinical distinction that a disc herniation is of long duration. There are no universally accepted definitions of the intervals that distinguish between acute, subacute, and chronic disc herniations. Serial MRIs revealing disc herniations that are unchanged in appearance over time may be characterized as chronic. Disc herniations associated with calcification or gas on CT may be suggested as being chronic. Even so, the presence of calcification or gas does not rule out an acutely herniated disc. Note that an acute disc herniation may be superimposed on a chronic disc herniation. MRI signal characteristics may, on rare occasion, allow differentiation of acute and chronic disc herniations.16,59,64 In such cases, acutely herniated disc material may appear brighter than the disc of origin on T2-weighted sequences.46,59,61 Also, see disc-osteophyte complex.
Claw osteophyte: Bony outgrowth arising very close to the disc margin, from the vertebral body apophysis, directed, with a sweeping configuration, toward the corresponding part of the vertebral body opposite the disc.
Collagenized disc or nucleus: A disc in which the mucopolysaccharide of the nucleus has been replaced by fibrous tissue.
Communicating disc, communication (n), communicate (v) (nonstandard): Communication refers to interruption in the periphery of the disc annulus, permitting free passage of fluid injected within the disc to the exterior of the disc, as may be observed during discography. Not synonymous with “uncontained.” See contained disc and uncontained disc.
Concentric fissure: Fissure of the annulus characterized by separation of annular fibers in a plane roughly parallel to the curve of the periphery of the disc, creating fluid-filled spaces between adjacent annular lamellae. See radial fissures, transverse fissures, HIZ.
Contained herniation, containment (n), contain (v)
- Displaced disc tissue existing wholly within an outer perimeter of uninterrupted outer annulus or posterior longitudinal ligament.
- (Nonstandard) A disc with its contents mostly, but not wholly, within annulus or capsule.
- (Nonstandard) A disc with displaced elements contained within any investiture of the vertebral canal.
A disc that is less than wholly contained by annulus, but under a distinct posterior longitudinal ligament, is contained. Designation as “contained” or “uncontained” defines the integrity of the ligamentous structures surrounding the disc, a distinction that is often but not always possible by advanced imaging. On CT and MRI scans, contained herniations typically have a smooth margin whereas uncontained herniations most often have irregular margins because the outer annulus and the posterior longitudinal ligament have been penetrated by the disc material.35,37 CT-discography also does not always allow one to distinguish whether the herniated components of a disc are contained but only whether there is communication between the disc space and the vertebral canal.
Continuity: Connection of displaced disc tissue by a bridge of disc tissue, however thin, to tissue within the disc of origin.
Dallas classification (of postdiscography imaging): Commonly used grading system for the degree of annular fissuring seen on CT scan of discs after discography. Dallas grade 0 is normal; grade 1, leakage of contrast into the inner one-third of the annulus; grade 2, leakage of contrast into the inner two-thirds of the annulus; grade 3, leakage through the entire thickness of the annulus; grade 4, contrast extends circumferentially; grade 5, contrast extravasates into the epidural space. See discogram, discography.
Dark disc (colloquial, nonstandard): Disc with nucleus showing decreased signal intensity on T2-weighted images (dark), usually because of desiccation of the nucleus secondary to degeneration. Also black disc (colloquial, nonstandard). See disc degeneration, Pfirrmann classification.
Degenerated disc, degeneration (n), degenerate (v)
- Changes in a disc characterized to varying degrees by 1 or more of the following: desiccation, cleft formation, fibrosis, and gaseous degradation of the nucleus; mucinous degradation, fissuring, and loss of integrity of the annulus; defects in and/or sclerosis of the endplates; and osteophytes at the vertebral apophyses.
- Imaging manifestation of such changes, including35 standard roentgenographical findings, such as disc space narrowing and peridiscal osteophytes, MRI disc findings (see Pfirrmann classification61), CT disc findings (see discogram/discography and Dallas classification42), and/or MRI findings of vertebral end plate and marrow reactive changes adjacent to a disc (see Modic classification38).
Degenerative disc disease (nonstandard term when used as an imaging description): A condition characterized by manifestations of disc degeneration and symptoms thought to be related to those of degenerative changes. Note: Causal connections between degenerative changes and symptoms are often difficult clinical distinctions. The term “degenerative disc disease” carries implications of illness that may not be appropriate if the only or primary indicators of illness are from imaging studies and thus this term should not be used when describing imaging findings. The preferred term for description of imaging manifestations is “degenerated disc” or “disc degeneration,” rather than “degenerative disc disease.”
Delamination: Separation of circumferential annular fibers along the planes parallel to the periphery of the disc, characterizing a concentric fissure of the annulus.
- Disc with reduced water content, usually primarily of nuclear tissues.
- Imaging manifestations of reduced water content of the disc, such as decreased (dark) signal intensity on T2-weighted images, or of apparent reduced water content, as from alterations in the concentration of hydrophilic glycosaminoglycans. Also, see dark disc (colloquial, nonstandard).
Disc (disk): Complex structure composed of nucleus pulposus, annulus fibrosus, cartilaginous endplates, and vertebral body ring apophyseal attachments of annulus. Note: Most English language publications use the spelling “disc” more often than “disk.”1,20,22,69,70Nomina Anatomica designates the structures as “disci intervertebrales” and Terminologia Anatomica as “discus intervertebralis/intervertebral disc.”22,70 See “disc level” for naming and numbering of a particular disc.
Disc height: The distance between the planes of the endplates of the vertebral bodies craniad and caudad to the disc. Disc height should be measured at the center of the disc and not at the periphery. If measured at the posterior or anterior margin of the disc on a sagittal image of the spine, this should be clearly specified as such.
Disc level: Level of the disc and vertebral canal between axial planes through the bony endplates of the vertebrae craniad and caudad to the disc being described.
- A particular disc is best named by naming the region of the spine and the vertebra above and below it; for example, the disc between the fourth and fifth lumbar vertebral bodies is named “lumbar 4–5,” commonly abbreviated as L4–L5, and the disc between the fifth lumbar vertebral body and the first sacral vertebral body is called “lumbosacral disc” or “L5–S1.” Common anomalies include patients with 6 lumbar vertebrae or transitional vertebrae at the lumbosacral junction that require, for clarity, narrative explanation of the naming of the discs.
- (Nonstandard) A disc is sometimes labeled by the vertebral body above it; for example, the disc between L4 and L5 may be labeled “the L4 disc.”
- Note: “A motion segment,” numbered in the same way, is a functional unit of the spine, comprising the vertebral body above and below, the disc, the facet joints, and the connecting soft tissues and is most often referenced with regard to the stability of the spine.
Disc of origin: Disc from which a displaced fragment originated. Synonym: parent disc. Note: Because displaced fragments often contain tissues other than nucleus, disc of origin is preferred to nucleus of origin. Parent disc is synonymous but more colloquial and nonpreferred.
Disc space: Space limited, craniad and caudad, by the endplates of the vertebrae and peripherally by the edges of the vertebral body ring apophyses, exclusive of osteophytes. Synonym: intervertebral disc space. See “disc level” for naming and numbering of discs.
Discogenic vertebral sclerosis: Increased bone density and calcification adjacent to the endplates of the vertebrae, craniad and caudad, to a degenerated disc, sometimes associated with intervertebral osteochondrosis. Manifested on MRI as Modic type III.
Discogram, discography: A diagnostic procedure in which contrast material is injected into the nucleus of the disc with radiographical guidance and observation, often followed by CT/discogram. The procedure is often accompanied by pressure measurements and assessment of pain response (provocative discography). The degree of annular fissuring identified by discography may be defined by the Dallas classification and its modifications. See Dallas classification.
Disc-osteophyte complex: Intervertebral disc displacement, whether bulge, protrusion, or extrusion, associated with calcific ridges or ossification. Sometimes called a hard disc or chronic disc herniation (nonpreferred). Distinction should be made between “spondylotic disc herniation,” or “calcified disc herniation” (nonpreferred), the remnants of an old disc herniation, and “spondylotic bulging disc,” a broad-based bony ridge presumably related to chronic bulging disc.
Displaced disc (nonstandard): A disc in which disc material is beyond the outer edges of the vertebral body ring apophyses (exclusive of osteophytes) of the craniad and caudad vertebrae or, as in the case of intravertebral herniation, has penetrated through the vertebral body endplate.
Note: “Displaced disc” is a general term that does not imply knowledge of the underlying pathology, cause, relationship to symptoms, or need for treatment. The term includes, but is not limited to, disc herniation and disc migration. See herniated disc, migrated disc.
Epidural membrane: See peridural membrane.
Extraforaminal zone: The peridiscal zone beyond the sagittal plane of the lateral edges of the pedicles, having no well-defined lateral border, but definitely posterior to the anterior zone. Synonym: “far lateral zone,” also “far-out zone” (nonstandard).
Extraligamentous: Posterior or lateral to the posterior longitudinal ligament. Note: Extraligamentous disc refers to displaced disc tissue that is located posterior or lateral to the posterior longitudinal ligament. If the disc has extruded through the posterior longitudinal ligament, it is sometimes called “transligamentous” or “perforated” and if through the peridural membrane, it is sometimes refined to “transmembranous.”
Extruded disc, extrusion (n), extrude (v): A herniated disc in which, in at least one plane, any one distance between the edges of the disc material beyond the disc space is greater than the distance between the edges of the base of the disc material beyond the disc space in the same plane or when no continuity exists between the disc material beyond the disc space and that within the disc space. Note: The preferred definition is consistent with the common image of extrusion, as an expulsion of material from a container through and beyond an aperture. Displacement beyond the outer annulus of the disc material with any distance between its edges greater than the distance between the edges of the base distinguishes extrusion from protrusion. Distinguishing extrusion from protrusion by imaging is best done by measuring the edges of the displaced material and the remaining continuity with the disc of origin, whereas relationship of the displaced portion to the aperture through which it has passed is more readily observed surgically. Characteristics of protrusion and extrusion may coexist, in which case the disc should be subcategorized as extruded. Extruded discs in which all continuity with the disc of origin is lost may be further characterized as “sequestrated.” Disc material displaced away from the site of extrusion may be characterized as “migrated.” See herniated disc, migrated disc, protruded disc.
Note: An alternative scheme is espoused by some respected radiologists who thought that it has better clinical application. This scheme defines extruded disc as synonymous with “uncontained disc” and does not use comparative measurements of the base versus the displaced material. Per this definition, a disc extrusion can be identified by the presence of a continuous line of low signal intensity surrounding the disc herniation. Future study will further determine the validity of this alternative definition. See contained disc.
Far lateral zone: The peridiscal zone beyond the sagittal plane of the lateral edge of the pedicle, having no well-defined lateral border, but definitely posterior to the anterior zone. Synonym: “extraforaminal zone.”
Fissure of annulus: See annular fissure.
Foraminal zone: The zone between planes passing through the medial and lateral edges of the pedicles. Note: The foraminal zone is sometimes called the “pedicle zone” (nonstandard), which can be confusing because pedicle zone might also refer to measurements in the sagittal plane between the upper and lower surfaces of a given pedicle that is properly called the “pedicle level.” The foraminal zone is also sometimes called the “lateral zone” (nonstandard), which can be confusing because the “lateral zone” can be confused with “lateral recess” (subarticular zone) and can also mean extraforaminal zone or an area including both the foraminal and extraforaminal zones.
- A fragment of disc that has separated from the disc of origin and has no continuous bridge of disc tissue with disc tissue within the disc of origin. Synonym: sequestrated disc.
- (Nonstandard) A fragment that is not contained within the outer perimeter of the annulus.
- (Nonstandard) A fragment that is not contained within the annulus, posterior longitudinal ligament, or peridural membrane.
Note: “Sequestrated disc” and “free fragment” are virtually synonymous. When referring to the condition of the disc, categorization as extruded with subcategorization as sequestrated is preferred, whereas when referring specifically to the fragment, free fragment is preferred.
Gap of annulus: See annular gap.
Hard disc (colloquial): Disc displacement in which the displaced portion has undergone calcification or ossification and may be intimately associated with apophyseal osteophytes. Note: The term “hard disc” is most often used in reference to the cervical spine to distinguish chronic hypertrophic and reactive changes at the periphery of the disc from the more acute extrusion of soft, predominantly nuclear tissue. See chronic disc herniation, disc-osteophyte complex.
Herniated disc, herniation (n), herniated (v): Localized or focal displacement of disc material beyond the normal margin of the intervertebral disc space. Note: “Localized” or “focal” means, by way of convention, less than 25% (90°) of the circumference of the disc.
Herniated disc material may include nucleus pulposus, cartilage, fragmented apophyseal bone, or annulus fibrosus tissue. The normal margins of the intervertebral disc space are defined, craniad and caudad, by the vertebral body endplates and peripherally by the edges of the vertebral body ring apophyses, exclusive of osteophytic formations. Herniated disc generally refers to displacement of disc tissues through a disruption in the annulus, the exception being intravertebral herniations (Schmorl nodes) in which the displacement is through the vertebral endplate. Herniated discs may be further subcategorized as protruded or extruded. Herniated disc is sometimes referred to as herniated nucleus pulposus, but the term “herniated disc” is preferred because displaced disc tissues often include cartilage, bone fragments, or annular tissues. The terms “prolapse” and “rupture” when referring to disc herniations are nonstandard and their use should be discontinued. Note: “Herniated disc” is a term that does not imply knowledge of the underlying pathology, cause, relationship to symptoms, or need for treatment.
Herniated nucleus pulposus (nonpreferred): See herniated disc.
High-intensity zone: Area of high intensity on T2-weighted MRIs of the disc, located commonly in the outer annulus. Note: HIZs within the posterior annular substance may indicate the presence of an annular fissure within the annulus, but these terms are not synonymous. An HIZ itself may represent the actual annular fissure or, alternatively, may represent vascularized fibrous tissue (granulation tissue) within the substance of the disc in an area adjacent to a fissure. The visualization of an HIZ does not imply a traumatic etiology or that the disc is a source of pain.
Infrapedicular level: The level between the axial planes of the inferior edges of the pedicles craniad to the disc in question and the inferior endplate of the vertebral body above the disc in question. Synonym: superior vertebral notch.
Internal disc disruption: Disorganization of structures within the disc. See intra-annular displacement.
Interspace: See disc space.
Intervertebral chondrosis: See intervertebral osteochondrosis.
Intervertebral disc: See disc.
Intervertebral disc space: See disc space.
Intervertebral osteochondrosis: Degenerative process of the disc and vertebral body endplates that is characterized by disc space narrowing, vacuum phenomenon, and vertebral body reactive changes. Synonym: osteochondrosis (nonstandard).
Intra-annular displacement: Displacement of central, predominantly nuclear, tissue to a more peripheral site within the disc space, usually into a fissure in the annulus. Synonym: intra-annular herniation (nonstandard), intradiscal herniation. Note: Intra-annular displacement is distinguished from disc herniation, that is, herniation of disc refers to displacement of disc tissues beyond the disc space. Intra-annular displacement is a form of internal disruption. When referring to intra-annular displacement, it is best not to use the term “herniation” to avoid confusion with disc herniation.
Intra-annular herniation (nonstandard): See intra-annular displacement.
Intradiscal herniation (nonstandard): See intra-annular displacement.
Intradural herniation: Disc material that has penetrated the dura so that it lies in an intradural extramedullary location.
Intravertebral herniation: A disc displacement in which a portion of the disc projects through the vertebral endplate into the centrum of the vertebral body. Synonym: Schmorl node.
Lateral recess: The portion of the subarticular zone that is medial to the medial border of the pedicle. It refers to the entire cephalad-caudad region that exists medial to the pedicle, where the same numbered thoracic or lumbar nerve root travels caudally before exiting the nerve root foramen under the caudal margin of the pedicle. It does not refer to the nerve root foramen itself. Also, see subarticular zone.
Lateral zone (nonstandard): See foraminal zone.
Leaking disc (nonstandard): See communicating disc.
Limbus vertebra: Separation of a segment of vertebral ring apophysis. Note: Limbus vertebra may be a developmental abnormality caused by failure of integration of the ossifying apophysis to the vertebral body; a chronic herniation (extrusion) of the disc into the vertebral body at the junction of the fusing apophyseal ring, with separation of a portion of the ring with bony displacement; or a fracture through the apophyseal ring associated with intrabody disc herniation. This occurs in children before the apophyseal ring fuses to the vertebral body. In adults, a limbus vertebra should not be confused with an acute fracture. A limbus vertebra does not imply that there has been an injury to the disc or the adjacent apophyseal endplate.
Marginal osteophyte: Osteophyte that protrudes from and beyond the outer perimeter of the vertebral endplate apophysis.
Marrow changes (of vertebral body): See Modic classification.
Migrated disc, migration (n), migrate (v)
- Herniated disc in which a portion of the extruded disc material is displaced away from the fissure in the outer annulus through which it has extruded in either the sagittal or axial plane.
- (Nonstandard) A herniated disc with a free fragment or sequestrum beyond the disc level.
Note: Migration refers to the position of the displaced disc material, rather than to its continuity with disc tissue within the disc of origin; therefore, it is not synonymous with sequestration.
Modic classification (types I, II, and III)30: A classification of degenerative changes involving the vertebral endplates and adjacent vertebral bodies associated with disc inflammation and degenerative disc disease, as seen on MRIs. Type I refers to decreased signal intensity on T1-weighted spin-echo images and increased signal intensity on T2-weighted images, representing penetration of the endplate by fibrovascular tissue, inflammatory changes, and perhaps edema. Type I changes may be chronic or acute. Type II refers to increased signal intensity on T1-weighted images and isointense or increased signal intensity on T2-weighted images, indicating replacement of normal bone marrow by fat. Type III refers to decreased signal intensity on both T1- and T2-weighted images, indicating reactive osteosclerosis. See discogenic vertebral sclerosis.
Motion segment: The functional unit of the spine. See disc level.
Nonmarginal osteophyte: An osteophyte that occurs at sites other than the vertebral endplate apophysis. See marginal osteophyte.
Normal disc: A fully and normally developed disc with no changes attributable to trauma, disease, degeneration, or aging. Note: Many congenital and developmental variations may be clinically normal, that is, they are not associated with symptoms, and certain adaptive changes in the disc may be normal considering adjacent pathology; however, classification and reporting for medical purposes are best served if such discs are not considered normal. Note, however, that a disc finding considered not normal does not necessarily imply a cause for clinical signs or symptomatology; the description of any variation of the disc is independent of clinical judgment regarding what is normal for a given patient.
Nucleus of origin (nonpreferred): The central, nuclear portion of the disc of reference, usually used to reference the disc from which the tissue has been displaced. Note: Because displaced fragments often contain tissues other than the nucleus, disc of origin is preferred to nucleus of origin. Synonym: disc of origin (preferred), parent nucleus (nonpreferred).
Osteochondrosis: See intervertebral osteochondrosis.
Osteophyte: Focal hypertrophy of the bone surface and/or ossification of the soft-tissue attachment to the bone.
Paracentral: In the right or left central zone of the vertebral canal. See central zone. Note: The terms “right central” and “left central” are preferable when speaking of a single site if the side can be specified, as when reporting the findings of imaging procedures. “Paracentral” is appropriate if the side is not significant or when speaking of mixed sites.
Parent disc (nonpreferred): See disc of origin.
Parent nucleus (nonpreferred): See nucleus of origin, disc of origin.
Pedicular level: The space between the axial planes through the upper and lower edges of the pedicle. Note: The pedicular level may be further designated with reference to the disc in question as “pedicular level above” or “pedicular level below” the disc in question.
Perforated (nonstandard): See transligamentous.
Peridural membrane: A delicate, translucent membrane that attaches to the undersurface of the deep layer of the posterior longitudinal ligament and extends laterally and posteriorly, encircling the bony spinal canal outside the dura. The veins of Batson plexus lie on the dorsal surface of the peridural membrane and pierce it ventrally. Synonym: lateral membrane, epidural membrane.
Pfirrmann classification: A grading system for the severity of degenerative changes within the nucleus of the intervertebral disc. A Pfirrmann grade I disc has a uniform high signal intensity in the nucleus on T2-weighted MRI scans; grade II shows a central horizontal line of low signal intensity on sagittal images; grade III shows high signal intensity in the central part of the nucleus, with lower intensity in the peripheral regions of the nucleus; grade IV shows low signal intensity centrally and blurring of the distinction between the nucleus and the annulus; and grade V shows homogeneous low signal intensity, with no distinction between the nucleus and the annulus.61
Prolapsed disc, prolapse (n, v) (nonstandard): The term is variously used to refer to herniated discs. Its use is not standardized and the term does not add to the precision of disc description, so it is regarded as nonstandard in deference to “protrusion” or “extrusion.”
Protruded disc, protrusion (n), protrude (v)
- One of the 2 subcategories of a “herniated disc” (the other being an “extruded disc”) in which disc tissue extends beyond the margin of the disc space, involving less than 25% of the circumference of the disc margin as viewed in the axial plane. The test of protrusion is that there must be localized (<25% of the circumference of the disc) displacement of disc tissue and the distance between the corresponding edges of the displaced portion must not be greater than the distance between the edges of the base of the displaced disc material at the disc space of origin. See base of displaced disc. Although sometimes used as a general term in the way herniation is defined, the use of the term “protrusion” is best reserved for subcategorization of herniation meeting the aforementioned criteria.
- (Nonstandard) Any or unspecified type of disc herniation.
Radial fissure: Disruption of annular fibers extending from the nucleus outward toward the periphery of the annulus, usually in the craniocaudal (vertical) plane, although, at times, with axial horizontal (transverse) components. “Fissure” is the preferred term to the nonstandard term “tear.” Neither term implies knowledge of injury or other etiology. Note: Occasionally, a radial fissure extends in the transverse plane to include an avulsion of the outer layers of the annulus from the apophyseal ring. See concentric fissures, transverse fissures.
Rim lesion (nonstandard): See limbus vertebra.
Rupture of annulus, ruptured annulus: See annular rupture.
Ruptured disc, rupture (nonstandard): A herniated disc. The term “ruptured disc” is an improper synonym for herniated disc, not to be confused with violent disruption of the annulus related to injury. Its use should be discontinued.
Schmorl node: See intravertebral herniation.
Sequestrated disc, sequestration (n), sequestrate (v) (variant: sequestered disc): An extruded disc in which a portion of the disc tissue is displaced beyond the outer annulus and maintains no connection by disc tissue with the disc of origin. Note: An extruded disc may be subcategorized as “sequestrated” if no disc tissue bridges the displaced portion and the tissues of the disc of origin. If even a tenuous connection by disc tissue remains between a displaced fragment and disc of origin, the disc is not sequestrated. If a displaced fragment has no connection with the disc of origin, but is contained within peridural membrane or under a portion of posterior longitudinal ligament that is not intimately bound with the annulus of origin, the disc is considered sequestrated. Sequestrated and sequestered are used interchangeably. Note: “Sequestrated disc” and “free fragment” are virtually synonymous. See free fragment. When referring to the condition of the disc, categorization as extruded with subcategorization as sequestered is preferred, whereas when referring specifically to the fragment, free fragment is preferred. See sequestrum.
Sequestrum (nonpreferred): Refers to disc tissue that has displaced from the disc space of origin and lacks any continuity with disc material within the disc space of origin. Synonym: free fragment (preferred). See sequestrated disc. Note: “Sequestrum” (nonpreferred) refers to the isolated free fragment itself, whereas sequestrated disc defines the condition of the disc.
Spondylitis: Inflammatory disease of the spine, other than degenerative disease. Note: Spondylitis usually refers to noninfectious inflammatory spondyloarthropathies.
- Common nonspecific term used to describe effects generally ascribed to degenerative changes in the spine, particularly those involving hypertrophic changes to the apophyseal endplates and zygapophyseal joints.
- (Nonstandard) Spondylosis deformans, for which spondylosis is a shortened form.
Spondylosis deformans: Degenerative process of the spine involving the annulus fibrosus and vertebral body apophysis, characterized by anterior and lateral marginal osteophytes arising from the vertebral body apophyses, whereas the intervertebral disc height is normal or only slightly decreased. See degeneration, spondylosis.
Subarticular zone: The zone, within the vertebral canal, sagittally between the plane of the medial edges of the pedicles and the plane of the medial edges of the facets and coronally between the planes of the posterior surfaces of the vertebral bodies and the anterior surfaces of the superior facets. Note: The subarticular zone cannot be precisely delineated in 2-dimensional depictions because the structures that define the planes of the zone are irregular. The lateral recess is that portion of the subarticular zone defined by the medial wall of the pedicle where the same numbered nerve root traverses before turning under the inferior wall of the pedicle into the foramen.
Subligamentous: Beneath the posterior longitudinal ligament. Note: Although the distinction between outer annulus and posterior longitudinal ligament may not always be identifiable, subligamentous has meaning distinct from subannular when the distinction can be made. When the distinction cannot be made, subligamentous is appropriate. Subligamentous contrasts to extraligamentous, transligamentous, or perforated. See extraligamentous, transligamentous.
Submembranous: Enclosed within the peridural membrane. Note: With reference to the displaced disc material, characterization of a herniation as submembranous usually infers that the displaced portion is extruded beyond the annulus and posterior longitudinal ligament so that only the peridural membrane invests it.
Suprapedicular level: The level within the vertebral canal between the axial planes of the superior endplate of the vertebra caudad to the disc space in question and the superior margin of the pedicle of that vertebra. Synonym: inferior vertebral notch.
Syndesmophytes: Thin and vertically oriented bony outgrowths extending from one vertebral body to the next and representing ossification within the outer portion of the annulus fibrosus.
Tear of annulus, torn annulus (nonstandard): See annular tear.
Thompson classification: A 5-point grading scale of degenerative changes in the human intervertebral disc, from 0 (normal) to 5 (severe degeneration), based on gross pathological morphology of midsagittal sections of the lumbar spine.
Traction osteophytes: Bony outgrowth arising from the vertebral body apophysis, 2 to 3 mm above or below the edge of the intervertebral disc, projecting in a horizontal direction.
Transligamentous: Displacement, usually extrusion, of disc material through the posterior longitudinal ligament. Synonym: perforated (nonstandard). Also, see extraligamentous, transmembranous.
Transmembranous: Displacement of extruded disc material through the peridural membrane.
Transverse fissure: Fissure of the annulus in the axial (horizontal) plane. When referring to a large fissure in the axial plane, the term is synonymous with a horizontally oriented radial fissure. Often “transverse fissure” refers to a more limited, peripheral separation of annular fibers including attachments to the apophysis. These more narrowly defined peripheral fissures may contain gas visible on radiographs or CT scans and may represent early manifestations of spondylosis deformans. See annular fissure, concentric fissure, radial fissure.
Uncontained disc: Displaced disc material that is not contained by the outer annulus and/or posterior longitudinal ligament. See discussion under contained disc.
Vacuum disc: A disc with imaging findings characteristic of gas (predominantly nitrogen) in the disc space, usually a manifestation of disc degeneration.
Vertebral body marrow changes: Reactive vertebral body signal changes associated with disc inflammation and disc degeneration, as seen on MRIs. See Modic classification.
Vertebral notch (inferior): Incisura of the upper surface of the pedicle corresponding to the lower part of the foramen (suprapedicular level).
Vertebral notch (superior): Incisura of the under surface of the pedicle corresponding to the upper part of the foramen (infrapedicular level).
- This revision of the 2001 “Nomenclature and Classification of Lumbar Disc Pathology” is a product of task forces of the NASS, the ASSR, and the ASNR and updates a workable standard terminology for clinicians, radiologists, and researchers.
- This article provides a simple diagnostic classification of lumbar disc pathology, which can be expanded into more precise subcategories.
- The definitions in the glossary are based on the anatomy and pathology of the lumbar disc, primarily as visualized on imaging studies.
The authors thank Andrea Gasten, MSc, Ms. Katherine Huffman, and Donna Lahey, RNFA, for their expertise and contributions in preparation of the manuscript. They also extend their gratitude to Chadi Tannoury, MD, for creating the original artwork for the figures in this publication.
“Supplementary appendix relating to this article, listing individuals who reviewed and contributed to this paper, can be found at http://links.lww.com/BRS/A906.
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annular fissure; annular tear; disc bulge (bulging disc); disc degeneration; disc extrusion; disc herniation; disc nomenclature; disc protrusion; high-intensity zone; lumbar intervertebral disc
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