The Myelography Examination of the Foramen Magnum

The clinical diagnosis of benign tumors in the region of the foramen magnum is often extremely difficult (2, 5, 8). Even if such a lesion is suspected, a satisfactory diagnosis may not be possible without roentgenologic evidence. In the presence of extradural malignant lesions, bone changes are generally detectable. The benign intradural tumors usually show no alterations on regular x-ray films, though a small proportion may exhibit thinning of one side of the arch of the atlas or ballooning of a cervical intervertebral foramen. Since these lesions may produce severe neurologic damage before complete spinal block appears, an accurate and safe method of confirming the diagnosis at an early stage has been a primary need. This appears to have been met by the development of the myelographic technic. Myelographic examination of the foramen magnum presents some special difficulties as well as special requirements. In this region lesions are easily missed; yet even minor changes can be readily appreciated with adequate methods of myelographic study. Technic The lumbar puncture and the instillation of oil are done in the usual manner, with the patient in the lateral recumbent position with the legs and back flexed, as shown in Figure 1, A. We prefer a short-beveled 18- or 19-gauge needle to the ordinary longer-beveled spinal needle; it is felt that the incidence of subdural or epidural injection is greatly reduced by the use of the short bevel and that the ease of oil removal is greater, since the needle opening can be brought nearer to the ventral surface of the canal during aspiration of the medium. A Queckenstedt test is usually performed at the time of the lumbar puncture. If an open system is demonstrated, an average of 12 c.c. of Pantopaque is used; if there is a complete block, the amount of oil is reduced 2 or 3 c.c. The cross-sectional areas of the cervical canal vary widely in different patients, as does also the fluid capacity (10). If, therefore, the routine injection of 12 c.c. appears inadequate after entering the cervical canal, a further 6 to 12 c.c. may be added. After the oil is introduced through the needle, the stilette is refitted and the patient is turned onto the abdomen, as in Figure 1, B. The patient is instructed to attempt to hold the head in whatever position it is placed by the examiner and told that it will be flexed and extended at various times. An attempt is made to instruct him in flexion and extension of the neck as separate functions from flexion and extension of the head. He is specifically warned that under no circumstances is the head to be turned laterally and that the movements in the vertical position, namely, flexion and extension, are to be made only at the hands of the examiner and not otherwise. The oil is then brought up into the cervical region, the only problem in doing this being to get it across the dorsal hump without it entering the head.