Quantitative analysis of radioisotope cisternography in the diagnosis of intracranial hypotension

OBJECT: The authors attempted a quantitative analysis of conventional radioisotope cisternography for the purpose of more accurate diagnosis of intracranial hypotension. METHODS: Fifty-seven patients suspected of having intracranial hypotension underwent radioisotope cisternography. Whole-body images were obtained 2.5, 6, and 24 hours after intrathecal injection of 111In-diethylenetriamine pentaacetic acid. Radioactivity in the cerebrospinal fluid (CSF) space was counted during scanning, and radioisotope clearance was studied. Direct signs of radioisotope leakage into the spinal epidural space were found in 25 patients. Most leaks were located in the lumbosacral region. Analysis of the radioisotope clearance curve revealed two different patterns. In patients without a radiographically demonstrated radioisotope leak, absolutely exponential curves were observed (R2 > 0.99). The activity of the radioisotope decreased at a rate of e(-003) to e(-0.107) (mean +/- standard deviation, e(-0.056 +/- 0.018); 32 patients). Clearance in patients with an overt radioisotope leak was not a simple exponential curve; it could be divided into an early rapid phase and a late slow phase. The clearance rate during the first 6 hours was e(-0.219 +/- 0.127) (25 patients) and e(-0.076 +/- 0.021) thereafter. The authors speculated that the early escape of undiluted radioisotope solution through an aberrant CSF outlet, such as a traumatic spinal dural tear, was responsible for this phenomenon. CONCLUSIONS: The quantitative analysis featured in this study seems to be useful in the diagnosis of intracranial hypotension. A small CSF leak below the limit of radioisotope cisternography resolution might be detected using this technique.