• Rungsak Siwanuwatn, Pushpa Deshmukh, Joseph M Zabramski, Mark C Preul, and Robert F Spetzler.
• Division of Neurological Surgery, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
• Neurosurgery. 2005 Oct 1; 57 (4 Suppl): 228-35; discussion 228-35.

ObjectiveSurgical approaches to ambient cistern lesions are complex. We investigated the microanatomy of the transtemporal-transchoroidal fissure approach to the ambient cistern with emphasis on exposure of the posterior cerebral artery.MethodsDissections were performed bilaterally in five silicone-injected cadaveric heads. Critical anatomic distances, specifically with reference to the P2 segment of posterior cerebral artery in relation to the inferior choroidal point and P2-P3 junction, were measured with digital calipers. Other landmarks (temporal lobe tip, points from the temporal base to the choroidal fissure) were included for quantitative analysis.ResultsThe transtemporal-transchoroidal fissure approach provided adequate exposure of the ambient cistern, minimized temporal lobe retraction, and allowed assessment of regional microanatomy. The mean distance from the temporal base to the choroidal fissure measured 18.09 mm (range, 16.9-21.9 mm). The distances from the choroidal fissure to P2 varied at the coronal plane of the inferior choroidal point (mean, 6.96 mm; range, 3.6-12.0 mm) and the P2-P3 junction (mean, 6.02 mm; range, 4.3-6.9 mm), respectively.ConclusionThe transtemporal-transchoroidal fissure approach provides a corridor to the ambient cistern and P2-P3 junction while minimizing temporal lobe retraction and avoiding interruption of temporal lobe venous drainage. Because of widely variable vascular anatomy, access to posterior cerebral artery lesions using this approach requires preoperative imaging to identify the specific location of the P2-P3 junction.

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