Microsurgical Anatomy of the Posterior Inferior Cerebellar Artery

Abstract

Fifty cerebellar hemispheres from 25 adult cadavers were examined. The posterior inferior cerebellar artery (PICA), by definition, arose from the vertebral artery. The vertebral artery was present in 49 and the PICA was present in 42 of the 50 hemispheres. Forty-one of the 42 PICAs arose as a single trunk and 1 arose as a duplicate trunk. The PICA was divided into five segments: the anterior medullary segment lay on the front of the medulla; the lateral medullary segment coursed beside the medulla and extended to the origin of the glossopharyngeal, vagal, and accessory nerves; the tonsillomedullary segment coursed around the caudal half of the cerebellar tonsil; the telovelotonsillar segment coursed in the cleft between the tela choroidea and the inferior medullary velum rostrally and the superior pole of the cerebellar tonsil caudally; and the cortical segment was distributed to the cerebellar surface. Thirty-seven of the 42 PICAs bifurcated into a medial and a lateral trunk. The medial trunk supplied the vermis and the adjacent part of the hemisphere, and the lateral trunk supplied the cortical surface of the tonsil and the hemisphere. The PICA gave off perforating, choroidal, and cortical arteries. The cortical arteries were divided into vermian, tonsillar, and hemispheric groups. Sixteen of the 42 PICAs passed between the rootlets of the accessory nerve, 10 passed between the rootlets of the vagus nerve, 13 passed between the vagus and the accessory nerves, 2 coursed rostral to the glossopharyngeal nerve, and 1 passed between the glossopharyngeal and the vagus nerves.

Extracranial Aneurysms of the Posterior Inferior Cerebellar Artery

“…In 16% of cases [2], only 1 PICA can be identified. Typically, it supplies blood to the caudal medulla, cerebellar tonsil, inferior portion of the cerebellar hemisphere and vermis, and the choroid plexus of the 4th ventricle [10].…”

“…While most PICA aneurysms originate from the PICA-vertebral artery junction and comprise up to 3% of all intracranial aneurysms [1, 12], distal locations along the PICA are less common and represent 0.5 to 1.0% of all intracranial aneurysms [2, 3, 13]. Some authors [1]have suggested that approximately two thirds of PICA aneurysms occur at the PICA-vertebral junction and that one third occurs more distally.…”

“…Dernbach et al [14], however, reviewed 130 distal PICA aneurysms, none of which was extracranial in location. Distal aneurysms can be associated with variations in the microvascular anatomy of the PICA and with anomalies of the vertebral artery [2, 12, 15]. The PICA can have a highly variable anatomic course, however, and anatomic studies have shown that its origin can be located between 14 mm below and 26 mm above the level of the foramen magnum [2].…”

“…Distal aneurysms can be associated with variations in the microvascular anatomy of the PICA and with anomalies of the vertebral artery [2, 12, 15]. The PICA can have a highly variable anatomic course, however, and anatomic studies have shown that its origin can be located between 14 mm below and 26 mm above the level of the foramen magnum [2]. Angiographic studies have shown that the PICA can originate from as much as 24 mm below and 45 mm above the foramen magnum [16], arising extracranially in 17–18% of cases [2].…”

“…Aneurysms of the distal PICA are much less common and represent from 0.5 to 1.0% of all intracranial aneurysms [1, 2, 3, 4]. Although distal PICA aneurysms have been well documented [3, 4], extracranial PICA aneurysms are exceedingly rare with only 6 cases previously reported in the literature [3, 5, 6, 7, 8, 9].…”