Foraminal Stenosis¶

Definition¶

Foraminal stenosis is narrowing of the neural foramen (intervertebral foramen), compressing the exiting nerve root and dorsal root ganglion. It is a common cause of radiculopathy, particularly in the cervical and lumbar spine, and is best evaluated on sagittal T2 MRI.

Anatomy¶

The neural foramen is bounded by:

Superior: pedicle of the vertebra above
Inferior: pedicle of the vertebra below
Anterior: disc and posterior vertebral body (+ uncovertebral joint in cervical spine)
Posterior: facet joint (superior articular process) and ligamentum flavum

Causes¶

Disc height loss — brings pedicles closer together, reducing foraminal height
Disc herniation (foraminal or far lateral)
Osteophyte formation — from vertebral endplate, uncovertebral joints (cervical), or facets
Facet hypertrophy — encroaches from posteriorly
Spondylolisthesis — changes foraminal geometry
Post-surgical — foraminal scarring or recurrent stenosis

Grading (Lee Classification on Sagittal MRI)¶

Grade	Description
0 (Normal)	Fat completely surrounds the nerve root
1 (Mild)	Perineural fat is partially obliterated; root morphology preserved
2 (Moderate)	Perineural fat completely obliterated; root morphology preserved
3 (Severe)	Nerve root is compressed and deformed; root morphology altered

Imaging Findings¶

MRI — Sagittal T2 is Key¶

Sagittal T2: bright epidural fat normally surrounds the dark nerve root in the foramen; stenosis = loss of this fat signal
Axial T2: evaluate the cause (disc, osteophyte, facet) and direction of compression
Look for nerve root edema (T2 hyperintensity) and enhancement (suggests active inflammation)

CT¶

Superior for evaluating bony foraminal narrowing
Uncovertebral osteophytes in the cervical spine are a major cause — best seen on CT
Sagittal reformats through the foramina are essential

Clinical Pearl

Sagittal T2 MRI is the single most useful sequence for evaluating foraminal stenosis. The normal bright epidural fat provides excellent contrast against the dark nerve root. When this fat is obliterated, the root is being compressed. Always review sagittal T1 images scrolled through the foramina — foraminal stenosis can be invisible on axial images if the slices don't pass through the exact level of maximal narrowing.

Key Points¶

Foraminal stenosis compresses the exiting nerve root and dorsal root ganglion
Sagittal T2 MRI is the most important sequence — loss of perineural fat = stenosis
Lee grading (0–3) classifies severity based on fat obliteration and root deformation
Multiple causes: disc loss, osteophytes, facet hypertrophy, spondylolisthesis
In the cervical spine, uncovertebral osteophytes are a major foraminal contributor

References¶

Lee S, Lee JW, Yeom JS, et al. A practical MRI grading system for lumbar foraminal stenosis. AJR Am J Roentgenol. 2010;194(4):1095-1098. https://www.ajronline.org/doi/10.2214/AJR.09.2772
Seo J, Lee JW. Magnetic Resonance Imaging Grading Systems for Central Canal and Neural Foraminal Stenoses of the Lumbar and Cervical Spines With a Focus on the Lee Grading System. Korean J Radiol. 2023;24(3):224-234. https://pmc.ncbi.nlm.nih.gov/articles/PMC9971835/
Park HJ, Kim SS, Lee SY, et al. A practical MRI grading system for cervical foraminal stenosis based on oblique sagittal images. Br J Radiol. 2013;86(1025):20120515. https://pubmed.ncbi.nlm.nih.gov/23410800/
Park HJ, Kim SS, Han CH, et al. The clinical correlation of a new practical MRI method for grading cervical neural foraminal stenosis based on oblique sagittal images. AJR Am J Roentgenol. 2014;203(2):412-417. https://pubmed.ncbi.nlm.nih.gov/25055278/
Sartoretti E, Wyss M, Alfieri A, et al. Introduction and reproducibility of an updated practical grading system for lumbar foraminal stenosis based on high-resolution MR imaging. Sci Rep. 2021;11(1):12000. https://www.nature.com/articles/s41598-021-91462-2
Radiopaedia. Neural exit foraminal stenosis. https://radiopaedia.org/articles/neural-exit-foraminal-stenosis