Surgical Trajectories for Clipping of Different PICA Aneurysms

Surgical clipping of different posterior inferior cerebellar artery (PICA) aneurysms requires 3D anatomical planning tailored to the configuration of the aneurysm. Factors to be considered for the selection of safe exposure and trajectories for clipping of PICA aneurysms include optimal exposure and visualisation of the neck, proximal and distal control, aneurysm size and its cranio-caudal location, vessel tortuosity and rigidity of its wall, and the proximity of cranial nerves. PICA aneurysm surgery involves choosing a lateral vs. posterior midline approach. For PICA aneurysms at its origin off the vertebral artery (VA), when the junction is caudal at the foramen magnum, i.e. a “proximal take-off”, a trajectory providing a direct viewing angle to the neck of the aneurysm is medial to lateral. This is readily provided through a midline suboccipital craniotomy widened ipsilaterally at the foramen magnum with the patient in the prone position. For a more distal PICA take-off the trajectory with a direct viewing angle is lateral to antero-medial and as the take-off approaches the vertebrobasilar junction (VBJ), it becomes lateral to superior-antero-medial. Therefore, it is best to approach these through a far lateral craniotomy with the patient in the lateral position. Aneurysms located anterolateral to the medulla, i.e. on the medullary loop being especially arising at the anterior medullary and also the lateral medullary segments, a far lateral craniotomy with the patient in the lateral position is best. Those aneurysms located on the tonsillar loop and beyond are simply approached through a midline suboccipital craniotomy in the prone position. The nuances of both approaches are presented with emphasis that in the vast majority of cases of PICA aneurysms there is no need to drill the occipital condyle.