High intensity zone

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High intensity zone is defined as a bright white signal on T2W images in the posterior annulus of the disc and represents a fissure/tear in the posterior annulus.

Etiology

A high intensity zone (HIZ) generally occurs due to:

  • post-traumatic changes 
  • instability of the spine and degenerative changes of the disc

Pathology

HIZs in the posterior annulus represent the in-growth of the vascularized granulation tissue into the tears in the posterior part of the painful disc induced by inflammation. The posterior annular fibers are structurally weaker as compared to the anterior annular fibers thereby predisposing them to disruption .

Radiographic features

MRI
  • T2: high signal intensity in the posterior annulus on sagittal images 
  • the HIZ can occur at the superior, middle or lower portions (most commonly) of the annulus
  • lumbar area at L4/5 and L5/S1 levels more commonly involved

See also