At the Viewbox: Thoracic Arachnoid Cyst Causing Cord Compression

Arachnoid cysts of the spinal canal have rarely been associated with cord compression.¹ The cysts may be intradural or extradural, and may be idiopathic in etiology or result from prior trauma, infection, or iatrogenia. Spinal canal arachnoid cysts are usually intradural, typically located anteriorly, and most commonly occur in the thoracic spine. Posterior cysts, on average, span approximately 3.5 vertebral levels, while anterior cysts are larger, averaging roughly 6 vertebral levels. Patients may present at any age; however, the peak incidence occurs between ages 30 and 50.²

MRI is the modality of choice for establishing the correct diagnosis. In the illustrative case above, the sagittal MR images demonstrate a cerebrospinal-fluid-filled, mid-thoracic posterior intradural lesion with decreased T1 signal (1A), increased T2 signal (1B), and pulsation artifact on short tau inversion recovery (STIR; 1C). The axial CT myelographic images (2) demonstrate the same dorsal, intradural lesion, causing significant spinal cord compression. The cyst was surgically excised with symptom resolution.

Spinal canal arachnoid cysts can be asymptomatic, or they can cause varying degrees of neurological symptoms, especially in the setting of spinal cord compression. As in the case above, surgical excision is considered when there is significant neurological compromise. Patients usually have excellent results with a low recurrence rate.²

1. Wenger M, Zobor N, Markwalder R, et al. Intradural extramedullary arachnoid cyst of the thoracic spine associated with cord compression. J Clin Neurosci 2007;14(7):693-696.
2. da Conceição Araújo Filho S, Brito da Silva H, Freitas de Albuquerque LA, et al. Giant intradural extramedullary arachnoid cyst of the thoracic spine. J Clin Neurosci 2009;16:1369-1371.