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 a...