Chiari-like malformation (CM) is the most common cause of foramen magnum obstruction and syringomyelia in the dog. CM is a condition characterised by mismatch in size between the brain (too big) and the skull (too small). There is not enough room for the brain and the back part (cerebellum and medulla) is pushed out the foramen magnum.
CM is a skull disorder which is characterized by an abnormal placement of part of the brain, cerebellar tonsils, through an opening in the skull, called foramen magnum. Spinal cords pass through this opening. This protrusion of brain into this opening causes obstruction in normal flow of cerebrospinal fluid (CFS).
Syringmyelia is the conseqential disorder which results from the obstruction in normal flow of cerebrospinal fluid–the development of fluid-filled cavities, or cysts, within the spinal cord. Syringomyelia occurs secondary to obstruction of cerebrospinal fluid (CSF).
These disorders may develop due to underlying health problems, but they have also been found to hereditary links in some breeds. Toy breeds including the Cavalier King Charles Spaniels, King Charles Spaniels, and Brussel Griffons are at an increased risk for developing this condition. This condition has also been reported in Staffordshire bull terriers.
Common symptoms associated with CM and syringmyelia include
Crying during defecation or posture changes
Distress during moments of normal excitement
Intermittent pain (more severe at night)
Sensitive to touch at shoulder, neck, ear, and sternum areas
Scratching or pawing at shoulder, ear, neck, or sternum
Scratching is more pronounced while walking and may be triggered by neck collar or excitement
Head pressing due to head pain
Uncoordinated walk, apparent dizziness, wobbly eye movements
Weakness, muscle fatigue
Lethargy, loss of consciousness