Imaging the equine neck

The equine cervical spine is an anatomically complex bony canal, which acts to protect and support the spinal cord and the emanating spinal nerves. Horses have seven cervical vertebrae, and eight pairs of cervical spinal nerves. The bony structures are largely identifiable by specific shapes and individual features when assessed using the variety of available diagnostic imaging modalities.

The first cervical vertebra (C1; atlas) is a flattened oval-shaped bone with large lateral wings that are palpable from the skin surface. The second cervical vertebra (C2; axis) is characterised by the odontoid process (dens), on the cranial margin, this is associated with a separate centre of ossification that closes around 7 months of age; this should not be confused with a fracture. The C2 vertebra has an extensive dorsal crest that is not found on other vertebrae. The third, fourth and fifth cervical vertebrae in many horses are similar to one another in structure and size, with prominent thin transverse processes extending to the left and right of the vertebral body, orientated ventrally. In young animals, open physes may be visible; the cranial growth plate of the vertebral body closes around 2 years of age, while the caudal physis closes much later, at 5 years of age. The sixth vertebra is typically shorter, and is associated with larger transverse processes than C3–C5, with an additional ventral component; considerable variation may be seen, however (Veera et al, 2016). The seventh vertebra is short, and often does not have a radiographically-visible transverse process, though there may be transposition of a transverse process of C6 onto C7, which can confuse interpretation. In some horses, a variably-sized spinous process of C7 can be present, mimicking that of T1.