Twenty-four-hour films as an aid in the recognition of mixed injections (subarachnoid, subdural, and epidural) in Pantopaque myelography.

Abstract

In faulty myelographic injections (mixed injections), in which a portion of the Pantopaque is in the subarachnoid space and another portion in the extra arachnoid space (subdural or epidural), a 24-hour film may disclose extension into paraspinal soft tissues along nerve roots. In addition, 24-hour lateral films obtained with a horizontal x-ray beam may show abnormal hold-ups of the Pantopaque in relation to surrounding structures and a failure of the hyperbaric componnd to recede to a dependent position. These 24-hour film studies confirm less evident changes that may have been overlooked at the initial examination and, in addition, in the absence of a cinefluoroscopic record, they will eliminate the subjective impression of the examiner about the flow rate of the contrast medium. These delayed films have been widely used in pneumoencephalography to uncover subdural collections of air which could not be seen on the immediate films , and the same practice should be followed in Pantopaque myelography. After twenty-four hours, the needle is no longer present and the patient can be manipulated in both the supine and the prone positions. After the contrast medium is collected in the lumbar or cervical regions, both prone and supine films should be obtained with the horizontal beam. Pantopaque is hyperbaric and, if it is outside the subarachnoid space, it will fail to assume the dependent position which one would expect. This is apparent in the horizontal beam films. If Pantopaque is seen at a distance from the vertebral bodies on the prone film, its extra-arachnoid location is verified. Conversely, if the Pantopaque has not appreciably shifted its position on the supine film obtained with the horizontal beam, its extra-arachnoid location is also confirmed. If the injection was partially epidural, the exit of the contrast material along nerve roots is easily recognizable after twenty-four hours, since it will then be seen within the paraspinal tissues. High dorsal myelography as well as cervical myelography entail keeping the patient in almost vertical position for prolonged intervals. Even under these circumstances, abnormally placed contrast material may have the opportunity to reach either the cervical or dorsal region. Should this heavy contrast substance reach the epidural space in the dorsal region, it flows readily into the paraspinal tissues, as Sharpey's ligament in the dorsal region does not limit its exit. Contrast medium which is retained in the spinal canal for prolonged periods usually finds an exit through the site of the spinal puncture or slightly below. Therefore, the nerve roots in this region may be minimally outlined. The outline of roots together with the large collections of contrast medium in the dorsal region is not seen unless the patient has been in an almost vertical position and the contrast medium was deposited in the extraarachnoid space.