Spinal intradural arachnoid cysts are rare, benign intradural lesions of the spinal cord that can arise as a primary lesion or secondary due to inflammatory processes. Symptoms can range from an asymptomatic incidental finding to progressive myelopathy, with paresthesia and neuropathic pain. We present the case of an 80-year-old female with a longstanding history of back pain, urinary incontinence, difficulty ambulating and frequent falls, with rapid progression of her symptoms prior to presentation. Physical examination revealed lower extremity weakness, decreased sensation and increased deep tendon reflexes. Thoracic spine MRI showed an extra-axial cystic lesion extending from T4 to T10, causing severe compression of the spinal cord. We performed two separate thoracic laminectomies at T4-T5 and at T9-T10, with microsurgical fenestration of the dorsal arachnoid cyst performed under continuous intraoperative neurophysiologic monitoring. Intraoperative fluoroscopy and ultrasound were used for localization purposes. The patient was discharged on postoperative day 6 to an inpatient rehabilitation facility with no neurological complications. She presented a month later with significant improvement in ambulation and lower extremity strength.