Resection of fourth ventricle tumors without splitting the vermis: the cerebellomedullary fissure approach.

OBJECTIVE: Standard surgical practice for excision of fourth ventricle tumors entails splitting the inferior vermis, but incision of the vermis and lateral retraction on the dentate nuclei and their outflow tracts have been implicated in the development of the so-called 'cerebellar mutism syndrome'. We describe a surgical approach in which the cerebellar vermis is preserved.
METHODS: Clinical experiences with 11 patients harboring fourth ventricle tumors were supplemented by fixed and fresh cadaver dissections. Anatomic illustrations, prosections and intraoperative photographs are presented. The authors' case material is tabulated, and clinical examples are discussed.
RESULTS: Dissection of the arachnoid membranes and division of filamentous arachnoidal attachments allow separation and elevation of the cerebellar tonsils and exposure of the tela choroidea along its attachment to the dorsal surface of the medulla at the taenia ventricularis. The tela can be opened by sharp microdissection from the foramen of Magendie to the foramen of Luschka to expose the lateral recess of the fourth ventricle. Division of the tela allows additional elevation of the cerebellar tonsils, which can be mobilized further by opening of the tonsillovermian fissures. Performance of this dissection bilaterally opens the entire inferior end of the fourth ventricle and, particularly after excision of a large fourth ventricle tumor, gives a panoramic view from one lateral recess to the other and from the obex to the aqueduct without incision of the vermis.
CONCLUSION: The cerebellomedullary fissure approach yields exposure comparable to what can be achieved by splitting the vermis and may minimize the risk of neurological complications.