Seventy Aneurysms of the Posterior Inferior Cerebellar Artery: Anatomical Features and Value of Computed Tomography Angiography in Microneurosurgery

Anatomical studies based on CTA are still scarce: the literature comprises, to our knowledge, only 1 series of 5 patients with PICA aneurysms (20). The present study provides 71 PICA aneurysms diagnosed by CTA. We present the angiographic anat- omy of VA and PICA and the characteris- tics of the aneurysms with respect to adjacent bony structures. -RESULTS: Each of the 70 patients had 1 aneurysm at the VAePICA junction. The proportion of small aneurysms (<7 mm) was high, 67%. The dome-to-neck ratio was <1.2 in 24 (34%) of the aneurysms. In the coronal view, 58 (83%) aneurysms projected cranially, and only 2 (3%) caudally. The aneurysms were located from 1 mm below the foramen magnum to 31 mm above it, most arising at the level of the jugular tubercle. The median distance to the aneurysm from the midline was 6 mm, ranging from 7.5 mm contralateral to the origin of the parent artery to 14 mm ipsilateral. Compared with the right VA, the left VA was larger, it harbored the most aneurysms, and its aneurysms were more often ruptured. -CONCLUSIONS: Relation of PICA aneurysms to skull base structures is highly variable; the aneurysms can also be extracranial, or lie on the site of the skull contralateral to the origin of the parent artery. These anatomical variations demand meticulous study of the angiography in each individual case, especially before surgical treatment of the aneurysm.