Macro- and microscopic findings, left panel from dog 1, and right panel from dog 2. (A) Sagittal section of the neck of dog 1 showing an absence of the dens (encircled area) of C2. (B) Grey matter lesions of dog 1 showing haemorrhage and numerous gitter cells (arrow heads). (C) White matter lesions in the ventral funiculi of dog 1 showing numerous spheroids (arrow) and dilated myelin sheaths with macrophages. (D) Axis from dog 2 (right) compared to axis from a normal, five-year-old boxer dog (left). In dog 2, the dens is absent and an irregular depressed area is present in the normal position of the dens. The cranial articular surfaces (asterisks) in dog 2 are smaller than in the normal dog. (E) Grey matter lesions of dog 2 showing an area of necrosis with gitter cells. (F) White matter lesions of dog 2 showing numerous spheroids (arrow) and dilated myelin sheaths. All histological sections shown (B,C,E,F) are from the atlantoaxial area of the spinal cord.