gms | German Medical Science

Objective: Prediction of outcome after surgery in patients with cervical spondylotic myelopathy remains difficult. Recent studies suggested a correlation between the extent of signal changes on the preoperative MRI and the clinical outcome but a meaningful prognosis of the degree of recovery after surgery still remains challenging. Therefore the development of improved imaging techniques is desirable. With diffusion-tensor magnetic resonance imaging (DT-MRI) the integrity of fibre tracts inside the myelon can be quantified. Although cranial DTI-MRI is routinely used, the measurement of spinal pathologies is still technically challenging.

Methods: DT-MRI based on the Brownian motion of protons, inside a neuron this movement is less inhibited along the axon than perpendicular to it. Although a single neuron can not be measured, it is possible to examine fibre tracts. Out of this data, the fractional anisotropy (FA) can be calculated which as a statistic gauge gives evidence of the integrity of fibre tracts. Therefore five patients (all male, mean age 62.3 years) with clinically apparent myelopathy and signal changes inside the myelon in the native T2 MRI were measured preoperatively and 6 months after surgery with DTI-MRI. The FA was identified inside the dorsal funiculus at the height of the lesion, cranial and caudal to it. The DTI was performed in addition to routine preoperative MRI-workup and prolonged the examination for an average of 6 minutes. To quantify the clinical status, the modified Japanese Orthopaedic Association Score (mJOA) was taken preoperatively and 6 months after admission.

Results: The relative change of the FA measured above and below the lesion was taken as a sign for the degree of impairment of the myelon. Because of the relatively small group, a statistically valid conclusion is yet not possible, but there seems to be the tendency to divide the patients in two subgroups according to their change in FA above and below the lesion: patients with less variation of the FA inside the dorsal funiculus seem to have a better outcome at the 6 month control, the mJOA increased at least about one point in this subgroup. Patients with high relative changes in the variety of FA showed no improvement in mJOA at the 6 month follow-up.

Conclusions: With increasing number of patients being measured and technical improvement, spinal DTI-MRI mayt become a useful tool in the diagnosis and prognosis of intramedullary pathologies.