Microanatomic study on retrosigmoid keyhole approach

Abstract

Objective The aim of the present study was to assess the retrosigmoid keyhole approach on a cadaveric model by using a neuronavigation system, and explore its indications. Methods Six cadaveric heads (twelve sides) injected with colored latex were used. The retrosigmoid keyhole approach was followed by the conventional retrosigmoid approach. The exposure areas of petroclivus and brainstem were measured and calculated under stryker frameless stereotactic navigation. Angles of attack for six different target points, which included the Meckle's cave, trigeminal nerve root, internal auditory meatal, facial nerve root, jugular foramen and glossopharyngeal nerve root, were measured. The exposure area and angles of attack between the two approacbes were compared and analyzed by student's t test. Results The retrosigmoid keyhole approach exposes nearly the same anatomic architecture as that of conventional approach, namely, it can expose the area superior to the anteriolateral margin of the tentorium, inferior to the foramen Magnum, medial to the anteriolateral of pons and medulla. The anatomic structure deeply seated in the ispilateral petroclivus can also be observed clearly through the cranial nerve intervals. Exposure area at the petroclivus and brainstem under the retrosignaoid keyhole approach was (304.73±28.93) mm2 and (143.9±31.87)mm2, respectively. The counterpart of the conventional retrosigmoid approach was (346.43 ±42.80) mm2 and (136.05±9.05) mm2, respectively. No statistical difference lies in the exposure area (P > 0.05). The vertical and horizontal attack angles under the conventional approach were wider than those of the keyhole approach at the selected six target points (P < 0.05). Conclusion The retrosigmoid keyhole approach provides similar exposure with that of the conventional retrosigmoid approach, not only can be used in microvascular decompression, also can be used to resect tumors located in cerebellopontine angle, upper petroclivus, middle petroclivus, anteriolateral of midbrain and pons. Key words: Keyhole surgery; Retrosigmoid approach; Cerebellopontine angle; Microanatomy