|Closed arrows||Caudal extent of synovial space|
|Open arrows||Biceps brachii tendon|
Cisternal puncture: Figures 813–818
Right lateral recumbent and ventrodorsal projections
The subarachnoid space is at its widest through the 1st and 2nd cervical vertebrae. The ventral column of contrast not infrequently bends slightly dorsally, as well as narrowing, at the 2nd to 3rd cervical intervertebral disc space. Slight narrowing of the ventral column with minor indentations may also occur over each of the subsequent intervertebral disc spaces.
The spinal cord is at its widest in the lower cervical region where it gives rise to the nerves of the brachial plexus. Through the 5th and 6th cervical vertebrae the ventral column often appears raised from the floor of the canal.
The use of a tilting table for this contrast technique enables positioning of the head and neck at an angle of 5 to 10 degrees from the horizontal in a dorsocranial–ventrocaudal direction, which encourages the caudal flow of the contrast medium along the subarachnoid space. In the absence of such a table temporarily placing the animal in sternal recumbency with the head moderately elevated has a similar effect.
Linear opacities representing the walls of the endotracheal tube can be seen superimposed on the 2nd and 3rd cervical vertebrae and on the cranial part of the 4th. In some cases such shadows create confusion in the interpretation of the myelogram.
There is a gradual redistribution of the contrast in the caudal thoracic subarachnoid space resulting in a well-filled dorsal column and a thinner ventral column.
Considerable tilting of the long axis of the spine in a dorsocranial–ventrocaudal direction was necessary in this case to further the flow of contrast medium beyond the caudal cervical region.
In the caudal thoracic region the dorsal column of contrast is much wider than the ventral. Through the cranial lumbar vertebrae the ventral column increases again in width. From the 4th lumbar vertebra the columns begin to converge as the spinal cord tapers into the cauda equina. Radiolucent linear filling defects obliquely crossing the cord at the 4th lumbar vertebra are caused by the emerging spinal nerve roots and confirm the subarachnoid distribution of the contrast medium.
Shallow undulations of the ventral column, lifting over the intervertebral spaces, are frequently seen in the lumbar region, occasionally with a slight break in the contrast.
Some widening of the cord at the 4th and 5th lumbar vertebrae, the origin of the nerves of the sacral plexus, may be apparent.