Introduction: Preclinical spinal cord injury (SCI) studies in rodents indicate that expansion of intramedullary lesions (IML) seen on MRI may be amenable to neuroprotection. In motor complete [ASIA Impairment Scale (AIS) A and B] subaxial SCI patients, IML expansion is approximately 900 micrometers per hour. In motor incomplete (AIS C and D) patients, IML has yet to be characterized. Our study compares lesion expansion in motor complete and incomplete patients.

Methods: Seventy-eight patients who had two MRIs within six days of SCI were enrolled. Data were analyzed by regression analysis.

Results: Mean age was 45.3 (±18.3) years, 56 patients had motor vehicle accidents or falls, and 77% were male. Mean Injury Severity Score (ISS) was 26.7 (±16.7), AIS was A in 23, B in 7, C in 7 and D in 40 patients. Mechanism was distraction in 26, compression in 22 and disc/osteophyte complex in 29 patients. Mean time between injury onset and first MRI (t1) was 10 (±8.7) hours, while mean time to second MRI (t2) was 60 (±29.6) hours. Mean length of lesion (LOL) in the first MRI was 38.8 (±20.4) mm and 51 (±36.5) mm in the second MRI. Mean time from first to second MRI (t3) was 49.9 (±28.4) hours and difference in LOL 12.6 (±20.7) mm, producing an expansion rate of 366 (±710) micrometers per hour. Lesion expansion in AIS A/B patients was 918 (±828) micrometers per hour and in AIS C/D patients 21 (±304) micrometers per hour. Univariate analysis indicated that AIS A/B versus C/D (p<0.0000), mechanism (p<0.005), age (p<0.05), ISS (p<0.05), ASIA Motor Score (p<0.05) and time to decompression (p<0.05) were predictors of lesion expansion. However, the sole determinant of IML expansion was AIS (p<0.005) in regression analysis.

Conclusions: In cervical SCI, motor complete had a significantly faster rate of lesion expansion than motor incomplete patients.

Patient Care: Previous studies have shown that spinal cord injury is a dynamic process, which includes not only the primary insult, but also a component of secondary injury where rostrocaudal expansion of the spinal cord tissue destruction continues for many hours after trauma. The rate of progression of this lesion had been described in motor complete spinal cord injury and one might assume that the rate of progression should be the same regardless of the type of spinal injury. However, we have demonstrated that the rate of progression is actually much slower in motor incomplete spinal cord injury. In fact, when our individual data are analyzed, many patients had intramedullary lesions that did not progress or even retracted, a phenomenon that has not been previously described. Therapies to reverse the initial insult to the spinal cord or halt progression of the injury continue to remain elusive, but better characterization of the injury itself and factors that may contribute to the severity of injury and its expansion will aid in the development of effective therapies and strategies to augment the clinical course and perhaps improve functional outcomes. Furthermore, measurement of intramedullary lesion expansion on MRI in patients with cervical spinal cord injuries is a relatively simple and non-invasive tool that utilizes current technology. A standardized method of measurement and well-characterized relationship to injury severity and outcomes would be immensely useful both in clinical and research settings. Correlation of intramedullary lesion length and rate of expansion to injury severity and outcomes may aid in prognostication and assessment of clinical progress, while rate of change may be a novel surrogate measure to monitor the therapeutic effects of surgical or drug trials.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the difference in rate of intramedullary lesion expansion on MRI between motor complete (AIS A and B) and motor incomplete (AIS C and D) cervical spinal cord injury patients, factors that may contribute to the difference in rate of expansion, and the finding of ASIA Impairment Scale grade as the sole determinant of rate of lesion expansion by regression analysis. 2) Discuss in small groups, the importance of characterizing intramedullary lesion expansion on MRI in patients with subaxial cervical spinal cord injury as it may serve as a marker of injury severity and potential method of monitoring treatment effectiveness. 3) Identify a practical method of utilizing intramedullary lesion expansion in the clinical setting to further define the severity and extent of spinal cord injury as well as guide research aimed at neuroprotection and halting the progression of such injury.

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