Pfirrmann grading system (spine)

The Pfirrmann grading system is used to grade lumbosacral disc degeneration on T2-weighted images.

Usage

The Pfirrmann grading system is the most widely known classification for intervertebral disc degeneration and is used in both clinical and research contexts ^2,3. The intra- and inter-observer agreement of the Pfirrmann grading system is excellent ³.

Although is primarily intended for use in the lumbosacral region, it has been employed in the thoracic and thoracic regions also ⁴.

Classification

The Pfirrmann grading system was first described in 2001 and focuses on the appearance of discs on sagittal T2-weighted scans ¹.

• grade I

  • disc is homogeneous with bright hyperintense white signal intensity and normal disc height

• grade II

  • disc is inhomogeneous but retains the hyperintense white signal

  • nucleus and annulus are clearly differentiated, and a gray horizontal band could be present

  • disc height is normal

• grade III

  • disc is inhomogeneous with an intermittent gray signal intensity

  • distinction between nucleus and annulus is unclear

  • disc height is normal or slightly decreased

• grade IV

  • disc is inhomogeneous with a hypointense dark gray signal intensity

  • there is no more distinction between the nucleus and annulus

  • disc height is slightly or moderately decreased

• grade V

  • disc is inhomogeneous with a hypointense black signal intensity

  • there is no more difference between the nucleus and annulus

  • the disc space is collapsed

Limitations and alternative systems

Limitations

Various limitations have been pointed out including ^2,5:

• limited separation of grades in older individuals, leading to a proposed modification (see below)

• the horizontal grey cleft should be considered normal, and grade I is therefore uncommon

• some discs can have narrowed disc height but remain normal in signal (e.g. L5/S1)

• in osteoporosis the central parts of the disc can become taller potentially resulting in under grading

Modified Pfirrman grading system

A modified classification was proposed in 2007 by Griffith et al. ² to better categorize degenerative discs in older patients where most discs are Pfirrman grade III or IV. 

It has, however, not been as widely adopted.

• grade 1

  • uniformly hyperintense, equal to CSF

  • distinct junction between inner and outer annular fibers posteriorly

  • normal disc height

• grade 2

  • hyperintense (between presacral fat and CSF) +/- hypointense intranuclear cleft

  • distinct junction between inner and outer annular fibers posteriorly

  • normal disc height

• grade 3

  • hyperintense (less than presacral fat)

  • distinct junction between inner and outer annular fibers posteriorly

  • normal disc height

• grade 4

  • midly hyperintense (slightly more than outer annular fibers)

  • indistinct junction between inner and outer annular fibers posteriorly

  • normal disc height

• grade 5

  • hypointense (equal to outer annular fibers)

  • indistinct junction between inner and outer annular fibers posteriorly

  • normal disc height

• grade 6

  • hypointense

  • indistinct junction between inner and outer annular fibers posteriorly

  • <30% reduction in disc height

• grade 7

  • hypointense

  • indistinct junction between inner and outer annular fibers posteriorly

  • 30-60% reduction in disc height

• grade 8

  • hypointense

  • indistinct junction between inner and outer annular fibers posteriorly

  • >60% reduction in disc height

Tufts Classification

In 2015 Riesenburger et al proposed a new classification system to include annular high signal intensity zone and Modic changes ⁶. This has yet to be widely adopted and may have reduced interoberserver reliability ⁷.