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A 65-year-old woman with a two year history of
lower backache. No radiculopathy and normal bloods (ESR, WBC, and CRP).
No fever. Her MRI (1.5 T) shows disc space narrowing and spondilolisthesis
at L4/5. There are Modic I changes at this level and the fat-sat T2 sagital
showed focal increased signal (fluid) in the disc space region. There was
contrast enhancement (linear) in the posterior aspect of the disc space,
adjacent to the end plate (I believe that the enhancement is within the
disc space and not end plate enhancement). I reported that the features
were consistent with discitis and the patient was treated for a four week
period. Her repeat MRI, obtained six weeks following the initial scan, showed
no change, and her symptoms have not resolved. The neurosurgeon has asked
me to review the diagnosis in view of this. I am aware that one can get
end plate enhancement in Modic I changes but have not seen enhancement within
the disc space before. Could these changes all be attributed to end plate
and discogenic degeneration? |
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Dr.
F.L. Chan reponds:
It is most important to distinguish whether the focal enhancement is
in the disc or the end-plate. Modic type I changes are known to have associated
gadolinium end-plate enhancement. Furthermore, enhancement of the central
portion of the degenerated disc has also been reported (Ross JS, Modic
MT, Masaryk TJ, Carter J, Marcus RE, Bohlman H. Assessment
of extradural degenerative disease with Gd-DTPA-enhanced MR imaging: correlation
with surgical and pathologic findings. AJNR 1989;10:1243-9). In
degenerative disease, however, the T2-weighted image will usually show
decreased T2 signal rather than the focal increased signal as mentioned
in this question.
In infectious conditions, the adjacent vertebral bodies are commonly
enhanced and often in a diffuse manner. Loss of end-plate definition on
non-enhanced T1 image is a specific early sign. It would also be expected
that the entire disc would be involved rather than a localized, abnormal
signal and enhancement. In other words, the changes described in the question
may be atypical features for sepsis. Alternatively, erosive intervertebral
osteochondrosis (an acute inflammatory disc degeneration) should also
be considered. Focal enhancement of the annulus occurs in this condition,
and the disc signal can be increased on T2 image from vascularization.
The end-plates are preserved in the presence of adjacent bone edema and
enhancement. This condition affects particularly L4/5 and L5/S1. (Stabler
A, Reiser MF. Imaging
of spinal infection. Radiol Clinic North Am 2001; 39:115-35.)
The infectious nature can be documented by image-guided biopsy, but interpretation
of the result may be affected by the preceding antibiotic treatment.
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