Developmental abnormalities of thoracic vertebrae are infrequent in horses. Hemivertebrae is a congenital spinal anomaly resulting from failure of formation on one side of a vertebral body. This condition can cause kyphosis, lordosis, or scoliosis with or without neurologic gait deficits. This report describes the clinical findings of congenital thoracic hemivertebrae in a filly. A nine-month old walking filly with a distinct mass over the back region was referred to the Veterinary Teaching Hospital of Ferdowsi University of Mashhad. According the owner, this mass was present since her birth and increased in size over time. There was no history of trauma. On physical examination the filly was alert and her body condition was normal. The respiratory rate, heart rate and temperature were within normal limits. Examination of the filly back revealed kyphoscoliosis over the thoracic vertebrae. No pain was detected on palpation. Mild ataxia and abnormal gait in hindlimbs were observed on examination of the limbs. In plain radiographs of thoracic vertebrae, multiple hemivertebrae were seen in 13th-15th thoracic vertebrae and vertebral canal stenosis with malformations of the vertebral bodies of T12, T16 and T17. In myelographic evaluation under general anesthesia, ventral and dorsal aspect of contrast medium column was not passed that revealed extradural compression of the spinal cord in mentioned thoracic regions. Various aspects of this disorder including its progression, treatment options, outcomes, prognosis, and animal’s welfare were fully explained to the owner, but the owner refused to its management. Thoracic vertebral malformations are an uncommon congenital disorder occurring in horses. Complete clinical examination and diagnostic imaging techniques are required to diagnosis of vertebral malformation.

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