VOL. 115, No. i E D I T 0 R I A L CISTERNOGRAPHY (CEREBRO SPINAL FLUID IMAGING): A VERSATILE DIAGNOSTIC PROCE DURE C ISTERNOGRAPHY (CSF imaging) is a diagnostic study based on the premise that certain radiopharmaceuticals, after proper subarachnoid injection, reflect the bulk movement of cerebrospinal fluid. The time course of movement after intrathecal injection of J131 human serum albumin has been shown to accurately depict CSF flow. Other radiopharmaceuticals such as Tc99#{176} HSA, In diethylenetriaminepentaacetic acid (DTPA), Ga67 DTPA, and Yb 69 DTPA have a movement pattern similar to P3 HSA. Based upon considerations regarding safety, photon emission, and physical half life, a particular radiopharmaceutical may be preferred depending upon the information sought from the study. Although cisternography in some form has been used as a diagnostic study for almost 20 years, a series of events contributed to its recent exponential growth in popularity. The communications calling attention to dementia resulting from an occult but treatable form of hvdrocephalus led to a search for a simple, innocuous diagnostic test to identify these patients. Almost simultaneous with the renewed clinical interest i n hydrocephalus, better imaging devices and improved radiopharm aceu ticals were being developed. It became possible to obtain images with enough structural detail to identify various cisterns and cerebrospinal fluid spaces. Based upon the clinical circumstance, findings at pneumoencephalography and cisternography, a number of patients were selected and successfully treated with cerebrospinal fluid diversionary shunts. Analysis of the patients response to this form of therapy and the findings of their diagnostic tests led to the conclusion that cisternography might have predictive value in identifying treatable patients. It was learned that those patients with communicating hydrocephalus who had lateral ventricular entry and stasis of the radiopharm aceutical would predictably benefit from the surgical shunt. Stasis has been defined as the radiopharmaceutical remaining in the lateral ventricles on the 24 and 48 hour images. Further experience has shown that stasis is not an absolute predictor of the expected benefit from a CSF shunt. We have encountered several patients who had progressive hydrocephalus following subarachnoid hemorrhage or meningitis; only on serial studies as their hydrocephalus progressed did stasis develop. These patients had dramatic neurological improvement following CSF diversionarv shunts. This does not diminish the importance of the observation of stasis, but emphasizes the value of serial studies in a changing clinical circumstance. Cisternography does appear to be of value not only in detecting patients with communicating hydrocephalus, but in predicting which patients might respond from definitive therapy. This series of events has led to increased interest in cisternography by neurologists, neurosurgeons, radiologists and persons specializing in nuclear medicine. One of the consequences of this development of CSF imaging is that it has been so 201
202 Editorial MAY, 1972 strongly associated with hydrocephalus that potential uses in other diagnostic areas have not been fully recognized. A very important development should be in detection and characterization of intracranial space occupying lesions. Cerebellopontine angle neoplasms which cause localized encroachments upon the CSF space at the base of the brain can be diagnosed by cisternography. Many peripheral lesions from any cause would be predicted to behave in much the same manner. Several laboratories are evaluating the use of CSF images in detecting and analyzing the abnormalities caused by subdural hematoma, convexity neoplasms, cerebral infarctions and in association with transient ischemic attacks. Localized enlargement of the space contaming cerebrospinal fluid might have important clinical consequences. Cisternography is extremely useful in characterizing these lesions, especially with regard to the dynamics of CSF movement into and out of this area. The importance of cisternography in evaluating Dandy-Walker cysts and meningoceles is easily predicted, but even more interesting may be the assessment of fluid containing lesions in which the communication with the subarachnoid space is not so apparent. Porencephalic cysts, subdural hygromas, syrinxes, and leptomeningeal cysts are being evaluated by cisternography. Experience with the newer uses of cisternography is too limited to give any reasonable assessment of its ultimate value, but preliminary data appear favorable. Cisternography is especially useful in the detection and quantification of rhinorrhea and otorrhea. The sensitivity of the method appears greater than injection of dyes or clinical examination. One interjection of caution, however, in evaluating CSF fistulae is that detection of these abnormalities by images is not as sensitive as radioactive counting of properly placed pledgets or swabs. Appropriate patient positioning to accumulate radiopharmaceutical in the area of interest will increase the accuracy of this study. The widespread use of CSF diversionary shunts to treat various forms of hydrocephalus has created a need for a simple method to analyze the changes in CSF flow caused by these shunts and to determine their patency (ultimately to quantify the patency). In patients whose noncommunicating (obstructive) hydrocephalus has been treated by a CSF diversionary shunt, it may be important to determine whether a normal peripheral CSF flow pattern to the parasagittal region has been re-established. CSF imaging is presently being evaluated in patients with arrested hydrocephalus (with and without CSF shunts), pseudo tumor cerebri (benign intracranial hypertension), achondroplasia, and Paget s disease. As with any relatively new procedure, a flurry of initial interest is followed by efficacy studies and comparisons with more generally accepted diagnostic techniques. The study is then placed in more reasonable perspective. Cisternography is now being evaluated in this manner and important information is accumulating. A frequently posed question is the relation of CSF imaging to pneumoencephalography. Since both of these diagnostic studies have many similarities, they quite understandably will be compared. Are they competitive or complementary? Which should be obtained first? Does radiopharmaceutical movement correspond to entry of air at pneumoencephalography? Should pneumoencephalograms and cisternograms be initiated with the same injection and do previous lumbar punctures increase the likelihood of a subsequent improper injection? Data are accumulating to offer substance to the opinions on many of these queries. The movement of radiopharmaceutical reflects, in general, the movement of injected air at the time of pneumoencephalography. However, on a number of occasions, we have seen entry of radiopharma-
VOL. 115, No, Editorial 203 ceuticals into areas which air would not enter. This is most commonly encountered in patients with normal pressure hydrocephalus, in which air will not pass over the cerebral cortex but on sequential images radiopharmaceutical will. The usual explanation offered for this phenomenon is the difference in the physical properties of fluid and air flow. This observation may be of little clinical importance as in these cases no normal concentration of radiopharmaceutical in the area of the arachnoid granulations occurs. In correlating pneumoencephalograms with cisternograms, it appears that radiopharmaceutical does not enter normal sized lateral ventricles and that the amount of ventricular entry of radiopharmaceutical does correspond to the size of the ventricles. The reason for ventricular entry of the radiopharmaceutical from a lumbar injection has not been fully explained. With enlargement of the ventricles, autoradiographic techniques have demonstrated transependymal migration of the radiopharmaceutical in the ventricular area. This would suggest that the explanation for ventricular entry of the radiopharmaceutical is that the lining of the ventricles is now participating in CSF absorption. Stasis also occurs much more commonly in ventricles that are markedly enlarged. Whether this is a physical phenomenon of pooling in an enlarged space or reflection of the physiologic change of more efficient absorption of CSF on a greater surface area has not yet been determined. Because of the practical consideration of patients remaining in the hospital for 48 or 72 hours for cisternography, a number of investigators have sought to combine CSF imaging with pneumoencephalography. Several unusual flow patterns have been observed when air and radiopharmaceutical are concomitantly injected. However, unexpected ventricular entry has not been commonly observed and we have not seen associated stasis in normal sized ventricles. Since we perform cisternography prior to radiopharmaceutical consideration of a pneumoencephalography in most ofour patients, it has not been our practice to combine these two studies. In evaluation of patients for hydrocephalus, we do not usually obtain a pneumoencephalogram if the cisternogram is normal. Regarding the relation of improper injections to previous lumbar punctures, statistical analysis of the cisternographic experience at the National Institutes of Health does not support the concept that improper injections are related to previous lumbar punctures. From this analysis and the studies in our laboratory we believe that images cannot be relied upon to detect improper injections. A method of monitoring transfer of the radiopharmaceutical from the subarachnoid into the vascular or extracellular fluid space is helpful in establishing the presence of an improper injection. If a chelated radiopharmaceutical is utilized, urine can be collected to monitor this transfer. This technique may also be useful in understanding the dynamics of CSF absorption in the various forms of hydrocephalus, in the prehydrocephalic patient, as well as in benign intracranial hypertension. Recognizing the potential danger of meningitis, we do not wish to minimize the importance of this hazard. When it has occurred in patients following injection with serum albumin, the meningitis has almost always been aseptic in type and self-limited in its course. No permanent neurologic deficits or late sequelae have been reported. We have encountered no episodes of meningitis with the chelated radiopharmaceuticals. Similarly, we must determine the radiation hazard to the patient from single and serial CSF imaging studies. Appropriate and realistic experimental models for accurate dosage calculations should be developed and determination made for each new radiopharmaceutical. The quantification of radiopharmaceutical movement and accumulation in specific
204 Editorial MAY, 1972 areas within the CSF space may, in the future, have clinical utility. The impor.. tance of relating flow of the radiopharmaceutical to the volume of fluid under consideration has been shown. To date several elegant techniques have been developed, but the clinical value of quantitative cisternography has not yet been established. In summary, the ability to image and monitor bulk flow and movement of cerebrospinal fluid as reflected by an intrathecally injected radiopharmaceutical is proving to have great clinical utility. CSF imaging (cisternography) appears to have merit in a number of circumstances in evaluation of neurologic disease. Cisternography does not replace pneumoencephalography or cerebral angiography, but is a complementary diagnostic technique. Its major virtues lie in the fact that it is an easily performed, safe, and reliable study to acquire both anatomic and physiologic data about the flow and absorption of cerebrospinal fluid. A. EVERETTE JAMES, JR., Sc.M., M.D. Department of Radiology Johns Hopkins Hospital 601 N. Broadway Baltimore, Maryland 21205
This article has been cited by: 1. Sherman C. Stein, Thomas W. Langfitt. 1974. Normal-pressure hydrocephalus. Journal of Neurosurgery 41:4, 463-470. [CrossRef]