An annular fissure (or tear) is the deficiency of one or more layers that make up the annulus fibrosus. They may be radial, transverse or concentric in orientation. Although very common, only a minority are identified on MRI, and are characterised by a region of high T2 signal in the otherwise low signal annulus.
Most are asymptomatic, however some are painful. The defect allows ingrowth of nerve endings and granulation tissue. Fissures near the dorsal root ganglion are especially likely to be painful.
The fissure may involve all layers or only some. The distinction is difficult if no disc extrusion is seen. Discography (introduction of contrast into the nucleus pulposus) can help distinguish partial thickeness vs full thickness annular fissure, although the clinical relevance of this is disputed.
Many authors prefer the term fissure over tear as the latter seems to imply acute injury. In the setting of severe trauma with disruption of the disc, then the term disc rupture should be used.
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