En-block removal of small to medium sized Acoustic Neuromas with Retrosigmoid transmeatal Approach

Abstract Surgery of acoustic neuroma (AN) has significantly refined over the past years due to a series of advances in diagnostics and surgical technique. Electrophysiologic investigation performed during surgery has greatly contributed to this progress, increasing the surgeon's understanding of the mechanism of damage and suggesting various changes in his or her surgical strategy.In this context, the advantages of the retrosigmoid "en-bloc" removal of small to medium size ANs have been examined in the present study. At the ENT Department of the University of Verona, 103 subjects with AN were operated on, from January 1990 to December 1995, with a retrosigmoid-transmeatal approach. Eighteen subjects (17.4%) presented pure a 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 reported in this paper for a total of 88 patients. The first 48 patients were operated on via the classic procedures described in the literature, characterized by removal of the tumor after "debulking" and limited exposure of the internal auditory canal (IAC). The following 40 subjects were operated on according to the technique of "en-bloc" removal of the tumor and wide exposure of the IAC.In the "en-bloc" group the tumor was first detached from the cerebellar flocculus and the pons, when necessary. The tumor was not debulked to preserve the anatomic relationship with the nerves and to facilitate identification, cleavage and dissection of the tumor from the neural structures. Thereafter, the posterior wall of the IAC was drilled out and opened in a circumferential range from 180 to 270 degrees . The IAC dura was subsequently opened, and the distal end of the AN along with the vestibular nerves were identified. The vestibular nerves were sectioned in the distal portion of the IAC and dissected with the tumor from the underlying facial and cochlear nerves. Dissection continued medially to the IAC porus. The AN was progressively dissected from the cochlear and facial nerves in the cerebellopontine angle (CPA) with multiple direction maneuvers, as required by the characteristics and degree of adherence to the neural structures.The anatomic and functional results obtained with this new procedure ("en-bloc" removal) were compared with the classic "debulking" technique. The statistical analysis shows an improvement in postoperative outcome for both auditory and facial nerve function. The "en-bloc" removal procedure along with the wide exposure of the content of the IAC and electrophysiologic monitoring of the seventh and eighth cranial nerves are, in our experience, the recommended strategies for improving outcomes in small to medium size ANs.