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Ossification of Posterior Longitudinal Ligament (OPLL)


KEY FACTS

Terminology

  • Ossification of posterior longitudinal ligament (OPLL)

Imaging

  • Flowing multilevel ossification posterior to vertebral bodies

    • Relatively minimal degenerative disc disease, absent facet ankylosis

    • Midcervical (C3-C5) > midthoracic (T4-T7)

    • PLL ossification narrows AP spinal canal dimension → spinal stenosis, cord compression

  • Characteristic “upside-down T” or “bowtie” PLL configuration on axial images

    • CT with sagittal reformats to confirm MR diagnosis, clarify extent of ossification for surgical planning

    • Sagittal T1WI, T2WI to evaluate spinal cord compression, extent of ligamentous ossification

Top Differential Diagnoses

  • Spondylosis

  • Calcified herniated disc

  • Meningioma

Pathology

  • Variable extent

    • Continuous

      • –

        Ossified mass over several vertebral segments

    • Segmental

      • –

        Fragmented ossified lesions behind each vertebral body

    • Mixed

      • –

        Combination of continuous and segmental

    • Focal

      • –

        Ossification confined to disc level

Clinical Issues

  • Spastic paresis → paralysis (17-22%)

  • ↑ risk for developing progressive myelopathy if > 60% canal stenosis, ↑ cervical range of motion

Sagittal graphic shows flowing multilevel ossification of the posterior longitudinal ligament (OPLL), producing canal narrowing and cord compression.

Axial postmyelogram bone CT shows the classic “upside-down T” configuration of OPLL
. This is causing mild compression of the contrast-filled thecal sac
but does not deform the spinal cord
.

Sagittal STIR MR shows the typical pattern of continuous-type OPLL seen as low signal ventral to the cord
with severe cord compression
. Note the associated diffuse idiopathic skeletal hyperostosis with multilevel fusion
.

Sagittal T1 C+ MR in the same case shows a slightly heterogeneous mass
ventral to the cervical cord, with severe cord compression at the C4 level
. OPLL may show low or heterogeneous increased signal on T1WI due to marrow content with fat elements.

TERMINOLOGY

Abbreviations

  • Ossification of posterior longitudinal ligament (OPLL)

Definitions

  • Ossification within spinal posterior longitudinal ligament (PLL)

IMAGING

General Features

  • Best diagnostic clue

    • Flowing multilevel ossification posterior to vertebral bodies, with relatively minimal degenerative disc disease, absent facet ankylosis

  • Location

    • Midcervical (C3-C5) > midthoracic (T4-T7)

  • Size

    • Mild focal thickening → extensive flowing ossification (≈ 2-5 mm thickness)

  • Morphology

    • PLL ossification narrows AP spinal canal dimension → spinal stenosis, cord compression

Radiographic Findings

  • Radiography

    • Flowing posterior ossification behind vertebral bodies

      • –

        Often superimposed over facet complex on lateral projection

      • –

        Requires high index of suspicion to diagnose; subtle finding, easy to overlook

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