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Nucleus pulposus of intervertebral disc

The nucleus pulposus (NP) is the central, gelatinous core of the intervertebral disc, encased by the anulus fibrosus. It is composed of water-rich proteoglycans (aggrecan), type II collagen fibers, and sparse chondrocyte-like cells, giving it a highly hydrated, gel-like consistency. This structure allows the NP to act as the primary shock absorber of the spine, distributing compressive loads evenly across the vertebral endplates.

The NP is most hydrated in early adulthood (~70–90% water content) and gradually loses hydration with aging or degeneration, resulting in disc desiccation and height loss. Its viscoelastic properties allow it to deform under pressure and restore its shape when unloaded, protecting the vertebral bodies and maintaining spinal flexibility.

Location

  • Centrally located within the intervertebral disc

  • Surrounded circumferentially by the anulus fibrosus

  • Extends from superior to inferior vertebral endplates

  • Present in cervical, thoracic, and lumbar discs

  • Lies posterior to the anterior longitudinal ligament and anterior to the posterior longitudinal ligament, in contact with vertebral bodies

Function

  • Acts as the primary shock absorber of the spine

  • Distributes compressive forces evenly to the vertebral endplates

  • Maintains disc height and spinal flexibility

  • Facilitates spinal load transmission and torsional stress resistance

  • Works with the anulus fibrosus to maintain intervertebral stability

Synonyms

  • NP

  • Central gelatinous disc core

  • Intervertebral disc nucleus

MRI Appearance

T1-weighted images:

  • NP appears as intermediate to slightly hyperintense relative to the anulus fibrosus, depending on hydration and age

  • In healthy discs, NP shows homogeneous signal, while desiccated or degenerated NP appears hypointense

  • T1 post-contrast enhancement is usually minimal in normal NP, but degenerative or inflamed discs may show mild peripheral enhancement

T2-weighted images:

  • NP is hyperintense (bright) in healthy, well-hydrated discs due to high water content

  • Loss of T2 signal indicates disc desiccation or degeneration

  • Herniated or extruded NP may appear as hyperintense material extending beyond the anulus fibrosus

STIR (Short Tau Inversion Recovery):

  • NP is high signal in normal discs

  • Edema, inflammation, or acute injury causes increased hyperintensity, useful for diagnosing acute disc injury or Modic type I changes in adjacent vertebrae

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal NP typically shows no significant enhancement

  • Peripheral enhancement may be seen in degenerative discs, annular tears, or inflammatory conditions

  • Helps distinguish sequestered or infected NP material from surrounding structures

CT Appearance:

  • NP appears as a soft tissue density within the disc space, slightly lower in density than the surrounding anulus fibrosus

  • Calcified NP (degeneration or dystrophic calcification) appears hyperdense

  • CT is primarily useful for assessing disc height, calcification, herniation, and vertebral endplate changes

MRI images

Nucleus pulposus of intervertebral disc sagittal image

MRI images

Nucleus pulposus of intervertebral disc

CT images

Nucleus pulposus of Intervertebral disc ct coronal image -img-00000-00000

MRI image

Nucleus pulposus of intervertebral disc MRI axial anatomy image-img-00000-00000