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MRI Artifact Mimicking Root Compression by Interbody Cage Displacement

Kwon, Do-Young MD; Kim, Byung-Jo MD; Park, Kun-Woo MD

American Journal of Physical Medicine & Rehabilitation: May 2008 - Volume 87 - Issue 5 - p 423-424
doi: 10.1097/PHM.0b013e31816dde0a
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From the Department of Neurology, Korea University Medical Center, Seoul, Korea.

All correspondence and requests for reprints should be addressed to Byung-Jo Kim, MD, PhD, Department of Neurology, Korea University Medical Center, #126-1, Anam-Dong 5Ga, Seongbuk-Gu, Seoul, 136-705, Korea.

Magnetic resonance imaging (MRI) is one of the most reliable diagnostic tools for the assessment of spine-related problems before and after surgery. However, physicians should be aware of the possibility that MRI artifacts could lead to misdiagnosis, especially in cases after spine surgery involving the insertion of materials.

A 72-yr-old woman presented to a university-affiliated spinal intervention clinic with complaints of severe right-sided low-back and leg pain that radiated to the great toe and lasted for 4 wks. Two years before, she underwent interbody fusion with bilateral facetectomy for low-back and bilateral leg pain that had lasted for more than 10 yrs and that had been caused by spondylolisthesis at the level of L4–5. She had been doing very well for 2 yrs after the surgery, but she suddenly experienced severe low-back and leg pain radiating to the right great toe, which became progressively worse. She underwent physical therapy for a period of 3 wks, but her symptoms were not relieved. Her symptoms worsened mostly with sitting, bending, and driving. Her symptoms were somewhat better when lying down. On examination, right-side ankle dorsiflexion was slightly weakened (grade IV). The straight-leg-raising test was positive on the right side. MRI study revealed a right-sided posterior extrusion of material from the intervertebral disc at the level of L4–5 into the spinal canal (Fig. 1). However, a computed tomography scan revealed that there were abnormal findings in MRI caused by an artifact in the interbody cage (Fig. 2). Extraforaminal disc protrusion on the right side at the level of L5–S1 was found by careful, repeated inspection of the MRI findings. The patient’s symptoms were significantly improved by transforaminal epidural injection three times with 2-wk intervals. At a 3-mo follow-up visit, her back pain was completely resolved, and she experienced only mild intermittent symptoms in her right leg.





There is still no generally accepted modality for assessing fusion status after spine surgery. MRI has been increasingly used to evaluate fusion status after spine surgery because it can offer a more accurate diagnosis and aid in the identification of undetected tiny lesions when used with other methods. After spinal fusion operation for degenerative disc disease, up to 30% of patients experience persistent or recurrent pain.1 It is crucial, therefore, to make a correct diagnosis in patients with recurrent pain. MRI was considered the most useful tool and should be the modality of choice when determining causes of failed back surgery and when evaluating recurrent pain after lumbar interbody fusion.2 However, the presence of artifacts can limit the usefulness of MRI alone,3,4 and, at times, it can lead to misdiagnosis and malpractice, especially if the localization of the recurrent symptoms corresponds to that of the “false pathology” caused by artifacts. In our case, we did not even notice the presence of artifacts in the initial evaluation, and we mistook the artifact for pathology because the clinical symptom was well explained by the abnormal signal on MRI. Computed tomography revealed the presence of an artifact. Computed tomography would help to compensate for the weakness of MRI, and vice versa. It is essential to be aware of the nature of magnetic susceptibility artifacts on MRI after spine fusion operation, to properly interpret the MRI findings and prevent unnecessary revision operations.

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