A 52-year-old woman presented with an intraspinal extradural meningeal cyst in the thoracolumbar region manifesting as progressive sensory disturbance of the bilateral lower extremities. Magnetic resonance imaging and computed tomography myelography showed an extradural meningeal cyst extending from the T-12 to L-4 levels in the thoracolumbar region with a dural defect and a valve-like mechanism developed in the enlarging cyst. Operative findings revealed a dural defect that allowed communication between the extradural cyst cavity and the subarachnoid space. Surgical resection of the cyst wall and repair of the dural defect resolved the symptoms.