Basilar Artery Aneurysm: Orbitozygomatic Craniotomy for Clipping

Basilar apex aneurysms include ruptured or unruptured basilar bifurcation aneurysms, superior cerebellar artery (SCA) aneurysms, and proximal posterior cerebral artery (PCA) aneurysms.

Patients who are young and have good clinical grades (Hunt and Hess grades I to III), broad neck aneurysms, aneurysms with branches originating from side walls, intraluminal thrombus, or significant mass effect from the aneurysm should be considered for microsurgical clipping.

Patients who are elderly (≥ 70 years old) and have poor clinical grades (Hunt and Hess grades IV and V)

Calcified aneurysms or aneurysm anatomy that is favorable for coiling (narrow neck, acute-angle branches of the PCA, or posterior aneurysm projection) should be considered for endovascular therapy.

Diagnostic imaging should include a computed tomography (CT) scan to evaluate for hydrocephalus and performance of ventriculostomy if ventricles are enlarged. Calcium or atherosclerotic changes in the aneurysm wall might preclude microsurgical clipping. Brain asymmetry (temporal lobe encephalomalacia, prior surgery, or sylvian anatomy) might affect the side of surgical approach. The relationship of the aneurysm neck to the posterior clinoid processes, dorsum sella, and clivus should be noted. The size of frontal sinuses is relevant. Intraluminal thrombus, which might be more apparent on CT angiography, should be noted and may be the inadvertent cause of distal emboli during manipulation of the aneurysm.

Angiography details aneurysm size, neck size, morphology, laterality, aneurysm projection (anterior, posterior, superior, or lateral), and location of aneurysm neck relative to the posterior clinoid processes, dorsum sella, and clivus. Anatomy of branches at the aneurysm neck (P1 PCA, SCA, and perforating arteries) is evident, as is any discrepancy between intraluminal size on angiography and extraluminal size on CT or magnetic resonance imaging (MRI) to suggest intraluminal thrombus. The posterior communicating artery (PCoA) and P1 PCA are examined for fetal anatomy and anterior-to-posterior collateral circulation. Other aneurysms might influence the side of surgical approach. The location of perforating arteries relative to the neck should be assessed. Other angiographic abnormalities may also be evident, such as early vasospasm, arterial occlusions, associated arteriovenous malformations, and moyamoya disease.

Special equipment may include a radiolucent head holder in the event an intraoperative angiogram is needed, reciprocating saw for orbitozygomatic osteotomies, diamond burr (1- or 2-mm diameter ball tip) or ultrasonic aspirator with bone curettage tip for removal of the posterior clinoid process with low-lying basilar apex aneurysms, aneurysm clips (permanent and temporary), Rhoton dissectors, Doppler flow probe, and intraoperative angiography either with conventional catheter angiography or indocyanine green dye.

The operating room setup may include bipolar cautery and Bovie cautery; operating microscope (foot pedal for focus and zoom, mouthpiece for fine adjustments); chair with armrests and floor wheels; and neurophysiologic monitoring equipment with somatosensory evoked potentials, motor evoked potentials, and electroencephalography.

Anesthetic issues include the following: On skin incision, 1 g of Ancef, 10 mg of dexamethasone (Decadron), and 1 g/kg of mannitol are administered. Cerebral perfusion pressure is maintained at greater than 70 mm Hg to prevent ischemia from brain retraction, temporary blood vessel occlusion, or vasospasm. Severe hypertension is treated aggressively with propofol, thiopental, or vasoactive drugs. Temperature is allowed to drift toward 34° C (93.2° F), and rewarming is started after aneurysm clipping. Relative hypervolemia and above-normal blood pressure are allowed after aneurysm clipping in patients with vasospasm.