Spinal Ataxia in a Horse Caused by an Arachnoid Diverticulum (Cyst)

Abstract

Incoordination or ataxia associated with spinal cord disease is common in the horse. There are many causes of ataxia in horses, including equine degenerative myelopathy,14 equine protozoal myeloencephalopathy,15 equine herpesvirus 1 myeloencephalopathy,9,15 rabies, other viral equine encephalomyelidities,15 focal cervical injury and trauma,9,16 fibrocartilaginous ischemic encephalomyelopathy,16 and intervertebral disc prolapse.16 Cervical stenotic myelopathy is the major cause of ataxia in young horses.9,16 Cervical stenosis and the resulting degenerative spinal cord changes are the result of a number of causes, including malformation of the vertebrae with stenosis of the vertebral foramen, malarticulation of cervical vertebrae with malalignment, instability, and subluxation, degenerative osteoarthropathy of intervertebral articular processes with osteophyte formation, enlargement of the vertebral dorsal lamina and ligamentum flavum,9,16 synovial cyst,5,16 and occipitoallantoaxial malformation.16 Here, we report an additional cause of spinal cord compression and ataxia in the horse. An 11-month-old cryptorchid Thoroughbred stallion was presented for necropsy because of progressive ataxia, poor growth, and mandibular swellings. The owner had purchased the colt when it was 7 months old. It was small for its age and had a history of mild ataxia attributed to a head injury sustained when it reared up and fell over backward at 3