Overview
This lecture covers the basics of MRI lumbar spine interpretation, including MRI protocols, normal anatomy, a systematic search pattern, and disc pathology nomenclature.
MRI Lumbar Spine Protocol & Anatomy
- Typical protocol includes sagittal, axial, and sometimes axial oblique images of the lumbar spine.
- T1-weighted images: fat is bright, CSF (cerebrospinal fluid) is dark, muscle is intermediate.
- T2-weighted images: fat and CSF are bright, muscle is intermediate.
- STIR (Short Tau Inversion Recovery): fat and bone marrow are dark, CSF is bright, highlights edema.
- Key anatomical structures: vertebral body, intervertebral discs, epidural fat, thecal sac, nerve roots, neural foramen, pedicles, and articular processes.
Search Pattern: ABCDE Approach
- A: Alignment—assess spinal curvature (lordosis, kyphosis, scoliosis) and look for listhesis (vertebral displacement).
- B: Bones—check for fractures, post-op changes, and bone marrow signal changes (bright marrow on T1 unless abnormal).
- C: Canal—evaluate epidural space, thecal sac, cord, conus medullaris, cauda equina, and for abnormalities like masses or edema.
- D: Degenerative changes—catalog disc abnormalities, osteophytes, facet and ligament hypertrophy, and spinal stenosis.
- E: Everything else—review the localizer, visible abdomen/pelvis, and check against clinical history.
Lumbar Disc Nomenclature & Pathology
- Disc bulge: annular tissue extends beyond vertebral edges, symmetric or asymmetric.
- Disc herniation: localized displacement (<25% of disc circumference), either protrusion (base wider than herniation) or extrusion (herniated fragment larger than base or sequestrated).
- Herniations categorized by location: central, subarticular/lateral recess, foraminal, and extraforaminal.
- Disc herniations can displace or compress nerve roots; facet/ligamentous hypertrophy or synovial cysts may also cause stenosis.
- Grading stenosis: based on CSF presence and nerve root aggregation (none, mild, moderate, severe).
Key Terms & Definitions
- T1-weighted image — MRI sequence where fat appears bright and CSF appears dark.
- T2-weighted image — MRI sequence where both fat and CSF appear bright.
- STIR — MRI sequence that suppresses fat signal and highlights edema.
- Thecal sac — membranous sheath surrounding the spinal cord and cauda equina.
- Modic changes — degenerative endplate marrow changes (type 1: edema; type 2: fatty replacement; type 3: sclerosis).
- Listhesis — slippage of one vertebral body over another.
- Stenosis — narrowing of spaces (spinal canal or foramen) that may compress nerves.
Action Items / Next Steps
- Review the standard lumbar disc nomenclature (version 2.0) for detailed terminology.
- Practice the ABCDE search pattern on lumbar spine MRIs.
- Study normal versus abnormal bone marrow signals on T1 images.
- Match MRI findings to clinical symptoms when reporting.