Application of RI-counting method for CSF rhinorrhea

Some diagnostic procedures for CSF rhinorrhea have been reported, but they can not always identify and localize CSF leakage. This method, using intranasal cotton pledgets after the intrathecal injection of radioisotope (¹¹¹In-DTPA) is thought to be reliable, informative and innocuous for localizing the sites of CSF leakage. This technique was named RI-counting method, and applied in two cases that were difficult to diagnose especially with positional-loading. The patients were first in the supine position, then in the sitting position, after the intrathecal injection of radioisotope and the intranasal insertion of cotton pledgets. After exchanging these pledgets, the patients were set in the prone position. After measuring the radioactivity of these pledgets and of 1 ml of blood, the ratios of the radioactivity of the pledgets to that of the blood were calculated. In case 1 the ratios of the left sphenoethmoid recess and the left middle meatus were significantly higher when the patient took the prone position, but in the supine or sitting position the ratios were in the normal range. In case 2 the ratio of right olfactory cleft was significantly higher in the sitting position or neck flexion. Both cases were operated and demonstrated that the location of the CSF leakage was presumable by using RI-counting method, regarding the anatomical relationship between the intranasal sites of pledgets and the opening of the paranasal sinuses. Positional-loading seemed to be essential. We obtained 72 pledgets of patients without CSF rhinorrhea, and the ratios of radioactivity of these pledgets had a mean value (M) of 0.156 and a standard deviation (SD) of 0.107. Therefore, the ratios over 0.37 (M + 2SD) were considered to be significantly higher than the normal range. CSF rhinorrhea after trauma produces the risk of meningitis, and in a few cases the onset is delayed by many months or even years. Cases in which a spontaneous closure is expected will still have the risk of meningitis. The RI-counting method should be applied in such cases and we recommend surgical repair of the dural laceration if rhinorrhea is detected.