The importance of the air shadow of the cisterna magna in encephalographic diagnosis.

Abstract

The cisterna magna frequently is the site of clinically obscure lesions that do not increase the intracranial pressure and that can be outlined by pneumoencephalography. Little has been written on this subject because, as a rule, neurological surgeons have preferred to use ventriculography in cases of suspected surgical lesions and, in addition, unless a special effort is made, the cisterna magna is seldom visualized. The value of pneumoencephalography in this respect is demonstrated by the analysis of an experience of one year to be presented here. Precautions In our institution, pneumoencephalography in itself has always been regarded as a surgical procedure. Therefore, the positioning of the patient, the induction of anesthesia, the injection of air, the radiography, the development and the examination of the films, all are carried out on the operating floor, where every surgical and anesthetic facility is at hand. Sterile packs of instruments for craniotomy and for ventricular tap are kept available at all times. If signs of increased intracranial pressure are present, the instruments are laid out and the scalp is prepared for craniotomy before the spinal air injection is started. The films are processed in a rapid developer; they are examined in the wet state and, if a surgical lesion is disclosed, the patient is kept under continuous observation in the surgical pavilion until the operation has been performed. When papilledema is present and obstructive hydrocephalus is suspected, encephalography is seldom employed and never without a preceding ventricular tap to relieve the intracranial tension. The technic of performing emergency ventricular tap has been simplified so that a cannula can be introduced into the ventricle within two minutes should indications arise. With this planning and these precautions, emergency situations will seldom develop. Over a period of twenty-eight years pneumoencephalography has proved, in our experience, to be a safe procedure and has disclosed many surgical lesions which could not have been diagnosed by any other method short of exploratory craniotomy. To employ ventriculography in place of encephalography in cases of suspected cerebral tumor without increased intracranial pressure, is not in the patient's best interest. Neither encephalography nor ventriculography, for that matter, should be undertaken without the precautions described above, since an expanding lesion will occasionally be disclosed even under the most unlikely circumstances. This possibility plus the hazards inherent in the use of any anesthetic agent can lead to disaster, if circumstances do not permit prompt counter measures. Technic Thiopental (Pentothal) sodium is the anesthetic agent usually employed. Ten milliliters of air is introduced before starting the removal of fluid, and thereafter the fluid is replaced with air in 5-ml. amounts, with pressure readings at frequent intervals.