[An experimental study of tumor cell infiltration into temporal bones--route into the inner ear from the arachnoid...

In humans, metastatic tumors which invaded the temporal bones have been studied in regard to the relationship between histopathologic findings and clinical symptoms. On the other hand, there is no experimental study using an animal model for tumor infiltration into the temporal bone. This study was designed to establish such an animal model and examine the temporal bones histopathologically. Rat thymic lymphoma cell (FTL-A2) were inoculated into the cisterna magna of Wistar rats. The animals were decapitated under deep anesthesia with pentobarbital sodium from the 1st to 8th day after inoculation. Their heads were fixed with Heiden-hain SuSa solution, decalcified, dehydrated, embedded in celloidin, and sectioned horizontally at a thickness of 25 microns. These were stained with hematoxylin and eosin, and histologically examined by light microscopy. Inoculated tumor cells showed active viability in the arachnoid space at a rate of 98%. Two major routes of tumor cell infiltration into the inner ear were found: the cochlear aqueduct and the internal auditory canal. At the early stage after the inoculation, tumor cells infiltrated the scala tympani through the cochlear aqueduct. Invading the fiber of the cochlear nerve, tumor cells infiltrated Rosenthal's canal via the tractus spiralis foraminosus, and passed through Rosenthal's canal and the osseous spiral lamina into the scala tymani. However, tumor cells did not infiltrate the organ of Corti through the habenula perporata. Tractus spiralis foraminosus and habenula perforata functioned as a barrier against tumor infiltration. In a few cases, tumor cells infiltrated over the macula cribrosa into the subepithelial space of the utricule and saccule. The macula cribrosa functioned as a barrier.