EN-BLOC REMOVAL OF SMALL-SIZED TO MEDIUM-SIZED ACOUSTIC NEUROMAS WITHRETROSIGMOID-TRANSMEATAL APPROACH

Surgery of acoustic neuroma (AN) has significantly refined over the pa st years due to a series of advances in diagnostics and surgical techn ique. Electrophysiologic investigation performed during surgery has gr eatly contributed to this progress, increasing the surgeon's understan ding of the mechanism of damage and suggesting various changes in his or her surgical strategy. In this context, the advantages of the retro sigmoid ''en-bloc'' removal of small to medium size ANs have been exam ined in the present study. At the ENT Department of the University of Verona, 103 subjects with AN were operated on, from January 1990 to De cember 1995, with a relrosigmoid-transmeatal approach. Eighteen subjec ts (17.4%) presented a pure intracanalar (IC) tumor and 85 (82.6%) had both IC and extracanalar (EC) involvement. All the IC tumors (n = 18) and 70 of the IC-EC neuromas with an EC size less than 25 mm are repo rted in this paper for a total of 58 patients. The first 48 patients w ere operated on via the classic procedures described in the literature , characterized by removal of the tumor after ''debulking'' and limite d exposure of the internal auditory canal (IAC). The following 10 subj ects were operated on according to the technique of ''en-bloc'' remova l of the tumor and wide exposure of the IAC. In the ''en-bloc'' group, the tumor was first detached from the cerebellar flocculus acid the p ons, when necessary. The tumor was not debulked to preserve the anatom ic relationship with the nerves and to facilitate identification, clea vage, and dissection of the tumor from the neural structures. Thereaft er, the posterior wall of the IAC was drilled out and opened in a circ umferential range from 180 to 270 degrees. The IAC dura was subsequent ly opened, and the distal end of the AN along with the vestibular nerv es were identified. The vestibular nerves were sectioned in the distal portion of the IAC and dissected with the tumor from the underlying f acial and cochlear nerves. Dissection continued medially to the IAC po rus. The AN was progressively dissected from the cochlear and facial n erves in the cerebellopontine angle (CPA) with multiple direction mane uvers; as required by the characteristics and degree of adherence to t he neural structures. The anatomic and functional results obtained wit h this new procedure (''en-bloc'' removal) were compared with the clas sic ''debulking'' technique. The statistical analysis shows an improve ment in postoperative outcome for both auditory and facial nerve funct ion. The ''en-bloc'' removal procedure along with the wide exposure of the content of the IAC and electrophysiologic monitoring of the seven th and eighth cranial nerves are, in our experience, the recommended s trategies for improving outcomes in small to medium size ANs.