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L1–L2 Intervertebral Disc

The L1–L2 intervertebral disc is located between the first and second lumbar vertebral bodies. It belongs to the upper lumbar region and is less commonly affected by disc herniation compared to the lower lumbar discs. Nevertheless, it plays an important role in load transmission, flexibility, and shock absorption.

Because it lies in the upper lumbar region, pathology at this level may cause atypical radiculopathy, presenting as pain radiating to the anterior thigh rather than the classic sciatica seen with lower lumbar discs.

Synonyms

  • Upper lumbar intervertebral disc

  • L1–L2 disc

  • First lumbar disc

Structure

  • Annulus fibrosus: Outer fibrocartilaginous lamellae providing tensile strength and containing the nucleus.

  • Nucleus pulposus: Central gelatinous, hydrated core acting as a shock absorber.

  • Cartilaginous endplates: Hyaline cartilage layers that attach the disc to the L1 and L2 vertebral bodies and allow nutrient diffusion.

Relations

  • Anteriorly: Anterior longitudinal ligament and retroperitoneal structures

  • Posteriorly: Posterior longitudinal ligament, epidural fat, and spinal canal containing the conus medullaris (nearby inferiorly) and cauda equina roots

  • Laterally: Exiting L1 nerve roots in the intervertebral foramina

  • Superiorly: Vertebral body of L1

  • Inferiorly: Vertebral body of L2

Function

  • Provides cushioning and shock absorption between L1 and L2 vertebrae

  • Contributes to spinal flexibility and upper lumbar motion

  • Helps distribute axial load across the upper lumbar spine

  • Maintains alignment and lumbar lordosis

Clinical Significance

  • Disc herniation (rare): Can compress the L2 nerve root, causing pain radiating to the anterior thigh, weakness in hip flexion, and sensory loss in the anterior thigh

  • Degeneration: May lead to chronic back pain and stiffness, though less common than lower lumbar discs

  • Infection (spondylodiscitis): May involve this disc, often secondary to hematogenous spread

  • Tumors/metastasis: May involve disc and adjacent vertebral bodies

  • Surgical relevance: Target in discectomy and spinal fusion procedures at upper lumbar levels

MRI Appearance

Normal Disc:

  • Annulus fibrosus: Low signal intensity on both T1 and T2 due to dense collagen fibers

  • Nucleus pulposus:

    • T1: Intermediate to low signal

    • T2: High signal (bright) due to high water content

Degenerated Disc:

  • Annulus fibrosus: May show annular tears with focal high signal on T2 (annular fissures)

  • Nucleus pulposus: Loses hydration → dark on T2 (loss of normal brightness) and low signal on T1

T1-weighted images:

  • Normal: annulus low signal, nucleus intermediate to low

  • Degenerated: diffuse low signal (dark disc)

  • Endplate fatty change (Modic II): bright signal in adjacent vertebral marrow

T2-weighted images:

  • Normal: nucleus bright, annulus dark

  • Degenerated: dark disc (loss of nucleus brightness)

  • Herniation: focal outpouching of low-to-intermediate signal compressing neural structures

STIR (Short Tau Inversion Recovery):

  • Normal: nucleus bright, annulus dark

  • Pathology (edema, inflammation, infection): bright hyperintensity in disc and/or endplates

T1 Fat-Sat Post-Contrast:

  • Normal: minimal or no enhancement

  • Degeneration: mild peripheral annular enhancement

  • Infection: diffuse disc and endplate enhancement

  • Tumor: irregular, intense enhancement

CT Appearance

Non-Contrast CT:

  • Disc appears as soft tissue density between L1 and L2 vertebrae

  • Degeneration: reduced disc height, vacuum phenomenon, calcifications

  • Herniation: focal posterior bulge or extrusion into canal or foramen

Post-Contrast CT:

  • Normal disc: no significant enhancement

  • Infection: diffuse enhancement of disc and endplates

  • Tumors: irregular, heterogeneous enhancement

  • Post-surgical changes: scar tissue enhances, residual or recurrent disc material does not

MRI image

L1–L2 Intervertebral Disc mri anatomy image

CT image

L1–L2 Intervertebral Disc CT sagittal anatomy image-img-00000-00000