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Clinical and Radiographical Differences Between Thoracic Idiopathic Spinal Cord Herniation and Spinal Arachnoid Cyst

Study Design. A retrospective, multicenter, case-controlled study. Objective. The aim of this study was to investigate the clinical and radiographical differences between thoracic idiopathic spinal cord herniation (ISCH) and spinal arachnoid cyst (SAC). Summary of Background Data. ISCH and SAC are relatively rare diseases. Preoperative misdiagnose was frequently reported in both; however, these clinical and radiographical differences remain unclear. Methods. Of 30,469 patients who underwent spinal surgery, 18 (0.059%) and 22 (0.072%) patients were diagnosed as ISCH or SAC at nine hospitals, respectively, and their clinical and radiographical data were retrospectively evaluated. The spinal cord kink angle was measured on magnetic resonance or computed tomography myelography sagittal images; the kink angle was the exterior angle formed between the two tangents to the dorsal-side inflection points at the maximally affected level. Results. There were no significant differences in age, gender, and duration of symptoms. Preoperative motor deficit was significantly higher (94.4%) and severer (manual muscle testing: 3.1 ± 1.1) in ISCH. Brown-Séquard syndrome was observed in 38.9% of ISCH, while no patients in SAC. In addition, leg sensory disorder and bladder rectal disorder were significantly more common in ISCH, while back pain was significantly frequent in SAC. With respect to radiographical findings, the length of disease (5.1 ± 2.7 levels) and altered cerebrospinal flow (CSF) (81.8%) in the lesion was significantly longer and more common in SAC. On the contrary, the kink angle was significantly greater in ISCH (54.0 ± 23.1°) than in SAC (14.1 ± 12.0°) (P < 0.001). The cut-off value of the kink angle to distinguish ISCH and SAC was 32.8°. Conclusion. Patients with ISCH commonly had severe preoperative neurological deficit, Brown-Séquard syndrome, and higher kink angle, while patients with SAC had back pain, longer length of disease, and altered CSF in the lesion. Level of Evidence: 4