• Tadashi Hamasaki, Motohiro Morioka, Hideo Nakamura, Shigetoshi Yano, Toshinori Hirai, and Jun-ichi Kuratsu.
• Department of Neurosurgery, Kumamoto University Medical School, Kumamoto, Japan. thamasaki- nsu@umin.ac.jp
• Neurosurgery. 2009 May 1; 64 (5 Suppl 2): 241-5; discussion 245-6.

ObjectiveThe planning of retrosigmoid craniotomies often relies on anatomic landmarks on the posterolateral surface of the cranium, such as the asterion. However, the location of the asterion is not fixed with respect to the underlying transverse-sigmoid sinus complex. We introduce a simple procedure that uses 3-dimensional (3D) computed tomographic imaging to project the transverse-sigmoid sinus complex onto the external surface of the cranium.MethodsWe enrolled 8 patients scheduled for retrosigmoid craniotomy (Group 1) and 30 patients without posterior fossa lesions (Group 2). The procedure consists of 3 steps: 1) marking the sinus on the internal surface on 3D images of the cranium, 2) transferring the marks to the external surface on axial images, and 3) checking the transferred marks on the external surface of the cranium on 3D images.ResultsIn Group 1, the craniotomies planned with the aid of our procedure coincided with findings made at surgery, indicating the accuracy of our procedure. When we applied it in morphometric studies in Group 2, we found that the relative location of the transverse-sigmoid sinus junction to the asterion, the superior nuchal line, and the posterior edge of the mastoid process exhibited a high degree of individual variation.ConclusionRetrosigmoid craniotomy standardized according to anatomic landmarks raises the risk for sinus injury because of variations in their location. We offer our 3D computed tomographic imaging-based procedure as a useful device for the planning of safer retrosigmoid craniotomies.

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