The Postoperative Lumbar Myelogram

Lumbar myelography is a well established radiographic technic in the diagnosis of lumbar disk protrusions. In a series of more than 700 “positive” myelograms, i.e., showing some abnormality, followed by lumbar hemilaminectomy for excision of protruded or extruded intervertebral disks, we have been impressed by the accuracy and reliability of this diagnostic procedure. We shall not, in this presentation, concern ourselves with the actual technic of lumbar myelography or the surgical technic for correction of lumbar disk protrusions. Rather, we shall limit our discussion to the problem of the postoperative myelogram, that is to say, a lumbar myelogram performed in a patient who has undergone laminectomy or hemilaminectomy for disk herniation. In our series of 38 cases, representing almost 5 per cent of the total number of laminectomies performed by the authors, we have gained certain impressions and come to certain conclusions which serve as the basis of this report. All of the myelographic examinations were carried out by the members of this group according to a uniform technic, employing 6 to 10 c.c. of Pantopaque introduced by a No. 18 spinal needle into the lumbar subarachnoid space and withdrawn as completely as possible following the examination. The indications for repeat myelography, as for the initial study, were signs and symptoms of lumbar nerve root irritation or compression, considered on clinical grounds to be consistent with the possibility of lumbar disk protrusion. Myelographic examinations were carried out in patients with objective neurological signs and in cases with long standing subjective complaints of low back or sciatic pain in whom conservative therapy had failed. The average period between the laminectomy and the performance of postoperative myelography was eleven months; the time interval varied from eight days to twenty-three months. In this report, we analyze the findings in 38 cases. In all, the initial myelogram had shown a definite lesion diagnosed as consistent with the protrusion of one or more intervertebral disks in the lumbar region. At various intervals following surgery, recurrence of symptoms, with or without new injury, or failure of the patient to improve led to myelographic re-examination. Of the 38 cases, 22 (58 per cent) showed postoperative myelographic findings which could be considered within normal limits. In the remaining 16 cases the presence of a myelographic defect either at the same level or at another level led to a second operation, with confirmation of gross pathology consistent with the myelogram. On a review of the 16 re-operated cases and an analysis of the repeat myelograms, the following observations were made: A. In 5 cases the original myelographic defect was no longer present, but a new defect at another lumbar level was found, consistent with a new herniation. This was confirmed by a second laminectomy. B. Eleven cases showed evidence of a myelographic defect at the original level.