Snake eye appearance (SEA) is a result of severe long-standing compression of the cervical spinal cord (usually due to spondylosis or ossification of the posterior longitudonal ligament).  It is characterized by cystic necrosis leading to cystic myelomalacia and is thought to have an ischemic (venous) as well as compressive etiology.  The cystic change is symmetrical and involves the mid-cord grey matter, conferring a poor prognosis by way of muscle weakness recovery following surgical decompression.