American Society for Peripheral Nerve

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Progressive Weakness due to an Anterior Arachnoid Cyst: An Indication for Nerve Transfer Surgery
Madhawi Mitwalli, MD1; Arvin Raj Wali, BA2; Justin Brown, MD2; Ross Mandeville, MD2
1University of Alabama at Birmingham, Birmingham, AL, 2University of California, San Diego, La Jolla, CA


Anterior Arachnoid Cyst is an uncommon cause of spinal cord compression that may result in severe disability. Most are located in the thoracic region, followed by lumbar then cervical regions. Clinical presentations are varied but predominantly include neck pain, variable degrees of weakness, and paresthesias. Laminectomy followed by cyst excision and cystoperitoneal or cystopleural shunting are accepted interventions aimed at cord decompression. Neurological recovery after surgery depends on duration and severity of compression. The presentation can be a major challenge for the neurologist and neurosurgeon, especially when imaging does not clearly delineate the cyst.

Case report:

A 31-year-old female presented with 10 years of progressive left hand and 1 year of progressive right arm weakness. Exam revealed atrophy and near complete weakness in the left hand intrinsic muscles (MRC 1), as well as significant right shoulder abduction, external rotation, and elbow flexion weakness (MRC 3). There was mild weakness in the right elbow extension, supination and pronation (MRC 4). No upper motor neuron, bowel/bladder, cerebellar, or sensory abnormalities were detected. Electromyography suggested severe chronic left C8-T1, and moderate-severe right C5-6, myotomal involvement with ongoing denervation in C5-6 myotomes. There were mild-moderate stable chronic neurogenic changes in the right C7-8 myotomes. MRI C-spine without contrast (pregnant) was repeatedly read as normal. However, given confidence in clinical localization, repeat imaging and reads revealed subtle enhancement within the cord, mild atrophy, and subtle signal abnormality anterior to the cervical and thoracic cord. Laminectomy and cysto-peritoneal shunt placement was successfully undertaken.


Initial differential included a neurodegenerative disorder or Hirayama disease until later imaging detected the likely culprit. This case emphasizes the limits of imaging and importance of clinical localization in determining how far to pursue workup. Given relative preservation of right median nerve axons and presumption of no further progression, a nerve transfer utilizing a single median nerve fascicle to biceps is planned to augment elbow flexion strength, which was predominantly lost over the last year and thus likely receptive to reinnervation. This would be the first case we know of where nerve transfer is applied to restore function lost from spinal cord compression by arachnoid cyst. Nerve transfer is becoming a lead surgical intervention to restore function in patients with weakness from numerous central and peripheral etiologies but awareness remains low; delay can result in missing the window of opportunity and poor outcomes.

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