Length of MRI signal may predict outcome in advanced cervical spondylotic myelopathy

Objective:

To study clinical and radiological factors that may correlate with independent walking (IW) following advanced cervical spondylotic myelopathy (CSM) surgery.

Methods:

A retrospective case series including all advanced CSM patients (Nurick 4 and 5) who underwent surgery from 2003-2010 in the Division of Neurosurgery, Department of Surgery, College of Medicine, King Saud University and King Khalid University Hospital, Riyadh, Saudi Arabia. Only patients with 6 months or more follow-up were included. A neuroradiologist who was blinded to the clinical data reviewed all MRI studies.

Results:

Forty-three patients were included (83% males, mean follow-up 29 months). A better preoperative neurological status was a positive predictor of IW after surgery (85.7% Nurick 4 versus 36.4% Nurick 5, p=0.001). Independent walking was less likely in patients with the following MRI features: longer T2-weighted image (T2WI) signal changes (p=0.001), well-circumscribed T2WI signal changes (p=0.028), T1WI hypointensity (p=0.001), and narrow spinal canal diameter (p=0.048). Multivariate regression revealed that both an increased T2WI signal change length and T1WI hypointensity were independent predictors. The risk of dependent walking increased by 1.35 times as the T2WI signal intensity length increased by one mm, and by 14-times with T1WI hypointensity.

Conclusions:

Regaining IW after surgery in patients with advanced CSM was less likely for cases showing MRI features of longer T2WI signal changes and T1WI hypointensity. Better baseline walking, less defined T2WI signal change, and a wider spinal canal were good prognostic factors.Cervical spondylotic myelopathy (CSM) may lead to significant disability.1-3 Progressive compression of the spinal cord causes chronic ischemia, local inflammatory response, and endothelial cell loss that may result in permanent spinal cord damage.4 In addition, there is an enhanced permeability in the blood-spinal cord barrier, leading to contact between the peripheral immune system and the spinal cord. Subsequently, there is an increased inflammatory reaction, resulting in more adverse effects on the spinal cord.5 Eventually, the spinal cord develops cystic cavitation, gliosis, degeneration of the central grey and medial white matter, Wallerian degeneration of the posterior columns and posterolateral tracts, and a loss of anterior horn cells. These changes are reflected on the clinical presentation and MRI features of the patients. The ability to detect changes related to spinal cord compression plays an important role in predicting clinical and functional outcomes. Several clinical and radiological factors have been studied as potential predictors for functional outcome. Relevant clinical predictors include the patient’s age at diagnosis, the duration of symptoms prior to surgery, medical comorbidities, the preoperative neurological status, and the surgical procedure performed.6,7The MRI predictors of unfavorable outcome include hypointensity on T1-weighted images (T1WI), the type of signal intensity on T2-weighted images (T2WI), and a reduction of the spinal canal diameter.6,8-12 The correlation between the length of signal change on T2WI MRI sequences and clinical outcome after surgery has not been established. Changes in the internal structure of the spinal cord could appear as alterations in the signal intensity on T1- and T2-weighted MRI sequences.8,13 Hyperintensity on T2WI corresponds to focal gliosis, myelomalacia, vascular ischemia, and edema. Therefore, it is possible that patients with longer MRI signals experience less favorable clinical recoveries after surgery, particularly if the changes correspond to hypointensity on T1WI. In the current study, our objective was to assess the correlation between clinical and MRI features and independent walking (IW) after surgery in an attempt to predict functional recovery. Only patients with advanced myelopathy were included to avoid any bias that may result from involvement of patients with different disease severity.