Ashraf Samy Youssef

The Carotid-oculomotor Window in Exposure of Upper Basilar Artery Aneurysms: A Cadaveric Morphometric Study

OBJECTIVE:The carotid-oculomotor window remains the traditional deep window in the exposure of aneurysms of the upper basilar artery. Although several techniques have been described to expand this window, few morphometric studies document either the degree of its expansion or its contribution to the exposure of the basilar artery. We review the microsurgical anatomy of the carotid-oculomotor window, describe expansion techniques, and analyze morphometrically the contribution of each step (i.e., extradural anterior clinoidectomy, mobilization of the internal carotid artery [ICA], and posterior clinoidectomy) to the expansion of the window and/or exposure of the artery. METHODS:Ten formalin-fixed, alcohol-preserved, cadaver heads injected with pigmented silicone were prepared for bilateral dissection. The vertebrobasilar system was injected with pigmented silicone mixed with barium (1:1), rendering it radiopaque. After completing a frontotemporal-orbitozygomatic craniotomy, we performed dissection in two stages: Stage I consisted of a conventional transsylvian exposure of the upper basilar artery through the carotid-oculomotor window; and Stage II added anterior clinoidectomy, ICA mobilization, and posterior clinoidectomy. A clip was applied to the lowest accessible point of the basilar trunk at each stage. Measurements obtained during each stage included: 1) the transverse carotid-oculomotor distance, that is, anteriorly between the oculomotor foramen and ICA, and posteriorly between the oculomotor nerve and ICA; and 2) the exposed length of the basilar artery, as seen under the microscope and on angiograms. RESULTS:Measurements were obtained before and after the addition of anterior clinoidectomy, mobilization of the ICA, and posterior clinoidectomy. Increases in expansion of the window and exposure of the upper basilar artery were documented as percentages of the control values. The anterior carotid-oculomotor distance averaged 7.1 mm (range, 5–10 mm) and 10.1 mm (range, 7–15 mm) before and after the additional surgical steps to expand the window, respectively. The posterior carotid-oculomotor distance averaged 12.7 mm (range, 9–18 mm) and 16.1 mm (range, 11–22 mm) before and after the additional surgical steps to expand the window, respectively. The exposed length of the basilar artery from the bifurcation to the clip was 4.2 mm (range, 1–13 mm) before expansion and 7 mm (range, 3–15 mm) after expansion. CONCLUSION:Anterior clinoidectomy and ICA mobilization increased the carotid-oculomotor space 44% anteriorly and 28% posteriorly. Posterior clinoidectomy increased the exposed length of the basilar artery by 69%. Superficial wide field exposure, expansion of the carotid-oculomotor window, and increased exposure of the upper basilar artery facilitate both visualization of the aneurysm for clip application and the use of proximal vascular control as an adjunct to basilar aneurysm surgery.

Novel application of computer-assisted cisternal endoscopy for the biopsy of pineal region tumors: cadaveric study

SummaryBackground. Long-standing debate continues about the management and biopsy of pineal tumors because of their complex microsurgical anatomy and deep location. Inspired by the concept of biopsy under direct visualization in the absence of hydrocephalus, we explored the effectiveness of neuroendoscope outside of its traditional territory using a new minimally invasive technique, computer-assisted cisternal endoscopy (CACE), for the biopsy of pineal tumors. Method. Five cadaver heads were dissected to expose the pineal region through the posterior fossa. In the other 5 heads, a rigid endoscope-wand combination was introduced in the supracerebellar space lateral to the arachnoid of the superior cerebellar cistern in midline. Endoscopic exposure of the pineal gland was correlated with the real-time image of the localizing wand. After the wand was removed, arachnoid was further dissected from the deep veins and the pineal gland, and a four-quadrant biopsy was obtained. Findings. The combination of technologies of frameless guided stereotaxy and neuroendoscopy enhanced our ability to navigate the ventriculoscope in narrow spaces (e.g., posterior fossa cisterns). Compared with transventricular and conventional stereotactic trajectories, application of CACE in supracerebellar infratentorial trajectory offered the shortest route to the pineal region, anatomical orientation, no violation of eloquent neurovascular structures, and adequate visibility to deep veins and arteries. Conclusions. CACE may be used to approach pineal lesions outside the cerebral ventricular system for biopsy or debulking. Continuous computer updates on the endoscope position allows its safe navigation in narrow spaces (e.g., cerebrospinal fluid cistern). Its success will await future surgical trials.