How to Read a Spine MRI: A Patient's Guide

Spine MRI Views and Sequences

Spine MRI is acquired in sagittal (side view) and axial (cross-section) planes. The sagittal view provides an overview of multiple vertebral levels, showing disc height, alignment, and the spinal canal. Axial images provide cross-sectional detail at specific disc levels, showing the relationship between disc material, nerve roots, and the spinal canal.

T1-weighted images show anatomy clearly — normal bone marrow appears bright (due to fat), while discs appear intermediate gray. T2-weighted images make fluid appear bright — cerebrospinal fluid (CSF) in the spinal canal appears white, providing excellent contrast for identifying disc herniations, stenosis, and nerve compression. STIR sequences are sensitive to edema and inflammation.

Intervertebral Discs

Healthy intervertebral discs appear bright on T2 images due to their high water content. As discs degenerate, they lose water and appear progressively darker — this is described as desiccation or disc dehydration. Disc degeneration is graded using the Pfirrmann classification from Grade 1 (normal) to Grade 5 (collapsed disc space). Disc bulging means the disc extends beyond the vertebral body margins diffusely. A herniation is focal and classified as protrusion, extrusion, or sequestration.

On axial images, herniations are classified by location: central, paracentral (most common), foraminal, or far lateral. The direction determines which nerve root is affected. For more on natural disc healing, see our article on herniated disc natural healing.

Spinal Stenosis

Spinal stenosis is narrowing of the spinal canal, lateral recesses, or neural foramina. On axial T2 images, central stenosis is assessed by evaluating the bright CSF visible around the thecal sac and nerve roots. In severe stenosis, there is no visible CSF and the nerve roots appear crowded. Foraminal stenosis is best assessed on sagittal T1 images by evaluating the bright fat signal normally surrounding the nerve root. Common causes include disc herniations, facet joint hypertrophy, ligamentum flavum thickening, and spondylolisthesis.

Nerve Compression

Identifying nerve compression requires correlating findings across views. On axial images, a compressed nerve root may be displaced, flattened, or surrounded by disc material. Signs of nerve inflammation include increased T2 signal within the nerve root itself. The level of compression determines the expected symptom pattern: L4-L5 herniation typically affects the L5 nerve root (causing foot drop), while L5-S1 affects the S1 root (causing calf weakness). For exercises that help with nerve compression, see our guide on spine exercises for herniated discs.

Vertebral Bodies, Alignment, and Posterior Elements

Vertebral bodies should be uniformly bright on T1 images. Dark signal on T1 with bright signal on T2/STIR suggests bone marrow edema from compression fracture, infection, or tumor. Modic changes are signal abnormalities in the vertebral endplates: Type 1 (edema, active inflammation), Type 2 (fatty replacement, chronic), and Type 3 (sclerosis). Spondylolisthesis (forward slippage of one vertebra on another) is easily identified on sagittal images.

The facet joints are paired synovial joints posteriorly at each spinal level. Facet arthropathy appears as joint space narrowing, osteophyte formation, and joint effusion. Hypertrophied facets contribute to stenosis. The ligamentum flavum normally measures less than 4 mm — thickening is a common contributor to spinal stenosis in the lumbar spine.

Key Takeaways

• Sagittal views provide an overview of alignment and disc levels; axial views show nerve compression in detail
• Healthy discs appear bright on T2; dark discs indicate degeneration and water loss
• Herniations are classified by type (protrusion, extrusion, sequestration) and location (central, paracentral, foraminal)
• Stenosis severity is graded by the amount of CSF visible around the nerve roots
• Modic changes in vertebral endplates characterize the inflammatory stage of disc degeneration
• Disc degeneration on MRI is extremely common with aging and does not always correlate with symptoms

Frequently Asked Questions