Spinal Canal Diameter Normals¶

AP Diameter of the Spinal Canal¶

Cervical Spine¶

Normal AP diameter: 17–18 mm (C3–C7)
<13 mm = relative stenosis (developmental narrowing)
<10 mm = absolute stenosis
Torg-Pavlov ratio (canal diameter / vertebral body AP diameter): <0.8 suggests developmental stenosis

Thoracic Spine¶

Normal AP diameter: 15–17 mm
The thoracic cord occupies a larger percentage of the canal than the cervical cord

Lumbar Spine¶

Normal AP diameter: 15–25 mm (wider than cervical/thoracic)
Developmental lumbar stenosis: AP diameter <12 mm (bony canal)
The effective canal size is reduced by soft tissue structures (disc, ligamentum flavum, facet joints)

Cord Diameter¶

Cervical cord: 8–10 mm AP (largest at C4–C6 enlargement)
Thoracic cord: 6–8 mm AP
Conus medullaris: 6–8 mm, tapering to the filum

Clinical Applications¶

Developmental stenosis — Congenitally narrow canal predisposes to cord compression from even mild degenerative changes
Acquired stenosis — Disc herniation, osteophytes, ligamentum flavum hypertrophy reduce the effective canal diameter
Torg-Pavlov ratio — Screening measurement for developmental cervical stenosis in athletes (particularly football players, contact sports)

Clinical Pearl

Patients with developmental cervical stenosis (canal AP diameter <13 mm) are at significantly increased risk for symptomatic cord compression from even mild degenerative changes that would be asymptomatic in a normal-sized canal. The Torg-Pavlov ratio <0.8 on lateral cervical radiograph is a simple screening tool, commonly used in the sports medicine setting.

Key Points¶

Cervical canal AP <13 mm = relative stenosis, <10 mm = absolute stenosis
Torg-Pavlov ratio <0.8 suggests developmental cervical stenosis
Developmental stenosis predisposes to cord compression from mild degenerative changes
Normal cervical cord diameter is 8–10 mm AP
Effective canal size is reduced by soft tissue structures

References¶

Pavlov H, Torg JS, Robie B, Jahre C. Cervical spinal stenosis: determination with vertebral body ratio method. Radiology. 1987;164(3):771-5. Available from: https://pubmed.ncbi.nlm.nih.gov/3615879/
Torg JS, Pavlov H, Genuario SE, Sennett B, Wisneski RJ, Robie BH, Jahre C. Neurapraxia of the cervical spinal cord with transient quadriplegia. J Bone Joint Surg Am. 1986;68(9):1354-70. Available from: https://pubmed.ncbi.nlm.nih.gov/3782207/
Ulbrich EJ, Schraner C, Boesch C, Hodler J, Busato A, Anderson SE, et al. Normative MR cervical spinal canal dimensions. Radiology. 2014;271(1):172-82. doi:10.1148/radiol.13120370.
Iclal ET, Lomasney LM, Jones NS, et al. A practical radiographic visual estimation technique for the prediction of developmental narrowing of cervical spinal canal. Br J Radiol. 2017;90(1078):20170286. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC5853360/
Steurer J, Roner S, Gnannt R, Hodler J. Quantitative radiologic criteria for the diagnosis of lumbar spinal stenosis: a systematic literature review. BMC Musculoskelet Disord. 2011;12:175. doi:10.1186/1471-2474-12-175. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC3161920/
Gaillard F, et al. Canal-to-body ratio of Torg and Pavlov. Radiopaedia.org. Available from: https://radiopaedia.org/articles/canal-to-body-ratio-of-torg-and-pavlov
Gaillard F, et al. Cervical canal stenosis. Radiopaedia.org. Available from: https://radiopaedia.org/articles/cervical-canal-stenosis
Gaillard F, et al. Lumbar canal stenosis. Radiopaedia.org. Available from: https://radiopaedia.org/articles/lumbar-canal-stenosis-1