A 6-month-old intact male rottweiler was referred for neurological evaluation and canine extraction at the Cornell University Hospital for Animals in January 1998. At the time of purchase, at 19-weeks-old, the owner noted that the mandibles of the dog were severely shortened and the inferior canines were protruding into the palate bilaterally upon closure of the mouth. In addition, when the dog ran, he moved with marked hypermetria of both thoracic limbs and he often fell.
The dog was bright and alert with normal body condition. The mandibles were approximately 3 cm shorter than expected with the inferior canines positioned caudal to the superior canines. The superior PM1 teeth were mildly displaced caudally and laterally by the inferior canines and an approximately 0.4-cm deep × 0.3-cm round ulcerated, crater was present just caudal to the superior canines, bilaterally and rostral to pre-molar 1 (PM1). Upon closure of the mouth, the inferior canines, which were erupted to approximately one-half of their potential adult length, penetrated into the ulcerated maxillary lesions.
On neurological examination the cranial nerves were normal. When the dog walked in a straight line, the gait was normal. When circled to the left, the right thoracic limb mildly abducted. When trotting, both thoracic limbs exhibited an abnormal cranial extension on protraction resulting in a hypermetric action. The joints were in extension during this action which gave them the appearance of floating or overreaching before weight bearing occurred. Hopping and paw replacement reactions were normal as were spinal reflexes. There was no discomfort elicited on manipulation of the neck. The anatomic diagnosis was a mild C1 to C5 spinal cord segment disorder. The most likely clinical diagnosis was a vertebral malformation-malarticulation with spinal cord compression. Differential diagnoses included cervical trauma, synovial cyst, atlantoaxial instability, congenital vertebral malformation, cervical spondylomyelopathy, leukoencephalomyelopathy of rottweilers, and neuroaxonal dystrophy of rottweilers (1
All blood parameters, including packed cell volume (PCV), blood urea nitrogen (BUN), creatinine, total protein, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and glucose were normal. Routine castration and extraction of both inferior canine teeth were performed. Lateral and dorsoventral cervical vertebral radiographs were obtained. The dens was absent from the axis () with no associated displacement between the atlas and axis. The vertebral canal was not compressed at this site. In addition, there was asymmetry of the transverse processes of the atlas. Surgical options were considered for therapy; however, the owner elected to not pursue therapy but observe the dog for any progression of the clinical neurological signs. For the next 9 y there was neither change in this dog’s neurological signs nor any development of neck discomfort.
Figure 1 Radiographs of a 6-month-old intact male rottweiler. Note the complete absence of the dens (black arrows) evident in both the lateral and dorsoventral views. In Figure 1a note the asymmetry of the wings of the atlas (white arrows) with the left being (more ...)
A grade 2 soft tissue sarcoma involving the rostral third of the mandibles was diagnosed when the dog was 9.5 y old. Treatment consisted of surgical resection, but the sarcoma recurred within 1 mo post-excision. In addition, advanced degenerative joint disease of the elbows and hips had developed and the owner elected to have the dog euthanized.
Necropsy was limited to the first 4 cervical vertebrae and associated spinal cord segments. The atlas and axis were severely malformed (). The dorsal atlantoaxial membrane and ligament were markedly thickened (~1.3 cm), compared to an age-matched female rottweiler of similar weight and stature (0.4 cm). This tissue was asymmetric with a bulbous, soft region that extended further to the left of midline (1 cm) than to the right of midline (0.7 cm). This connective tissue was white and composed of loosely arranged layers.
Necropsy specimens of the same rottweiler collected at 9.5 years of age. In 2a note the same asymmetry of the wings of the atlas (arrows). In 2b there is confirmation of the complete absence of the dens (arrow).
The transverse processes of the atlas were asymmetric with the right transverse process being smaller and more round than normal. The left transverse process was caudally displaced, rectangular, and about 1 1/2 times larger than the right transverse process. From a dorsal view the rostral articular fovea and transverse processes were shifted about 10 degrees in a caudal plane. A 1 × 0.2 × 0.3 cm rounded osteophyte was centered to the right of midline on the rostral aspect of the cranial articular fovea of the atlas.
The rostral portion of the spinous process of the axis was shifted to the right. The bulbous proliferation of the dorsal atlantoaxial membrane and ligament protruded from the left side of the spinous process and the deviated spinal process was dorsal to the ligament on the right side of midline. The right transverse process of the axis was about 0.4 cm shorter than the left process. The resultant angulation of the atlantoaxial joint was shifted about 10 degrees caudally. The dens was completely missing as was the apical ligament of the dens. The alar ligaments of the dens were attached laterally to the rostral articular surface of the axis about 0.8 cm apart. The attachments of the alar ligaments to the occipital bone medial to the occipital condyles were normal. The articular cartilage of the cranial articular surface of the axis was tan, mildly pitted, and roughened. There was mild osteophyte production on the ventral cranial articular surface of the axis. Dural ossification was present in the form of 2 hard masses in the dura to the right of the midline ventral to the first 2 spinal cord segments. Both masses were elongate, pink-tan, and hard. The cranial mass was about 0.4 × 0.2 × 0.8 cm. The more caudal mass was 0.3 × 0.2 × 1 cm.
Six transverse sections of the cervical spinal cord from C1 to C4 were examined histopathologically. There were occasional dilated myelin sheaths containing macrophages within the dorsal lateral tracts within the transverse sections of spinal cord cranial to the atlantoaxial joint. Rare similar dilated myelin sheaths were located within the deep portion of the ventral funiculus at the level of C2–C3 articulation. Only 2 to 3 dilated myelin sheaths were noted per transverse section of spinal cord examined.
In summary, the necropsy findings included: 1) malformation of the transverse processes of the atlas; 2) degenerative joint disease with osteophyte production on the atlas cranioventrally; 3) absence of the dens of the axis; 4) spinous process malformation (deviated to the right rostrally) of the axis; 5) transverse process malformation (right process is shorter) of the axis, 6) absence of the apical ligament of the dens; 7) moderate to severe degenerative joint disease of the atlantoaxial joint with osteophyte production on the axis cranioventrally; 8) severe dorsal atlantoaxial membrane and ligament fibrosis; 9) multi-focal dural ossification ventral to the C1 and C2 spinal cord segments; and 10) mild, chronic ascending and descending Wallerian degeneration of the spinal cord.