The posterior subtemporal keyhole approach combined with the transchoroidal approach to the ambient cistern: microsurgical anatomy and image-guided quantitative analysis

Abstract

The aim of this study is to describe microsurgical anatomy and to quantitatively analyze exposure using the posterior subtemporal keyhole (PSK) approach combined with the transchoroidal keyhole (TCK) approach to the ambient cistern. We determined the proper location of craniotomy of such combined keyhole approach on 16 sides of cadaver heads. The PSK approach and the TCK approach were performed in the same minicraniotomy to observe microanatomic features and to quantitatively measure exposure limits of the ambient cistern and related structures using image-guided system. Some superficial and bone landmarks could be used to find the proper location of such combined minicraniotomy. In the PSK approach, the exposure distances of the trigeminal nerve and the anterior portion of the P2 segment (P2a) were 10.02 ± 0.76mm and 16.32 ± 2.02mm, respectively. The superior, inferior, anterior, and posterior exposure limit of brainstem from the intersection point of the lateral mesencephalic sulcus and pontomesencephalic sulcus was 7.5 ± 0.19mm, 11.04 ± 0.27mm, 15.72 ± 0.52mm, and 10.16 ± 0.38mm, respectively. In the TCK approach, the vertical distances between the taenia fimbriae and the lateral geniculate body without and with mild caudal retraction of the hippocampus were 5.28 ± 0.46mm and 11.18 ± 0.57mm, respectively. The linear exposure distances of the posterior portion of the P2 segment (P2p) or P3 segment were 12.14 ± 1.88mm. Except of one case, the P2p could be exposed using the TCK approach. The midpoint of the medial edge of the parahippocampal gyrus on the coronal magnetic resonance images provides landmark to choose the appropriate approach. The PSK combined with the TCK approach can simultaneously expose the lower and upper ambient cistern in a proper minicraniotomy.