Retrosigmoidal approach to the posterior cranial fossa. An anatomical study.

An anatomical study was performed in order to obtain help for orientation regarding the retrosigmoid approach and its osteoclastic craniotomy. The insertions of the sternocleidomastoid, the splenius capitis, the longissimus capitis and the obliquus capitis superior muscles were measured. The relationships of the insertions to different landmarks were also ascertained (FHP, suprameatal spine). In 37 specimens 6 burrholes with a standardized relationship to the Frankfurt Horizontal Plane (FHP) and the external auditory meatus, were performed. Due to the results of the relationship between burrholes and the sigmoid and transverse sinuses it is possible to give an optimal position for the initial burrhole of the osteoclastic craniotomy. A burrhole performed according to the result of this study has a relatively small risk concerning iatrogenic bleeding from the sigmoid and transverse sinuses caused by the burrhead of the drill.