Disc bulge

A disc bulge  represents displacement of the outer fibres of the annulus fibrosus beyond the margins of the adjacent vertebral bodies, involving more than one quarter (25% or 90 degrees) of the circumference of an intervertebral disc 3. Because it is limited by the annulus fibrosus it does not extend above or below the attached margins of the disc 3. Disc bulges, along with vertebral endplate bowing, are responsible for the disc height loss that is seen with ageing.

Bulges are always gradual and broad, and can be further divided according to how much of the circumference they involve: 

  • circumferential bulge: involves the entire disc circumference
  • asymmetric bulge: does not involve the entire circumference, but nonetheless more than 90 degrees


Disc protrusion is distinguished form a disc bulge in that it involves less than 25% of the circumference. 

NoteA number of definitions of what exactly constitutes a disc protrusion have been proposed/used over the years, and it is important to realise that these differ substantially from one another 1-3.  At the time of writing (August 2016) the most recent and widely used terminology was proposed in 2014 by Fardon et al, and represents a consensus of the North American Spine Society, the American Society of Spine Radiology and the American Society of Neuroradiology 3

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Article information

rID: 6187
Synonyms or Alternate Spellings:
  • Bulging of the disk
  • Bulging of the disc
  • Disk bulge

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Cases and figures

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    Figure 1: Illustration
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    Figure 2: disc bulge
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    Figure 3: normal disc
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