Rare CSF Fistulas: The Role of Sternberg´s Canal, Tympano-Meningeal Duct, The Glossopharyngeal Nerve and the Tympanic Canal

Objective: CSF fistulas occur mainly after trauma, intracranial or skull base procedures. In many cases the surgeon is opposed to a major therapeutic and operative problem that needs often an interdisciplinary approach. However, the location of the fistula and its origin is known in most of these cases. The diagnostic and therapeutic problem is by far bigger in spontaneous CSF fistulas. They are often misdiagnosed due to minimal CSF flow and come into discussion after one or several meningitises.

Method: Seven patients with spontaneous CSF fistulas and/or meningitis are reported. As diagnostic procedures served high resolution CT, CT cisternography and in special cases MRI cisternography with Gadolinum as well as intrathecal fluorescein application. By these means the pathologies could be clearly detected. The individual operative procedures are described and were successful in all but one case.

Results: In 4 cases a persisting Sternberg´s canal was found and in two additional cases besides the Sternberg´s canal a pseudo tympano-meningeal duct (Hyrtl´s fissure) was present. Pseudo, because no contact to the tympanon was detected, but an intra-extracranial communication along the glossopharyngeal nerve into the extracranial space from the intracranial opening of Hyrtl`s fissure to the extracranial area of the opening of the tympanic canal. These patients had additional bony defects of the skull base and/or meningoceles. Another patient depicted a defect at the cribriform plate and multiple other basal defects. In this case a pseudotumor cerebri was apparent. All patients were operated, sometimes multiple times and in other institutions. Finally an occlusion of the different types of fistulas was achieved with muscle, fat tamponade and glueing procedures.

Conclusion: In spontaneous CSF fistulas malformations and abnormalities of the skull base should be taken into account. Besides the Sternberg`s canal and Hyrtl`s fissure, the possibility of another type of spontaneous fistula along the glossopharyngeal nerve is described. Combinations of abnormalities are possible and enhance the diagnostic and therapeutic problem. Surgery is often difficult and needs an interdisciplinary approach but remains in most cases the only way to fix the problem.