Parameters for contralateral approach to ophthalmic segment aneurysms of the internal carotid artery

OBJECTIVE: This study was undertaken to define move accurately the feasibil ity and indications of the contralateral pterional approach to ophthalmic s egment aneurysms of the internal carotid artery (ICA). METHODS: Between 1995 and 1999, 46 patients with ophthalmic segment aneurys ms of the ICA were surgically treated in our institution. Eleven of the 46 aneurysms were operated using the contralateral pterional approach. AII ane urysms were successfully clipped without complications; three patients requ ired bone resection around the aneurysm neck. We studied the 11 patients wh o were treated with the contralateral approach by defining six parameters t o assess the feasibility of the approach and to predict the necessity for b one resection: 1) Parameter A, the distance between the anterior aspect of the optic chiasm and the limbus sphenoidale; 2) Parameter BI the distance b etween the bilateral optic nerves at the entrance to the optic canal; 3) Pa rameter C, the interrelation of the optic nerve and the ICA, expressed as a /b in which a is the length from the midline to the optic nerve and b is th e length from the midline to the ICA; 4) Parameter D, the size of the aneur ysm neck; 5) Parameter E, the direction of the aneurysm from the ICA wall o n the anteroposterior angiogram; and 6) Parameter F, the distance from the medial side of the estimated distal dural ring to the proximal aneurysm nec k on the lateral angiogram. RESULTS: Parameters A to F were 8.8 mm (range, 5.4-11.1 mm), 14.5 mm (range , 10.4-22.2 mm), 0.9 mm (range, 0.6-1.3 mm), and 3.0 mm (range, 2.3-4.7 mm) , 5 to 160 degrees, and 1.3 mm (range, 0.3-2.4 mm), respectively. All patie nts had excellent operative outcomes without visual dysfunction. Three pati ents required drilling of the bone around the optic canal on the craniotomy side; bone drilling was not required when Parameter E was between 30 and 1 60 degrees and Parameter F was more than 1 mm. CONCLUSION: Parameters A to D are important for assessing the feasibility o f the contralateral approach to ICA-ophthalmic segment aneurysms, and Param eters E and F are most useful for calculating the difficulty of this approa ch.