CT of the canine lumbosacral spine in extension - flexion rotation; part II: soft tissue window

Computed tomography (CT) is more and more indicated to get reliable findings because myelography is not always of diagnostic value. For this study twelve dogs (7 German Shepherd dogs, 4 Cross-breds, and 1 Rottweiler) of different age and sex were taken which had been referred for CT examination of the lumbosacral area. Plain radiographs were without pathological findings. The anesthetized dogs were positioned in dorsal recumbency with the legs firstly extended and secondly flexed according to flexion-extension radiography. Slice thickness was 2 mm, the CT images were evaluated in both bony and soft tissue windows. (The lumbosacral skeleton has been described in part I of the study). Soft tissue window showed the course of the myelon and its cauda equina nerve roots of L6, L7, S1, and S2, surrounded by fatty tissue. The lumbosacral intervertebral disc appeared slightly hyperdense, oval-shaped, and smooth; the dorsal surface was concave or flat. Dorsal and ventral longitudinal ligaments were not seen in every dog. Yellow ligaments were seen in every case. They appeared as soft tissue densities ventrally adjacent to the intervertebral joints during extension. During flexion they were seen as tense thin sections of soft tissue roofing the interarcual space. Intervertebral ventral venous plexus could be identified after contrast medium had been administered intravenously. The venous anastomosis of the plexus and the intervertebral vein at the connecting point in the caudal part of the intervertebral foramen appeared to be 2 to 8 mm broad; it was drained off into the common iliac vein. CT anatomy of the lumbosacral spine a lows identification of all important structures therein and gives hints for evaluating possible cases of lumbosacral instability which causes cauda equina syndrome. The obligatory use of contrast medium will detect dilated venous plexus or varicose anastomosis as additional differential cause of lumbosacral disease when plain images of bony and soft tissues show no pathological findings. (author)