Transcrusal approach to the retrochiasmatic region with special reference to temporal lobe retraction: an anatomical study.

Abstract

The retrochiasmatic region is one of the most challenging areas to surgically expose. The authors evaluated the transcrusal approach, which involves removal of the superior and posterior semicircular canal from the ampulla to the common crus, to expose the retrochiasmatic region and compared it with the retrolabyrinthine approach, both of which are a variation of the posterior petrosal approach with hearing preservation, with a special emphasis on the influence of temporal lobe retraction. Six sides of silicone-injected cadaveric heads were dissected using two approaches: the transcrusal approach and the retrolabyrinthine approach. For each craniotomy, 3 exposure parameters in the retrochiasmatic region were measured: (1) horizontal distance, (2) vertical distance, and (3) triangular area of exposure, at three different levels of temporal lobe retractions: 0, 5, and 10 mm of retraction from the level of the tentorial incisura. Without temporal lobe retraction, only the transcrusal and not the retrolabyrinthine approach provided a direct exposure of the retrochiasmatic region, especially in the horizontal distance (p < 0.001). At all levels of temporal lobe retraction, the transcrusal approach provided greater exposure in the horizontal and vertical distances and in the area of exposure. Nonetheless, in the horizontal distance, the difference between the transcrusal and retrolabyrinthine approaches decreased along with increased temporal lobe retraction, and almost no difference was obtained at 10 mm of retraction. Posterior petrosal approaches can provide an excellent exposure of the retrochiasmatic region. Of these two approaches, namely, transcrusal and retrolabyrinthine with hearing preservation, the transcrusal approach offers greater exposure than the retrolabyrinthine approach. The beneficial effect of partial labyrinthectomy of the transcrusal approach to the retrochiasmatic region is accentuated in the exposure of the horizontal distance with less temporal lobe retraction.