Chiari Malformation

Chiari malformation is a congenital abnormality that involves the skull. In certain dogs (usually small breeds) the portion of the skull that houses the brainstem is abnormally small. This puts direct pressure on the brainstem and can alter the flow patterns of spinal fluid, resulting in changes in the cervical spinal cord (Figure 1). Some of the clinical signs associated with this disease include scratching, weakness, abnormal coordination, head tilt, and pain. Chiari malformation can only be reliably diagnosed through brain MRI. In some cases it can be treated with medications that reduce spinal fluid production or inflammation. Surgical treatment consists of removing a small portion of the back of the skull and the first cervical vertebra. Any fibrous tissue that is impinging the brain is also removed.

Figure 1: Sagittal T2 weighted MRI from a Cavalier King Charles Spaniel with features of Chiari-like malformation. The small arrows point to a lesion within the spinal cord that is consistent with a fluid cavity (syringohydromyelia or SHM). The large arrowhead points to bone indenting the caudal cerebellum and displacing it out the foramen magnum.