Recently, radioisotope cisternography has become a widely used method for the morphological assessment of cerebrospinal fluid (CSF) dynamics by means of radioactive materials introduced into the subarachnoid space. This technique provides useful information regarding the intracranical subarachnoid CSF dynamics. A wide variety of radioactive agents have been used with varying success to make the CSF space visible. In particular, in respect to stability, molecular weight and half-life, (169)Yb-DTPA has been found to be one of the best radio-pharmaceuticals for cisternography. The purpose of this paper is to discuss the characteristics of (169)Yb-DTPA compared with (131)I-HSA in cisternography, based on the author's experimental data and clinical experience. Experimental studies: (1) After injecting (131)I-HSA, (169)Yb-DTPA and (99m)Tc-pertechnetate respectively into the lumbar subarachnoid space of three groups of dogs, the author investigated serially the movement of these tracers with a scintillation camera and the transport of these isotopes from CSF space to blood by counting the radiosctivity of the blood samples with a well-type scintillation counter. The author observed that there is a good possibility that (169)Yb-DTPA will show the dynamics of CSF absorption in both spinal and intracranial subarachnoid spaces. (2) Ten ml of autologous whole blood was injected into the cisterna magna of dogs, and the injection was repeated 2-3 times at weekly intervals. Three to five weeks after the last injection, chronic subarachnoid hemorrhage was achieved. In both chronic subarachnoid hemorrhage dogs and control dogs, laminectomy was performed at C(2) level and silicon tube was cannulated into the intrathecal or intracranial subarachnoid space, and then, the intrathecal subarachnoid space was completely divided from intracranial subarachnoid space by extradural ligation. After 100
μCi of (169)Yb-DTPA was injected into the intrathecal or intracranial subarachnoid space, 1.0ml
of physiological saline solution was injected into the same place from the tube. Then, CSF pressure changes were recorded continuously by the pressure transducer and blood samples were taken at regular time intervals from the veins in order to determine the amount of activity of (169)Yb-DTPA transported into the blood from the subarachnoid space. In control cases, the elevated pressure immediately after injection of saline solution decreased to the level of 100-150 mmH(2)O for the period of approximately 10 minutes. According to these pressure changes, large amount of (169)Yb-DTPA were transported into the blood from the subarachnoid space, but in chronic subarachnoid hemorrhage cases, prolonged elevation of CSF pressure was seen and little (169)Yb-DTPA was transported into the blood. These results suggest that the transportation of (169)Yb-DTPA into the blood from the subarachnoid space is closely related to the absorption dynamics of CSF in the intrathecal and intracranial subarachnoid space. Clinical studies: In clinical cases, the author tried to determine how clearly one can see CSF dynamics, particularly in the intrathecal subarachnoid space by (169)Yb-DTPA cisternography combined with the (169)Yb-DTPA transfer test. With the patient in a lateral position, a spinal puncture was performed at L(4)-5 interspace. After measuring CSF uressure, the author injected
500 μCi of (169)Yb-DTPA into the lumbar subarachnoid space. Then scintigrams of the head and lumbar regions were taken 1, 2, 6, 24 and 48 hours after the injection. In addition, at varying time intervals up to 6 hours, blood samples were taken from the veins in order to determine the amount of activity of (169)Yb-DTPA transported to the blood from the subarachnoid space. Here, the author considered the (169)Yb-DTPA concentration curve in the blood from a time immediately after the injection up to 1 hour thereafter (when (169)Yb-DTPA was still located only in the intrathecal space), reflects the absorption dynamics of CSF in the intrathecal subarachnoid space. In normal cases, the concentration curve of (169)Yb-DTPA in the blood showed two peaks around 1-2 and 4-5 hours after injection. This finding agree with the canine experimental data. First of all, the author studied the correlation between the changes in the (169)Yb-DTPA concentration curve in the blood and CSF pressure. When CSF pressure was under 100 mmH(2)O, the concentration curve in the blood was plotted in the lower levels at about 1/5 of the height of normal CSF pressure cases. On the other hand, when the movement of (169)Yb-DTPA into the blood was rapid and little (169)Yb-DTPA went up into intracranial space, the CSF pressure was inclined to be somewhat higher. This means that (169)Yb-DTPA was rapidly transported to the blood from the subarachnoid space in the cases with high CSF pressure like a brain tumor case. There are some occasions to use (131)I-HSA instead of (169)Yb-DTPA in such cases. The molecular weight of (131)I-HSA is 100 times greater than that of (169)Yb-DTPA, and from this reason (131)I-HSA is less likely to be absorbed from the intrathecal subarachnoid space. In addition, the author may note that there was no close relation between the amount of CSF protein or CSF osmotic pressure and the pattern of concentration curve in the blood. In the next place, the cases which had subarachnoid hemorrhage following the ruptured aneurysm, showed various abnormal CSF dynamics, such as low absorption from the intrathecal space and from the parasagittal arachnoid villi and reflux of (169)Yb-DTPA into the venricular system. In some of these cases, when ventricular dilatation is strong and ventricular stasis of (169)Yb-DTPA is observed over a 24 hour period the (169)Yb-DTPA concentration curve came to show high levels when a great deal of (169)Yb-DTPA appeared in the ventricles. This may mean that CSF is absorbed from the ventricular system in pathological condition. Lastly, when performing (169)Yb-DTPA cisternography, it is very important to know whether (169)Yb-DTPA was injected correctly into the lumbar subarbchnoid space. To determine this, it is useful to monitor the (169)Yb-DTPA concentration curve in the blood for several minutes, in addition to taking scintigram of the lumbar region, because when (169)Yb-DTPA is injected extradurally, the (169)Yb-DTPA concentration curve in the blood shows the same form as that in the blood after the direct intravenous injection. As mentioned above, the author consider that (169)Yb-DTPA is an unique and useful radio-pharmaceutical for cisternography, particularly when it is necessary to study the absorption dynamics of CSF not only from intracranial, but also from intrathecal subarachnoid space.