An inexpensive blue filter for fluorescein-assisted repair of cerebrospinal fluid rhinorrhea.

INTRODUCTION The endoscopic approach to the repair of cerebrospinal fluid (CSF) rhinorrhea represents a considerable advance over open approaches. Advantages of the endoscopic approach include a high success rate, rapid recovery and discharge, preservation of olfaction, avoidance of frontal lobe retraction, and avoidance of a craniotomy scar. Intraoperatively, repair cannot be attempted until the exact leak site has been definitively visualized. Often, the leak site will be obvious. Occasionally, however, the flow of CSF must be identified first, then traced back to its origin to determine the exact leak site. Minor and intermittent leaks can be extremely difficult to visualize. Furthermore, at the conclusion of a repair procedure, the integrity of the repair can be difficult to judge. Intraoperative identification of CSF leaks may be aided with techniques that increase the flow of CSF. These include use of the Trendelenburg position, anesthetic techniques to perform a prolonged forced inspiration, and the injection of fluid intrathecally. However, the most effective technique to improve leak site identification is the use of intrathecal fluorescein, which colors the CSF a bright yellow-green. The fluorescent properties of fluorescein may be understood as follows: white light consists of a mixture of light of different wavelengths. When white light shines on an object, the object appears a particular color as it reflects that particular color’s wavelength. Concentrated fluorescein appears orange as it reflects orange wavelengths (585–620 nm). However, once diluted to concentrations between 0.1% and 0.0000001% and exposed to white light, fluorescein emits a yellow-green glow. This is due to fluorescein molecules undergoing excitation by the blue portion of white light at 460 to 490 nm and temporarily entering a higher energy state. As the fluorescein molecules return to their unexcited state, the absorbed energy is released, creating a yellowgreen light of 520 to 530 nm. This effect is intensified with a pure blue light source. A typical ear, nose, and throat (ENT) light source produces light of a mixture of wavelengths to create white light. Placing a blue filter in front of an ENT light source results in the transmission of light solely in the blue portion of the spectrum, as all other wavelengths are blocked by the filter. The use of a blue filter aids in the identification of very small quantities of fluorescein. This can be of assistance in identifying minor leak sites and in confirming the integrity of a repair at the conclusion of a procedure. When using a blue filter, the likelihood of detection is improved by direct visualization through the endoscope, rather than using a camera and monitor. A commercially produced blue filter is available (fluorescein blue filter system, part # 2