Spinal Extradural Arachnoid Cysts
Extradural arachnoid cysts in the spine are rare and are seldom a cause of spinal cord compression. They are thought to arise from congenital defects in the dura mater, and they almost always communicate with the intrathecal subarachnoid space through a small defect in the dura. The mainstay of treatment in patients with neurological symptoms is surgical removal of the cyst together with ligation of the communicating pedicle and closure of the dural defect. In the present paper the authors review the literature and discuss the clinical and pathological features, mechanisms of pathogenesis, neuroimaging characteristics, and surgical management of spinal extradural arachnoid cysts. The surgical technique for removal of these lesions is illustrated in a patient with a large thoracolumbar spinal extradural arachnoid cyst causing neurogenic claudication.

Spinal extradural arachnoid cysts are a rare cause of spinal cord compression. These cysts most commonly occur in the middle to lower thoracic spine (65%) but also have been reported in the lumbar and lumbosacral (13%), thoracolumbar (12%), sacral (7%), and cervical regions (3%). Cyst enlargement can result in symptomatic spinal cord compression. Extradural a rachnoid cysts develop from protrusions of arachnoid herniating through a small dural defect. The cysts have a pedicle in communication with the spinal subarachnoid space and, because of their origin, contain CSF (Fig. 1). The cause of these cysts has not been determined definitively, although they most probably have a congenital origin. Some may be acquired from trauma, infection, or inflammation.


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A: Drawing of a spinal cross section showing a dural defect and cyst communication with the subarachnoid space. B: Drawing of a Type IA spinal, extradural arachnoid cyst with a communicating pedicle at the site of the dural defect. (Reprinted with permission from Bergland RM: J Neurosurg 28: 495–499, 1968).

Magnetic resonance imaging is useful in detecting the mass, and the signal characteristics are consistent with those of CSF. Computed tomography myelography is better for detecting the dural defect when communication between the cyst and the subarachnoid space occurs and thus allows accurate diagnosis of these lesions. Symptomatic cysts are primarily treated with excision and obliteration of the communicating dural defect. In this article, we review the clinical features, pathological features, mechanisms of pathogenesis, neuroimaging characteristics, and surgical management of spinal extradural arachnoid cysts.