Cerebrospinal fluid fistulae in a canine model

Various diagnostic techniques currently are used to detect the presence of a cerebrospinal fluid fistula. High resolution computerized tomography scanning with the instillation of an intrathecal nonionic contrast medium yields the most accurate diagnostic results. Occasionally, even with optimal conditions, little information is gained other than the confirmation of the presence of a fistula. Intrathecal fluorescein can provide accurate information on the exact location of the fistula. The current study was designed to refine the clinical examination for cerebrospinal fluid fistulae with the use of intrathecal fluorescein. The canine model that we used also served as a vehicle to investigate the histopathologic effects of fluorescein on the central nervous system. We modified a commonly used xenon light source to enable examination with 490 nm light. In the canine model, this allowed accurate visualization of surgically created fistulae using very low doses of intrathecal fluorescein. An examination of the histopathologic features of the central nervous system of the canine model after acute instillation of a higher dose of fluorescein revealed microscopic changes consistent with the introduction of an irritant material. The changes induced by the chemical trauma may explain the serious neurologic sequelae sometimes seen in patients after the instillation of intrathecal fluorescein. Recommendations on the correct dosage of intrathecal fluorescein for diagnosis of cerebrospinal fluid fistulae are proposed.