Arachnoidal Diverticula of Sacral Extradural Meningeal Cyst: A Novel Definition and Case Series

BACKGROUND: Sacral cysts are classically divided into Tarlov cysts and meningeal diverticula. However, the pathogenesis of sacral cysts remains unclear. This study aimed to clarify a novel type of sacral extradural spinal meningeal cyst with a specific arachnoidal structure. METHODS: Nine patients with prophylactic diverticula were included in the study. All patients underwent MRI preoperative reconstruction and traditional neck transfixation. RESULTS: All patients presented with more than one symptom. The major symptom was lower extremity pain, followed by lower extremity numbness (77.8%, 7/9), lower extremity weakness (55.6%, 5/9), bowel/bladder and sexual dysfunction (55.6%, 5/9), and tenesmus (22.2%, 2/9). After long-term follow-up, the outcome was classified as improved in 9 patients (100%). CONCLUSIONS: The clinical findings of this study illustrate a special subtype and may help explain the mechanism of sacral cyst formation.