American Journal of Neuroradiology 26:2430-2431, October 2005
© 2005 American Society of Neuroradiology
Letter
Reporting Terminology for Lumbar Disk Herniations: Axial Segmentation of the Preneural Foraminal Portion of the Lumbar Nerve Roots
Departments of Radiology and Neurosurgery
Rassoul Akram University Hospital
Tehran, Iran
Through the past decades, many attempts have been made to standardize lumbar disk herniation–related terminology (1, 2). Two different, and not necessarily parallel, sets of characteristics of a herniated disk (HD) are taken into account in the reporting of cross-sectional images of the lumbar spine. First, is the absolute attributes of the HD (ie, morphology, location, volume, etc), and second is the relationship of the HD to its neighboring neural structures. The absolute attributes of a HD are only one set of factors that determine the pattern and degree of compromise of the neighboring neural structures. The morphology and cross-sectional areas of the involved lumbar vertebral and neural foraminae, along with the degree of the epidural fat, are the other determining factors.
Although standardized nomenclature has been proposed for the absolute attributes of a HD, descriptive terminology is used for the elaboration of the relationship of a HD to its neighboring neural structures. Terms such as "abuts," "impinges," "flattens," "indents," "compresses," "displaces," and "distorts" are useful in the description of the effects of a HD on the adjacent thecal sac (TS) and intracanalicular dural nerve root sleeves (DNRSs). The effects of a HD on specific intracanalicular nerve roots may at times also be ascertained by using high-resolution axial T2-weighted sequences of the lumbar spine. In particular, compromise (or maximal degree of compromise) of a lumbar nerve root (LNR) at a level just proximal to its respective neural foraminal exit could be pinpointed to a specific segment of the nerve.
In this context, a 3-tiered descriptive division of the preneural foraminal portion of a LNR, into the lateral thecal sac, junctional, and dural root sleeve segments (Figs 1 and 2) may be of value. This partitioning is particularly suitable at the lower lumbar levels that demonstrate a distinguishable lateral recess and parallels the compartmentalization of the preneural foraminal portion of dural coverings of the LNRs.
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The intracanalicular portions of the LNRs demonstrate an intradural topography (the LNRs pierce the dura at the level of their respective neural foraminae) (3), either within the TS (Fig 1A) or in a DNRS (Fig 1C). These sleeves are pinched off from the ventrolateral angles of the TS. This TS-DNRS transition may be evident as "waisting" (Fig 2A) of the ventrolateral angles of the TS. More distally, the passage of the DNRS within the epidural fat (Fig 1C) is reminiscent of the intraorbital course of the optic nerve within the orbital fat.
These proposed segments do not necessarily comply with the localization system proposed by Wiltse et al (4) and later endorsed by the 2001 multidisciplinary task force (1). A particular "zone" may harbor different segments of a LNR (Fig 1), whereas a specific "level" may accommodate different segments of the opposing LNRs (Fig 3).
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Awareness of the varying appearances of a LNR within the vertebral foramen may be of value in localizing the level—or maximal level—of neural structural compromise and correlating the imaging findings with the patient’s symptoms. This is especially valuable in herniated disks that demonstrate a volume-neural structural compromise discordance (eg, a small-volume posteriorly HD may cause significant impingement of a neighboring ventrally located preneural foraminal LNR) (Fig 4), and may have a potential role in patient management.
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References
- Fardon DF, Millette PC. Nomenclature and classification of lumbar disc pathology: recommendations of the combined task forces of the North American Spine Society, American Society of Spine Radiology, and American Society of Neuroradiology. http://www.asnr.org/spine_nomenclature/ (accessed March 20, 2005)
- Milette PC. The proper terminology for reporting lumbar intervertebral disk disorders. AJNR Am J Neuroradiol 1997;18:1859–1866[Medline]
- Clemente CD. Gray’s anatomy. Philadelphia: Lea & Febiger; 1985:1191–1192
- Wiltse LL, Berger PE, McCulloch JA. A system for reporting the size and location of lesions of the spine. Spine 1997;22:1534–1537[Medline]
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