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Objectives and questions: To investigate the ability of the spinal subarachnoid space (SAS) to accommodate the acutely injured spinal cord in rodents compared to humans.

Material and methods: We retrospectively analyzed a patient cohort including 21 patients with acute tSCI. Surgical decompression and realignment were performed via dorsal laminectomy and segmental instrumented fusion. An intraoperative ultrasound was obtained to assess SAS patency. A preoperative MRI was available in 14 patients. Paired and unpaired t-tests were performed to determine statistical significance. Thereafter, fifteen female Long-Evans rats prospectively underwent moderate cervical (n=6) or thoracic (n=9) traumatic spinal cord injuries (tSCI). Post-injury assessments included high-resolution midline ultrasound imaging to measure the diameters of the spinal cord, SAS, and dural sleeve.

Results: Rodent Data:Both cervical and thoracic contused spinal cords exhibited significant swelling, resulting in an approximately 9% increase of the SC diameter and complete SAS obliteration at the injury center in all animals as determined by high-resolution ultrasound (p = 0.001 cervical; p <0.001 thoracic tSCI). Following durotomy the SC diameter enlarged by 25% compared to the pre-injury diameter and expanded beyond the confinements of the dural sack.

Clinical Data: Our patient cohort had a median age of 62.0 years and 81% of tSCIs involved the cervical spine. Pre-operative MRI depicted complete effacement of the SAS in all patients. More than two thirds of our patient underwent surgical realignment and decompression within 24 hours of the injury. Upon completion of the surgery, successful restoration of SAS patency was documented in all patients using Intraoperative ultrasound. Neurological improvement was observed in 61.9% of patients at discharge compared to admission.

Discussion and conclusions: This study highlights critical species differences of the SAS dimensions and the ability to accommodate the contused spinal cord in humans compared to rodent tSCI. Further research is needed to determine the impact of SAS patency onto the validity of rodent tSCI models for neuroprotective therapy research.