Introduction:
Neurite orientation dispersion and density imaging (NODDI) is a new diffusion magnetic resonance imaging technique that can provide specific microstructural evaluation including nervous tissue density, free water fraction, and neurite orientation dispersion. In this study, we explored the microstructural changes in reduced area (RA) and T2 high signal intensity (T2-HSI) postoperative cervical cords with cervical spondylotic myelopathy (CSM) by NODDI.

Material and methods:
A prospective study. CSM patients with surgery planned were recruited in Beijing Jishuitan Hospital from September 2016 to March 2017 (excluding other cervical spondylosis and spinal diseases and postoperative stenosis) and underwent postoperative NODDI scans and modified Japanese Orthopaedic Association (mJOA) scoring. The patients were divided into RA and T2-HSI, normal area (NA) and T2-HSI, and NA and non-T2HSI groups. The differences in NODDI metrics and mJOA score between different groups were assessed respectively.

Results:
Nervous tissue density in cervical cords with postoperative constant RA was decreased (RA-T2HSI (0.510, 0.330–0.670) vs. NA-T2HSI (0.585, 0.380–0.870) (p = 0.019), RA-T2HSI vs. NA-nT2HSI (0.620, 0.460–0.770) (p = 0.003)), and a certain degree of free water increase and nervous tissue density decline was observed in postoperative cervical cords with T2-HSI, even if not all of the outcomes were very significant. Moreover, the postoperative mJOA score in combined RA and T2-HSI was lower than that in single T2-HSI.

Conclusions:
The microstructural changes in postoperative RA and T2-HSI cervical cords could be evaluated by NODDI metrics and RA and T2-HSI were useful as brief evaluations for postoperative CSM cervical cords.