Spinal Extradural Meningeal Cysts An MRI Evaluation of a Case Series and Literature Review

Study Design: Case series and literature review. Objective: To analyze the characteristics of extradural spinal meningeal cysts (SMCs) by magnetic resonance imaging (MRI) and discuss their classifications and etiology, as well as exploring the choice of treatment. Summary of Background Data: Spinal extradural meningeal cysts are a rare type of SMC. They are also known as extradural/epidural spinal arachnoid cysts. According to Nabors' classification, they belong to the category of types I and II meningeal cysts. The etiology of spinal extradural cysts remains unclear. Materials and Methods: We retrospectively analyzed the MRI scans of 18 cases of extradural arachnoid cyst, which were consecutively treated surgically at our institutions between June 1990 and November 2009. All cases were confirmed by surgery. Disonics 0.35T and Philips Gyroscan Intera 1.5T scanner with surface coils were used for patient scanning. MRI examination included routine sagittal T1-weighted/ spin-echo, sagittal, and transverse T2-weighted scanning. The above scans were repeated after the administration of intravenous contrast 3 medium (gadolinium) in 12 patients. Results: Seven of the 18 cases were located in the middle and lower thoracic spine, 3 in the lumbar spine, and 8 in the thoracolumbar junction. All cystic lesions were isointense compared with cerebrospinal fluid on the T1 and T2-weighted images. The lesions showed no enhancement after gadolinium administration. Conclusions: MRI had great sensitivity to and specificity for extradural arachnoid cysts and seemed to be the diagnostic procedure of choice before and after surgery. Accurate understanding of MRI features helps clinicians make preoperative diagnoses and guides the operation. The definitive treatment of SMCs involves total removal of the cyst and repair of the dural defect.